This Info file documents GNU troff version 1.16.

Published by the Free Software Foundation 59 Temple Place, Suite 330 Boston, MA  02111-1307  USA

Copyright (C) 1994-2000 Free Software Foundation, Inc.

Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies.

Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one.

Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that this permission notice may be stated in a translation approved by the Foundation.

Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided also that the section entitled ``GNU General Public License'' is included exactly as in the original, and provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one.

Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that the section entitled ``GNU General Public License'' may be included in a translation approved by the Free Software Foundation instead of in the original English.

This Info file documents groff version 1.16, the GNU implementation of the troff typesetting system.

This is an in-progress document; contributions, comments, or contributions are welcome.  Send them to bug-groff@gnu.org.

GNU GENERAL PUBLIC LICENSE
**************************

Version 2, June 1991

     Copyright © 1989, 1991 Free Software Foundation, Inc.
     59 Temple Place, Suite 330, Boston, MA 02111, USA

     Everyone is permitted to copy and distribute verbatim copies of this
     license document, but changing it is not allowed.

Preamble
========

The licenses for most software are designed to take away your freedom to share and change it.  By contrast, the GNU General Public License is intended to guarantee your freedom to share and change free software -- to make sure the software is free for all its users.  This General Public License applies to most of the Free Software Foundation's software and to any other program whose authors commit to using it. (Some other Free Software Foundation software is covered by the GNU Library General Public License instead.)  You can apply it to your programs, too.

When we speak of free software, we are referring to freedom, not price. Our General Public Licenses are designed to make sure that you have the freedom to distribute copies of free software (and charge for this service if you wish), that you receive source code or can get it if you want it, that you can change the software or use pieces of it in new free programs; and that you know you can do these things.

To protect your rights, we need to make restrictions that forbid anyone to deny you these rights or to ask you to surrender the rights.  These restrictions translate to certain responsibilities for you if you distribute copies of the software, or if you modify it.

For example, if you distribute copies of such a program, whether gratis or for a fee, you must give the recipients all the rights that you have. You must make sure that they, too, receive or can get the source code. And you must show them these terms so they know their rights.

We protect your rights with two steps: (1) copyright the software, and (2) offer you this license which gives you legal permission to copy, distribute and/or modify the software.

Also, for each author's protection and ours, we want to make certain that everyone understands that there is no warranty for this free software.  If the software is modified by someone else and passed on, we want its recipients to know that what they have is not the original, so that any problems introduced by others will not reflect on the original authors' reputations.

Finally, any free program is threatened constantly by software patents. We wish to avoid the danger that redistributors of a free program will individually obtain patent licenses, in effect making the program proprietary.  To prevent this, we have made it clear that any patent must be licensed for everyone's free use or not licensed at all.

The precise terms and conditions for copying, distribution and modification follow.

TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION

 0. This License applies to any program or other work which contains a notice placed by the copyright holder saying it may be distributed under the terms of this General Public License.  The ``Program'', below, refers to any such program or work, and a ``work based on the Program'' means either the Program or any derivative work under copyright law: that is to say, a work containing the Program or a portion of it, either verbatim or with modifications and/or translated into another language. (Hereinafter, translation is included without limitation in the term ``modification''.)  Each licensee is addressed as ``you''.

     Activities other than copying, distribution and modification are not covered by this License; they are outside its scope.  The act of running the Program is not restricted, and the output from the Program is covered only if its contents constitute a work based on the Program (independent of having been made by running the Program).  Whether that is true depends on what the Program does.

 1. You may copy and distribute verbatim copies of the Program's source code as you receive it, in any medium, provided that you conspicuously and appropriately publish on each copy an appropriate copyright notice and disclaimer of warranty; keep intact all the notices that refer to this License and to the absence of any warranty; and give any other recipients of the Program a copy of this License along with the Program.

     You may charge a fee for the physical act of transferring a copy, and you may at your option offer warranty protection in exchange for a fee.

 2. You may modify your copy or copies of the Program or any portion of it, thus forming a work based on the Program, and copy and distribute such modifications or work under the terms of Section 1 above, provided that you also meet all of these conditions:

      a. You must cause the modified files to carry prominent notices stating that you changed the files and the date of any change.

      b. You must cause any work that you distribute or publish, that in whole or in part contains or is derived from the Program or any part thereof, to be licensed as a whole at no charge to all third parties under the terms of this License.

      c. If the modified program normally reads commands interactively when run, you must cause it, when started running for such interactive use in the most ordinary way, to print or display an announcement including an appropriate copyright notice and a notice that there is no warranty (or else, saying that you provide a warranty) and that users may redistribute the program under these conditions, and telling the user how to view a copy of this License.  (Exception: if the Program itself is interactive but does not normally print such an announcement, your work based on the Program is not required to print an announcement.)

     These requirements apply to the modified work as a whole.  If identifiable sections of that work are not derived from the Program, and can be reasonably considered independent and separate works in themselves, then this License, and its terms, do not apply to those sections when you distribute them as separate works.  But when you distribute the same sections as part of a whole which is a work based on the Program, the distribution of the whole must be on the terms of this License, whose permissions for other licensees extend to the entire whole, and thus to each and every part regardless of who wrote it.

     Thus, it is not the intent of this section to claim rights or contest your rights to work written entirely by you; rather, the intent is to exercise the right to control the distribution of derivative or collective works based on the Program.

     In addition, mere aggregation of another work not based on the Program with the Program (or with a work based on the Program) on a volume of a storage or distribution medium does not bring the other work under the scope of this License.

 3. You may copy and distribute the Program (or a work based on it, under Section 2) in object code or executable form under the terms of Sections 1 and 2 above provided that you also do one of the following:

      a. Accompany it with the complete corresponding machine-readable source code, which must be distributed under the terms of Sections 1 and 2 above on a medium customarily used for software interchange; or,

      b. Accompany it with a written offer, valid for at least three years, to give any third party, for a charge no more than your cost of physically performing source distribution, a complete machine-readable copy of the corresponding source code, to be distributed under the terms of Sections 1 and 2 above on a medium customarily used for software interchange; or,

      c. Accompany it with the information you received as to the offer to distribute corresponding source code.  (This alternative is allowed only for noncommercial distribution and only if you received the program in object code or executable form with such an offer, in accord with Subsection b above.)

     The source code for a work means the preferred form of the work for making modifications to it.  For an executable work, complete source code means all the source code for all modules it contains, plus any associated interface definition files, plus the scripts used to control compilation and installation of the executable.  However, as a special exception, the source code distributed need not include anything that is normally distributed (in either source or binary form) with the major components (compiler, kernel, and so on) of the operating system on which the executable runs, unless that component itself accompanies the executable.

     If distribution of executable or object code is made by offering access to copy from a designated place, then offering equivalent access to copy the source code from the same place counts as distribution of the source code, even though third parties are not compelled to copy the source along with the object code.

 4. You may not copy, modify, sublicense, or distribute the Program except as expressly provided under this License.  Any attempt otherwise to copy, modify, sublicense or distribute the Program is void, and will automatically terminate your rights under this License.  However, parties who have received copies, or rights, from you under this License will not have their licenses terminated so long as such parties remain in full compliance.

 5. You are not required to accept this License, since you have not signed it.  However, nothing else grants you permission to modify or distribute the Program or its derivative works.  These actions are prohibited by law if you do not accept this License.  Therefore, by modifying or distributing the Program (or any work based on the Program), you indicate your acceptance of this License to do so, and all its terms and conditions for copying, distributing or modifying the Program or works based on it.

 6. Each time you redistribute the Program (or any work based on the Program), the recipient automatically receives a license from the original licensor to copy, distribute or modify the Program subject to these terms and conditions.  You may not impose any further restrictions on the recipients' exercise of the rights granted herein.  You are not responsible for enforcing compliance by third parties to this License.

 7. If, as a consequence of a court judgment or allegation of patent infringement or for any other reason (not limited to patent issues), conditions are imposed on you (whether by court order, agreement or otherwise) that contradict the conditions of this License, they do not excuse you from the conditions of this License.  If you cannot distribute so as to satisfy simultaneously your obligations under this License and any other pertinent obligations, then as a consequence you may not distribute the Program at all.  For example, if a patent license would not permit royalty-free redistribution of the Program by all those who receive copies directly or indirectly through you, then the only way you could satisfy both it and this License would be to refrain entirely from distribution of the Program.

     If any portion of this section is held invalid or unenforceable under any particular circumstance, the balance of the section is intended to apply and the section as a whole is intended to apply in other circumstances.

     It is not the purpose of this section to induce you to infringe any patents or other property right claims or to contest validity of any such claims; this section has the sole purpose of protecting the integrity of the free software distribution system, which is implemented by public license practices.  Many people have made generous contributions to the wide range of software distributed through that system in reliance on consistent application of that system; it is up to the author/donor to decide if he or she is willing to distribute software through any other system and a licensee cannot impose that choice.

     This section is intended to make thoroughly clear what is believed to be a consequence of the rest of this License.

 8. If the distribution and/or use of the Program is restricted in certain countries either by patents or by copyrighted interfaces, the original copyright holder who places the Program under this License may add an explicit geographical distribution limitation excluding those countries, so that distribution is permitted only in or among countries not thus excluded.  In such case, this License incorporates the limitation as if written in the body of this License.

 9. The Free Software Foundation may publish revised and/or new versions of the General Public License from time to time.  Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns.

     Each version is given a distinguishing version number.  If the Program specifies a version number of this License which applies to it and ``any later version'', you have the option of following the terms and conditions either of that version or of any later version published by the Free Software Foundation.  If the Program does not specify a version number of this License, you may choose any version ever published by the Free Software Foundation.

 10. If you wish to incorporate parts of the Program into other free programs whose distribution conditions are different, write to the author to ask for permission.  For software which is copyrighted by the Free Software Foundation, write to the Free Software Foundation; we sometimes make exceptions for this.  Our decision will be guided by the two goals of preserving the free status of all derivatives of our free software and of promoting the sharing and reuse of software generally.

     NO WARRANTY

 11. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW.  EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM ``AS IS'' WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU.  SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR OR CORRECTION.

 12. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.

END OF TERMS AND CONDITIONS

How to Apply These Terms to Your New Programs
=============================================

If you develop a new program, and you want it to be of the greatest possible use to the public, the best way to achieve this is to make it free software which everyone can redistribute and change under these terms.

To do so, attach the following notices to the program.  It is safest to attach them to the start of each source file to most effectively convey the exclusion of warranty; and each file should have at least the ``copyright'' line and a pointer to where the full notice is found.

     ONE LINE TO GIVE THE PROGRAM'S NAME AND AN IDEA OF WHAT IT DOES.
     Copyright (C) 19YY NAME OF AUTHOR

     This program is free software; you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published by
     the Free Software Foundation; either version 2 of the License, or (at
     your option) any later version.

     This program is distributed in the hope that it will be useful, but
     WITHOUT ANY WARRANTY; without even the implied warranty of
     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
     General Public License for more details.

     You should have received a copy of the GNU General Public License
     along with this program; if not, write to the Free Software
     Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111, USA.

Also add information on how to contact you by electronic and paper mail.

If the program is interactive, make it output a short notice like this when it starts in an interactive mode:

     Gnomovision version 69, Copyright (C) 19YY NAME OF AUTHOR
     Gnomovision comes with ABSOLUTELY NO WARRANTY; for details type
     `show w'.  This is free software, and you are welcome to redistribute
     it under certain conditions; type `show c' for details.

The hypothetical commands show w and show c should show the appropriate parts of the General Public License.  Of course, the commands you use may be called something other than show w and show c; they could even be mouse-clicks or menu items -- whatever suits your program.

You should also get your employer (if you work as a programmer) or your school, if any, to sign a ``copyright disclaimer'' for the program, if necessary.  Here is a sample; alter the names:

     Yoyodyne, Inc., hereby disclaims all copyright interest
     in the program `Gnomovision' (which makes passes at compilers)
     written by James Hacker.

     SIGNATURE OF TY COON, 1 April 1989
     Ty Coon, President of Vice

This General Public License does not permit incorporating your program into proprietary programs.  If your program is a subroutine library, you may consider it more useful to permit linking proprietary applications with the library.  If this is what you want to do, use the GNU Library General Public License instead of this License.

Introduction
************

GNU troff (or groff) is a system for typesetting documents.  troff is very flexible and has been in existence (and use) for about 3 decades.  It is quite widespread and firmly entrenched in the UNIX community.

What Is groff?
==============

groff belongs to an older generation of document preparation systems, which operate more like compilers than the more recent interactive WYSIWYG (What You See Is What You Get) systems.  groff and its contemporary counterpart, TeX, both work using a batch paradigm: The input (or source) files are normal text files with embedded formatting commands.  These files can then be processed by groff to produce a typeset document on a variety of devices.

Likewise, groff should not be confused with a word processor, since that term connotes an integrated system that includes an editor and a text formatter.  Also, many word processors follow the WYSIWYG paradigm discussed earlier.

Although WYSIWYG systems may be easier to use, they have a number of disadvantages compared to troff:

  * They must be used on a graphics display to work on a document.

  * Most of the WYSIWYG systems are either non-free or are not very portable.

  * troff is firmly entrenched in all UNIX systems.

  * It is difficult to have a wide range of capabilities available within the confines of a GUI/window system.

  * It is more difficult to make global changes to a document.

     ``GUIs normally make it simple to accomplish simple actions and impossible to accomplish complex actions.''  --Doug Gwyn (22/Jun/91 in comp.unix.wizards)

History
=======

troff can trace its origins back to a formatting program called runoff, written by J. E. Saltzer, which ran on MIT's CTSS operating system in the mid-sixties.  This name came from the common phrase of the time ``I'll run off a document.''  Bob Morris ported it to the 635 architecture and called the program roff (an abbreviation of runoff).  It was rewritten as rf for the PDP-7 (before having UNIX), and at the same time (1969), Doug McIllroy rewrote an extended and simplified version of roff in the BCPL programming language.

The first version of UNIX was developed on a PDP-7 which was sitting around Bell Labs.  In 1971 the developers wanted to get a PDP-11 for further work on the operating system.  In order to justify the cost for this system, they proposed that they would implement a document formatting system for the AT&T patents division. This first formatting program was a reimplementation of McIllroy's roff, written by J. F. Ossanna.

When they needed a more flexible language, a new version of roff called nroff (``Newer roff'') was written.  It had a much more complicated syntax, but provided the basis for all future versions. When they got a Graphic Systems CAT Phototypesetter, Ossanna wrote a version of nroff that would drive it.  It was dubbed troff, for ``typesetter roff'', although many people have speculated that it actually means ``Times roff'' because of the use of the Times font family in troff by default.  As such, the name troff is pronounced `t-roff' rather than `trough'.

With troff came nroff (they were actually the same program except for some #ifdefs), which was for producing output for line printers and character terminals.  It understood everything troff did, and ignored the commands which were not applicable (e.g. font changes).

Since there are several things which cannot be done easily in troff, work on several preprocessors began.  These programs would transform certain parts of a document into troff, which made a very natural use of pipes in UNIX.

The eqn preprocessor allowed mathematical formulæ to be specified in a much simpler and more intuitive manner.  tbl is a preprocessor for formatting tables.  The refer preprocessor (and the similar program, bib) processes citations in a document according to a bibliographic database.

Unfortunately, Ossanna's troff was written in PDP-11 assembly language and produced output specifically for the CAT phototypesetter. He rewrote it in C, although it was now 7000 lines of uncommented code and still dependent on the CAT.  As the CAT became less common, and was no longer supported by the manufacturer, the need to make it support other devices became a priority.  However, before this could be done, Ossanna was killed in an auto accident.

So, Brian Kernighan took on the task of rewriting troff.  The newly rewritten version produced a device independent code which was very easy for postprocessors to read and translate to the appropriate printer codes.  Also, this new version of troff (called ditroff for ``device independent troff'') had several extensions, which included drawing functions.

Due to the additional abilities of the new version of troff, several new preprocessors appeared.  The pic preprocessor provides a wide range of drawing functions.  Likewise the ideal preprocessor did the same, although via a much different paradigm.  The grap preprocessor took specifications for graphs, but, unlike other preprocessors, produced pic code.

James Clark began work on a GNU implementation of ditroff in early 1989.  The first version, groff 0.3.1, was released June 1990.  groff included:

  * A replacement for ditroff with many extensions.

  * The soelim, pic, tbl, and eqn preprocessors.

  * Postprocessors for character devices, POSTSCRIPT, TeX DVI, and X windows.  GNU troff also eliminated the need for a separate nroff program with a postprocessor which would produce ASCII output.

  * A version of the me macros and an implementation of the man macros.

Also, a front-end was included which could construct the, sometimes painfully long, pipelines required for all the post- and preprocessors.

Development of GNU troff progressed rapidly, and saw the additions of a replacement for refer, an implementation of the ms and mm macros, and a program to deduce how to format a document (grog).

It was declared a stable (i.e. non-beta) package with the release of version 1.04 around November 1991.

Beginning in 1999, groff has new maintainers (the package was an orphan for a few years).  As a result, new features and programs like grn, a preprocessor for gremlin images, and an output device to produce HTML output have been added.

groff Capabilities
==================

So what exactly is groff capable of doing?  groff provides a wide range of low-level text formatting operations.  Using these, it is possible to perform a wide range of formatting tasks, such as footnotes, table of contents, multiple columns, etc.  Here's a list of the most important operations supported by groff:

  * text filling, adjusting, and centering

  * hyphenation

  * page control

  * font and character size control

  * vertical spacing (i.e. double spacing)

  * line length and indenting

  * macros, strings, diversions, and traps

  * number registers

  * tabs, leaders, and fields

  * input and output conventions and character translation

  * overstrike, bracket, line drawing, and zero-width functions

  * local horizontal and vertical motions and the width function

  * three-part titles

  * output line numbering

  * conditional acceptance of input

  * environment switching

  * insertions from the standard input

  * input/output file switching

  * output and error messages

Macro Packages
==============

Since groff provides such low-level facilities, it can be quite difficult to use by itself.  However, groff provides a macro facility to specify how certain routine operations (e.g. starting paragraphs, printing headers and footers, etc.) should be done.  These macros can be collected together into a macro package.  There are a number of macro packages available; the most common (and the ones described in this manual) are man, mdoc, me, ms, and mm.

Preprocessors
=============

Although groff provides most functions needed to format a document, some operations would be unwieldy (e.g. to draw pictures). Therefore, programs called preprocessors were written which understand their own language and produce the necessary groff operations. These preprocessors are able to differentiate their own input from the rest of the document via markers.

To use a preprocessor, UNIX pipes are used to feed the output from the preprocessor into groff.  Any number of preprocessors may be used on a given document; in this case, the preprocessors are linked together into one pipeline.  However, in groff, the user does not need to construct the pipe, but only tell groff what preprocessors to use.

groff currently has preprocessors for producing tables (tbl), typesetting equations (eqn), drawing pictures (pic and grn), and for processing bibliographies (refer).  An associated program which is useful when dealing with preprocessors is soelim.

A free implementation of grap, a preprocessor for drawing graphs, can be obtained as an extra package; groff can use grap also.

There are other preprocessors in existence, but, unfortunately, no free implementations are available.  Among them are preprocessors for drawing mathematical pictures (ideal) and chemical structures (chem).

Output Devices
==============

groff actually produces device independent code which may be fed into a postprocessor to produce output for a particular device. Currently, groff has postprocessors for POSTSCRIPT devices, character terminals, X Windows (for previewing), TeX DVI format, HP LaserJet 4 and Canon LBP printers (which use CAPSL), and HTML.

Credits
=======

Large portions of this manual were taken from existing documents, most notably, the manual pages for the groff package by James Clark, and Eric Allman's papers on the me macro package.

The section on the man macro package is partly based on Susan G. Kleinmann's groff_man manual page written for the Debian GNU/Linux system.

Invoking groff
**************

This section focuses on how to invoke the groff front end.  This front end takes care of the details of constructing the pipeline among the preprocessors, gtroff and the postprocessor.

It has become a tradition that GNU programs get the prefix g to distinguish it from its original counterparts provided by the host (see Environment, for more details).  Thus, for example, geqn is GNU eqn.  On operating systems like Linux or the Hurd, which don't contain proprietary software, and on MS-DOS/MS-Windows, where troff and associated programs are not available at all, this prefix is omitted since GNU troff is the only used incarnation of troff.  Exception: groff is never replaced by roff.

Options
=======

groff normally runs the gtroff program and a postprocessor appropriate for the selected device.  The default device is ps (but it can be changed when groff is configured and built).  It can optionally preprocess with any of gpic, geqn, gtbl, ggrn, grap, grefer, or gsoelim.

This section only documents options to the groff front end.  Many of the arguments to groff are passed on to gtroff, therefore those are also included.  Arguments to pre- or postprocessors can be found in Invoking gpic, Invoking geqn, Invoking gtbl, Invoking ggrn, Invoking grefer, Invoking gsoelim, Invoking grotty, Invoking grops, Invoking grohtml, Invoking grodvi, Invoking grolj4, Invoking grolbp, and Invoking gxditview.

The command line format for groff is:

     groff [ -abeghilpstvzCEGNRSUVXZ ] [ -FDIR ] [ -mNAME ]
           [ -TDEF ] [ -fFAM ] [ -wNAME ] [ -WNAME ]
           [ -MDIR ] [ -dCS ] [ -rCN ] [ -nNUM ]
           [ -oLIST ] [ -PARG ] [ -LARG ] [ -IDIR ]
           [ FILES... ]

The command line format for gtroff is as follows.

     gtroff [ -abivzCERU ] [ -wNAME ] [ -WNAME ] [ -dCS ]
            [ -fFAM ] [ -mNAME ] [ -nNUM ]
            [ -oLIST ] [ -rCN ] [ -TNAME ]
            [ -FDIR ] [ -MDIR ] [ FILES... ]

Obviously, many of the options to groff are actually passed on to gtroff.

Options without an argument can be grouped behind a single -. A filename of - denotes the standard input.  It is possible to have whitespace between an option and its parameter.

The grog command can be used to guess the correct groff command to format a file.

Here's the description of the command-line options:

-h
     Print a help message.

-e
     Preprocess with geqn.

-t
     Preprocess with gtbl.

-g
     Preprocess with ggrn.

-G
     Preprocess with grap.

-p
     Preprocess with gpic.

-s
     Preprocess with gsoelim.

-R
     Preprocess with grefer.  No mechanism is provided for passing arguments to grefer because most grefer options have equivalent commands which can be included in the file.  See grefer, for more details.

     Note that gtroff also accepts a -R option, which is not accessible via groff.  This option prevents the loading of the troffrc and troffrc-end files.

-v
     Make programs run by groff print out their version number.

-V
     Print the pipeline on stdout instead of executing it.

-z
     Suppress output from gtroff.  Only error messages are printed.

-Z
     Do not postprocess the output of gtroff.  Normally groff automatically runs the appropriate postprocessor.

-PARG
     Pass ARG to the postprocessor.  Each argument should be passed with a separate -P option.  Note that groff does not prepend - to ARG before passing it to the postprocessor.

-l
     Send the output to a spooler for printing.  The command used for this is specified by the print command in the device description file (see Font Files, for more info).  If not present, -l is ignored.

-LARG
     Pass ARG to the spooler.  Each argument should be passed with a separate -L option.  Note that groff does not prepend a - to ARG before passing it to the postprocessor.  If the print keyword in the device description file is missing, -L is ignored.

-TDEV
     Prepare output for device DEV.  The default device is ps, unless changed when groff was configured and built.  The following are the output devices currently available:

     ps
          For POSTSCRIPT printers and previewers.

     dvi
          For TeX DVI format.

     X75
          For a 75dpi X11 previewer.

     X100
          For a 100dpi X11 previewer.

     ascii
          For typewriter-like devices.

     latin1
          For typewriter-like devices that support the Latin-1 (ISO 8859-1) character set.

     utf8
          For typewriter-like devices which use the Unicode (ISO 10646) character set with UTF-8 encoding.

     cp1047
          For typewriter-like devices which use the EBCDIC encoding IBM cp1047.

     lj4
          For an HP LaserJet4-compatible (or other PCL5-compatible) printer.

     lbp
          For Canon CAPSL printers (LBP-4 and LBP-8 series laser printers).

     html
          To produce HTML output.  Note that the HTML driver consists of two parts, a preprocessor (pre-grohtml) and a postprocessor (post-grohtml).

     The predefined gtroff string register .T contains the current output device; the read-only number register .T is set to 1 if this option is used (which is always true if groff is used to call gtroff).  See Built-in Registers.

     The postprocessor to be used for a device is specified by the postpro command in the device description file.  (see Font Files, for more info.)  This can be overridden with the -X option.

-X
     Preview with gxditview instead of using the usual postprocessor. This is unlikely to produce good results except with -Tps.

     Note that this is not the same as using -TX75 or -TX100 to view a document with gxditview: The former uses the metrics of the specified device, whereas the latter uses X-specific fonts and metrics.

-N
     Don't allow newlines with eqn delimiters.  This is the same as the -N option in geqn.

-S
     Safer mode.  Pass the -S option to gpic and disable the open, opena, pso, sy, and pi requests.  For security reasons, this is enabled by default.

-U
     Unsafe mode.  Reverts to the old unsafe behaviour.

-a
     Generate an ASCII approximation of the typeset output.  The read-only register .A is then set to 1.  See Built-in Registers.  A typical example is

          groff -a -man -Tdvi troff.man | less

     which shows how lines are broken for the DVI device.  Note that this option is rather useless today since graphic output devices are available virtually everywhere.

-b
     Print a backtrace with each warning or error message.  This backtrace should help track down the cause of the error.  The line numbers given in the backtrace may not always be correct: gtroff can get confused by as or am requests while counting line numbers.

-i
     Read the standard input after all the named input files have been processed.

-wNAME
     Enable warning NAME.  Available warnings are described in Debugging.  Multiple -w options are allowed.

-WNAME
     Inhibit warning NAME.  Multiple -W options are allowed.

-E
     Inhibit all error messages.

-C
     Enable compatibility mode.  See Implementation Differences, for the list of incompatibilities between groff and traditional Unix troff.

-dCS
-dNAME=s
     Define C or NAME to be a string S.  C must be a one-letter name; NAME can be of arbitrary length.  All string assignments happen before loading any macro file (including the start-up file).

-fFAM
     Use FAM as the default font family.  See Font Families.

-mNAME
     Read in the file NAME.tmac.  Normally groff searches for this in its macro directories.  If it isn't found, it tries tmac.NAME (and searches in the same directories).

-nNUM
     Number the first page NUM.

-oLIST
     Output only pages in LIST, which is a comma-separated list of page ranges; N means print page N, M-N means print every page between M and N, -N means print every page up to N, N- means print every page beginning with N.  gtroff exits after printing the last page in the list.  All the ranges are inclusive on both ends.

     Within gtroff, this information can be extracted with the .P register.  See Built-in Registers.

     If your document restarts page numbering at the beginning of each chapter, then gtroff prints the specified page range for each chapter.

-rCN
-rNAME=N
     Set number register C or NAME to the value N.  C must be a one-letter name; NAME can be of arbitrary length. N can be any gtroff numeric expression.  All register assignments happen before loading any macro file (including the start-up file).

-FDIR
     Search DIR for subdirectories devNAME (NAME is the name of the device), for the DESC file, and for font files before looking in the standard directories.

-MDIR
     Search directory DIR for macro files before the standard directories.

-IDIR
     This option is as described in gsoelim.  It implies the -s option.

Environment
===========

There are also several environment variables (of the operating system, not within gtroff) which can modify the behavior of groff.

GROFF_COMMAND_PREFIX
     If this is set to X, then groff runs Xtroff instead of gtroff.  This also applies to tbl, pic, eqn, grn, refer, and soelim.  It does not apply to grops, grodvi, grotty, pre-grohtml, post-grohtml, grolj4, and gxditview.

GROFF_TMAC_PATH
     A colon-separated list of directories in which to search for macro files (before the default directories are tried).

GROFF_TYPESETTER
     The default output device.

GROFF_FONT_PATH
     A colon-separated list of directories in which to search for the devNAME directory (before the default directories are tried).

GROFF_BIN_PATH
     This search path, followed by PATH, is used for commands executed by groff.

GROFF_TMPDIR
     The directory in which groff creates temporary files.  If this is not set and TMPDIR is set, temporary files are created in that directory.  Otherwise temporary files are created in a system-dependent default directory (on Unix and GNU/Linux systems, this is usually /tmp).  grops, grefer, pre-grohtml, and post-grohtml can create temporary files in this directory.

Note that MS-DOS and MS-Windows ports of groff use semi-colons, rather than colons, to separate the directories in the lists described above.

Invocation Examples
===================

This section lists several common uses of groff and the corresponding command lines.

     groff file

This command processes file without a macro package or a preprocessor.  The output device is the default, ps, and the output is sent to stdout.

     groff -t -mandoc -Tascii file | less

This is basically what a call to the man program does. gtroff processes the manual page file with the mandoc macro file (which in turn either calls the man or the mdoc macro package), using the tbl preprocessor and the ASCII output device.  Finally, the less pager displays the result.

     groff -X -m me file

Preview file with gxditview, using the me macro package.  Since no -T option is specified, use the default device (ps).  Note that you can either say -m me or -me; the latter is an anachronism from the early days of UNIX. (The same is true for the other main macro packages that come with groff: man, mdoc, ms, mm, and mandoc.  This won't work in general; for example, to load trace.tmac, either -mtrace or -m trace must be used.)

     groff -man -rD1 -z file

Check file with the man macro package, forcing double-sided printing -- don't produce any output.

grog
----

grog reads files, guesses which of the groff preprocessors and/or macro packages are required for formatting them, and prints the groff command including those options on the standard output.  It generates one or more of the options -e, -man, -me, -mm, -ms, -mdoc, -mdoc-old, -p, -R, -g, -G, -s, and -t.

A special file name - refers to the standard input.  Specifying no files also means to read the standard input.  Any specified options are included in the printed command.  No space is allowed between options and their arguments.  The only options recognized are -C (which is also passed on) to enable compatibility mode, and -v (if it is the only parameter) to print the version number.

For example,

     grog -Tdvi paper.ms

guesses the appropriate command to print paper.ms and then prints it to the command line after adding the -Tdvi option.  For direct execution, enclose the call to grog in backquotes at the UNIX shell prompt:

     `grog -Tdvi paper.ms` > paper.dvi

As seen in the example, it is still necessary to redirect the output to something meaningful (i.e. either a file or a pager program like less).

Tutorial for Macro Users
************************

Most users tend to use a macro package to format their papers.  This means that the whole breadth of groff is not necessary for most people.  This chapter covers the material needed to efficiently use a macro package.

Basics
======

This section covers some of the basic concepts necessary to understand how to use a macro package. (This section is derived from Writing Papers with nroff using -me by Eric P. Allman.) References are made throughout to more detailed information, if desired.

gtroff reads an input file prepared by the user and outputs a formatted document suitable for publication or framing.  The input consists of text, or words to be printed, and embedded commands (requests and escapes), which tell gtroff how to format the output.  For more detail on this, see Embedded Commands.

The word argument is used in this chapter to mean a word or number which appears on the same line as a request, and which modifies the meaning of that request.  For example, the request

     .sp

spaces one line, but

     .sp 4

spaces four lines.  The number 4 is an argument to the sp request which says to space four lines instead of one.  Arguments are separated from the request and from each other by spaces (no tabs).  More details on this can be found in Request Arguments.

The primary function of gtroff is to collect words from input lines, fill output lines with those words, justify the right-hand margin by inserting extra spaces in the line, and output the result.  For example, the input:

     Now is the time
     for all good men
     to come to the aid
     of their party.
     Four score and seven
     years ago,...

is read, packed onto output lines, and justified to produce:

     Now is the time for all good men to come to the aid of their party. Four score and seven years ago,...

Sometimes a new output line should be started even though the current line is not yet full; for example, at the end of a paragraph.  To do this it is possible to cause a break, which starts a new output line.  Some requests cause a break automatically, as normally do blank input lines and input lines beginning with a space.

Not all input lines are text to be formatted.  Some input lines are requests which describe how to format the text.  Requests always have a period (.) or an apostrophe (') as the first character of the input line.

The text formatter also does more complex things, such as automatically numbering pages, skipping over page boundaries, putting footnotes in the correct place, and so forth.

Here are a few hints for preparing text for input to gtroff.

  * First, keep the input lines short.  Short input lines are easier to edit, and gtroff packs words onto longer lines anyhow.

  * In keeping with this, it is helpful to begin a new line after every comma or phrase, since common corrections are to add or delete sentences or phrases.

  * End each sentence with two spaces -- or better, start each sentence on a new line.  gtroff recognizes characters that usually end a sentence, and inserts sentence space accordingly.

  * Do not hyphenate words at the end of lines -- gtroff is smart enough to hyphenate words as needed, but is not smart enough to take hyphens out and join a word back together.  Also, words such as ``mother-in-law'' should not be broken over a line, since then a space can occur where not wanted, such as ``mother- in-law''.

gtroff double spaces output text automatically if you use the request .ls 2.  Reactivate single spaced mode by typing .ls 1.

A number of requests allow to change the way the output looks, sometimes called the layout of the output page.  Most of these requests adjust the placing of white space (blank lines or spaces).

The .bp request starts a new page, causing a line break.

The request .sp N leaves N lines of blank space.  N can be omitted (meaning skip a single line) or can be of the form Ni (for N inches) or Nc (for N centimeters).  For example, the input:

     .sp 1.5i
     My thoughts on the subject
     .sp

leaves one and a half inches of space, followed by the line ``My thoughts on the subject'', followed by a single blank line (more measurement units are available, see Measurements).

Text lines can be centered by using the ce request.  The line after ce is centered (horizontally) on the page.  To center more than one line, use .ce N (where N is the number of lines to center), followed by the N lines.  To center many lines without counting them, type:

     .ce 1000
     lines to center
     .ce 0

The .ce 0 request tells groff to center zero more lines, in other words, stop centering.

All of these requests cause a break; that is, they always start a new line.  To start a new line without performing any other action, use br.

Common Features
===============

gtroff provides very low-level operations for formatting a document.  There are many common routine operations which are done in all documents.  These common operations are written into macros and collected into a macro package.

All macro packages provide certain common capabilities which fall into the following categories.

Paragraphs
----------

One of the most common and most used capability is starting a paragraph.  There are a number of different types of paragraphs, any of which can be initiated with macros supplied by the macro package. Normally, paragraphs start with a blank line and the first line indented, like the text in this manual.  There are also block style paragraphs, which omit the indentation:

     Some   men  look   at  constitutions   with  sanctimonious
     reverence, and deem them like the ark of the covenant, too
     sacred to be touched.

And there are also indented paragraphs which begin with a tag or label at the margin and the remaining text indented.

     one   This is  the first paragraph.  Notice  how the first
           line of  the resulting  paragraph lines up  with the
           other lines in the paragraph.

     longlabel
           This  paragraph   had  a  long   label.   The  first
           character of text on the first line does not line up
           with  the  text  on  second  and  subsequent  lines,
           although they line up with each other.

A variation of this is a bulleted list.

Sections and Chapters
---------------------

Most macro packages supply some form of section headers.  The simplest kind is simply the heading on a line by itself in bold type.  Others supply automatically numbered section heading or different heading styles at different levels.  Some, more sophisticated, macro packages supply macros for starting chapters and appendices.

Headers and Footers
-------------------

Every macro package gives some way to manipulate the headers and footers (or titles) on each page.  Some packages allow for different ones on the even and odd pages (for material printed in a book form).

The titles are called three-part titles, that is, there is a left-justified part, a centered part, and a right-justified part.  An automatically generated page number may be put in any of these fields with the % character (see Page Layout, for more details).

Page Layout
-----------

Most macro packages let the user specify top and bottom margins and other details about the appearance of the printed pages.

Displays
--------

Displays are sections of text to be set off from the body of the paper. Major quotes, tables, and figures are types of displays, as are all the examples used in this document.

Major quotes are quotes which are several lines long, and hence are set in from the rest of the text without quote marks around them.

A list is an indented, single spaced, unfilled display.  Lists should be used when the material to be printed should not be filled and justified like normal text, such as columns of figures or the examples used in this paper.

A keep is a display of lines which are kept on a single page if possible.  An example for a keep might be a diagram.  Keeps differ from lists in that lists may be broken over a page boundary whereas keeps are not.

Floating keeps move relative to the text.  Hence, they are good for things which are referred to by name, such as ``See figure 3''.  A floating keep appears at the bottom of the current page if it fits; otherwise, it appears at the top of the next page.  Meanwhile, the surrounding text `flows' around the keep, thus leaving no blank areas.

Footnotes and Annotations
-------------------------

There are a number of requests to save text for later printing.

Footnotes are printed at the bottom of the current page.

Delayed text is very similar to a footnote except that it is printed when called for explicitly.  This allows a list of references to appear (for example) at the end of each chapter, as is the convention in some disciplines.

Most macro packages which supply this functionality also supply a means of automatically numbering either type of annotation.

Table of Contents
-----------------

Tables of contents are a type of delayed text having a tag (usually the page number) attached to each entry after a row of dots. The table accumulates throughout the paper until printed, usually after the paper has ended.  Many macro packages provide the ability to have several tables of contents (e.g. a standard table of contents, a list of tables, etc).

Indices
-------

While some macro packages use the term index, none actually provide that functionality.  The facilities they call indices are actually more appropriate for tables of contents.

Paper Formats
-------------

Some macro packages provide stock formats for various kinds of documents.  Many of them provide a common format for the title and opening pages of a technical paper.  The mm macros in particular provide formats for letters and memoranda.

Multiple Columns
----------------

Some macro packages (but not man) provide the ability to have two or more columns on a page.

Font and Size Changes
---------------------

The built-in font and size functions are not always intuitive, so all macro packages provide macros to make these operations simpler.

Predefined Strings
------------------

Most macro packages provide various predefined strings for a variety of uses; examples are sub- and superscripts, printable dates, quotes and various special characters.

Preprocessor Support
--------------------

All macro packages provide support for the various preprocessors and may extend their functionality.

For example, all macro packages mark tables (which are processed with gtbl) by placing them between .TS and .TE macros. The ms macro package has an option, .TSH, that prints a caption at the top of a new page (when the table is too long to fit on a single page).

Configuration and Customization
-------------------------------

Some macro packages provide means of customizing many of the details of how the package behaves.  This ranges from setting the default type size to changing the appearance of section headers.

Macro Packages
**************

This chapter documents the main macro packages that come with groff.

man
===

This is the most popular and probably the most important macro package of groff.  It is easy to use, and a vast majority of manual pages are based on it.

Options
-------

The command line format for using the man macros with groff is:

     groff -m man [ -rcR=1 ] [ -rC1 ] [ -rD1 ] [ -rPNNN ]
           [ -rSXX ] [ -rXNNN ] [ FILES... ]

It is possible to use -man instead of -m man.

-rcR=1
     This option (the default if a tty output device is used) creates a single, very long page instead of multiple pages.  Use -rcR=0 to disable it.

-rC1
     If more than one manual page is given on the command line, number the pages continuously, rather than starting each at 1.

-rD1
     Double-sided printing.  Footers for even and odd pages are formatted differently.

-rPNNN
     Page numbering starts with NNN rather than with 1.

-rSXX
     Use XX (which can be 10, 11, or 12pt) as the base document font size instead of the default value of 10pt.

-rXNNN
     After page NNN, number pages as NNNa, NNNb, NNNc, etc.  For example, the option -rX2 produces the following page numbers: 1, 2, 2a, 2b, 2c, etc.

Usage
-----

This section describes the available macros for manual pages.  For further customization, put additional macros and requests into the file man.local which is loaded immediately after the man package.

 -- Macro: .TH, title section [extra1] [extra2] [extra3]
     Set the title of the man page to TITLE and the section to SECTION, which must have a value between 1 and 8.  The value of SECTION may also have a string appended, e.g. .pm, to indicate a specific subsection of the man pages.

     Both TITLE and SECTION are positioned at the left and right in the header line (with SECTION in parentheses immediately appended to TITLE.  EXTRA1 is positioned in the middle of the footer line.  EXTRA2 is positioned at the left in the footer line (or at the left on even pages and at the right on odd pages if double-sided printing is active).  EXTRA3 is centered in the header line.

     For HTML output, headers and footers are completely suppressed.

     Additionally, this macro starts a new page; the new line number is 1 again (except if the -rC1 option is given on the command line) -- this feature is intended only for formatting multiple man pages; a single man page should contain exactly one TH macro at the beginning of the file.

 -- Macro: .SH, [heading]
     Set up an unnumbered section heading sticking out to the left.  Prints out all the text following SH up to the end of the line (or the text in the next line if there is no argument to SH) in bold face, one size larger than the base document size.  Additionally, the left margin for the following text is reset to its default value.

 -- Macro: .SS, [heading]
     Set up an unnumbered (sub)section heading.  Prints out all the text following SS up to the end of the line (or the text in the next line if there is no argument to SS) in bold face, at the same size as the base document size.  Additionally, the left margin for the following text is reset to its default value.

 -- Macro: .TP, [nnn]
     Set up an indented paragraph with label.  The indentation is set to NNN if that argument is supplied (the default unit is n if omitted), otherwise it is set to the default indentation value.

     The first line of text following this macro is interpreted as a string to be printed flush-left, as it is appropriate for a label.  It is not interpreted as part of a paragraph, so there is no attempt to fill the first line with text from the following input lines.  Nevertheless, if the label is not as wide as the indentation, then the paragraph starts at the same line (but indented), continuing on the following lines. If the label is wider than the indentation, then the descriptive part of the paragraph begins on the line following the label, entirely indented.  Note that neither font shape nor font size of the label is set to a default value; on the other hand, the rest of the text has default font settings.

 -- Macro: .LP
 -- Macro: .PP
 -- Macro: .P
     These macros are mutual aliases.  Any of them causes a line break at the current position, followed by a vertical space downwards by the amount specified by the PD macro.  The font size and shape are reset to the default value (10pt roman).  Finally, the current left margin is restored.

 -- Macro: .IP, [designator] [nnn]
     Set up an indented paragraph, using DESIGNATOR as a tag to mark its beginning.  The indentation is set to NNN if that argument is supplied (default unit is n), otherwise the default indentation value is used.  Font size and face of the paragraph (but not the designator) are reset to their default values.  To start an indented paragraph with a particular indentation but without a designator, use "" (two double quotes) as the first argument of IP.

     For example, to start a paragraph with bullets as the designator and 4en indentation, write

          .IP \(bu 4

 -- Macro: .HP, [nnn]
     Set up a paragraph with hanging left indentation.  The indentation is set to NNN if that argument is supplied (default unit is n), otherwise the default indentation value is used.  Font size and face are reset to their default values.

 -- Macro: .RS, [nnn]
     Move the left margin to the right by the value NNN if specified (default unit is n); otherwise the default indentation value is used.  Calls to the RS macro can be nested.

 -- Macro: .RE, [nnn]
     Move the left margin back to level NNN; if no argument is given, it moves one level back.  The first level (i.e., no call to RS yet) has number 1, and each call to RS increases the level by 1.

To summarize, the following macros cause a line break with the insertion of vertical space (which amount can be changed with the PD macro): SH, SS, TP, LP (PP, P), IP, and HP.

The macros RS and RE also cause a break but do not insert vertical space.

Macros to set fonts
-------------------

The standard font is roman; the default text size is 10 point.

 -- Macro: .SM, [text]
     Set the text on the same line or the text on the next line in a font that is one point size smaller than the default font.

 -- Macro: .SB, [text]
     Set the text on the same line or the text on the next line in boldface font, one point size smaller than the default font.

 -- Macro: .BI, text
     Set its arguments alternately in bold face and italic.  Thus,

          .BI this "word and" that

     would set ``this'' and ``that'' in bold face, and ``word and'' in italics.

 -- Macro: .IB, text
     Set its arguments alternately in italic and bold face.

 -- Macro: .RI, text
     Set its arguments alternately in roman and italic.

 -- Macro: .IR, text
     Set its arguments alternately in italic and roman.

 -- Macro: .BR, text
     Set its arguments alternately in bold face and roman.

 -- Macro: .RB, text
     Set its arguments alternately in roman and bold face.

 -- Macro: .R, [text]
     Set TEXT in roman font.  If no text is present on the line where the macro is called, then the text of the next line appears in roman. This is the default font to which text is returned at the end of processing of the other macros.

 -- Macro: .B, [text]
     Set TEXT in bold face.  If no text is present on the line where the macro is called, then the text of the next line appears in bold face.

 -- Macro: .I, [text]
     Set TEXT in italic.  If no text is present on the line where the macro is called, then the text of the next line appears in italic.

Miscellaneous macros
--------------------

The default indentation is 7.2n for all output devices except for grohtml which ignores indentation.

 -- Macro: .DT
     Set tabs every 0.5 inches.  Since this macro is always called during a TH request, it makes sense to call it only if the tab positions have been changed.

 -- Macro: .PD, [nnn]
     Adjust the empty space before a new paragraph (or section).  The optional argument gives the amount of space (default unit is v); without parameter, the value is reset to its default value (1 line for tty devices, 0.4v otherwise).

This affects the macros SH, SS, TP, LP (as well as PP and P), IP, and HP.

Predefined strings
------------------

The following strings are defined:

 -- String: *S
     Switch back to the default font size.

 -- String: *R
     The `registered' sign.

 -- String: Tm
     The `trademark' sign.

 -- String: lq
 -- String: rq
     Left and right quote.  This is equal to \(lq and \(rq, respectively.

Preprocessors in man pages
--------------------------

If a preprocessor like gtbl or geqn is needed, it has become common usage to make the first line of the man page look like this:

     .\" WORD

Note the single space character after the double quote.  WORD consists of letters for the needed preprocessors: e for geqn, r for grefer, t for gtbl. Modern implementations of the man program read this first line and automatically call the right preprocessor(s).

mdoc
====

ms
==

me
==

mm
==

gtroff Reference
****************

This chapter covers all of the facilities of gtroff. Users of macro packages may skip it if not interested in details.

Text
====

gtroff input files contain text with control commands interspersed throughout.  But, even without control codes, gtroff still does several things with the input text:

  * filling and adjusting

  * adding additional space after sentences

  * hyphenating

  * inserting implicit line breaks

Filling and Adjusting
---------------------

When gtroff reads text, it collects words from the input and fits as many of them together on one output line as it can.  This is known as filling.

Once gtroff has a filled line, it tries to adjust it.  This means it widens the spacing between words until the text reaches the right margin (in the default adjustment mode).  Extra spaces between words are preserved, but spaces at the end of lines are ignored. Spaces at the front of a line cause a break (breaks are explained in Implicit Line Breaks)

See Manipulating Filling and Adjusting.

Hyphenation
-----------

Since the odds are not great for finding a set of words, for every output line, which fit nicely on a line without inserting excessive amounts of space between words, gtroff hyphenates words so that it can justify lines without inserting too much space between words.  It uses an internal hyphenation algorithm (a simplified version of the algorithm used within TeX) to indicate which words can be hyphenated and how to do so.  When a word is hyphenated, the first part of the word is added to the current filled line being output (with an attached hyphen), and the other portion is added to the next line to be filled.

See Manipulating Hyphenation.

Sentences
---------

Although it is often debated, some typesetting rules say there should be different amounts of space after various punctuation marks.  For example, the Chicago typsetting manual says that a period at the end of a sentence should have twice as much space following it as would a comma or a period as part of an abbreviation.

gtroff does this by flagging certain characters (normally !, ?, and .) as end of sentence characters. When gtroff encounters one of these characters at the end of a line, it appends a normal space followed by a sentence space in the formatted output.  (This justifies one of the conventions mentioned in Input Conventions.)

In addition, the following characters or glyphs are treated transparently while handling end of sentence characters: ", ', ), ], *, dg, and rq.

See the cflags request in Using Symbols, for more details.

To prevent the insertion of extra space after an end of sentence character (at the end of a line), append \&.

Tab Stops
---------

gtroff translates tabulator characters, also called tabs (normally code point ASCII 0x09 or EBCDIC 0x05), in the input into movements to the next tabulator stop.  These tab stops are initially located every half inch across the page.  Using this, simple tables can be made easily. However, it can often be deceptive as the appearance (and width) of the text on a terminal and the results from gtroff can vary greatly.

Also, a possible sticking point is that lines beginning with tab characters are still filled, again producing unexpected results. For example, the following input

1   2   3

  4   5

produces

1   2   3       4   5

See Tabs and Fields.

Implicit Line Breaks
--------------------

An important concept in gtroff is the break.  When a break occurs, gtroff outputs the partially filled line (unjustified), and resumes collecting and filling text on the next output line.

There are several ways to cause a break in gtroff.  A blank line not only causes a break, but it also outputs a one line vertical space (effectively a blank line).  Note that this behaviour can be modified with the blank line macro request blm.

A line that begins with a space causes a break and the space is output at the beginning of the next line.  Note that this space isn't adjusted, even in fill mode.

The end of file also causes a break -- otherwise the last line of the document may vanish!

Certain requests also cause breaks, implicitly or explicitly.  This is discussed in Manipulating Filling and Adjusting.

Input Conventions
=================

Since gtroff does filling automatically, it is traditional in groff not to try and type things in as nicely formatted paragraphs.  These are some conventions commonly used when typing gtroff text:

  * Break lines after punctuation, particularly at the end of a sentence and in other logical places.  Keep separate phrases on lines by themselves, as entire phrases are often added or deleted when editing.

  * Try to keep lines less than 40-60 characters, to allow space for inserting more text.

  * Do not try to do any formatting in a WYSIWYG manner (i.e., don't try using spaces to get proper indentation).

Measurements
============

gtroff (like many other programs) requires numeric parameters to specify various measurements.  Most numeric parameters (those that specify vertical or horizontal motion or a type size) may have a measurement unit attached.  These units are specified as a single character which immediately follows the number or expression.  Each of these units are understood, by gtroff, to be a multiple of its basic unit.  So, whenever a different measurement unit is specified gtroff converts this into its basic units.  This basic unit, represented by a u, is a device dependent measurement which is quite small, ranging from 1/75th to 1/72000th of an inch.  The values may be given as fractional numbers; however, fractional basic units are always rounded to integers.

Some of the measurement units are completely independent of any of the current settings (e.g. type size) of gtroff.

i
     Inches.  An antiquated measurement unit still in use in certain backwards countries with incredibly low-cost computer equipment.  One inch is equal to 2.54cm.

c
     Centimeters.  One centimeter is equal to 0.3937in.

p
     Points.  This is a typesetter's measurement used for measure type size. It is 72 points to an inch.

P
     Pica.  Another typesetting measurement.  6 Picas to an inch (and 12 points to a pica).

s
z
     See Fractional Type Sizes, for a discussion of these units.

The other measurements understood by gtroff depend on settings currently in effect in gtroff.  These are very useful for specifying measurements which should look proper with any size of text.

m
     Ems.  This unit is equal to the current font size in points.  So called because it is approximately the width of the letter m in the current font.

n
     Ens.  This is half of an em.

v
     Vertical space.  This is equivalent to the current line spacing. See Sizes, for more information about this.

M
     100ths of an em.

Default Units
-------------

Many requests take a default unit.  While this can be helpful at times, it can cause strange errors in some expressions.  For example, the line length request expects em units.  Here are several attempts to get a line length of 3.5 inches and their results:

     3.5i      =>   3.5i
     7/2       =>   0i
     7/2i      =>   0i
     7i/2      =>   0.1i
     7i/2u     =>   3.5i

Everything is converted to basic units first.  In the above example it is assumed that 1i equals 240u, and 1m equals 10p (thus 1m equals 33u).  The value 7i/2 is first handled as 7i/2m, then converted to 1680u/66u which is 25u, and this is approximately 0.1i.

Thus, the safest way to specify measurements is to always attach a scaling indicator.  If you want to multiply or divide by a certain scalar value, use u as the unit for that value.

Expressions
===========

gtroff has most arithmetic operators common to other languages:

  * Arithmetic: + (addition), - (subtraction), / (division), * (multiplication), % (modulo).

     gtroff only provides integer arithmetic.  The internal type used for computing results is int, which is usually a 32bit signed integer.

  * Comparison: < (less than), > (greater than), <= (less than or equal), >= (greater than or equal), = (equal), == (the same as =).

  * Logical: & (logical and), : (logical or).

  * Unary operators: - (negating, i.e. changing the sign), + (just for completeness; does nothing in expressions), ! (logical not; this works only within if and while requests).  See below for the use of unary operators in motion requests.

  * Extrema: >? (maximum), <? (minimum).  For example, 5>?3 yields 5.

  * Scaling: (C;E).  Evaluate E using C as the default scaling indicator.  If C is missing, ignore scaling indicators in the evaluation of E.

Parentheses may be used as in any other language.  However, in gtroff they are necessary to ensure order of evaluation. gtroff has no operator precedence; expressions are evaluated left to right.  This means that gtroff evaluates 3+5*4 as if it were parenthesized like (3+5)*4, not as 3+(5*4), as might be expected.

For many requests which cause a motion on the page, the unary operators work differently.  The + and - operators then indicate a motion relative to the current position (down or up, respectively), and the | operator indicates an absolute position on the page or input line. + and - are also treated differently by the following requests and escapes: bp, in, ll, lt, nm, nr, pl, pn, po, ps, rt, ti, \R, and \s.  Here the plus and minus signs indicate increments and decrements.

See Setting Registers.

Due to the way arguments are parsed, spaces are not allowed in expressions, unless the entire expression is surrounded by parentheses.

See Request Arguments, and Conditionals and Loops.

Identifiers
===========

Like any other language, gtroff has rules for properly formed identifiers.  In gtroff, an identifier can be made up of almost any printable character, with the exception of the following characters:

  * Whitespace characters (spaces, tabs, and newlines).

  * Backspace (ASCII 0x08 or EBCDIC 0x16) and character code 0x01.

  * The following input characters are invalid and are ignored if groff runs on a machine based on ASCII, causing a warning message of type input (see Debugging, for more details): 0x00, 0x0B, 0x0D-0x1F, 0x80-0x9F.

     And here are the invalid input characters if groff runs on an EBCDIC host: 0x00, 0x08, 0x09, 0x0B, 0x0D-0x14, 0x17-0x1F, 0x30-0x3F.

     Currently, some of these reserved codepoints are used internally, thus making it non-trivial to extend gtroff to cover Unicode or other character sets and encodings which use characters of these ranges.

     Note that invalid characters are removed before parsing; an identifier foo, followed by an invalid character, followed by bar is treated as foobar.

For example, any of the following is valid.

     br
     PP
     (l
     end-list
     @_

Note that identifiers longer than two characters with a closing bracket (]) in its name can't be accessed with escape sequences which expect an identifier as a parameter.  For example, \[foo]] accesses the glyph foo, followed by ], whereas \C'foo]' really asks for glyph foo].

 -- Escape: \\A, ', ident, '
     Test whether an identifier IDENT is valid in gtroff.  It expands to the character 1 or 0 according to whether its argument (usually delimited by quotes) is or is not acceptable as the name of a string, macro, diversion, number register, environment, or font.  It returns 0 if no argument is given.  This is useful for looking up user input in some sort of associative table.

          \A'end-list'
              => 1

See Escapes, for details on parameter delimiting characters.

Identifiers in gtroff can be any length, but, in some contexts, gtroff needs to be told where identifiers end and text begins (and in different ways depending on their length):

  * Single character.

  * Two characters.  Must be prefixed with ( in some situations.

  * Arbitrary length (gtroff only).  Must be bracketed with [ and ] in some situations.  Any length identifier can be put in brackets.

Unlike many other programming languages, undefined identifiers are silently ignored or expanded to nothing. When gtroff finds an undefined identifier, it emits a warning then:

  * If the identifier is a string, macro, or diversion, gtroff defines it as empty.

  * If the identifier is a number register, gtroff defines it with a value of 0.

See Warnings.

See Interpolating Registers, and Strings.

Embedded Commands
=================

Most documents need more functionality beyond filling, adjusting and implicit line breaking.  In order to gain further functionality, gtroff allows commands to be embedded into the text, in two ways.

The first is a request which takes up an entire line, and does some large-scale operation (e.g. break lines, start new pages).

The other is an escape which can be embedded anywhere in the text, or even as an argument to a request. Escapes generally do more minor operations like sub- and superscripts, print a symbol, etc.

Requests
--------

A request line begins with a control character, which is either a single quote (', the no-break control character) or a period (., the normal control character).  These can be changed; see Character Translations, for details.  After this there may be optional tabs or spaces followed by an identifier which is the name of the request.  This may be followed by any number of space-separated arguments (no tabs here).

Since a control character followed by whitespace only is ignored, it is common practice to use this feature for structuring the source code of documents or macro packages.

     .de foo
     .  tm This is foo.
     ..
     .
     .
     .de bar
     .  tm This is bar.
     ..

Another possibility is to use the blank line macro request blm by assigning an empty macro to it.

     .de do-nothing
     ..
     .blm do-nothing  \" activate blank line macro

     .de foo
     .  tm This is foo.
     ..

     .de bar
     .  tm This is bar.
     ..

     .blm             \" deactivate blank line macro

To begin a line with a control character without it being interpreted, precede it with \&.  This represents a zero width space, which means it does not affect the output.

In most cases the period is used as a control character.  Several requests cause a break implicitly; using the single quote control character prevents this.

Request Arguments
.................

Arguments to requests (and macros) are processed much like the shell: The line is split into arguments according to spaces.  An argument which is intended to contain spaces can either be enclosed in double quotes, or have the spaces escaped with backslashes.

Here are a few examples:

     .uh The Mouse Problem
     .uh "The Mouse Problem"
     .uh The\ Mouse\ Problem

The first line is the uh macro being called with 3 arguments, The, Mouse, and Problem.  The latter two have the same effect of calling the uh macro with one argument, The Mouse Problem. (The last solution, i.e., using escaped spaces, is ``classical'' in the sense that it can be found in most troff documents.  Nevertheless, it is not optimal in all situations, since \  inserts a fixed-width, non-breaking space character which can't stretch.  gtroff provides a different command \~ to insert a stretchable, non-breaking space.)

A double quote which isn't preceded by a space doesn't start a macro argument.  If not closing a string, it is printed literally.

For example,

     .xxx a" "b c" "de"fg"

has the arguments a", b c, de, and fg".

Duoble quotes in the ds request are handled differently. See Strings, for more details.

Macros
------

gtroff has a macro facility for defining a series of lines which can be invoked by name.  They are called in the same manner as requests -- arguments also may be passed in the same manner.

See Writing Macros, and Request Arguments.

Escapes
-------

Escapes may occur anywhere in the input to gtroff.  They usually begin with a backslash and are followed by a single character which indicates the function to be performed.  The escape character can be changed; see Character Translations.

Escape sequences which require an identifier as a parameter accept three possible syntax forms.

  * The next single character is the identifier.

  * If this single character is an opening parenthesis, take the following two characters as the identifier.  Note that there is no closing parenthesis after the identifier.

  * If this single character is an opening bracket, take all characters until a closing bracket as the identifier.

Examples:

     \fB
     \n(XX
     \*[TeX]

Other escapes may require several arguments and/or some special format. In such cases the argument is traditionally enclosed in single quotes (and quotes are always used in this manual for the definitions of escape sequences).  The enclosed text is then processed according to what that escape expects.  Example:

     \l'1.5i\(bu'

Note that the quote character can be replaced with any other character which does not occur in the argument (even a newline or a space character) in the following escapes: \o, \b, and \X.  This makes e.g.

     A caf
     \o
     e\'

     in Paris
       => A café in Paris

possible, but it is better not to use this feature to avoid confusion.

The following escapes sequences (which are handled similarly to characters since they don't take a parameter) are also allowed as delimiters: \%, \ , \|, \^, \{, \}, \', \`, \-, \_, \!, \?, \@, \), \/, \,, \&, \~, \0, \a, \c, \d, \e, \E, \p, \r, \t, and \u.  Again, don't use these if possible.

No newline characters as delimiters are allowed in the following escapes: \A, \Z, \C, and \w.

Finally, the escapes \D, \h, \H, \l, \L, \N, \R, \s, \S, \v, and \x can't use the following characters as delimiters:

  * The digits 0-9.

  * The (single-character) operators +-/*%<>=&:()..

  * The space, tab, and newline characters.

  * All escape sequences except \%, \{, \}, \', \`, \-, \_, \!, \@, \/, \c, \e, and \p.

To have a backslash (actually, the current escape character) appear in the output several escapes are defined: \\, \e or \E. These are very similar, and only differ with respect to being used in macros or diversions.  See Copy-in Mode, and Diversions, for more information.

See Identifiers, and Character Translations.

Comments
........

Probably one of the most (Unfortunately, this is a lie.  But hopefully future gtroff hackers will believe it :-)) common forms of escapes is the comment.

 -- Escape: \\", , ,
     Start a comment.  Everything to the end of the input line is ignored.

     This may sound simple, but it can be tricky to keep the comments from interfering with the appearance of the final output.

     If the escape is to the right of some text or a request, that portion of the line is ignored, but the space leading up to it is noticed by gtroff.  This only affects the .ds and .as request.

     One possibly irritating idiosyncracy is that tabs must not be used to line up comments.  Tabs are not treated as white space between the request and macro arguments.

     A comment on a line by itself is treated as a blank line, because after eliminating the comment, that is all that remains:

          Test
          \" comment
          Test

     produces

          Test

          Test

     To avoid this, it is common to start the line with .\" which causes the line to be treated as an undefined request and thus ignored completely.

     Another commenting scheme seen sometimes is three consecutive single quotes (''') at the beginning of a line.  This works, but gtroff gives a warning about an undefined macro (namely ''), which is harmless, but irritating.

 -- Escape: \\#, , ,
     To avoid all this, gtroff has a new comment mechanism using the \# escape.  This escape works the same as \" except that the newline is also ignored:

          Test
          \# comment
          Test

     produces

          Test Test

     as expected.

 -- Request: .ig, yy
     Ignore all input until gtroff encounters the macro named .YY on a line by itself (or .. if YY is not specified).  This is useful for commenting out large blocks of text:

          text text text...
          .ig
          This is part of a large block
          of text that has been
          temporarily(?) commented out.

          We can restore it simply by removing
          the .ig request and the ".." at the
          end of the block.
          ..
          More text text text...

     produces

          text text text...  More text text text...

     Note that the commented-out block of text does not cause a break.

     The input is read in copy-mode; auto-incremented registers are affected (see Auto-increment).

Registers
=========

Numeric variables in gtroff are called registers.  There are a number of built-in registers, supplying anything from the date to details of formatting parameters.

See Identifiers, for details on register identifiers.

Setting Registers
-----------------

Define or set registers using the nr request or the \R escape.

 -- Request: .nr, ident value
 -- Escape: \\R, ', ident value, '
     Set number register IDENT to VALUE.  If IDENT doesn't exist, gtroff creates it.

     The argument to \R usually has to be enclosed in quotes. See Escapes, for details on parameter delimiting characters.

For example, the following two lines are equivalent:

     .nr a 1
     \R'a 1'

Both nr and \R have two additional special forms to increment or decrement a register.

 -- Request: .nr, ident +value
 -- Request: .nr, ident -value
 -- Escape: \\R, ', ident +value, '
 -- Escape: \\R, ', ident -value, '
     Increment (decrement) register IDENT by VALUE.

          .nr a 1
          .nr a +1
          \na
              => 2

     To assign the negated value of a register to another register, some care must be taken to get the desired result:

          .nr a 7
          .nr b 3
          .nr a -\nb
          \na
              => 4
          .nr a (-\nb)
          \na
              => -3

     The surrounding parentheses prevent the interpretation of the minus sign as a decrementing operator.  An alternative is to start the assignment with a 0:

          .nr a 7
          .nr b -3
          .nr a \nb
          \na
              => 4
          .nr a 0\nb
          \na
              => -3

 -- Request: .rr, ident
     Remove number register IDENT.  If IDENT doesn't exist, the request is ignored.

 -- Request: .rnn, ident1 ident2
     Rename number register IDENT1 to IDENT2.  If either IDENT1 or IDENT2 doesn't exist, the request is ignored.

 -- Request: .aln, ident1 ident2
     Create an alias IDENT1 for a number register IDENT2.  The new name and the old name are exactly equivalent.  If IDENT1 is undefined, a warning of type reg is generated, and the request is ignored.  See Debugging, for information about warnings.

Interpolating Registers
-----------------------

Numeric registers can be accessed via the \n escape.

 -- Escape: \\n, , i,
 -- Escape: \\n, (, id,
 -- Escape: \\n, [, ident, ]
     Interpolate number register with name IDENT (one-character name I, two-character name ID).  This means that the value of the register is expanded in-place while gtroff is parsing the input line.  Nested assignments (also called indirect assignments) are possible.

          .nr a 5
          .nr as \na+\na
          \n(as
              => 10

          .nr a1 5
          .nr ab 6
          .ds str b
          .ds num 1
          \n[a\n[num]]
              => 5
          \n[a\*[str]]
              => 6

Auto-increment
--------------

Number registers can also be auto-incremented and auto-decremented. The increment or decrement value can be specified with a third argument to the nr request or \R escape.

 -- Request: .nr, ident value incr
     Set number register IDENT to VALUE; the increment for auto-incrementing is set to INCR.  Note that the \R escape doesn't support this notation.

To activate auto-incrementing, the escape \n has a special syntax form.

 -- Escape: \\n, +, i,
 -- Escape: \\n, -, i,
 -- Escape: \\n, (+, id,
 -- Escape: \\n, (-, id,
 -- Escape: \\n, +(, id,
 -- Escape: \\n, -(, id,
 -- Escape: \\n, [+, ident, ]
 -- Escape: \\n, [-, ident, ]
 -- Escape: \\n, +[, ident, ]
 -- Escape: \\n, -[, ident, ]
     Before interpolating, increment or decrement IDENT (one-character name I, two-character name ID) by the auto-increment value as specified with the nr request (or the \R escape).  If no auto-increment value has been specified, these syntax forms are identical to \n.

For example,

     .nr a 0 1
     .nr xx 0 5
     .nr foo 0 -2
     \n+a, \n+a, \n+a, \n+a, \n+a
     .br
     \n-(xx, \n-(xx, \n-(xx, \n-(xx, \n-(xx
     .br
     \n+[foo], \n+[foo], \n+[foo], \n+[foo], \n+[foo]

produces

     1, 2, 3, 4, 5
     -5, -10, -15, -20, -25
     -2, -4, -6, -8, -10

To change the increment value without changing the value of a register (A in the example), the following can be used:

     .nr a \na 10

Assigning Formats
-----------------

When a register is used in the text of an input file (as opposed to part of an expression), it is textually replaced (or interpolated) with a representation of that number.  This output format can be changed to a variety of formats (numbers, Roman numerals, etc.).  This is done using the af request.

 -- Request: .af, ident format
     Change the output format of a number register.  The first argument IDENT is the name of the number register to be changed, and the second argument FORMAT is the output format.  The following output formats are available:

     1
          Decimal arabic numbers.  This is the default format: 0, 1, 2, 3, ...

     0...0
          Decimal numbers with as many digits as specified.  So, 00 would result in printing numbers as 01, 02, 03, ...

          In fact, any digit instead of zero will do; gtroff only counts how many digits are specified.  As a consequence, af's default format 1 could be specified as 0 also (and exactly this is returned by the \g escape, see below).

     I
          Upper-case Roman numerals: 0, I, II, III, IV, ...

     i
          Lower-case Roman numerals: 0, i, ii, iii, iv, ...

     A
          Upper-case letters: 0, A, B, C, ..., Z, AA, AB, ...

     a
          Lower-case letters: 0, a, b, c, ..., z, aa, ab, ...

     Omitting the number register format causes a warning of type missing.  See Debugging, for more details.  Specifying a nonexistent format causes an error.

     The following example produces 10, X, j, 010:

          .nr a 10
          .af a 1           \" the default format
          \na,
          .af a I
          \na,
          .af a a
          \na,
          .af a 001
          \na

     The largest number representable for the i and I formats is 39999 (or -39999); UNIX troff uses z and w to represent 10000 and 5000 in Roman numerals, and so does gtroff.  Currently, the correct glyphs of Roman numeral five thousand and Roman numeral ten thousand (Unicode code points U+2182 and U+2181, respectively) are not available.

     If IDENT doesn't exist, it is created.

     Changing the output format of a read-only register causes an error.  It is necessary to first copy the register's value to a writeable register, then apply the af request to this other register.

 -- Escape: \\g, , i,
 -- Escape: \\g, (, id,
 -- Escape: \\g, [, ident, ]
     Return the current format of the specified register IDENT (one-character name I, two-character name ID).  For example, \ga after the previous example would produce the string 000.  If the register hasn't been defined yet, nothing is returned.

Built-in Registers
------------------

The following lists some built-in registers which are not described elsewhere in this manual.  Any register which begins with a . is read-only.  A complete listing of all built-in registers can be found in Register Index.

.H
     Horizontal resolution in basic units.

.V
     Vertical resolution in basic units.

dw
     Day of the week (1-7).

dy
     Day of the month (1-31).

mo
     Current month (1-12).

year
     The current year.

yr
     The current year minus 1900.  Unfortunately, the documentation of UNIX Version 7's troff had a year 2000 bug: It incorrectly claimed that yr contains the last two digits of the year.  That claim has never been true of either traditional troff or GNU troff.  Old troff input that looks like this:

          '\" The following line stopped working after 1999
          This document was formatted in 19\n(yr.

     can be corrected as follows:

          This document was formatted in \n[year].

     or, to be portable to older troff versions, as follows:

          .nr y4 1900+\n(yr
          This document was formatted in \n(y4.

.c
c.
     The current input line number.  Register .c is read-only, whereas c. (a gtroff extension) is writable also, affecting both .c and c..

ln
     The current output line number after a call to the nm request to activate line numbering.

     See Miscellaneous, for more information about line numbering.

.x
     The major version number.  For example, if the version number is 1.03 then .x contains 1.

.y
     The minor version number.  For example, if the version number is 1.03 then .y contains 03.

.Y
     The revision number of groff.

.g
     Always 1.  Macros should use this to determine whether they are running under GNU troff.

.A
     If the command line option -a is used to produce an ASCII approximation of the output, this is set to 1, zero otherwise.  See Groff Options.

.P
     This register is set to 1 (and to 0 otherwise) if the current page is actually being printed, i.e., if the -o option is being used to only print selected pages.  See Groff Options, for more information.

.T
     If gtroff is called with the -T command line option, the number register .T is set to 1, and zero otherwise. See Groff Options.

     Additionally, gtroff predefines a single read-write string register .T which contains the current output device (for example, latin1 or ps).

Manipulating Filling and Adjusting
==================================

Various ways of causing breaks were given in Implicit Line Breaks.  The br request likewise causes a break.  Several other requests also cause breaks, but implicitly.  These are bp, ce, cf, fi, fl, in, nf, rj, sp, ti, and trf.

 -- Request: .br,
     Break the current line, i.e., the input collected so far is emitted without adjustment.

     If the no-break control character is used, gtroff suppresses the break:

          a
          'br
          b
              => a b

Initially, gtroff fills and adjusts text to both margins. Filling can be disabled via the nf request and re-enabled with the fi request.

 -- Request: .fi,
 -- Register: \n[.u]
     Activate fill mode (which is the default).  This request implicitly enables adjusting; it also inserts a break in the text currently being filled.  The read-only number register .u is set to 1.

     The fill mode status is associated with the current environment (see Environments).

 -- Request: .nf,
     Activate no-fill mode.  Input lines are output as-is, retaining line breaks and ignoring the current line length.  This command implicitly disables adjusting; it also causes a break.  The number register .u is set to 0.

     The fill mode status is associated with the current environment (see Environments).

 -- Request: .ad, [mode]
 -- Register: \n[.j]
     Set adjusting mode.

     Activation and deactivation of adjusting is done implicitly with calls to the fi or nf requests.

     MODE can have one of the following values:

     l
          Adjust text to the left margin.  This produces what is traditionally called ragged-right text.

     r
          Adjust text to the right margin, producing ragged-left text.

     c
          Center filled text.  This is different to the ce request which only centers text without filling.

     b
     n
          Justify to both margins.  This is the default used by gtroff.

     With no argument, gtroff adjusts lines in the same way it did before adjusting was deactivated (with a call to na, for example).

          text
          .ad r
          text
          .ad c
          text
          .na
          text
          .ad  \" back to centering
          text

     The current adjustment mode is available in the read-only number register .j; it can be stored and subsequently used to set adjustment.

     The adjustment mode status is associated with the current environment (see Environments).

 -- Request: .na,
     Disable adjusting.  This request won't change the current adjustment mode: A subsequent call to ad uses the previous adjustment setting.

     The adjustment mode status is associated with the current environment (see Environments).

 -- Escape: \\p, , ,
     Adjust the current line and cause a break.

     In most cases this produces very ugly results, since gtroff doesn't have a sophisticated paragraph building algorithm (as TeX have, for example); instead, gtroff fills and adjusts a paragraph line by line:

            This is an uninteresting sentence.
            This is an uninteresting sentence.\p
            This is an uninteresting sentence.

     is formatted as

            This is  an uninteresting  sentence.   This  is an
            uninteresting                            sentence.
            This is an uninteresting sentence.

 -- Request: .ss, word_space_size [sentence_space_size]
 -- Register: \n[.ss]
 -- Register: \n[.sss]
     Change the minimum size of a space between filled words.  It takes its units as one twelfth of the space width parameter for the current font.  Initially both the WORD_SPACE_SIZE and SENTENCE_SPACE_SIZE are 12.

     If two arguments are given to the ss request, the second argument sets the sentence space size.  If the second argument is not given, sentence space size is set to WORD_SPACE_SIZE.  The sentence space size is used in two circumstances: If the end of a sentence occurs at the end of a line in fill mode, then both an inter-word space and a sentence space are added; if two spaces follow the end of a sentence in the middle of a line, then the second space is a sentence space.  If a second argument is never given to the ss request, the behaviour of UNIX troff is the same as that exhibited by GNU troff.  In GNU troff, as in UNIX troff, a sentence should always be followed by either a newline or two spaces.

     The read-only number registers .ss and .sss hold the values of the parameters set by the first and second arguments of the ss request.

     The word space and sentence space values are associated with the current environment (see Environments).

     Contrary to traditional Unix troff, this request is not ignored if a tty output device is used; the given values are then rounded down to a multiple of 12.

     The request is ignored if there is no parameter.

 -- Request: .ce, [nnn]
 -- Register: \n[.ce]
     Center text.  While the .ad c request also centers text, it fills the text as well.  ce does not fill the text it affects.  This request causes a break.

     The following example demonstrates the differences. Here the input:

          .ll 4i
          .ce 1000
          This is a small text fragment which shows the differences
          between the `.ce' and the `.ad c' request.
          .ce 0

          .ad c
          This is a small text fragment which shows the differences
          between the `.ce' and the `.ad c' request.

     And here the result:

            This is a small text fragment which
                   shows the differences
          between the `.ce' and the `.ad c' request.

            This is a small text fragment which
          shows the differences between the `.ce'
                  and the `.ad c' request.

     With no arguments, ce centers the next line of text.  NNN specifies the number of lines to be centered.  If the argument is zero or negative, centering is disabled.

     The basic length for centering text is the line length (as set with the ll request) minus the indentation (as set with the in request).  Temporary indentation is ignored.

     As can be seen in the previous example, it is a common idiom to turn on centering for a large number of lines, and to turn off centering after text to be centered.  This is useful for any request which takes a number of lines as an argument.

     The .ce read-only number register contains the number of lines remaining to be centered, as set by the ce request.

 -- Request: .rj, [nnn]
 -- Register: \n[.rj]
     Justify unfilled text to the right margin.  Arguments are identical to the ce request.  The .rj read-only number register is the number of lines to be right-justified as set by the rj request.  This request causes a break.

Manipulating Hyphenation
========================

As discussed in Hyphenation, gtroff hyphenates words. There are a number of ways to influence hyphenation.

 -- Request: .hy, [mode]
 -- Register: \n[.hy]
     Enable hyphenation.  The request has an optional numeric argument, MODE, to restrict hyphenation if necessary:

     1
          The default argument if MODE is omitted.  Hyphenate without restrictions.  This is also the start-up value of gtroff.

     2
          Do not hyphenate the last word on a page or column.

     4
          Do not hyphenate the last two characters of a word.

     8
          Do not hyphenate the first two characters of a word.

     Values in the previous table are additive.  For example, the value 12 causes gtroff to neither hyphenate the last two nor the first two characters of a word.

     The current hyphenation restrictions can be found in the read-only number register .hy.

     The hyphenation mode is associated with the current environment (see Environments).

 -- Request: .nh,
     Disable hyphenation (i.e., set the hyphenation mode to zero).  Note that the hyphenation mode of the last call to hy is not remembered.

     The hyphenation mode is associated with the current environment (see Environments).

 -- Request: .hlm, [nnn]
 -- Register: \n[.hlm]
 -- Register: \n[.hlc]
     Set the maximum number of consecutive hyphenated lines to NNN. If this number is negative, there is no maximum.  The default value is -1 if NNN is omitted.  This value is associated with the current environment (see Environments).  Only lines output from a given environment count towards the maximum associated with that environment.  Hyphens resulting from \% are counted; explicit hyphens are not.

     The current setting of hlm is available in the .hlm read-only number register.  Also the number of immediately preceding consecutive hyphenated lines are available in the read-only number register .hlc.

 -- Request: .hw, word1 word2 ...
     Define how WORD1, WORD2, etc. are to be hyphenated.  The words must be given with hyphens at the hyphenation points.  For example:

          .hw in-sa-lub-rious

     Besides the space character, any character whose hyphenation code value is zero can be used to separate the arguments of hw (see the documentation for the hcode request below for more information). In addition, this request can be used more than once.

     Hyphenation exceptions specified with the hw request are associated with the current hyphenation language; it causes an error if there is no current hyphenation language.

     This request is ignored if there is no parameter.

     In old versions of troff there was a limited amount of space to store such information; fortunately, with gtroff, this is no longer a restriction.

 -- Escape: \\%, , ,
     To tell gtroff how to hyphenate words on the fly, use the \% escape, also known as the hyphenation character. Preceding a word with this character prevents it from being hyphenated; putting it inside a word indicates to gtroff that the word may be hyphenated at that point.  Note that this mechanism only affects that one occurrence of the word; to change the hyphenation of a word for the entire document, use the hw request.

 -- Request: .hc, [char]
     Change the hyphenation character to CHAR.  This character then works the same as the \% escape, and thus, no longer appears in the output.  Without an argument, hc resets the hyphenation character to be \% (the default) only.

     The hyphenation character is associated with the current environment (see Environments).

 -- Request: .hpf, pattern_file
     Read in a file of hyphenation patterns.  This file is searched for in the same way as NAME.tmac (or tmac.NAME) is searched for if the -mNAME option is specified.

     It should have the same format as the argument to the \patterns primitive in TeX (without using TeX's macro expansion); the letters appearing in this file are interpreted as hyphenation codes.  A % character in the patterns file introduces a comment that continues to the end of the line.

     If no hpf request is specified (either in the document or in a macro package), gtroff won't hyphenate at all.

     The set of hyphenation patterns is associated with the current language set by the hla request.  The hpf request is usually invoked by the troffrc or troffrc-end file; by default, troffrc loads hyphenation patterns for American English (in file hyphen.us).

     Invoking hpf causes an error if there is no current hyphenation language.

 -- Request: .hcode, c1 code1 c2 code2 ...
     Set the hyphenation code of character C1 to CODE1, that of C2 to CODE2, etc.  A hyphenation code must be a single input character (not a special character) other than a digit or a space.  Initially each lower-case letter (a-z) has its hyphenation set to itself, and each upper-case letter (A-Z) has a hyphenation code which is the lower-case version of itself.

     This request is ignored if it has no parameter.

 -- Request: .hym, [length]
 -- Register: \n[.hym]
     Set the (right) hyphenation margin to LENGTH.  If the current adjustment mode is not b or n, the line is not hyphenated if it is shorter than LENGTH.  Without an argument, the hyphenation margin is reset to its default value, which is 0. The default scaling indicator for this request is m.  The hyphenation margin is associated with the current environment (see Environments).

     A negative argument resets the hyphenation margin to zero, emitting a warning of type range.

     The current hyphenation margin is available in the .hym read-only number register.

 -- Request: .hys, [hyphenation_space]
 -- Register: \n[.hys]
     Set the hyphenation space to HYPHENATION_SPACE.  If the current adjustment mode is b or n, don't hyphenate the line if it can be justified by adding no more than HYPHENATION_SPACE extra space to each word space.  Without argument, the hyphenation space is set to its default value, which is 0.  The default scaling indicator for this request is m.  The hyphenation space is associated with the current environment (see Environments).

     A negative argument resets the hyphenation space to zero, emitting a warning of type range.

     The current hyphenation space is available in the .hys read-only number register.

 -- Request: .shc, [char]
     Set the soft hyphen character to CHAR.  If the argument is omitted, the soft hyphen character is set to the default character \(hy (this is the start-up value of gtroff also).  The soft hyphen character is the character that is inserted when a word is hyphenated at a line break.  If the soft hyphen character does not exist in the font of the character immediately preceding a potential break point, then the line is not broken at that point.  Neither definitions (specified with the char request) nor translations (specified with the tr request) are considered when finding the soft hyphen character.

 -- Request: .hla, language
 -- Register: \n[.hla]
     Set the current hyphenation language to the string LANGUAGE. Hyphenation exceptions specified with the hw request and hyphenation patterns specified with the hpf request are both associated with the current hyphenation language.  The hla request is usually invoked by the troffrc or the troffrc-end files; troffrc sets the default language to us.

     The current hyphenation language is available as a string in the read-only number register .hla.

          .ds curr_language \n[.hla]
          \*[curr_language]
              => us

Manipulating Spacing
====================

 -- Request: .sp, [distance]
     Space downwards DISTANCE.  With no argument it advances 1 line.  A negative argument causes gtroff to move up the page the specified distance.  If the argument is preceded by a | then gtroff moves that distance from the top of the page.  This request causes a line break.  The default scaling indicator is v.

 -- Request: .ls, [nnn]
 -- Register: \n[.L]
     Output NNN-1 blank lines after each line of text. With no argument, gtroff uses the previous value before the last ls call.

          .ls 2    \" This causes double-spaced output
          .ls 3    \" This causes triple-spaced output
          .ls      \" Again double spaced

     The line spacing is associated with the current environment (see Environments).

     The read-only number register .L contains the current line spacing setting.

 -- Escape: \\x, ', spacing, '
 -- Register: \n[.a]
     Sometimes, extra vertical spacing is only needed occasionally, e.g. to allow space for a tall construct (like an equation).  The \x escape does this.  The escape is given a numerical argument, usually enclosed in quotes (like \x'3p'); the default scaling indicator is v.  If this number is positive extra vertical space is inserted below the current line.  A negative number adds space above. If this escape is used multiple times on the same line, the maximum of the values is used.

     See Escapes, for details on parameter delimiting characters.

     The .a read-only number register contains the most recent (nonnegative) extra vertical line space.

 -- Request: .ns,
 -- Register: \n[.ns]
     Enable no-space mode.  In this mode, spacing (either via sp or via blank lines) is disabled.  The bp request to advance to the next page is also disabled, except if it is accompanied by a page number (see Page Control, for more information).  This mode ends when actual text is output or the rs request is encountered.  The read-only number register .ns is set to 1.

     This request is useful for macros which want to avoid that subsequent macros inadvertently insert some vertical space before the text starts (for example, to set up the first paragraph after a section header).

 -- Request: .rs,
     Disable no-space mode.

Tabs and Fields
===============

A tab character (ASCII char 9, EBCDIC char 5) causes a horizontal movement to the next tab stop (much like it did on a typewriter).

 -- Escape: \\t, , ,
     This escape is a non-interpreted tab character.  In copy mode (see Copy-in Mode), \t is the same as a real tab character.

 -- Request: .ta, [n1 n2 ... nn T r1 r2 ... rn]
 -- Register: \n[.tabs]
     Change tab stop positions.  This request takes a series of tab specifiers as arguments (optionally divided into two groups with the letter T) which indicate where each tab stop is to be (overriding any previous settings).

     Tab stops can be specified absolutely, i.e., as the distance from the left margin.  For example, the following sets 6 tab stops every one inch.

          .ta 1i 2i 3i 4i 5i 6i

     Tab stops can also be specified using a leading + which means that the specified tab stop is set relative to the previous tab stop.  For example, the following is equivalent to the previous example.

          .ta 1i +1i +1i +1i +1i +1i

     gtroff supports an extended syntax to specify repeat values after the T mark (these values are always taken as relative) -- this is the usual way to specify tabs set at equal intervals.  The following is, yet again, the same as the previous examples.  It does even more since it defines an infinite number of tab stops separated by one inch.

          .ta T 1i

     Now we are ready to interpret the full syntax given at the beginning: Set tabs at positions N1, N2, ..., NN and then set tabs at NN+R1, NN+R2, ..., NN+RN and then at NN+RN+R1, NN+RN+R2, ..., NN+RN+RN, and so on.

     Example: 4c +6c T 3c 5c 2c is equivalent to 4c 10c 13c 18c 20c 23c 28c 30c ....

     The material in each tab column (i.e., the column between two tab stops) may be justified to the right or left or centered in the column.  This is specified by appending R, L, or C to the tab specifier.  The default justification is L.  Example:

          .ta 1i 2iC 2iR

     Some notes:

       * The default unit of the ta request is m.

       * A tab stop is converted into a non-breakable horizontal movement which can be neither stretched nor squeezed.  For example,

               .ds foo a\tb\tc
               .ta T 5i
               \*[foo]

          creates a single line which is a bit longer than 10 inches (a string is used to show exactly where the tab characters are).  Now consider the following:

               .ds bar a\tb b\tc
               .ta T 5i
               \*[bar]

          gtroff first converts the tab stops of the line into unbreakable horizontal movements, then splits the line after the second b (assuming a sufficiently short line length).  Usually, this isn't what the user wants.

       * Superfluous tabs (i.e., tab characters which do not correspond to a tab stop) are ignored except the first one which delimits the characters belonging to the last tab stop for right-justifying or centering. Consider the following example

               .ds Z   foo\tbar\tfoo
               .ds ZZ  foo\tbar\tfoobar
               .ds ZZZ foo\tbar\tfoo\tbar
               .ta 2i 4iR
               \*[Z]
               .br
               \*[ZZ]
               .br
               \*[ZZZ]
               .br

          which produces the following output:

               foo                 bar              foo
               foo                 bar           foobar
               foo                 bar              foobar

          The first line right-justifies the second `foo' relative to the tab stop.  The second line right-justifies `foobar'.  The third line finally right-justifies only `foo' because of the additional tab character which marks the end of the string belonging to the last defined tab stop.

       * Tab stops are associated with the current environment (see Environments).

       * Calling ta without an argument removes all tab stops.

       * The start-up value of gtroff is T 0.5i.  This value is used even for tty output devices (contrary to UNIX nroff which has tab stops preset every 0.8i).

     The read-only number register .tabs contains a string representation of the current tab settings suitable for use as an argument to the ta request.

          .ds tab-string \n[.tabs]
          \*[tab-string]
              => T120u

 -- Request: .tc, [fill-char]
     Normally gtroff fills the space to the next tab stop with whitespace.  This can be changed with the tc request.  With no argument gtroff reverts to using whitespace, which is the default.  The value of this tab repetition character is associated with the current environment (see Environments).

Leaders
-------

Sometimes it may may be desirable to use the tc request to fill a particular tab stop with a given character (for example dots in a table of contents), but also normal tab stops on the rest of the line.  For this gtroff provides an alternate tab mechanism, called leaders which does just that.

A leader character (character code 1) behaves similarly to a tab character: It moves to the next tab stop.  The only difference is that for this movement, the fill character defaults to a period character and not to space.

 -- Escape: \\a, , ,
     This escape is a non-interpreted leader character.  In copy mode (see Copy-in Mode), \a is the same as a real leader character.

 -- Request: .lc, [fill-char]
     Declare the leader character.  Without an argument, leaders act the same as tabs (i.e., using whitespace for filling).  gtroff's start-up value is ..  The value of this leader repetition character is associated with the current environment (see Environments).

For a table of contents, to name an example, tab stops may be defined so that the section number is one tab stop, the title is the second with the remaining space being filled with a line of dots, and then the page number slightly separated from the dots.

     .ds entry 1.1\tFoo\a\t12
     .lc .
     .ta 1i 5i +.25i
     \*[entry]

This produces

     1.1  Foo..........................................  12

Fields
------

Fields are a more general way of laying out tabular data.  A field is defined as the data between a pair of delimiting characters. It contains substrings which are separated by padding characters. The width of a field is the distance on the input line from the position where the field starts to the next tab stop.  A padding character inserts stretchable space similar to TeX's \hss command (thus it can even be negative) to make the sum of all substring lengths plus the stretchable space equal to the field width.  If more than one padding character is inserted, the available space is evenly distributed among them.

 -- Request: .fc, [delim-char [padding-char]]
     Define a delimiting and a padding character for fields.  If the latter is missing, the padding character defaults to a space character.  If there is no argument at all, the field mechanism is disabled (which is the default).  Note that contrary to e.g. the tab repetition character, delimiting and padding characters are not associated to the current environment (see Environments).

     Example:

          .fc # ^
          .ta T 3i
          #foo^bar^smurf#
          .br
          #foo^^bar^smurf#

     and here the result:

          foo         bar          smurf
          foo            bar       smurf

Character Translations
======================

The control character (.) and the no-break control character (') can be changed with the cc and c2 requests, respectively.

 -- Request: .cc, [c]
     Set the control character to C.  With no argument the default control character . is restored.  The value of the control character is associated with the current environment (see Environments).

 -- Request: .c2, [c]
     Set the no-break control character to C.  With no argument the default control character ' is restored.  The value of the no-break control character is associated with the current environment (see Environments).

 -- Request: .eo,
     Disable the escape mechanism completely.  After executing this request, the backslash character \ no longer starts an escape sequence.

     This request can be very helpful in writing macros since it is not necessary then to double the escape character.  Here an example:

          .\" This is a simplified version of the
          .\" .BR request from the man macro package
          .eo
          .de BR
          .  ds result \&
          .  while (\n[.$] >= 2) \{\
          .    as result \fB\$1\fR\$2
          .    shift 2
          .  \}
          .  if \n[.$] .as result \fB\$1
          \*[result]
          .  ft R
          ..
          .ec

 -- Request: .ec, [c]
     Set the escape character to C.  With no argument the default escape character \ is restored.  It can be also used to re-enable the escape mechanism after an eo request.

     Note that changing the escape character globally will likely break macro packages since gtroff has no mechanism (like TeX) to `intern' macros, i.e., to convert a macro definition into an internal form which is independent of its representation.  If a macro is called, it is executed literally.

 -- Escape: \\e, , ,
     This escape sequence prints the current escape character (which is the backslash character \ by default).

A translation is a mapping of an input character to an output character.  The default mappings are given in the font definition files for the specific output device (see Font Files); all mappings (both with tr and in the font definition files) occur at output time, i.e., the input character gets assigned the metric information of the mapped output character.

 -- Request: .tr, abcd...
     Translate character A to B, character C to D, etc.  If there is an odd number of arguments, the last one is translated to the space character.

     Some notes:

       * Special characters (\(XX, \[XXX], \C'XXX', \', \`, \-, \_), characters defined with the char request, and numbered characters (\N'XXX') can be translated also.

       * The \e escape can be translated also.

       * Characters can be mapped onto the \% and \~ escapes (but \% and \~ can't be mapped onto another character).

       * The following characters can't be translated: space (with one exception, see below), backspace, newline, leader (and \a), tab (and \t).

       * Translations are not considered for finding the soft hyphen character set with the shc request.

       * The character pair C\& (this is an arbitrary character C followed by the zero width space character) maps this character to nothing.

               .tr a\&
               foo bar
                   => foo br

          It is even possible to map the space character to nothing:

               .tr aa \&
               foo bar
                   => foobar

          As shown in the example, the space character can't be the first character pair as an argument of tr.  Additionally, it is not possible to map the space character to any other character; requests like .tr aa x undo .tr aa \& instead.

          If justification is active, lines are justified in spite of the `empty' space character (but there is no minimal distance, i.e. the space character, between words).

       * After an output character has been constructed (this happens at the moment immediately before the character is appended to an output character list, either by direct output, in a macro, diversion, or string), it is no longer affected by tr.

       * Without an argument, the tr request is ignored.

 -- Request: .trnt, abcd...
     trnt is the same as the tr request except that the translations do not apply to text that is transparently throughput into a diversion with \!.  See Diversions, for more information.

     For example,

          .tr ab
          .di x
          \!.tm a
          .di
          .x

     prints b to the standard error stream; if trnt is used instead of tr it prints a.

Troff and Nroff Mode
====================

Originally, nroff and troff were two separate programs, the former for tty output, the latter for everything else.  With GNU troff, both programs are merged into one executable, sending its output to a device driver (grotty for tty devices, grops for POSTSCRIPT, etc.) which interprets the intermediate output of gtroff.  For UNIX troff it makes sense to talk about Nroff mode and Troff mode since the differences are hardcoded.  For GNU troff, this distinction is not appropriate because gtroff simply takes the information given in the font files for a particular device without handling requests specially if a tty output device is used.

Usually, a macro package can be used with all output devices. Nevertheless, it is sometimes necessary to make a distinction between tty and non-tty devices: gtroff provides two built-in conditions n and t for the if, ie, and while requests to decide whether gtroff shall behave like nroff or like troff.

 -- Request: .troff,
     Make the t built-in condition true (and the n built-in condition false) for if, ie, and while conditional requests.  This is the default if gtroff (not groff) is started with the -R switch to avoid loading of the start-up files troffrc and troffrc-end.  Without -R, gtroff stays in troff mode if the output device is not a tty (e.g. `ps').

 -- Request: .nroff,
     Make the n built-in condition true (and the t built-in condition false) for if, ie, and while conditional requests.  This is the default if gtroff uses a tty output device; the code for switching to nroff mode is in the file tty.tmac which is loaded by the start-up file troffrc.

See Conditionals and Loops, for more details on built-in conditions.

For tty output devices, underlining is done by emitting sequences of _ and \b (the backspace character) before the actual character.  Literally, this is printing an underline character, then moving back one character position, and printing the actual character at the same position as the underline character (similar to a typewriter).  Usually, a modern terminal can't interpret this (and the original Teletype machines for which this sequence was appropriate are no longer in use).  You need a pager program like less which translates this into ISO 6429 SGR sequences to control terminals.

Line Layout
===========

The following drawing shows the dimensions which gtroff uses for placing a line of output onto the page.  They are labeled with the request which manipulates each dimension.

                     -->| in |<--
                        |<-----------ll------------>|
                   +----+----+----------------------+----+
                   |    :    :                      :    |
                   +----+----+----------------------+----+
                -->| po |<--
                   |<--------paper width---------------->|

These dimensions are:

po
     Page offset -- this is the leftmost position of text on the final output, defining the left margin.

in
     Indentation -- this is the distance from the left margin where text is printed.

ll
     Line length -- this is the distance from the left margin to right margin.

     .in +.5i
     .ll -.5i
     A bunch of really boring text which should
     be indented from both margins.
     Replace me with a better (and more) example!
     .in -.5i
     .ll +.5i

 -- Request: .po, [offset]
 -- Request: .po, +offset
 -- Request: .po, -offset
 -- Register: \n[.o]
     Set horizontal page offset to OFFSET (or increment or decrement the current value by OFFSET).  Note that this request does not cause a break, so changing the page offset in the middle of text being filled may not yield the expected result.  The initial value is 1i.  For tty output devices, it is set to 0 in the startup file troffrc; the default scaling indicator is m (and not v as incorrectly documented in the original UNIX troff manual).

     The current page offset can be found in the read-only number register .o.

     If po is called without an argument, the page offset is reset to the previous value before the last call to po.

          .po 3i
          \n[.o]
              => 720
          .po -1i
          \n[.o]
              => 480
          .po
          \n[.o]
              => 720

 -- Request: .in, [indent]
 -- Request: .in, +indent
 -- Request: .in, -indent
 -- Register: \n[.i]
     Set indentation to INDENT (or increment or decrement the current value by INDENT).  This request causes a break. Initially, there is no indentation.

     If in is called without an argument, the indentation is reset to the previous value before the last call to in.  The default scaling indicator is m.

     The indentation is associated with the current environment.

     If a negative indentation value is specified (which is not allowed), gtroff emits a warning of type range and sets the indentation to zero.

     The effect of in is delayed until a partially collected line (if it exists) is output.  A temporary indent value is reset to zero also.

     The current indentation (as set by in) can be found in the read-only number register .i.

 -- Request: .ti, offset
 -- Request: .ti, +offset
 -- Request: .ti, -offset
 -- Register: \n[.in]
     Temporarily indent the next output line by OFFSET.  If an increment or decrement value is specified, adjust the temporary indentation relative to the value set by the in request.

     This request causes a break; its value is associated with the current environment.  The default scaling indicator is m.  A call of ti without an argument is ignored.

     If the total indentation value is negative (which is not allowed), gtroff emits a warning of type range and sets the temporary indentation to zero.  `Total indentation' is either OFFSET if specified as an absolute value, or the temporary plus normal indentation, if OFFSET is given as a relative value.

     The effect of ti is delayed until a partially collected line (if it exists) is output.

     The read-only number register .in is the indentation that applies to the current output line.

     The difference between .i and .in is that the latter takes into account whether a partially collected line still uses the old indentation value or a temporary indentation value is active.

 -- Request: .ll, [length]
 -- Request: .ll, +length
 -- Request: .ll, -length
 -- Register: \n[.l]
 -- Register: \n[.ll]
     Set the line length to LENGTH (or increment or decrement the current value by LENGTH).  Initially, the line length is set to 6.5i.  The effect of ll is delayed until a partially collected line (if it exists) is output.  The default scaling indicator is m.

     If ll is called without an argument, the line length is reset to the previous value before the last call to ll.  If a negative line length is specified (which is not allowed), gtroff emits a warning of type range and sets the line length to zero.

     The line length is associated with the current environment.

     The current line length (as set by ll) can be found in the read-only number register .l.  The read-only number register .ll is the line length that applies to the current output line.

     Similar to .i and .in, the difference between .l and .ll is that the latter takes into account whether a partially collected line still uses the old line length value.

Page Layout
===========

gtroff provides some very primitive operations for controlling page layout.

 -- Request: .pl, [length]
 -- Request: .pl, +length
 -- Request: .pl, -length
 -- Register: \n[.p]
     Set the page length to LENGTH (or increment or decrement the current value by LENGTH).  This is the length of the physical output page.  The default scaling indicator is v.

     The current setting can be found in the read-only number register .p.

     Note that this only specifies the size of the page, not the top and bottom margins.  Those are not set by gtroff directly. See Traps, for further information on how to do this.

     Negative pl values are possible also, but not very useful: No trap is sprung, and each line is output on a single page (thus suppressing all vertical spacing).

     If no argument or an invalid argument is given, pl sets the page length to 11i.

gtroff provides several operations which help in setting up top and bottom titles (or headers and footers).

 -- Request: .tl, 'left'center'right'
     Print a title line.  It consists of three parts: a left justified portion, a centered portion, and a right justified portion. The argument separator ' can be replaced with any character not occurring in the title line.  The % character is replaced with the current page number.  This character can be changed with the pc request (see below).

     Without argument, tl is ignored.

     Some notes:

       * A title line is not restricted to the top or bottom of a page.

       * tl prints the title line immediately, ignoring a partially filled line (which stays untouched).

       * It is not an error to omit closing delimiters.  For example, .tl /foo is equivalent to .tl /foo///: It prints a title line with the left justified word foo; the centered and right justfied parts are empty.

       * Any modifications to the current environment within tl (e.g. changing the font or font size) are undone after processing tl.

       * tl accepts the same parameter delimiting characters as the \A escape; see Escapes.

 -- Request: .lt, [length]
 -- Request: .lt, +length
 -- Request: .lt, -length
 -- Register: \n[.lt]
     The title line is printed using its own line length, which is specified (or incremented or decremented) with the lt request. Initially, the title line length is set to 6.5i.  If a negative line length is specified (which is not allowed), gtroff emits a warning of type range and sets the title line length to zero. The default scaling indicator is m.  If lt is called without an argument, the title length is reset to the previous value before the last call to lt.

     The current setting of this is available in the .lt read-only number register; it is associated with the current environment (see Environments).

 -- Request: .pn, page
 -- Request: .pn, +page
 -- Request: .pn, -page
 -- Register: \n[.pn]
     Change (increase or decrease) the page number of the next page. The only argument is the page number; the request is ignored without a parameter.

     The read-only number register .pn contains the number of the next page: either the value set by a pn request, or the number of the current page plus 1.

 -- Register: \n[%]
     A read-write register holding the current page number.

 -- Request: .pc, [char]
     Change the page number character (used by the tl request) to a different character.  With no argument, this mechanism is disabled. Note that this doesn't affect the number register %.

See Traps.

Page Control
============

 -- Request: .bp, [page]
 -- Request: .bp, +page
 -- Request: .bp, -page
     Stop processing the current page and move to the next page.  This request causes a break.  It can also take an argument to set (increase, decrease) the page number of the next page.  The only difference between bp and pn is that pn does not cause a break or actually eject a page.

          .de newpage                         \" define macro
          'bp                                 \" begin page
          'sp .5i                             \" vertical space
          .tl 'left top'center top'right top' \" title
          'sp .3i                             \" vertical space
          ..                                  \" end macro

     bp has no effect if not called within the top-level diversion (see Diversions).

 -- Request: .ne, [space]
     It is often necessary to force a certain amount of space before a new page occurs.  This is most useful to make sure that there is not a single orphan line left at the bottom of a page.  The ne request ensures that there is a certain distance, specified by the first argument, before the next page is triggered (see Traps, for further information).  The default unit for ne is v; the default value of SPACE is 1v if no argument is given.

     For example, to make sure that no fewer than 2 lines get orphaned, do the following before each paragraph:

          .ne 2
          text text text

 -- Request: .sv, [space]
     sv is similar to the ne request; it reserves the specified amount of vertical space.  If the desired amount of space exists before the next trap (bottom page boundary), the space is output immediately (ignoring a partial filled line which stays untouched).  If there is not enough space, it is stored for later output via the os request.  The default value is 1v if no argument is given; the default unit is v.

Fonts
=====

gtroff can switch fonts at any point in the text.

The basic set of fonts is R, I, B, and BI. These are Times Roman, Italic, Bold, and Bold Italic.  For non-tty devices, there is also at least one symbol font which contains various special symbols (Greek, mathematics).

Changing Fonts
--------------

 -- Request: .ft, [font]
 -- Escape: \\f, , f,
 -- Escape: \\f, (, fn,
 -- Escape: \\f, [, font, ]
     The ft request and the \f escape change the current font to FONT (one-character name F, two-character name FN).

     If FONT is a style name (as set with the sty request or with the styles command in the DESC file), use it within the current font family (as set with the fam request or with the family command in the DESC file).

     With no argument or using P as an argument, .ft switches to the previous font.  Use \fP or \f[P] to do this with the escape.

     Fonts are generally specified as upper-case strings, which are usually 1 to 4 characters representing an abbreviation or acronym of the font name.  This is no limitation, just a convention.

     The example below produces two identical lines.

          eggs, bacon,
          .ft B
          spam
          .ft
          and sausage.

          eggs, bacon, \fBspam\fP and sausage.

     See Font Positions, for an alternative syntax.

 -- Request: .ftr, f [g]
     Translate font F to font G.  Whenever a font named F is referred to in a \f escape sequence, or in the ft, ul, bd, cs, tkf, special, fspecial, fp, or code requests, font G is used.  If G is missing or equal to F the translation is undone.

Font Families
-------------

Due to the variety of fonts available, gtroff has added the concept of font families and font styles.  The fonts are specified as the concatenation of the font family and style.  Specifying a font without the family part causes gtroff to use that style of the current family.

Currently, only POSTSCRIPT fonts are set up to this mechanism. By default, gtroff uses the Times family with the four styles R, I, B, and BI.

This way, it is possible to use the basic four fonts and to select a different font family on the command line (see Groff Options).

 -- Request: .fam, [family]
 -- Register: \n[.fam]
     Switch font family to FAMILY.  If no argument is given, switch back to the previous font family.  The current font family is available in the read-only number register .fam (this is a string-valued register); it is associated with the current environment.

          spam,
          .fam H    \" helvetica family
          spam,     \" used font is family H + style R = HR
          .ft B     \" family H + style B = font HB
          spam,
          .fam T    \" times family
          spam,     \" used font is family T + style B = TB
          .ft AR    \" font AR (not a style)
          baked beans,
          .ft R     \" family T + style R = font TR
          and spam.

 -- Request: .sty, n style
     Associate STYLE with font position N.  A font position can be associated either with a font or with a style.  The current font is the index of a font position and so is also either a font or a style.  When it is a style, the font that is actually used is the font the name of which is the concatenation of the name of the current family and the name of the current style.  For example, if the current font is 1 and font position 1 is associated with style R and the current font family is T, then font TR will be used.  If the current font is not a style, then the current family is ignored.  When the requests cs, bd, tkf, uf, or fspecial are applied to a style, then they will instead be applied to the member of the current family corresponding to that style.

     N must be a non-negative integer value.

     The default family can be set with the -f option (see Groff Options).  The styles command in the DESC file controls which font positions (if any) are initially associated with styles rather than fonts.  For example, the default setting for POSTSCRIPT fonts

          styles R I B BI

     is equivalent to

          .sty 1 R
          .sty 2 I
          .sty 3 B
          .sty 4 BI

     .fam always checks whether the current font position is valid; this can give surprising results if the current font position is associated with a style.

     In the following example, we want to access the POSTSCRIPT font FooBar from the font family Foo:

          .sty \n[.fp] Bar
          .fam Foo
              => warning: can't find font `FooR'

     The default font position at start-up is 1; for the POSTSCRIPT device, this is associated with style R, so gtroff tries to open FooR.

     A solution to this problem is to use a dummy font like the following:

          .fp 0 dummy TR    \" set up dummy font at position 0
          .sty \n[.fp] Bar  \" register style `Bar'
          .ft 0             \" switch to font at position 0
          .fam Foo          \" activate family `Foo'
          .ft Bar           \" switch to font `FooBar'

     See Font Positions.

Font Positions
--------------

For the sake of old phototypesetters and compatibility with old versions of troff, gtroff has the concept of font positions, on which various fonts are mounted.

 -- Request: .fp, pos font [external-name]
 -- Register: \n[.f]
 -- Register: \n[.fp]
     Mount font FONT at position POS (which must be a non-negative integer).  This numeric position can then be referred to with font changing commands.  When gtroff starts it is using font position 1 (which must exist; position 0 is unused usually at start-up).

     The current font in use, as a font position, is available in the read-only number register .f.  This can be useful to remember the current font for later recall.  It is associated with the current environment (see Environments).

          .nr save-font \n[.f]
          .ft B
          ... text text text ...
          .ft \n[save-font]

     The number of the next free font position is available in the read-only number register .fp.  This is useful when mounting a new font, like so:

          .fp \n[.fp] NEATOFONT

     Fonts not listed in the DESC file are automatically mounted on the next available font position when they are referenced.  If a font is to be mounted explicitly with the fp request on an unused font position, it should be mounted on the first unused font position, which can be found in the .fp register.  Although gtroff does not enforce this strictly, it is not allowed to mount a font at a position whose number is much greater (approx. 1000 positions) than that of any currently used position.

     The fp request has an optional third argument.  This argument gives the external name of the font, which is used for finding the font description file.  The second argument gives the internal name of the font which is used to refer to the font in gtroff after it has been mounted.  If there is no third argument then the internal name is used as the external name.  This feature makes it possible to use fonts with long names in compatibility mode.

Both the ft request and the \f escape have alternative syntax forms to access font positions.

 -- Request: .ft, nnn
 -- Escape: \\f, , n,
 -- Escape: \\f, (, nn,
 -- Escape: \\f, [, nnn, ]
     Change the current font position to NNN (one-digit position N, two-digit position NN), which must be a non-negative integer.

     If NNN is associated with a style (as set with the sty request or with the styles command in the DESC file), use it within the current font family (as set with the fam request or with the family command in the DESC file).

          this is font 1
          .ft 2
          this is font 2
          .ft                   \" switch back to font 1
          .ft 3
          this is font 3
          .ft
          this is font 1 again

     See Changing Fonts, for the standard syntax form.

Using Symbols
-------------

A glyph is a graphical representation of a character. While a character is an abstract entity containing semantic information, a glyph is something which can be actually seen on screen or paper.  It is possible that a character has multiple glyph representation forms (for example, the character `A' can be either written in a roman or an italic font, yielding two different glyphs); sometimes more than one character maps to a single glyph (this is a ligature -- the most common is `fi').

Please note that currently the distinction between glyphs and characters in this reference is not clearly carried out.  This will be improved eventually in the next revision.

A symbol is simply a named glyph.  Within gtroff, all glyph names of a particular font are defined in its font file.  If the user requests a glyph not available in this font, gtroff looks up an ordered list of special fonts.  By default, the POSTSCRIPT output device supports the two special fonts SS (slanted symbols) and S (symbols) (the former is looked up before the latter).  Other output devices use different names for special fonts.  Fonts mounted with the fonts keyword in the DESC file are globally available.  To install additional special fonts locally (i.e. for a particular font), use the fspecial request.

See Font Files, and Special Fonts, for more details.

 -- Escape: \\, (, nm,
 -- Escape: \\, [, name, ]
     Insert a symbol NAME (two-character name NM).  There is no special syntax for one-character names -- the natural form \N would collide with escapes.

     If NAME is undefined, a warning of type char is generated, and the escape is ignored.  See Debugging, for information about warnings.

     The list of available symbols is device dependent; see Glyph Name Index for some of them discussed in this reference.

 -- Escape: \\C, ', xxx, '
     Typeset the character named XXX.  Normally it is more convenient to use \[XXX], but \C has the advantage that it is compatible with newer versions of ditroff and is available in compatibility mode.

 -- Escape: \\N, ', n, '
     Typeset the character with code N in the current font (this is not the input character code).  N can be any integer.  Most devices only have characters with codes between 0 and 255; the Unicode output device uses codes in the range 0--65535.  If the current font does not contain a character with that code, special fonts are not searched.  The \N escape sequence can be conveniently used in conjunction with the char request:

          .char \[phone] \f[ZD]\N'37'

     The code of each character is given in the fourth column in the font description file after the charset command.  It is possible to include unnamed characters in the font description file by using a name of ---; the \N escape sequence is the only way to use these.

 -- Request: .cflags, n c1 c2 ...
     Each character has certain properties associated with it.  These properties can be modified with the cflags request.  The first argument is the the sum of the desired flags and the remaining arguments are the characters to have those properties.  It is possible to omit the spaces between the characters.

     1
          the character ends sentences (initially characters .?! have this property)

     2
          lines can be broken before the character (initially no characters have this property)

     4
          lines can be broken after the character (initially the characters -\(hy\(em have this property)

     8
          the character overlaps horizontally (initially the characters \(ul\(rn\(ru have this property)

     16
          the character overlaps vertically (initially character \(br has this property)

     32
          an end of sentence character followed by any number of characters with this property is treated as the end of a sentence if followed by a newline or two spaces; in other words the character is transparent for the purposes of end of sentence recognition -- this is the same as having a zero space factor in TeX (initially characters "')]*\(dg\(rq have this property).

 -- Request: .char, c [string]
     Define a new character C to be STRING (which can be empty).  Every time character C needs to be printed, STRING is processed in a temporary environment and the result is wrapped up into a single object.  Compatibility mode is turned off and the escape character is set to \ while STRING is being processed.  Any emboldening, constant spacing or track kerning is applied to this object rather than to individual characters in STRING.  A character defined by this request can be used just like a normal character provided by the output device.  In particular, other characters can be translated to it with the tr request; it can be made the leader character by the lc request; repeated patterns can be drawn with the character using the \l and \L escape sequences; words containing the character can be hyphenated correctly, if the hcode request is used to give the character a hyphenation code.  There is a special anti-recursion feature: Use of character within the character's definition is handled like normal characters not defined with char.

 -- Request: .rchar, c1 c2 ...
     Remove the definitions of characters C1, C2, ... This undoes the effect of a char request.

     It is possible to omit the whitespace between arguments.

See Special Characters.

Special Fonts
-------------

To be written.

Artificial Fonts
----------------

There are a number of requests for artificially creating fonts.  These are largely vestiges of the days when output devices did not have a wide variety of fonts, and when nroff and troff were separate programs.  These are no longer necessary in GNU troff.  Nevertheless, they are supported.

 -- Request: .ul, [lines]
     The ul request normally underlines subsequent lines if a tty output device is used.  Otherwise, the lines are printed in italics (only the term `underlined' is used in the following).  The single argument is the number of input lines to be underlined; with no argument, the next line is underlined.  If LINES is zero or negative, stop the effects of ul (if it was active).  Requests and empty lines do not count for computing the number of underlined input lines, even if they produce some output like tl.  Lines inserted by macros (e.g. invoked by a trap) do count.

     At the beginning of ul, the current font is stored and the underline font is activated.  Within the span of a ul request, it is possible to change fonts, but after the last line affected by ul the saved font is restored.

     This command is associated with the current environment.  The underline font can be changed with the uf request.

     See Troff and Nroff Mode, for a discussion how underlining is implemented in for tty output devices, and which problems can arise.

     The ul request does not underline spaces.

 -- Request: .cu, [lines]
     The cu request is similar to ul but underlines spaces as well (if a tty output device is used).

 -- Request: .uf, font
     Set the underline font (globally) used by ul and cu.  By default, this is the font at position 2.  FONT can be either a non-negative font position or the name of a font.

 -- Request: .bd, font [offset]
 -- Request: .bd, font1 font2 [offset]
 -- Register: \n[.b]
     Artificially create a bold font by printing each character twice, slightly offset.

     Two syntax forms are available.

       * Imitate a bold font unconditionally.  The first argument specifies the font to embolden, and the second is the number of basic units, minus one, by which the two characters is offset.  If the second argument is missing, emboldening is turned off.

          FONT can be either a non-negative font position or the name of a font.

          OFFSET is available in the .b read-only register if a special font is active; in the bd request, its default unit is u.

       * Imitate a bold form conditionally.  Embolden FONT1 by OFFSET only if font FONT2 is the current font.  This command can be issued repeatedly to set up different emboldening values for different current fonts.  If the second argument is missing, emboldening is turned off for this particular current font.

          This affects special fonts only (either set up with the special command in font files or with the fspecial request).

 -- Request: .cs, font [width [em-size]]
     Switch to and from constant character space mode.  If activated, the width of every character is WIDTH/36 ems.  The em size is given absolutely by EM-SIZE; if this argument is missing, the em value is taken from the current font size (as set with the ps request) when the font is effectively in use.  Without second and third argument, constant character space mode is deactivated.

     Default unit for EM-SIZE is z; WIDTH is an integer.

Ligatures and Kerning
---------------------

Ligatures are groups of characters that are run together.  For example, the letters `f' and `i' can form a ligature `fi' as in the word `file'.  This produces a cleaner look (albeit subtle) to the printed output.  Usually, ligatures are not available in fonts for tty output devices.

Most POSTSCRIPT fonts support the fi and fl ligatures.  The C/A/T typesetter that was the target of AT&T troff also supported `ff', `ffi', and `ffl' ligatures.  Advanced typesetters or `expert' fonts may include ligatures for `ft' and `ct', although GNU troff does not support these (yet).

 -- Request: .lg, [flag]
 -- Register: \n[.lg]
     The ligature mechanism can be switched on or off with the lg request; if the parameter is non-zero or missing, ligatures are enabled, otherwise disabled.  Default is on.  The current ligature mode can be found in the read-only number register .lg (set to 1 or 2 if ligatures are enabled, 0 otherwise).

     Setting the ligature mode to 2 enables the two-character ligatures (fi, fl, and ff) and disables the three-character ligatures (ffi and ffl).

Pairwise kerning is another subtle typesetting mechanism that modifies the distance between a character pair to improve readability. In most cases (but not always) the distance is decreased. Typewriter-like fonts and fonts for terminals where all characters have the same width don't use kerning.

 -- Request: .kern, [flag]
 -- Register: \n[.kern]
     Kerning can be activated with the kern request.  If the parameter is non-zero or missing, enable pairwise kerning, otherwise disable it.  The read-only number register .kern is set to 1 if pairwise kerning is enabled, 0 otherwise.

     If the font description file contains pairwise kerning information, characters from that font are kerned.  Kerning between two characters can be inhibited by placing \& between them: V\&A.

     See Font File Format.

Track kerning expands or reduces the space between characters. This can be handy, for example, if you need to squeeze a long word onto a single line or spread some text to fill a narrow column.  It must be used with great care since it is usually considered bad typography if the reader notices the effect.

 -- Request: .tkf, f s1 n1 s2 n2
     Enable track kerning for font F.  If the current font is F the width of every character is increased by an amount between N1 and N2 (N1, N2 can be negative); if the current point size is less than or equal to S1 the width is increased by N1; if it is greater than or equal to S2 the width is increased by N2; if the point size is greater than or equal to S1 and less than or equal to S2 the increase in width is a linear function of the point size.

     The default unit is z for S1 and S2, p for N1 and N2.

Sometimes, when typesetting letters of different fonts, more or less space at such boundaries are needed.  There are two escapes to help with this.

 -- Escape: \\/, , ,
     Increase the width of the preceding character so that the spacing between that character and the following character is correct if the following character is a roman character.  For example, if an italic f is immediately followed by a roman right parenthesis, then in many fonts the top right portion of the f overlaps the top left of the right parenthesis.  Use this escape sequence whenever an italic character is immediately followed by a roman character without any intervening space.  This small amount of space is also called italic correction.

 -- Escape: \\\,, , ,
     Modify the spacing of the following character so that the spacing between that character and the preceding character is correct if the preceding character is a roman character.  Use this escape sequence whenever a roman character is immediately followed by an italic character without any intervening space.  In analogy to above, this space could be called left italic correction, but this term isn't used widely.

 -- Escape: \\&, , ,
     Insert a zero-width character, which is invisible.  Its intended use is to stop interaction of a character with its surrounding.

       * It prevents the insertion of extra space after an end of sentence character.

               Test.
               Test.
                   => Test.  Test.
               Test.\&
               Test.
                   => Test. Test.

       * It prevents interpretation of a control character at the beginning of an input line.

               .Test
                   => warning: `Test' not defined
               \&.Test
                   => .Test

       * It prevents kerning between two characters.

       * It is needed to map an arbitrary character to nothing in the tr request (see Character Translations).

Sizes
=====

gtroff uses two dimensions with each line of text, type size and vertical spacing.  The type size is approximately the height of the tallest character. (This is usually the parenthesis. Note that in most cases the real dimensions of the glyphs in a font are not related to its type size!  For example, the standard POSTSCRIPT font families `Times Roman', `Helvetica', and `Courier' can't be used together at 10pt; to get acceptable output, the size of `Helvetica' has to be reduced by one point, and the size of `Courier' must be increased by one point.)  Vertical spacing is the amount of space gtroff allows for a line of text; normally, this is about 20% larger than the current type size.  Ratios smaller than this can result in hard-to-read text; larger than this, it spreads the text out more vertically (useful for term papers).  By default, gtroff uses 10 point type on 12 point spacing.

The difference between type size and vertical spacing is known, by typesetters, as leading.

Changing Type Sizes
-------------------

 -- Request: .ps, [size]
 -- Request: .ps, +size
 -- Request: .ps, -size
 -- Escape: \\s, , size,
 -- Register: \n[.s]
     Use the ps request or the \s escape to change (increase, decrease) the type size (in points).  Specify SIZE as either an absolute point size, or as a relative change from the current size. The size 0, or no argument, goes back to the previous size.

     Default unit of size is z.  If size is zero or negative, it is set to 1u.

     The read-only number register .s returns the point size in points as a decimal fraction.  This is a string.  To get the point size in scaled points, use the .ps register instead.

     .s is associated with the current environment (see Environments).

          snap, snap,
          .ps +2
          grin, grin,
          .ps +2
          wink, wink, \s+2nudge, nudge,\s+8 say no more!
          .ps 10

     The \s escape may be called in a variety of ways.  Much like other escapes there must be a way to determine where the argument ends and the text begins.  Any of the following forms are valid:

     \sN
          Set the point size to N points.  N must be either 0 or in the range 4 to 39.

     \s+N
     \s-N
          Increase or decrease the point size by N points.  N must be exactly one digit.

     \s(NN
          Set the point size to NN points.  NN must be exactly two digits.

     \s+(NN
     \s-(NN
     \s(+NN
     \s(-NN
          Increase or decrease the point size by NN points.  NN must be exactly two digits.

     See Fractional Type Sizes, for yet another syntactical form of using the \s escape.

     Some devices may only have certain permissible sizes, in which case gtroff rounds to the nearest permissible size.

 -- Request: .vs, [space]
 -- Request: .vs, +space
 -- Request: .vs, -space
 -- Register: \n[.v]
     Change (increase, decrease) the vertical spacing by SPACE.  The default unit is p.

     If vs is called without an argument, the vertical spacing is reset to the previous value before the last call to vs.

     gtroff creates a warning of type range if SPACE is zero or negative; the vertical spacing is then set to the vertical resolution (as given in the .V register).

     The read-only number register .v contains the current vertical spacing; it is associated with the current environment (see Environments).

Fractional Type Sizes
---------------------

A scaled point is equal to 1/SIZESCALE points, where SIZESCALE is specified in the DESC file (1 by default).  There is a new scale indicator z which has the effect of multiplying by SIZESCALE.  Requests and escape sequences in gtroff interpret arguments that represent a point size as being in units of scaled points, but they evaluate each such argument using a default scale indicator of z.  Arguments treated in this way are the argument to the ps request, the third argument to the cs request, the second and fourth arguments to the tkf request, the argument to the \H escape sequence, and those variants of the \s escape sequence that take a numeric expression as their argument (see below).

For example, suppose SIZESCALE is 1000; then a scaled point is equivalent to a millipoint; the request .ps 10.25 is equivalent to .ps 10.25z and thus sets the point size to 10250 scaled points, which is equal to 10.25 points.

gtroff disallows the use of the z scale indicator in instances where it would make no sense, such as a numeric expression whose default scale indicator was neither u nor z.  Similarly it would make no sense to use a scaling indicator other than z or u in a numeric expression whose default scale indicator was z, and so gtroff disallows this as well.

There is also new scale indicator s which multiplies by the number of units in a scaled point.  So, for example, \n[.ps]s is equal to 1m.  Be sure not to confuse the s and z scale indicators.

 -- Register: \n[.ps]
     A read-only number register returning the point size in scaled points.

     .ps is associated with the current environment (see Environments).

 -- Register: \n[.psr]
 -- Register: \n[.sr]
     The last-requested point size in scaled points is contained in the .psr read-only number register.  The last requested point size in points as a decimal fraction can be found in .sr.  This is a string-valued read-only number register.

     Note that the requested point sizes are device-independent, whereas the values returned by the .ps and .s registers are not. For example, if a point size of 11pt is requested for a DVI device, 10.95pt are actually used (as specified in the DESC file).

     Both registers are associated with the current environment (see Environments).

The \s escape has the following syntax for working with fractional type sizes:

\s[N]
\s'N'
     Set the point size to N scaled points; N is a numeric expression with a default scale indicator of z.

\s[+N]
\s[-N]
\s+[N]
\s-[N]
\s'+N'
\s'-N'
\s+'N'
\s-'N'
     Increase or or decrease the point size by N scaled points; N is a numeric expression with a default scale indicator of z.

See Font Files.

Strings
=======

gtroff has string variables, which are entirely for user convenience (i.e. there are no built-in strings exept .T, but even this is a read-write string variable).

 -- Request: .ds, name [string]
 -- Escape: \\*, , n,
 -- Escape: \\*, (, nm,
 -- Escape: \\*, [, name, ]
     Define and access a string variable NAME (one-character name N, two-character name NM).  If NAME already exists, ds overwrites the previous definition.

     Example:

          .ds UX \s-1UNIX\s0\u\s-3tm\s0\d
          .
          The \*(UX Operating System

     The \* escape interpolates (expands in-place) a previously-defined string variable.  To be more precise, the stored string is pushed onto the input stack which is then parsed by gtroff.  Similar to number registers, it is possible to nest strings, i.e. a string variables can be called within string variables.

     If the string named by the \* does not exist, it is defined as empty, and a warning of type mac is emitted (see Debugging, for more details).

     Caution: Unlike other requests, the second argument to the ds request takes up the entire line including trailing spaces. This means that comments on a line with such a request can introduce unwanted space into a string.

          .ds UX \s-1UNIX\s0\u\s-3tm\s0\d \" UNIX trademark

     Instead the comment should be put on another line or have the comment escape adjacent with the end of the string.

          .ds UX \s-1UNIX\s0\u\s-3tm\s0\d\"  UNIX trademark

     To produce leading space the string can be started with a double quote.  No trailing quote is needed; in fact, any trailing quote is included in your string.

          .ds sign "           Yours in a white wine sauce,

     Strings are not limited to a single line of text.  A string can span several lines by escaping the newlines with a backslash.  The resulting string is stored without the newlines.

          .ds foo lots and lots \
          of text are on these \
          next several lines

     It is not possible to have real newlines in a string.

     Strings, macros, and diversions (and boxes) share the same name space. Internally, even the same mechanism is used to store them.  This has some interesting consequences.  For example, it is possible to call a macro with string syntax and vice versa.

          .de xxx
          a funny test.
          ..
          This is \*[xxx]
              => This is a funny test.

          .ds yyy a funny test
          This is
          .yyy
              => This is a funny test.

     Diversions and boxes can be also called with string syntax.  It is not possible to pass arguments to a macro if called with \*.

     Another consequence is that you can copy one-line diversions or boxes to a string.

          .di xxx
          a \fItest\fR
          .br
          .di
          .ds yyy This is \*[xxx]\c
          \*[yyy].
              => This is a test.

     As the previous example shows, it is possible to store formatted output in strings.  The \c escape prevents the insertion of an additional blank line in the output.

     Copying diversions longer than a single output line produces unexpected results.

          .di xxx
          a funny
          .br
          test
          .br
          .di
          .ds yyy This is \*[xxx]\c
          \*[yyy].
              => test This is a funny.

     Usually, it is not predictable whether a diversion contains one or more output lines, so this mechanism should be avoided.  With UNIX troff, this was the only solution to strip off a final newline from a diversion.  Another disadvantage is that the spaces in the copied string are already formatted, making them unstretchable.  This can cause ugly results.

     A clean solution to this problem is available in GNU troff, using the requests chop to remove the final newline of a diversion, and unformat to make the horizontal spaces stretchable again.

          .box xxx
          a funny
          .br
          test
          .br
          .box
          .chop xxx
          .unformat xxx
          This is \*[xxx].
              => This is a funny test.

     See Gtroff Internals, for more information.

 -- Request: .as, name [string]
     The as request is similar to ds but appends STRING to the string stored as NAME instead of redefining it.  If NAME doesn't exist yet, it is created.

          .as sign " with shallots, onions and garlic,

Rudimentary string manipulation routines are given with the next two requests.

 -- Request: .substring, str n1 [n2]
     Replace the string in register STR with the substring defined by the indices N1 and N2.  The first character in the string has index one.  If N2 is omitted, it is taken to be equal to the string's length.  If the index value N1 or N2 is negative or zero, it is counted from the end of the string, going backwards: The last character has index 0, the character before the last character has index -1, etc.

          .ds xxx abcdefgh
          .substring xxx 2 -3
          \*[xxx]
              => bcde

 -- Request: .length, reg str
     Compute the length of STR and returns it in the number register REG.  If REG doesn't exist, it is created.

          .ds xxx abcdefgh
          .length yyy xxx
          \n[yyy]
              => 8

 -- Request: .rn, xx yy
     Rename the request, macro, or string XX to YY.

 -- Request: .rm, xx
     Remove the request, macro, or string XX.  gtroff treats subsequent invocations as if the object had never been defined.

 -- Request: .als, new old
     Create an alias named NEW for the request, string, macro, or diversion object named OLD.  The new name and the old name are exactly equivalent (it is similar to a hard rather than a soft link). If OLD is undefined, gtroff generates a warning of type mac and ignores the request.

 -- Request: .chop, xx
     Remove (chop) the last character from the macro, string, or diversion named XX. This is useful for removing the newline from the end of diversions that are to be interpolated as strings.  This command can be used repeatedly; see Gtroff Internals, for details on nodes inserted by gtroff automatically.

See Identifiers, and Comments.

Conditionals and Loops
======================

Operators in Conditionals
-------------------------

In if and while requests, there are several more operators available:

e
o
     True if the current page is even or odd numbered (respectively).

n
     True if the document is being processed in nroff mode (i.e., the .nroff command has been issued).

t
     True if the document is being processed in troff mode (i.e., the .troff command has been issued).

v
     Always false.

'XXX'YYY'
     True if the string XXX is equal to the string YYY.  Other characters can be used in place of the single quotes; the same set of delimiters as for the \D escape is used (see Escapes). gtroff formats the strings before being compared:

          .ie "|"\fR|\fP" \
          true
          .el \
          false
              => true

     The resulting motions, character sizes, and fonts have to match, (The created output nodes must be identical. See Gtroff Internals.) and not the individual motion, size, and font requests.  In the previous example, | and \fR|\fP both result in a roman | character with the same point size and at the same location on the page, so the strings are equal.  If .ft I had been added before the .ie, the result would be ``false'' because (the first) | produces an italic | rather than a roman one.

r XXX
     True if there is a number register named XXX.

d XXX
     True if there is a string, macro, diversion, or request named XXX.

c CH
     True if there is a character CH available; CH is either an ASCII character or a special character (\(CH or \[CH]); the condition is also true if CH has been defined by the char request.

Note that these operators can't be combined with other operators like : or &; only a leading ! (without whitespace between the exclamation mark and the operator) can be used to negate the result.

     .nr xxx 1
     .ie !r xxx \
     true
     .el \
     false
         => false

A whitespace after ! always evaluates to zero (this bizarre behaviour is due to compatibility with UNIX troff).

     .nr xxx 1
     .ie ! r xxx \
     true
     .el \
     false
         => r xxx true

It is possible to omit the whitespace before the argument to the r, d, and c operators.

See Expressions.

if-else
-------

gtroff has if-then-else constructs like other languages, although the formatting can be painful.

 -- Request: .if, expr anything
     Evaluate the expression EXPR, and executes ANYTHING (the remainder of the line) if EXPR evaluates to non-zero (true). ANYTHING is interpreted as though it was on a line by itself (except that leading spaces are swallowed).  See Expressions, for more info.

          .nr xxx 1
          .nr yyy 2
          .if ((\n[xxx] == 1) & (\n[yyy] == 2)) true
              => true

 -- Request: .ie, expr anything
 -- Request: .el, anything
     Use the ie and el requests to write an if-then-else. The first request is the `if' part and the latter is the `else' part.

          .ie n .ls 2 \" double spacing in nroff
          .el   .ls 1 \" single spacing in troff

In many cases, an if (or if-else) construct needs to execute more than one request.  This can be done using the \{ and \} escapes.  The following example shows the possible ways to use these escapes (note the position of the opening and closing braces).

     .ie t \{\
     .    ds lq ``
     .    ds rq ''
     .\}
     .el \
     .\{\
     .    ds lq "
     .    ds rq "\}

See Expressions.

while
-----

gtroff provides a looping construct using the while request, which is used much like the if (and related) requests.

 -- Request: .while, expr anything
     Evaluate the expression EXPR, and repeatedly execute ANYTHING (the remainder of the line) until EXPR evaluates to 0.

          .nr a 0 1
          .while (\na < 9) \{\
          \n+a,
          .\}
          \n+a
              => 1, 2, 3, 4, 5, 6, 7, 8, 9, 10

     Some remarks.

       * The body of a while request is treated like the body of a de request: gtroff temporarily stores it in a macro which is deleted after the loop has been exited.  It can considerably slow down a macro if the body of the while request (within the macro) is large.  Each time the macro is executed, the while body is parsed and stored again as a temporary macro.

               .de xxx
               .  nr num 10
               .  while (\\n[num] > 0) \{\
               .    \" many lines of code
               .    nr num -1
               .  \}
               ..

          The traditional and ofter better solution (UNIX troff doesn't have the while request) is to use a recursive macro instead which is parsed only once during its definition.

               .de yyy
               .  if (\\n[num] > 0) \{\
               .    \" many lines of code
               .    nr num -1
               .    yyy
               .  \}
               ..
               .
               .de xxx
               .  nr num 10
               .  yyy
               ..

          Note that the number of available recursion levels is set to 1000 (this is a compile-time constant value of gtroff).

       * The closing brace of a while body must end a line.

               .if 1 \{\
               .  nr a 0 1
               .  while (\n[a] < 10) \{\
               .    nop \n+[a]
               .\}\}
                   => unbalanced \{ \}

 -- Request: .break,
     Break out of a while loop.  Be sure not to confuse this with the br request (causing a line break).

 -- Request: .continue,
     Finishes the current iteration of a while loop, immediately restarting the next iteration.

See Expressions.

Writing Macros
==============

A macro is a collection of text and embedded commands which can be invoked multiple times.  Use macros to define common operations.

 -- Request: .de, name [end]
     Define a new macro named NAME.  gtroff copies subsequent lines (starting with the next one) into an internal buffer until it encounters the line .. (two dots).  The optional second argument to de changes this to a macro to .END.

     Note that no leading whitespace is allowed in the line containing the ending token (either .. or the macro .END).

     Here a small example macro called P which causes a break and inserts some vertical space.  It could be used to separate paragraphs.

          .de P
          .  br
          .  sp .8v
          ..

 -- Request: .am, xx
     Works similarly to de except it appends onto the macro named XX.  So, to make the previously defined P macro actually do indented instead of block paragraphs, add the necessary code to the existing macro like this:

          .am P
          .ti +5n
          ..

 -- Request: .als, new old
     Create an alias named NEW for the request, string, macro, or diversion object named OLD.  The new name and the old name are exactly equivalent (it is similar to a hard rather than a soft link). If OLD is undefined, gtroff generates a warning of type mac and ignores the request.

     The de, am, di, da, ds, and as requests only create a new object if the name of the macro, diversion or string diversion is currently undefined or if it is defined to be a request; normally they modify the value of an existing object.

Copy-in Mode
------------

When gtroff reads in the text for a macro or diversion, it copies the text (including request lines, but excluding escapes) into an internal buffer.  Escapes are converted into an internal form, except for \n, \$, \*, \\ and \RET which are evaluated and inserted into the text where the escape was located.  This is known as copy-in mode or copy mode.

What this means is that you can specify when these escapes are to be evaluated (either at copy-in time or at the time of use) by insulating the escapes with an extra backslash.  Compare this to the \def and \edef commands in TeX.

The following example prints the numbers 20 and 10:

     .nr x 20
     .de y
     .nr x 10
     \&\nx
     \&\\nx
     ..
     .y

Parameters
----------

The arguments to a macro can be examined using a variety of escapes. The number of arguments is available in the .$ number register. Any individual argument can be retrieved with one of the following escapes:

 -- Escape: \\$, n, ,
 -- Escape: \\$, (, nn,
 -- Escape: \\$, [, nnn, ]
     The escapes \$N, \$(NN and \$[NNN] retrieve the Nth, NNth or NNNth argument.  As usual, the first form only accepts a single number (larger than zero), the second a two-digit number (larger or equal to 10), and the third any positive integer value (larger than zero).  Macros can have an unlimited number of arguments.  Note that due to copy-in mode, use two backslashes on these in actual use to prevent interpolation until the macro is actually invoked.

 -- Request: .shift, [n]
     Shifts the arguments 1 position, or as many positions as specified by its argument.  After executing this request, argument I becomes argument I-N; arguments 1 to N are no longer available.  Shifting by negative amounts is currently undefined.

 -- Escape: \\$*, , ,
 -- Escape: \\$@, , ,
     In some cases it is convenient to use all of the arguments at once (for example, to pass the arguments along to another macro).  The \$* escape concatenates all the arguments separated by spaces.  A similar escape is \$@, which concatenates all the arguments with each surrounded by double quotes, and separated by spaces.

 -- Escape: \\$0, , ,
     The name used to invoke the current macro. The als request can make a macro have more than one name.

          .de vl
          .ie \\n(.$=1 .ds Vl Pre-Release Version
          .el          .ds Vl Version \\$3, \\$4.
          ..

     This would be called as

          .vl $Id: groff.texinfo,v 1.77 2001/05/07 13:36:24 wlemb Exp $

See Request Arguments.

Page Motions
============

 -- Request: .sp, [len]
     Motions up and down the page can be done with the sp request. However, this causes a break so that the actual effect is to move to the left margin and then to the specified location.

 -- Request: .mk, [reg]
 -- Request: .rt, reg
     The request mk can be used to mark a location on a page, for movement to later.  This request takes a register name as an argument in which to store the current page location.  With no argument it stores the location in an internal register.  The results of this can be used later by the rt or the sp request.  The rt request returns upwards to the location given in the register name given as an argument; with no argument it returns to the location marked with the mk request.

The following escapes give fine control of movements about the page.

 -- Escape: \\v, ', e, '
     The \v'E' escape enables arbitrary vertical motion from the current location on the page.  The argument E specifies the distance to move; positive is downwards and negative upwards.  The default unit for this escape v.  Beware, however, that gtroff continues text processing at the point where the motion ends, so you should always balance motions to avoid interference with text processing.

There are some special case escapes for vertical motion.

\r
     move upwards 1v.

\u
     move upwards .5v.

\d
     move down .5v.

 -- Escape: \\h, ', e, '
     The \h'E' escape provides horizontal motions.  The expression E indicates how far to move: positive is rightwards and negative leftwards.

There are a number of special case escapes for horizontal motion:

\SP
     An unbreakable and unpaddable (i.e. not expanded during filling) space.  (Note: This is a backslash followed by a space.)

\~
     An unbreakable space that stretches like a normal inter-word space when a line is adjusted.

\|
     A 1/6th em space.  Ignored for tty output devices (rounded to zero).

\^
     A 1/12th em space.  Ignored for tty output devices (rounded to zero).

\0
     A space the size of a digit.

\&
     A zero width space.

\)
     Like \& except that it behaves like a character declared with the cflags request to be transparent for the purposes of end of sentence recognition.

The following string sets the TeX logo:

     .ds TeX T\h'-.1667m'\v'.224m'E\v'-.224m'\h'-.125m'X

 -- Escape: \\w, ', text, '
     Used as \w'TEXT', returns the width of the specified TEXT in basic units. This allows horizontal movement based on the width of some arbitrary text (e.g. given as an argument to a macro).

     Font changes may occur in TEXT which don't affect current settings.

     After use, \w sets several registers:

     st
     sb
          The highest and lowest point, respectively, in TEXT.

     rst
     rsb
          Like the st and sb registers, but takes account of the heights and depths of characters.

     ct
          Defines the kinds of characters occurring in TEXT:

          0
               only short characters, no descenders or tall characters.

          1
               at least one descender.

          2
               at least one tall character.

          3
               at least one each of a descender and a tall character.

     ssc
          The amount of horizontal space (possibly negative) that should be added to the last character before a subscript.

     skw
          How far to right of the center of the last character in the \w argument, the center of an accent from a roman font should be placed over that character.

 -- Escape: \\k, ', x, '
     Stores the current horizontal position in register X. Use this, for example, to return to the beginning of a string for highlighting or other decoration.

 -- Register: \n[.k]
     A read-only number register containing the current horizontal output position.

Drawing Requests
================

gtroff provides a number of ways to draw lines and other figures on the page.  Used in combination with the page motion commands (see Page Motions, for more info), a wide variety of figures can be drawn.  However, for complex drawings these operations can be quite cumbersome, and it may be wise to use graphic preprocessors like gpic or ggrn.  See gpic, and ggrn, for more information.

All drawing is done via escapes.

 -- Escape: \\l, ', l c, '
     Draws a line rightwards from the current location.  The full syntax for this escape is:

          \l'LC'

     where L is the length of the line to be drawn, starting at the current location; positive numbers draw to the right, and negative numbers draw towards the left.  This can also be specified absolutely (i.e. with a leading |) which draws back to the beginning of the line.

     The optional second parameter C is a character to draw the line with.  If this second argument is not specified, gtroff uses the underscore character.

     To separate the two arguments (to prevent gtroff from interpreting a drawing character as a scaling indicator) use \&.

     Here a small useful example:

          .de box
          \(br\\$*\(br\l'|0\(rn'\l'|0\(ul'
          ..

     Note that this works by outputting a box rule (a vertical line), then the text given as an argument and then another box rule.  Then the line drawing escapes both draw from the current location to the beginning of the input line.

 -- Escape: \\L, ', l c, '
     Draws vertical lines.  Its parameters are similar to the \l escape.  The movement is downwards for positive values, and upwards for negative values.  The default character is the box rule character.  As with the vertical motion escapes, text processing blindly continues where the line ends.

 -- Escape: \\D, ', command arg ..., '
     The \D escape provides a variety of drawing functions. While the previous escapes work on a character device, these escapes do not.

     \D'l DX DY'
          Draw a line from the current location to the relative point specified by (DX,DY).

     \D'c D'
          Draw a circle with a diameter of D with the leftmost point at the current position.

     \D'C D'
          Draw a solid circle with the same parameters as an outlined circle.

     \D'e DX DY'
          Draw an ellipse with a horizontal diameter of DX and a vertical diameter of DY with the leftmost point at the current position.

     \D'E DX DY'
          Draw a solid ellipse with the same parameters as an outlined ellipse.

     \D'a DX1 DY1 DX2 DY2'
          Draw an arc clockwise from the current location through the two specified locations (DX1,DY1) and (DX2,DY2).

     \D'~ DX1 DY1 DX2 DY2 ...'
          Draw a spline from the current location to (DX1,DY1) and then to (DX2,DY2), and so on.

     \D'f N'
          Set the shade of gray to be used for filling solid objects to N; N must be an integer between 0 and 1000, where 0 corresponds solid white and 1000 to solid black, and values in between correspond to intermediate shades of gray.  This applies only to solid circles, solid ellipses and solid polygons.  By default, a level of 1000 is used.

     \D'p DX1 DY1 DX2 DY2 ...'
          Draw a polygon from the current location to (DX1,DY1) and then to (DX2,DY2) and so on.  When the specified data points are exhausted, a line is drawn back to the starting point.

     \D'P DX1 DY1 DX2 DY2 ...'
          Draw a solid polygon with the same parameters as an outlined polygon.

     \D't N'
          Set the current line thickness to N machine units.  A value of zero selects the smallest available line thickness.  A negative value makes the line thickness proportional to the current point size (this is the default behaviour of ditroff).

 -- Escape: \\b, ', string, '
     Piles a sequence of characters vertically, and centers it vertically on the current line.  Use it to build large brackets and braces.

          \b'\(lt\(bv\(lk\(bv\(lb'

See Drawing Functions.

Traps
=====

Traps are locations, which, when reached, call a specified macro.  These traps can occur at a given location on the page, at a given location in the current diversion, after a certain number of input lines or at the end of input.

Page Location Traps
-------------------

Page location traps perform an action when gtroff reaches a certain vertical location on the page.  Page location traps have a variety of purposes, including:

  * setting headers and footers

  * setting body text in multiple columns

  * setting footnotes

 -- Request: .vpt, flag
 -- Register: \n[.vpt]
     Enables vertical position traps if FLAG is non-zero, or disables them otherwise.  Vertical position traps are traps set by the wh or dt requests.  Traps set by the it request are not vertical position traps.  The parameter that controls whether vertical position traps are enabled is global.  Initially vertical position traps are enabled.  The current setting of this is available in the .vpt read-only number register.

 -- Request: .wh, dist macro
     Sets a page location trap.  Positive values for DIST set the trap relative to the top of the page; negative values set the trap relative to the bottom of the page.

     MACRO is the name of the macro to execute when the trap is sprung.

     The following is a simple example of how many macro packages set headers and footers.

          .de hd                \" Page header
          'sp .5i
          .tl 'Title''date'
          'sp .3i
          ..
          .de fo                \" Page footer
          'sp 1v
          .tl ''%''
          'bp
          ..
          .wh 0   hd            \" trap at top of the page
          .wh -1i fo            \" trap one inch from bottom

 -- Register: \n[.t]
     A read-only number register holding the distance to the next trap.

 -- Request: .ch, dist macro
     Changes the location of a trap. The first argument is the name of the macro to be invoked at the trap, and the second argument is the new location for the trap (note that the parameters are specified the opposite of the .wh request). This is useful for building up footnotes in a diversion to allow more space at the bottom of the page for them.

 -- Register: \n[.ne]
     The read-only number register .ne contains the amount of space that was needed in the last ne request that caused a trap to be sprung.  Useful in conjunction with the .trunc register. See Page Control, for more information.

 -- Register: \n[.trunc]
     A read-only register containing the amount of vertical space truncated by the most recently sprung vertical position trap, or, if the trap was sprung by an ne request, minus the amount of vertical motion produced by the ne request.  In other words, at the point a trap is sprung, it represents the difference of what the vertical position would have been but for the trap, and what the vertical position actually is.

Diversion Traps
---------------

 -- Request: .dt, dist macro
     Sets a trap within a diversion. DIST is the first argument is the location of the trap (identical to the .wh request) and MACRO is the name of the macro to be invoked.  The number register .t still works within diversions. See Diversions, for more information.

Input Line Traps
----------------

 -- Request: .it, n macro
     Sets an input line trap. N is the number of lines of input which may be read before springing the trap, MACRO is the macro to be invoked. Request lines are not counted as input lines.

     For example, one possible use is to have a macro which prints the next N lines in a bold font.

          .de B
          .it \\$1 B-end
          .ft B
          ..
          .de B-end
          .ft R
          ..

End-of-input Traps
------------------

 -- Request: .em, macro
     Sets a trap at the end of input.  The MACRO specified is executed after the last line of the input file has been processed.

     For example, if the document had to have a section at the bottom of the last page for someone to approve it, the em request could be used.

          .de approval
          .ne 5v
          .sp |(\\n(.t-6v)
          .in +4i
          .lc _
          .br
          Approved:\t\a
          .sp
          Date:\t\t\a
          ..
          .em approval

Diversions
==========

In gtroff it is possible to divert text into a named storage area.  Due to the similarity to defining macros it is sometimes said to be stored in a macro.  This is used for saving text for output at a later time, which is useful for keeping blocks of text on the same page, footnotes, tables of contents and indices.

 -- Request: .di, macro
 -- Request: .da, macro
     Begins a diversion.  Like the de request, it takes an argument of a macro name to divert subsequent text into.  The da macro appends to an existing diversion.

     di or da without an argument ends the diversion.

 -- Register: \n[.z]
 -- Register: \n[.d]
     Diversions may be nested.  The read-only number register .z contains the name of the current diversion (this is a string-valued register).  The read-only number register .d contains the current vertical place in the diversion.  If not in a diversion it is the same as the register nl.

 -- Register: \n[.h]
     The high-water mark on the current page.  It corresponds to the text baseline of the lowest line on the page.  This is a read-only register.

 -- Register: \n[dn]
 -- Register: \n[dl]
     After completing a diversion, the read-write number registers dn and dl contain the vertical and horizontal size of the diversion.

          .\" Center text both horizontally & vertically
          .de (c
          .br
          .nf
          .di @c
          ..

          .de )c
          .br
          .di
          .nr @s (((\\n(.tu-\\n(dnu)/2u)-1v)
          .sp \\n(@su
          .ce 1000
          .nf
          .
          .br
          .ce 0
          .sp \\n(@su
          .br
          .fi
          .rr @s
          ..

 -- Escape: \\!, , ,
 -- Escape: \\?, , anything, \\?
     Prevents requests, macros and escapes from being interpreted when read into a diversion.  This takes the given text and transparently embeds it into the diversion.  This is useful for macros which shouldn't be invoked until the diverted text is actually output.

     The \! escape transparently embeds text up to and including the end of the line. The \? escape transparently embeds text until the next occurrence of the \? escape.  For example:

          \?ANYTHING\?

     ANYTHING may not contain newlines; use \!  to embed newlines in a diversion.  The escape sequence \? is also recognized in copy mode and turned into a single internal code; it is this code that terminates anything.  Thus the following example prints 4.

          .nr x 1
          .nf
          .di d
          \?\\?\\\\?\\\\\\\\nx\\\\?\\?\?
          .di
          .nr x 2
          .di e
          .d
          .di
          .nr x 3
          .di f
          .e
          .di
          .nr x 4
          .f

 -- Request: .asciify, div
     Unformats the diversion specified by DIV in such a way that ASCII and space characters that were formatted and diverted are treated like ordinary input characters when the diversion is reread.  It can be also used for gross hacks; for example, the following sets register n to 1.

          .tr @.
          .di x
          @nr n 1
          .br
          .di
          .tr @@
          .asciify x
          .x

     See Copy-in Mode.

Environments
============

It happens frequently that some text should be printed in a certain format regardless of what may be in effect at the time, for example, in a trap invoked macro to print headers and footers.  To solve this gtroff processes text in environments.  An environment contains most of the parameters that control text processing.  It is possible to switch amongst these environments; by default gtroff processes text in environment 0.  The following is the information kept in an environment.

  * font parameters (size, family, style, character height and slant, space and sentence space size)

  * page parameters (line length, title length, vertical spacing, line spacing, indentation, line numbering, hyphenation data)

  * fill and adjust mode

  * tab stops, tab and leader characters, escape character, no-break and hyphen indicators, margin character data

  * partially collected lines

These environments may be given arbitrary names (see Identifiers, for more info).  Old versions of troff only had environments named 0, 1 and 2.

 -- Request: .ev, env
 -- Register: \n[.ev]
     Switches to another environment.  The argument ENV is the name of the environment to switch to.  With no argument, gtroff switches back to the previous environment.  There is no limit on the number of named environments; they are created the first time that they are referenced.  The .ev read-only register contains the name or number of the current environment.  This is a string-valued register.

     Note that a call to ev (with argument) pushes the previously active environment onto a stack.  If, say, environments foo, bar, and zap are called (in that order), the first ev request without parameter switches back to environment bar (which is popped off the stack), and a second call switches back to environment foo.

     Here is an example:

          .ev footnote-env
          .fam N
          .ps 6
          .vs 8
          .ll -.5i
          .ev

          ...

          .ev footnote-env
          \(dg Note the large, friendly letters.
          .ev

 -- Request: .evc, env
     Copies the environment ENV into the current environment.

Suppressing output
==================

 -- Escape: \\O, , num,
     Disables or enables output depending on the value of NUM:

     \O0
          Disable any ditroff glyphs from being emitted to the device driver.

     \O1
          Enable output of glyphs.

     \O0 and \O1 also reset the four registers opminx, opminy, opmaxx, and opmaxy to -1. See Register Index.  These four registers mark the top left and bottom right hand corners of a box which encompasses all written glyphs.

     The following two forms of \O are specific to grohtml.

     \O2
          Disable any ditroff glyphs from being emitted to the device driver.  Also write out to stderr the page number and four registers encompassing the glyphs previously written since the last call to \O.

     \O3
          Enable output of glyphs (the default).  Also write out to stderr the page number and four registers encompassing the glyphs previously written since the last call to \O.

I/O
===

gtroff has several requests for including files:

 -- Request: .so, file
     Reads in the specified FILE and includes it in place of the so request.  This is quite useful for large documents, e.g. keeping each chapter in a separate file. See gsoelim, for more information.

 -- Request: .mso, file
     Identical to the so request except that gtroff searches for the specified FILE in the same directories as macro files for the the -m command line option.  If the file name to be included has the form NAME.tmac and it isn't found, mso tries to include tmac.NAME and vice versa.

 -- Request: .cf, file
 -- Request: .trf, file
     Transparently outputs the contents of FILE.  Each line is output as it were preceded by \!; however, the lines are not subject to copy mode interpretation.  If the file does not end with a newline, then a newline is added.  For example, to define a macro x containing the contents of file f, use

          .di x
          .trf f
          .di

     The request .cf FILENAME, when used in a diversion, embeds an object in the diversion which, when reread, causes the contents of FILENAME to be transparently copied through to the output.

     In UNIX troff, the contents of FILENAME is immediately copied through to the output regardless of whether there is a current diversion; this behaviour is so anomalous that it must be considered a bug.  This request causes a line break.

     With trf, unlike cf, the file cannot contain characters such as NUL that are not valid gtroff input characters (see Identifiers).  This request causes a line break.

 -- Request: .nx,
     Forces gtroff to continue processing of the file specified as an argument.

 -- Request: .rd,
     The rd request reads from standard input, and includes what is read as though it were part of the input file.  Text is read until a blank line is encountered.

Using the nx and rd requests, it is easy to set up form letters.  The form letter template is constructed like this:

     .ce
     \*(td
     .sp 2
     .nf
     .rd
     .sp
     .rd
     .fi
     Body of letter.
     .bp
     .nx repeat.let

When this is run, the following file should be redirected in.  Note that requests included in this file are executed as though they were part of the form letter.  The last block of input is the ex requests which tells groff to stop processing.  If this was not there, groff would not know when to stop.

     Trent A. Fisher
     708 NW 19th Av., #202
     Portland, OR  97209

     Dear Trent,

     Len Adollar
     4315 Sierra Vista
     San Diego, CA  92103

     Dear Mr. Adollar,

     .ex

 -- Request: .pi, pipe
     Pipes the output of gtroff to the shell command(s) specified by PIPE.  This request must occur before gtroff has a chance to print anything.

 -- Request: .sy, cmds
 -- Register: \n[systat]
     In unsafe mode, executes the shell command(s) specified by CMDS.  The output is not saved anyplace, so it is up to the user to do so.

     For example, the following example introduces the current time into a document:

          .sy perl -e 'printf ".nr H %d\\n.nr M %d\\n.nr S %d\\n",\
          	     (localtime(time))[2,1,0]' > /tmp/x\n[$$]
          .so /tmp/x\n[$$]
          .sy rm /tmp/x\n[$$]
          \nH:\nM:\nS

     Note that this works by having the perl script (run by sy) print out the nr requests which set the number registers H, M and S, and then reads those commands in with the so request.

     The systat read-write number register contains the return value of the system() function executed by the last sy request.

 -- Request: .open, stream file
 -- Request: .opena, stream file
     Opens the specified FILE for writing and associates the specified STREAM with it.

     The opena is like open, but if the file exists, append to it instead of truncating it.

 -- Request: .write, stream data
     Writes to the file associated with the specified STREAM. The stream must previously have been the subject of an open request.  The remainder of the line is interpreted as the ds request reads its second argument: A leading " is stripped, and it is read in copy-in mode.

 -- Request: .close, stream
     Closes the specified STREAM; the stream is no longer an acceptable argument to the write request.

 -- Escape: \\V, ', xxx, '
     Interpolates the contents of the specified environment variable, as returned by the function getenv. Specify the argument to \V as an identifier, i.e. \VX, \V(XX or \V[XXX].  \V is interpreted in copy-in mode.

Postprocessor Access
====================

There are two escapes which give information directly to the postprocessor.  This is particularly useful for embedding POSTSCRIPT into the final document.

 -- Escape: \\X, ', xxx, '
     Embeds its argument into the gtroff output preceded with x X.

 -- Escape: \\Y, ', xxx, '
     The \Y escape is called with an identifier (i.e. \YX, \Y(XX or \Y[XXX]).  This is approximately equivalent to \X'\*[XXX]'.  However, the contents of the string or macro XXX are not interpreted; also it is permitted for XXX to have been defined as a macro and thus contain newlines (it is not permitted for the argument to \X to contain newlines).  The inclusion of newlines requires an extension to the UNIX troff output format, and confuses drivers that do not know about this extension.

See Output Devices.

Miscellaneous
=============

This section documents parts of gtroff which cannot (yet) be categorized elsewhere in this manual.

 -- Request: .nm, start inc space indent
     Prints line numbers in the left margin. START is the line number of the next output line; this defaults to 1.  INC indicates on which lines numbers are printed, i.e. 5 means put line numbers on every 5 lines; this defaults to 1.  SPACE is the space to be left between the number and the text; this defaults to 1.  The fourth argument is the indentation of the line numbers. Without arguments, line numbers are turned off.

 -- Request: .nn, [skip]
     Temporarily turns off line numbering.  The argument is the number of lines not to be numbered; this defaults to 1.

 -- Request: .mc, char dist
     Prints margin characters to the right of the text. The first argument is the character to be printed, and the second argument is the distance away from the main body text.  With no arguments the margin characters are turned off.  If this occurs before a break, no margin character is printed.

     This is quite useful for indicating text that has changed, and, in fact, there are programs available for doing this (they are called nrchbar and changebar and can be found in any comp.sources.unix archive.

 -- Request: .lf, line filename
     A debugging aid for documents which are split into many files, then put together with soelim and other preprocessors.  The second argument is the name of the file and the first argument is the input line number in that file.  This way gtroff can produce error messages which are intelligible to the user.

gtroff Internals
================

gtroff processes input in three steps.  One or more input characters are converted to an input token.  Then, one or more input tokens are converted to an output node.  Finally, output nodes are converted to the intermediate output language understood by all output devices.

For example, the input string fi\[:u] is converted in a character token f, a character token i, and a special token :u (representing u umlaut).  Later on, the character tokens f and i are merged to a single output node representing the ligature glyph fi; the same happens with :u.  All output glyph nodes are `processed' which means that they are invariably associated with a given font, font size, advance width, etc.  During the formatting process, gtroff itself adds various nodes to control the data flow.

Macros, diversions, and strings collect elements in two chained lists: a list of input tokens which have been passed unprocessed, and a list of output nodes.  Consider the following the diversion.

     .di xxx
     a
     \!b
     c
     .br
     .di

It contains these elements.

node list                 token list   element number

line start node       ---          1
glyph node a   ---          2
word space node       ---          3
---                       b     4
---                       \n    5
glyph node c   ---          6
vertical size node    ---          7
vertical size node    ---          8
---                       \n    9

Elements 1, 7, and 8 are inserted by gtroff; the latter two (which are always present) specify the vertical extent of the last line, possibly modified by \v.  The br request finishes the current partial line, inserting a newline input token which is subsequently converted to a space when the diversion is reread.  Note that the word space node has a fixed width which isn't stretchable anymore.  To convert horizontal space nodes back to input tokens, use the unformat request.

Macros only contain elements in the token list (and the node list is empty); diversions and strings can contain elements in both lists.

Debugging
=========

gtroff is not easy to debug, but there are some useful features and strategies for debugging.

 -- Request: .tm, string
     Sends the STRING to the standard error stream; this is very useful for printing debugging output among other things.

 -- Request: .ab, [string]
     Similar to the tm request, except that it causes gtroff to stop processing.  With no argument it prints User Abort.

 -- Request: .ex,
     The ex request also causes gtroff to stop processing if encountered at the topmost level; see also I/O.

When doing something involved it is useful to leave the debugging statements in the code and have them turned on by a command line flag.

     .if \n(DB .tm debugging output

To activate these statements say

     groff -rDB=1 file

If it is known in advance that there will be many errors and no useful output, gtroff can be forced to suppress formatted output with the -z flag.

 -- Request: .pm,
     The pm request prints out the entire symbol table on stderr.

 -- Request: .pnr,
     Prints the names and contents of all currently defined number registers on stderr.

 -- Request: .ptr,
     Prints the names and positions of all traps (not including input line traps and diversion traps) on stderr. Empty slots in the page trap list are printed as well, because they can affect the priority of subsequently planted traps.

 -- Request: .fl,
     Instructs gtroff to flush its output immediately.  The intent is for interactive use. gtroff; there is little other use for it.  This request causes a line break.

 -- Request: .backtrace,
     The backtrace request prints a backtrace of the input stack to the standard error stream.

gtroff has command line options for printing out more warnings (-w) and for printing backtraces (-b) when a warning or an error occurs.  The most verbose level of warnings is -ww.

 -- Request: .warn, [flags]
 -- Register: \n[.warn]
     Controls the level of warnings checked for.  The FLAGS are the sum of the numbers associated with each warning that is to be enabled; all other warnings are disabled.  The number associated with each warning is listed below.  For example, .warn 0 disables all warnings, and .warn 1 disables all warnings except that about missing characters.  If an argument is not given, all warnings are enabled.

     The read-only number register .warn contains the current warning level.

Warnings
--------

The warnings that can be given to gtroff are divided into the following categories.  The name associated with each warning is used by the -w and -W options; the number is used by the warn request and by the .warn register.

char
1
     Non-existent characters.  This is enabled by default.

number
2
     Invalid numeric expressions.  This is enabled by default. See Expressions.

break
4
     In fill mode, lines which could not be broken so that their length was less than the line length.  This is enabled by default.

delim
8
     Missing or mismatched closing delimiters.

el
16
     Use of the el request with no matching ie request. See if-else.

scale
32
     Meaningless scaling indicators.

range
64
     Out of range arguments.

syntax
128
     Dubious syntax in numeric expressions.

di
256
     Use of di or da without an argument when there is no current diversion.

mac
512
     Use of undefined strings, macros and diversions.  When an undefined string, macro or diversion is used, that string is automatically defined as empty.  So, in most cases, at most one warning is given for each name.

reg
1024
     Use of undefined number registers.  When an undefined number register is used, that register is automatically defined to have a value of 0. A definition is automatically made with a value of 0.  So, in most cases, at most one warning is given for use of a particular name.

tab
2048
     Use of a tab character where a number was expected.

right-brace
4096
     Use of \} where a number was expected.

missing
8192
     Requests that are missing non-optional arguments.

input
16384
     Illegal input characters.

escape
32768
     Unrecognized escape sequences.  When an unrecognized escape sequence is encountered, the escape character is ignored.

space
65536
     Missing space between a request or macro and its argument.  This warning is given when an undefined name longer than two characters is encountered, and the first two characters of the name make a defined name.  The request or macro is not invoked.  When this warning is given, no macro is automatically defined.  This is enabled by default. This warning never occurs in compatibility mode.

font
131072
     Non-existent fonts.  This is enabled by default.

all
     All warnings except di, mac and reg.  It is intended that this covers all warnings that are useful with traditional macro packages.

w
     All warnings.

Implementation Differences
==========================

GNU troff has a number of features which cause incompatibilities with documents written with old versions of troff.

Long names cause some incompatibilities.  UNIX troff interprets

     .dsabcd

as defining a string ab with contents cd.  Normally, GNU troff interprets this as a call of a macro named dsabcd.  Also UNIX troff interprets \*[ or \n[ as references to a string or number register called [.  In GNU troff, however, this is normally interpreted as the start of a long name.  In compatibility mode GNU troff interprets long names in the traditional way (which means that they are not recognized as names). Compatibility mode can be turned on with the -C command line option, and turned on or off with the cp request.  The number register .C is 1 if compatibility mode is on, 0 otherwise.

GNU troff does not allow the use of the escape sequences \|, \^, \&, \{, \}, \SP, \', \`, \-, \_, \!, \%, and \c in names of strings, macros, diversions, number registers, fonts or environments; UNIX troff does.  The \A escape sequence (see Identifiers) may be helpful in avoiding use of these escape sequences in names.

Fractional point sizes cause one noteworthy incompatibility.  In UNIX troff the ps request ignores scale indicators and thus

     .ps 10u

sets the point size to 10 points, whereas in GNU troff it sets the point size to 10 scaled points.  See Fractional Type Sizes, for more information.

In GNU troff there is a fundamental difference between unformatted, input characters, and formatted, output characters. Everything that affects how an output character is output is stored with the character; once an output character has been constructed it is unaffected by any subsequent requests that are executed, including bd, cs, tkf, tr, or fp requests. Normally output characters are constructed from input characters at the moment immediately before the character is added to the current output line.  Macros, diversions and strings are all, in fact, the same type of object; they contain lists of input characters and output characters in any combination.  An output character does not behave like an input character for the purposes of macro processing; it does not inherit any of the special properties that the input character from which it was constructed might have had.  For example,

     .di x
     \\\\
     .br
     .di
     .x

prints \\ in GNU troff; each pair of input backslashes is turned into one output backslash and the resulting output backslashes are not interpreted as escape characters when they are reread. UNIX troff would interpret them as escape characters when they were reread and would end up printing one \.  The correct way to obtain a printable backslash is to use the \e escape sequence: This always prints a single instance of the current escape character, regardless of whether or not it is used in a diversion; it also works in both GNU troff and UNIX troff.  To store, for some reason, an escape sequence in a diversion that will be interpreted when the diversion is reread, either use the traditional \! transparent output facility, or, if this is unsuitable, the new \? escape sequence.

See Diversions, for more information.

Summary
=======

Preprocessors
*************

This chapter describes all preprocessors that come with groff or which are freely available.

geqn
====

Invoking geqn
-------------

gtbl
====

Invoking gtbl
-------------

gpic
====

Invoking gpic
-------------

ggrn
====

Invoking ggrn
-------------

grap
====

A free implementation of grap, written by Ted Faber, is available as an extra package from the following address:

     http://www.lunabase.org/~faber/Vault/software/grap/

grefer
======

Invoking grefer
---------------

gsoelim
=======

Invoking gsoelim
----------------

Output Devices
**************

Special Characters
==================

See Font Files.

grotty
======

Invoking grotty
---------------

grops
=====

Invoking grops
--------------

Embedding POSTSCRIPT
--------------------

grodvi
======

Invoking grodvi
---------------

grolj4
======

Invoking grolj4
---------------

grolbp
======

Invoking grolbp
---------------

grohtml
=======

Invoking grohtml
----------------

gxditview
=========

Invoking gxditview
------------------

File formats
************

gtroff Output
=============

This section describes the format output of GNU troff.  The output format used by GNU troff is very similar -- but not identical -- to that used by UNIX device-independent troff (ditroff).

Output Format
-------------

The output format is text based, as opposed to a binary format (like TeX DVI).  The output format is 8-bit clean, thus single characters can have the eighth bit set, as can the names of fonts and special characters.

The output format consists of single command characters with attached parameters which are separated from subsequent text by whitespace or a newline.

The names of characters and fonts can be of arbitrary length; drivers should not assume that they are only two characters long (as ditroff does).

When a character is to be printed, that character is always in the current font.  Unlike ditroff, it is not necessary for drivers to search special fonts to find a character.

HN

VN

hN

vN

cN

CN

NNC

tXXX
     XXX is any sequence of characters terminated by a space or a newline; the first character should be printed at the current position, the the current horizontal position should be increased by the width of the first character, and so on for each character.  The width of the character is that given in the font file, appropriately scaled for the current point size, and rounded so that it is a multiple of the horizontal resolution.  Special characters cannot be printed using this command.

     This command is only allowed if the tcommand line is present in the DESC file.

uN XXX
     This is same as the t command except that after printing each character, the current horizontal position is increased by the sum of the width of that character and N.

     This command is only allowed if the tcommand line is present in the DESC file.

nAB

pN

sN
     The argument to the s command is in scaled points (units of points/N, where N is the argument to the sizescale command in the DESC file).

fN

x ... \n
     Device control.

DC X...\n

Device Control
--------------

The x command is normally followed by a letter or word indicating the function to perform, followed by white space separated arguments.

The first argument can be abbreviated to the first letter.

x init

x T

x res N H V

x H
     The argument to the x Height command is also in scaled points.

The first three output commands are guaranteed to be:

     x T device
     x res n h v
     x init

For example, the input

     crunchy \fH\s+2frog\s0\fP!?

produces

Drawing Functions
-----------------

The D drawing command has been extended.  These extensions are used by GNU pic only if the -x option is given.

See Drawing Requests.

Df N
     Set the shade of gray to be used for filling solid objects to N; N must be an integer between 0 and 1000, where 0 corresponds solid white and 1000 to solid black, and values in between correspond to intermediate shades of gray.  This applies only to solid circles, solid ellipses and solid polygons.  By default, a level of 1000 is used.  Whatever color a solid object has, it should completely obscure everything beneath it.  A value greater than 1000 or less than 0 can also be used: this means fill with the shade of gray that is currently being used for lines and text.  Normally this is black, but some drivers may provide a way of changing this.

DC D
     Draw a solid circle with a diameter of D with the leftmost point at the current position.

DE DX DY
     Draw a solid ellipse with a horizontal diameter of DX and a vertical diameter of DY with the leftmost point at the current position.

Dp DX1 DY1 DX2 DY2 ... DXN DYN
     Draw a polygon with automatic closure.  The first vertex is at the current position, the second vertex at an offset (DX1,DY1) from the current position, the second vertex at an offset (DX2,DY2) from the first vertex, and so on up to the Nth vertex.  At the moment, GNU pic only uses this command to generate triangles and rectangles.

DP DX1 DY1 DX2 DY2 ... DXN DYN
     Like Dp but draw a solid rather than outlined polygon.

Dt N
     Set the current line thickness to N machine units. Traditionally, UNIX troff drivers use a line thickness proportional to the current point size; drivers should continue to do this if no Dt command has been given, or if a Dt command has been given with a negative value of N.  A zero value of N selects the smallest available line thickness.

A difficulty arises in how the current position should be changed after the execution of these commands.  This is not of great importance since the code generated by GNU pic does not depend on this.  Given a drawing command of the form

     \D'C X1 Y1 X2 Y2 ... XN YN'

where C is not one of c, e, l, a or ~, UNIX troff treats each x value as a horizontal quantity, and each y value as a vertical quantity; it assumes that the width of the drawn object is the sum of all x values, and that the height is the sum of all y values. (The assumption about the height can be seen by examining the st and sb registers after using such a D command in a \w escape sequence.)  This rule also holds for all the original drawing commands with the exception of De.  For the sake of compatibility GNU troff also follows this rule, even though it produces an ugly result in the case of the Df, Dt, and, to a lesser extent, DE commands.  Thus after executing a D command of the form

     DC X1 Y1 X2 Y2 ... XN YN

the current position should be increased horizontally by the sum of all x values and vertically by the sum of all y values.

Line Continuation
-----------------

There is a continuation convention which permits the argument to the x X command to contain newlines: When outputting the argument to the x X command, GNU troff follows each newline in the argument with a + character (as usual, it terminates the entire argument with a newline); thus if the line after the line containing the x X command starts with +, then the newline ending the line containing the x X command should be treated as part of the argument to the x X command, the + should be ignored, and the part of the line following the + should be treated like the part of the line following the x X command.

Font Files
==========

The gtroff font format is roughly a superset of the ditroff font format.  Unlike the ditroff font format, there is no associated binary format; all files are text files.  The font files for device NAME are stored in a directory devNAME.  There are two types of file: a device description file called DESC and for each font F a font file called F.

DESC File Format
----------------

The DESC file can contain the following types of line:

res N
     There are N machine units per inch.

hor N
     The horizontal resolution is N machine units.

vert N
     The vertical resolution is N machine units.

sizescale N
     The scale factor for point sizes.  By default this has a value of 1. One scaled point is equal to one point/N.  The arguments to the unitwidth and sizes commands are given in scaled points. See Fractional Type Sizes, for more information.

unitwidth N
     Quantities in the font files are given in machine units for fonts whose point size is N scaled points.

tcommand
     This means that the postprocessor can handle the t and u output commands.

sizes S1 S2 ... SN 0
     This means that the device has fonts at S1, S2, ... SN scaled points.  The list of sizes must be terminated by a 0.  Each SI can also be a range of sizes M-N.  The list can extend over more than one line.

styles S1 S2 ... SM
     The first M font positions are associated with styles S1 ... SM.

fonts N F1 F2 F3 ... FN
     Fonts F1 ... FN are mounted in the font positions M+1, ..., M+N where M is the number of styles.  This command may extend over more than one line.  A font name of 0 means no font is mounted on the corresponding font position.

family FAM
     The default font family is FAM.

charset
     This line and everything following in the file are ignored.  It is allowed for the sake of backwards compatibility.

The res, unitwidth, fonts and sizes lines are mandatory.  Other commands are ignored by gtroff but may be used by postprocessors to store arbitrary information about the device in the DESC file.

Font File Format
----------------

A font file has two sections.  The first section is a sequence of lines each containing a sequence of blank delimited words; the first word in the line is a key, and subsequent words give a value for that key.

name F
     The name of the font is F.

spacewidth N
     The normal width of a space is N.

slant N
     The characters of the font have a slant of N degrees. (Positive means forward.)

ligatures LIG1 LIG2 ... LIGN [0]
     Characters LIG1, LIG2, ..., LIGN are ligatures; possible ligatures are ff, fi, fl, ffi and ffl.  For backwards compatibility, the list of ligatures may be terminated with a 0.  The list of ligatures may not extend over more than one line.

special
     The font is special; this means that when a character is requested that is not present in the current font, it is searched for in any special fonts that are mounted.

Other commands are ignored by gtroff but may be used by postprocessors to store arbitrary information about the font in the font file.

The first section can contain comments which start with the # character and extend to the end of a line.

The second section contains one or two subsections.  It must contain a charset subsection and it may also contain a kernpairs subsection.  These subsections can appear in any order.  Each subsection starts with a word on a line by itself.

The word charset starts the character set subsection.  The charset line is followed by a sequence of lines.  Each line gives information for one character.  A line comprises a number of fields separated by blanks or tabs.  The format is

     NAME METRICS TYPE CODE COMMENT

NAME identifies the character: If NAME is a single character C then it corresponds to the gtroff input character C; if it is of the form \C where C is a single character, then it corresponds to the gtroff input character \C; otherwise it corresponds to the groff input character \[NAME].  (If it is exactly two characters XX it can be entered as \(XX.)  gtroff supports 8-bit characters; however some utilities have difficulties with eight-bit characters.  For this reason, there is a convention that the name charN is equivalent to the single character whose code is N.  For example, char163 would be equivalent to the character with code 163 which is the pounds sterling sign in ISO Latin-1 character set.  The name --- is special and indicates that the character is unnamed; such characters can only be used by means of the \N escape sequence in gtroff.

The TYPE field gives the character type:

1
     the character has an descender, for example, `p';

2
     the character has an ascender, for example, `b';

3
     the character has both an ascender and a descender, for example, `('.

The CODE field gives the code which the postprocessor uses to print the character.  The character can also be input to gtroff using this code by means of the \N escape sequence.  The code can be any integer.  If it starts with 0 it is interpreted as octal; if it starts with 0x or 0X it is interpreted as hexadecimal.

Anything on the line after the CODE field is ignored.

The METRICS field has the form:

     WIDTH[,HEIGHT[,DEPTH[,ITALIC_CORRECTION
       [,LEFT_ITALIC_CORRECTION[,SUBSCRIPT_CORRECTION]]]]]

There must not be any spaces between these subfields (it has been split here into two lines for better legibility only).  Missing subfields are assumed to be 0.  The subfields are all decimal integers.  Since there is no associated binary format, these values are not required to fit into a variable of type char as they are in ditroff. The WIDTH subfield gives the width of the character.  The HEIGHT subfield gives the height of the character (upwards is positive); if a character does not extend above the baseline, it should be given a zero height, rather than a negative height.  The DEPTH subfield gives the depth of the character, that is, the distance below the lowest point below the baseline to which the character extends (downwards is positive); if a character does not extend below above the baseline, it should be given a zero depth, rather than a negative depth. The ITALIC_CORRECTION subfield gives the amount of space that should be added after the character when it is immediately to be followed by a character from a roman font.  The LEFT_ITALIC_CORRECTION subfield gives the amount of space that should be added before the character when it is immediately to be preceded by a character from a roman font.  The SUBSCRIPT_CORRECTION gives the amount of space that should be added after a character before adding a subscript.  This should be less than the italic correction.

A line in the charset section can also have the format

     NAME "

This indicates that NAME is just another name for the character mentioned in the preceding line.

The word kernpairs starts the kernpairs section.  This contains a sequence of lines of the form:

     C1 C2 N

This means that when character C1 appears next to character C2 the space between them should be increased by N. Most entries in the kernpairs section have a negative value for N.

Installation
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Request Index
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Requests appear without the leading control character (normally either . or ').

Glyph Name Index
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A glyph name xx consisting of exactly two characters can be accessed as \(xx.  Glyph names xxx of any length can be accessed as \[xxx].