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 which includes an editor and a text formatter.  Also, many word processors follow the WYSIWYG paradigm which was 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 do any operations 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 has then been 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 which 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 grohtml, 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 which will 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 will be printed.

-Z
     Do not postprocess the output of gtroff.  Normally groff will automatically run 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 printer.  The command used for this is specified by the print command in the device description file.

-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.

-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.

     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 will use the metrics of the specified device, whereas the latter will use 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 use the -msafer macros with gtroff (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.

-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 incompatibilites 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.

-fFAM
     Use FAM as the default font family.

-mNAME
     Read in the file tmac.NAME.  Normally this will be searched for in the library directory of groff.

-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 will exit 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.

-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.

-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 directory.

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

-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 will run Xtroff instead of gtroff.  This also applies to tbl, pic, eqn, grn, refer, and soelim.  It does not apply to grops, grodvi, grotty, grohtml, grolj4, and gxditview.

GROFF_TMAC_PATH
     A colon-separated list of directories in which to search for macro files.

GROFF_TYPESETTER
     The default output device.

GROFF_FONT_PATH
     A colon-separated list of directories in which to search for the devNAME directory.

PATH
     The search path for commands executed by groff.

GROFF_TMPDIR
     The directory in which temporary files will be created.  If this is not set and TMPDIR is set, temporary files will be created in that directory.  Otherwise temporary files will be created in a system-dependent default directory (on Unix and GNU/Linux systems, this is usually /tmp).  The grops and grefer commands 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 will list several common uses of groff and the command line which will accomplish it.

     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.  The manual page file is processed with the mandoc macros (which in turn either calls the man or the mdoc macro package), using the tbl preprocessor and the ASCII output device.  Finally, the result is displayed with the less pager.

     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 tmac.safer, either -msafer or -m safer 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. The options generated are one of -e, -man, -me, -mm, -ms, -p, -R, -g, -G, -s, and -t.

A special file name - is taken to refer to the standard input. If no files are specified the standard input will be read.  Any specified options will be included in the printed command.  No space is allowed between options and their arguments.  For example,

     grog -Tdvi paper.ms

will guess the appropriate command to print paper.ms and then print 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.  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,...

will be 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 do blank input lines and input lines beginning with a space.

Not all input lines are text to be formatted.  Some of the 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 will pack words onto longer lines anyhow.  In keeping with this, it is helpful to begin a new line after every period, comma, or phrase, since common corrections are to add or delete sentences or phrases.  Secondly, do not hyphenate words at the end of lines -- gtroff is smart enough to hyphenate words for the user 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 will double space output text automatically if you use the request .ls 2.  Single spaced mode can be reactivated 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.

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 will not line up
           with  the  text  on  second  and  subsequent  lines,
           although they will 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 will 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 will not.

Floating keeps move relative to the text.  Hence, they are good for things which will be referred to by name, such as ``See figure 3''. A floating keep will appear at the bottom of the current page if it will fit; otherwise, it will appear at the top of the next page.  Meanwhile, the surrounding text will `flow' around the keep, thus leaving now 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 will provide the ability to have several tables of contents (i.e. one standard one, one for tables, etc).

Indices
-------

While some macro packages will 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.

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 [ -rC1 ] [ -rD1 ] [ -rPNNN ] [ -rSXX ]
           [ -rXNNN ] [ FILES... ]

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

-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
     Enumeration of pages will start 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 will produce 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 will be loaded immediately after tmac.an.

 -- Macro: TH title section [EXTRA1] [EXTRA2] [EXTRA3]
     Sets 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 will be positioned in the middle of the footer line.  EXTRA2 will be positioned at the left in the footer line (resp. 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. _Defmac

      -- Macro: SH [HEADING]
          Sets up an unnumbered section heading sticking out to the left.  Prints out all the text following SH up to the end of the line (resp. 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. _Defmac

           -- Macro: SS [HEADING]
               Sets up an unnumbered section heading.  Prints out all the text following SS up to the end of the line (resp. 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. _Defmac

                -- Macro: TP [NNN]
                    Sets 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 will have default font settings. _Defmac

                     -- 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 resp. Roman).  Finally, the current left
                         margin is restored.
                         _Defmac

                          -- Macro: IP [DESIGNATOR] [NNN]
                              Sets 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

                              _Defmac

                               -- Macro: HP [NNN]
                                   Sets 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.
                                   _Defmac

                                    -- Macro: RS [NNN]
                                        This macro moves 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.
                                        _Defmac

                                         -- Macro: RE [NNN]
                                        This macro moves 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.
                                        _Defmac

                                        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]
     Causes the text on the same line or the text on the next line to appear in a font that is one point size smaller than the default font. _Defmac

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

           -- Macro: BI text
               Causes text on the same line to appear alternately in bold face and italic.  The text must be on the same line as the macro call.  Thus,

                    .BI this "word and" that

               would cause ``this'' and ``that'' to appear in bold face, while ``word and'' appears in italics. _Defmac

                -- Macro: IB text
                    Causes text to appear alternately in italic and bold face.  The text must be on the same line as the macro call. _Defmac

                     -- Macro: RI text
                         Causes text on the same line to appear alternately in roman and italic. The text must be on the same line as the macro call. _Defmac

                          -- Macro: IR text
                              Causes text on the same line to appear alternately in italic and roman. The text must be on the same line as the macro call. _Defmac

                               -- Macro: BR text
                                   Causes text on the same line to appear alternately in bold face and roman.  The text must be on the same line as the macro call. _Defmac

                                    -- Macro: RB text
                                        Causes text on the same line to appear alternately in roman and bold face.  The text must be on the same line as the macro call. _Defmac

                                         -- Macro: R [TEXT]
                                        Causes TEXT to appear 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. _Defmac

                                         -- Macro: B [TEXT]
                                        Causes TEXT to appear 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. _Defmac

                                         -- Macro: I [TEXT]
                                        Causes TEXT to appear 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. _Defmac

Miscellaneous
-------------

The default indentation is 7.2n for all output devices except for grohtml which uses 1.2i instead.

 -- Macro: DT
     Sets 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. _Defmac

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

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

          The following strings are defined:

           -- Macro: \*S
               Switch back to the default font size. _Defmac

                -- Macro: \*R
                    The `registered' sign. _Defmac

                     -- Macro: \*(Tm
                         The `trademark' sign. _Defmac

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

                              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
==

Programming Tutorial
********************

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 will still do several things with the input text: filling and adjusting, adding additional space after sentences, hyphenating and inserting implicit line breaks.

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

When gtroff reads in text it collects words from 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 will try to adjust it.  This means it will widen 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 will cause a break (breaks will be 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 will fit nicely on a line without inserting excessive amounts of space between words, gtroff will hyphenate words so that lines can be justified without there being 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 will be added to the current filled line being output (with an attached hyphen), and the other portion will be 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 will append two sentence spaces in the formatted output. (This justifies one of the conventions mentioned in Input Conventions.)

In addition, the following characters resp. 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 resp. 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 easily be made. 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 will still be filled, again producing unexpected results. For example, the following input

1   2   3

  4   5

will produce

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 will output the partially filled line (unjustified), and resume collecting and filling text on the next output line.

There are several ways to cause a break in gtroff.  A blank line will not only cause a break, but it will also cause a one line vertical space (effectively a blank line) to be output.

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

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

Certain requests also cause breaks, implicitly or explicitly.  This will be 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 and use spaces to get proper indentation).

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

gtroff (like any 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.  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 are dependent 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 will be 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 will be first handled as 7i/2m, then converted to 1680u/66u which is 25u, and this is approximately 0.1i.

As a conclusion, 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 of 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 3+5*4 is evaluated 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 resp. 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 (space, tabs, and newlines).

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

  * The following input characters are invalid and will be 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 resp. encodings which use characters of these ranges.

     Note that invalid characters will be removed before parsing; an identifier foo, followed by an invalid character, followed by bar will be 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]] will access the glyph foo, followed by ], whereas \C'foo]' really asks for glyph foo].

 -- Escape: \A ident
     Whether an identifier IDENT is valid in gtroff can be tested with the \A escape.  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 will return 0 if no argument is given.  This is useful for looking up user input in some sort of associative table.

          \A'end-list'
              => 1

     _Deffn

     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.

     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.

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

In most cases the period is used as a control character.  Several requests will cause a break implicitly; using the single quote control character will prevent 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 quotes (single or double), 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 or 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.)

Note, however, that the ds request works 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 (resp. 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 will be ignored, but the space leading up to it will be noticed by gtroff.  This only affects the .ds 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 will be treated as a blank line, because after eliminating the comment, that is all that remains:

          Test
          \" comment
          Test

     will produce

          Test

          Test

     As a consequence, it is common to start the line with .\" which will cause 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 will give a warning about an undefined macro (namely ''), which is harmless, but irritating. _Deffn

      -- 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

          will produce

               Test Test

          as expected. _Deffn

          For commenting away large blocks of text, the ig request may be useful.

          See Strings.

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
-----------------

Registers are defined resp. set via 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, it will be created.

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

     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 resp. 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

          _Deffn

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

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

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

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

Numeric registers can be accessed via the \n escape.

 -- Escape: \n ident
     Interpolate number register IDENT.  This means that the value of the register is expanded in-place while gtroff is parsing the input line.

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

     _Deffn

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

Number registers can also be auto-incremented and auto-decremented.  The increment resp. decrement factor 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. _Deffn

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

      -- Escape: \n +ident
      -- Escape: \n -ident
          Before interpolating, increment resp. decrement IDENT by the
          auto-increment value as specified with the nr request (or the
          \R escape).  If no auto-increment value has been specified, both
          syntax forms are identical to \n.
          _Deffn

          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,
          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: 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: A, B, C, ..., Z, AA, AB, ...

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

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

     The following example will produce 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 (resp. -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 will be 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. _Deffn

      -- Escape: \g ident
          Return the current format of the specified register IDENT.  For example, \ga after the previous example would produce the string 000.  If the register hasn't been defined yet, nothing is returned. _Deffn

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.

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

.y
     The minor version number.  For example, if the version number is 1.03 then .y will contain 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 will likewise cause a break.  Several other requests will 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 will be emitted without adjustment.

     If the no-break control character is used, no break will happen:

          a
          'br
          b
              => a b

     _Deffn

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

      -- Request: fi
          Activate fill mode (which is the default).  This request implicitly enables adjusting; it will also cause a break in the text currently being filled.  The number register .u is set to 1.

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

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

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

                -- Request: ad [MODE]
                    Set adjusting mode.

                    Activation and deactivation of adjusting will be implicitly done with calls to the fi resp. 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 will adjust lines in the same way it did before adjusting has been 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 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). _Deffn

                     -- Request: na
                         Disable adjusting.  This request won't change the current adjustment mode: A call to ad afterwards will use the previous adjustment setting.

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

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

                              In most cases this will produce very ugly results, since gtroff doesn't have a sophisticated paragraph building algorithm (as TeX does, 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.

                              _Deffn

                               -- Request: ss word_space_size [SENTENCE_SPACE_SIZE]
                                   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 will be 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 will be added; if two spaces follow the end of a sentence in the middle of a line, then the second space will be a sentence space. Note that the behaviour of UNIX troff will be exactly that exhibited by GNU troff if a second argument is never given to the ss request.  In GNU troff, as in UNIX troff, a sentence should always be followed by either a newline or two spaces.

                                   The 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).

                                   This request is ignored in nroff mode; it is also ignored if there is no parameter. _Deffn

                                    -- Request: ce [NNN]
                                        Center text.  While the .ad c request will also center text, it has the side effect of filling the text.  ce will not fill the text it affects.  This request causes a break.

                                        With no arguments, ce will center 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.

                                        A common idiom is 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.

                                        .ce 1000
                                        replace this
                                        with
                                        something
                                        more interesting
                                        ...
                                        .ce 0

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

                                         -- Request: rj [NNN]
                                        Justify unfilled text to the right margin.  Arguments are identical to the ce request.  The .rj number register is the number of lines to be right-justified as set by the rj request.  This request causes a line break. _Deffn

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

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

 -- Request: hy [MODE]
     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 number register .hy.

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

      -- 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). _Deffn

           -- Request: hlm [NNN]
               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 register.  Also the number of immediately preceding consecutive hyphenated lines are available in the number register .hlc. _Deffn

                -- 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 will cause 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. _Deffn

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

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

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

                               -- Request: hpf pattern_file
                                   Read in a file of hyphenation patterns.  This file will be searched for in the same way as 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).

                                   hpf will cause an error if there is no current hyphenation language. _Deffn

                                    -- Request: hcode c1 code1 c2 code2 ...
                                        Sets 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 will be ignored if it has no parameter. _Deffn

                                         -- Request: hym [LENGTH]
                                        Set the (right) hyphenation margin to LENGTH.  If the current adjustment mode is not b, the line will not be hyphenated if it is shorter than LENGTH.  Without argument, the hyphenation margin will be 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 will reset the hyphenation margin to zero, emitting a warning of type range.

                                        The current hyphenation margin is available in the .hym register. _Deffn

                                         -- Request: hys [HYPHENATION_SPACE]
                                        Set the hyphenation space to HYPHENATION_SPACE.  If the current adjustment mode is b, 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 will reset the hyphenation space to zero, emitting a warning of type range.

                                        The current hyphenation space is available in the .hys register. _Deffn

                                         -- Request: shc [CHAR]
                                        Set the soft hyphen character to CHAR.  If the argument is omitted, the soft hyphen character will be set to the default character \(hy (this is the start-up value of gtroff also).  The soft hyphen character is the character which will be 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 will not be 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. _Deffn

                                         -- Request: hla language
                                        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

                                        _Deffn

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

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

      -- Request: ls [NNN]
          Output NNN-1 blank lines after each line of text.  With no argument gtroff will use 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 number register .L contains the current line spacing setting. _Deffn

           -- Escape: \x spacing
               Sometimes, extra vertical spacing is only needed occasionally, e.g. to allow space for a tall construct (like an equation).  The \x escape will do 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 will be inserted below the current line.  A negative number will add 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 number register contains the most recent (nonnegative) extra vertical line space.

               _Deffn

                -- Request: 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 will end when actual text is output or the rs request is encountered.

                    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).  It is associated with the current diversion level.

                    _Deffn

                     -- Request: rs
                         Disable no-space mode.  This request is associated with the current diversion level.

                         _Deffn

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. _Deffn

      -- Request: ta [N1 N2 ... NN T R1 R2 ... RN]
          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 will set 6 tab stops every one inch.

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

          Tab stops can also be specified relatively (using a leading +) which means that the specified tab stop will be set that distance from 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 resp. 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 will unset all tab stops.

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

          The 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

          _Deffn

           -- Request: tc [FILL-CHAR]
               Normally gtroff will fill the space to the next tab stop with space.  This can be changed with the tc request.  With no argument gtroff will revert to using space, which is the default. The value of this tab repitition character is associated with the current environment (see Environments). _Deffn

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 will do 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. _Deffn

      -- Request: lc [FILL-CHAR]
          The character that will be repeated can be declared with the lc request.  Without an argument, leaders will act the same as tabs (i.e., using space for filling).  gtroff's start-up value is .. The value of this leader repitition character is associated with the current environment (see Environments). _Deffn

          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 repitition 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

     _Deffn

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). _Deffn

      -- 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). _Deffn

           -- 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

               _Deffn

                -- 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 will be executed literally. _Deffn

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

                         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 will be 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 \% escape (but \% 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) will map 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 will undo .tr aa \& instead.

                                   If justification is active, lines will be justified inspite 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.

                              _Deffn

                               -- 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

                                   will print b; if trnt is used instead of tr it will print a. _Deffn

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.

Usually, a macro package can be used with both nroff and troff.  Nevertheless, it is sometimes necessary to make a distinction between the two programs (resp. modes), and 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'). _Deffn

      -- 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 tmac.tty which will be loaded by the start-up file troffrc. _Deffn

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

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 will be 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
     Set horizontal page offset to OFFSET (resp. 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 if in troff mode, and 0 if in nroff mode (see Troff and Nroff Mode); 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 built-in 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

     _Deffn

      -- Request: in [INDENT]
      -- Request: in +indent
      -- Request: in -indent
          Set indentation to INDENT (resp. 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.

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

           -- Request: ti offset
           -- Request: ti +offset
           -- Request: ti -offset
               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 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 resp. a temporary indentation value is active.
               _Deffn

                -- Request: ll [LENGTH]
                -- Request: ll +length
                -- Request: ll -length
                    Set the line length to LENGTH (resp. 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
                    built-in number register .l.  The 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.
                    _Deffn

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

gtroff provides some very primitive operations for controlling page layout.

 -- Request: pl [LENGTH]
 -- Request: pl +length
 -- Request: pl -length
     Set the page length to LENGTH (resp. 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 built-in number register
     .p.

     Note that this only specifies the size of the page, not the top and
     bottom margins.  Those are not set by groff 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).
     _Deffn

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

     The tl request will print a title line, which consists of
     three parts: a left justified portion, a centered portion and a right
     justified portion.  The argument to tl is specified as
     'LEFT'CENTER'RIGHT'.  The % character is
     replaced with the current page number.  This character can be changed
     with the pc request (see below).

     The title line is printed using its own line length, which is specified
     with the lt request.  The current setting of this is available in
     the .lt number register.

     The pn request will change the page number of the next
     page.  The only argument is the page number.

     The current page number is stored in the number register %.  The
     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.

     The pc request will change the page number character (used by the
     tl request) to a different character.  With no argument, this
     mechanism is disabled.

     See Traps.

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

To stop processing the current page, and move to the next page, invoke the bp request.  This request will also cause a break.  It can also take an argument of what the next page should be numbered.  The only difference between bp and pn is that pn does not cause a break or actually eject a page.

     .de newpage
     'bp
     'sp .5i
     .tl 'left top'center top'right top'
     'sp .3i
     ..

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 will ensure 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 and the default argument is 1v.

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

     .ne 2
     .ti +5n
     text

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 will be output immediately.  If there is not enough space, it is stored for later output via the os request.  The default argument is 1v and the default unit is v.

Fonts
=====

gtroff has the ability to switch fonts at any point in the text. There are two ways to do this, via the ft request and the \f 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.

The basic set of fonts are R, I, B, and BI. These are Times Roman, Italic, Bold, and Bold Italic.  There is also at least one symbol font which contains various special symbols (Greek, mathematics).  Such symbols fonts cannot be used directly, but should be used via an escape.

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

Font changes can be done either with the ft request or the \f request.  With no arguments, it will switch to the previous font (also known as P).

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

The \f escape is useful for changing fonts in the middle of words:

     eggs, bacon, \fBspam\fP and sausage.

Both of the above examples will produce the same output.  Note the usage of P to indicate the previous font -- using \f it is not possible to omit this parameter.

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

The \/ escape increases the width of the preceding character so that the spacing between that character and the following character will be 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 will overlap the top left of the right parenthesis.  It is a good idea to 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.

The \, escape modifies the spacing of the following character so that the spacing between that character and the preceding character will be correct if the preceding character is a Roman character.  It is a good idea to 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.

The ftr request will translate fonts; its syntax is

     .ftr F G

which translates 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 will be used.  If G is missing, or equal to F then font F will not be translated.

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

Due to the variety of fonts available, gtroff has added the concept of font families.  Each of these families has four styles (R, I, B and BI).

The fonts are specified as the concatenation of the font family and style.  Specifying a font without the family part will cause gtroff to use that style of the current family.  By default, gtroff uses the Times family.

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

Font families can be switched with the fam request.  The current font family is available in the number register .fam.  This is a string-valued register.

     spam,
     .fam H
     spam,
     .ft B
     spam,
     .fam T
     spam,
     .ft AR
     baked beans,
     .ft R
     and spam.

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

For the sake of old phototypesetters and compatability with old versions of troff, gtroff has the concept of font positions, on which various fonts are mounted.  The last one or two are reserved for the symbol font(s).

New fonts can be mounted with the fp request.  These numeric positions can then be referred to with font changing commands.  When gtroff starts it is using font number one.

     .fp 1 H
     .fp 2 HI
     .fp 3 HB
     wink, wink,
     .ft 2
     nudge, nudge,
     .ft
     .ft 3
     say no more!
     .ft

Note that after these font changes have taken place, the original font is restored.

The current font in use, as a font position, is available in number register .f.  This can be useful to remember the current font, for later recall.

     .nr save-font \n(.f
     ... lots 'o text ...
     .ft \n[save-font]

The number of the next free font position is available in the 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 will not allow a font to be mounted at a position whose number is much greater 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 will be used as the external name.  This feature make it possible to use fonts with long names in compatibility mode.

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

Symbols can be inserted by using a special escape sequence.  This escape is simply the escape character (usually a backslash) followed by an identifier.  The symbol identifiers have to be two or more characters, since single characters conflict with all the other escapes.  The identifier can be either preceded by a parenthesis if it is two characters long, or surrounded by square brackets.  So, the symbol for the mathematical Greek letter `pi' can be produced either by \(*p or \[*p].

     area = \(*p\fIr\fP\u2\d

The escape \C'XXX' will typeset the character named XXX.  Normally it is more convenient to use \[XXX]. But \C has the advantage that it is compatible with recent versions of ditroff and is available in compatibility mode.

The escape \N'N' will typeset the character with code N in the current font.  N can be any integer.  Most devices only have characters with codes between 0 and 255.  If the current font does not contain a character with that code, special fonts will not be searched.  The \N escape sequence can be conveniently used on 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.

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.

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 will be 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).

New characters can be created with the char request.  It is called as

     .char C STRING

This defines character C to be STRING.  Every time character C needs to be printed, STRING will be processed in a temporary environment and the result will be wrapped up into a single object.  Compatibility mode will be turned off and the escape character will be set to \ while STRING is being processed.  Any emboldening, constant spacing or track kerning will be 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 will be handled like normal characters not defined with char.

A character definition can be removed with the rchar request. Its arguments are the characters to be removed.  This undoes the effect of a char request.

See Special Characters.

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

There are a number of requests for artificially creating fonts.  These are largely vestigial remains from 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.

The ul request will print subsequent lines in italics on a device capable of it, or underline the text on a character output device.  The single argument is the number of lines to be ``underlined,'' with no argument, the next line will be underlined.

The cu request is similar to ul ...

The uf request will set the underline font used by ul and cu.

The bd request artificially creates a bold font by printing each character twice, slightly offset.  The first argument specifies the font to embolden, and the second is the number of basic units, minus one, by which the two characters will be offset.  If the second argument is missing, emboldening will be turned off.

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

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 number register .lg (set to 1 if ligatures are enabled, 0 otherwise).

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

Kerning can be activated with the kern request.  If the parameter is non-zero or missing, enable pairwise kerning, otherwise disable it. The number register .kern is set to 1 if pairwise kerning is enabled, 0 otherwise.

Track kerning must be used with great care since it is usually considered bad typography if the reader notices the effect.  The syntax of the tkf request is like this:

     .tkf F S1 N1 S2 N2

Enable track kerning for font F.  If the current font is F the width of every character will be increased by an amount between N1 and N2; if the current point size is less than or equal to S1 the width will be increased by N1; if it is greater than or equal to S2 the width will be 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.

Sizes
=====

gtroff uses two dimensions with each line of text, type size and vertical spacing.  The type size is the height from the text baseline to the top of the tallest character (descenders may drop below this baseline).  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 that this, it will spread 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
-------------------

Using the ps request and the \s escape the type size can be changed.  The vs request will change the vertical spacing. The default unit for the ps and vs requests are points. The number registers .s and .v contain the current type size and vertical spacing.

These requests take parameters in units of points.  It is possible to specify sizes as an absolute size, or as a relative change from the current size.  The size 0 means go back to the previous size.  With no argument it will also revert to the previous size.

     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 resp. 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 resp. 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 will round to the nearest permissible size.

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 will be 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.

It would make no sense to use the z scale indicator in a numeric expression whose default scale indicator was neither u nor z, and so gtroff disallows this.  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.

The number register .s returns the point size in points as decimal fraction.  There is also a new number register .ps that returns the point size in scaled points.

The last-requested point size in scaled points is contained in the .psr number register.  The last requested point size in points as a decimal fraction can be found in .sr.  This is a string-valued register.

\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 resp. 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).  They are defined via the ds request.

     .ds UX \s-1UNIX\s0\u\s-3tm\s0\d

They are interpolated, or expanded in-place, via the \* escape:

     The \*(UX Operating System

If the string named by the \* does not exist, the escape will be replaced by nothing.

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,

The as request will append a string to another string.  It works similar to the ds request except that it appends the second argument onto the string named by the first argument.

     .as sign " with shallots, onions and garlic,

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 will be stored without the newlines.

     .ds foo lots and lots \
     of text are on these \
     next several lines

Rudimentary string manipulation routines are given with the substring and length requests.  The former has the following syntax:

     .substring XX N1 [N2]

It replaces the string in register XX 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 will be 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.

Here the syntax of the length request:

     .length XX STRING

It computes the length of STRING and returns it in the number register XX (which is not necessarily defined before).

See Identifiers, and Comments.

Conditionals and Loops
======================

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.

t
     True if the document is being processed in troff mode.

'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 strings are ``formatted'' before being compared.

rXXX
     True if there is a number register named XXX.

dXXX
     True if there is a string, macro, diversion, or request named XXX.

cCH
     True if there is a character CH available; CH is either an ASCII character or a special character (\(CH or \[CH]); the condition will also be true if CH has been defined by the char request.

if-else
-------

gtroff has if-then-else constructs like other languages, although the formatting can be painful.

The if request has the following syntax:

     .if EXPR ANYTHING

where EXPR is the expression to be evaluated; ANYTHING (the remainder of the line) will be executed if EXPR evaluates to non-zero (true).  ANYTHING will be interpreted as though it was on a line by itself.  See Expressions, for more info.

Here are some examples:

     .if t .ls 2				\" double spacing in troff
     .if 0 .ab how'd this happen?

An if-then-else is written using two requests ie and el. The first request is the `if' part and the latter is the `else' part.

     .ie
     .el

In many cases more than one request is to be executed as a result of any of these requests.  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 "\}
     .ds qq "

See Expressions.

while
-----

gtroff provides a looping construct using the while request, which is used much like the if (and related) requests. The first argument is an expression which will be evaluated.  The while request will interpret the remainder of the line until the expression evaluates to 0 or false.

     .nr a 0 1
     .while (\na<9) \&\n+a,
     \&\n+a

The preceding example produces:

     1, 2, 3, 4, 5, 6, 7, 8, 9, 10

Note the usage of the \& escape to avoid a control character at the beginning of a line.

The break request will break out of a while loop.  Be sure not to confuse this with the br request (causing a line break). The continue request will finish 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.  Macros are used for defining common operations. Macros are defined using the de request.  This request takes a name for the macro as the first argument.  Subsequent lines are copied into an internal buffer until the line .. is encountered.  The optional second argument to de can change this ending token.

Here a small example macro called P which will cause a break and the insertion of some vertical space.  It could be used to separate paragraphs.

     .de P
     .br
     .sp .8v
     ..

The am request works similarly to de except it appends onto the macro named by the first argument.  So, to make the previously defined P macro actually do indented instead of block paragraphs, is is possible to add the necessary code to the existing macro like this:

     .am P
     .ti +5n
     ..

Macros can be aliased with the als request.

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 will be 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.

For example, the following will result in the numbers 20 and c10 being printed:

     .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:

The escapes \$N, \$(NN and \$[NNN] will result in the Nth, NNth or NNNth argument.  As usual, the first form only accepts a single number (larger than zero), the second only 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, two backslashes should be used on these in actual use to prevent interpolation until the macro is actually invoked.

The request shift will shift the arguments 1 position, or as many positions as specified by its argument.  After executing this request, argument I will become argument I-N; arguments 1 to N will no longer be available.  Shifting by negative amounts is currently undefined.

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 is the concatenation of all the arguments separated by spaces.  A similar escape is \$@, which is the concatenation of all the arguments with each surrounded by double quotes, and separated by spaces.

The \$0 escape is the name by which the current macro was invoked.  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 1.40 2000/06/18 10:13:51 wlemb Exp $

See Request Arguments.

Page Motions
============

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.

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 will store the location in an internal register.  The results of this can be used later by the rt or the sp request.  The rt request will return upwards to the location given in the register name given as an argument, with no argument it will return to the location marked with the mk request

The following escapes give fine control of movements about the page.

The \v'E' 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 is vertical spaces, v's.  Beware, however, that gtroff will leave text processing to continue wherever the motion ends, so to avoid interference with text processing, motions should be balanced.

There are some special case escapes for vertical motion.

\r
     move upwards 1v.

\u
     move upwards .5v.

\d
     move down .5v.

Horizontal motions can be done via the \h'E' escape.  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.

\^
     a 1/12th em space.

\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.

A frequent need is to do horizontal movement based on the width of some arbitrary text (e.g. given as an argument to a macro).  For that, there is the escape \w'TEXT' which will interpolate to the width of the given TEXT in basic units.

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
     is set according to what kinds of characters occur in TEXT:

     0
          only short characters, no descenders or tall characters.

     1
          descender.

     2
          tall character.

     3
          both 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.

\k

.k

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.

The \l escape will draw a line rightwards from the current location.  The full syntax for this escape is like this:

     \l'LC'

where L is the length of the line to be drawn, starting at the current location; positive numbers will draw to the right, and negative will draw towards the left.  This can also be specified absolutely (i.e. with a leading |) which will draw 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 will use 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.

Vertical lines are drawn using the \L escape.  Its parameters are specified similar to the \l escape.  If the length is positive, the movement will be downwards, and upwards for negative values.  The default character is the box rule character.  As with the vertical motion escapes, text processing will blindly continue where the line ends.

More flexible drawing functions are available via the \D escape. While the previous escapes will work on a character device, these escapes will 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 will be 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).

The \b escape will pile a sequence of characters vertically, and center it vertically on the current line.  This can be used to build large brackets and braces.

     \b'\(lt\(bv\(lk\(bv\(lb'

See Drawing Functions.

Traps
=====

Traps are locations, which, when reached, will 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 are frequently used for page headers and footers. The following is a simple example of this.

     .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

The number register .t is the distance to the next trap.

The location of a trap can be changed later on with the ch request.  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. This is useful for building up footnotes in a diversion to allow more space at the bottom of the page for them.

The vpt request will enable vertical position traps if the argument is non-zero, disable 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 number register .vpt.

The number register .trunc contains the amount of vertical space truncated by the most recently sprung vertical position trap, or, if the trap was sprung by a 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.

The 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.

Diversion Traps
---------------

Traps can also be set within a diversion using the dt request.  Like wh the first argument is the location of the trap and the second argument is the name of the macro to be invoked.  The number register .t will still work within diversions. See Diversions, for more information.

Input Line Traps
----------------

The it request will set an input line trap.  The format for calling this is

     .it N NAME

where N is the number of lines of input which may be read before springing the trap, NAME 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 will print the next N lines in a bold font.

     .de B
     .it B-end \\$1
     .ft B
     ..
     .de B-end
     .ft R
     ..

End-of-input Traps
------------------

The em request will set a trap at the end of input.  The macro specified as an argument will be 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.

A diversion is initiated by the di request.  Like the de request, it takes an argument of a macro name to divert subsequent text into.  The da macro will append to an existing diversion.

di (resp. da) without an argument ends the diversion.

Diversions may be nested.  The number register .z contains the name of the current diversion.  The number register .d contains the current vertical place in the diversion.  If not in a diversion it is the same as the register nl.

.h

After completing a diversion, the built-in 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
     ..

Requests, macros and escapes are interpreted when read into a diversion. There are two ways to prevent this; either way will take the given text and transparently embed it into the diversion.  The first method is to prefix the line with \!.  This will cause the entire line to be transparently inserted into the diversion.  This is useful for macros which shouldn't be invoked until the diverted text is actually output.

The other way is to surround the text by the \? escape, i.e.

     \?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 will print 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

The asciify request only exists in order to make certain gross hacks work with GNU troff.  It unformats the diversion specified as an argument in such a way that ASCII characters that were formatted and diverted will be treated like ordinary input characters when the diversion is reread.  For example, the following will set 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 has environments in which text is processed.  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.

The ev request will switch to another environment.  The single argument is the name of the environment to switch to.  With no argument gtroff will switch back to the previous environment.  There is no limit on the number of named environments; they will be created the first time that they are referenced.  The .ev register contains the name or number of the current environment.  This is a string-valued register.

Note that a call to ev (with argument) will push 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 will switch back to environment bar (which will be popped off the stack), and a second call will switch back to environment foo.

Here is another example:

     .ev footnote-env
     .fam N
     .ps 6
     .vs 8
     .ll -.5i
     .ev
     ...
     .ev footnote-env
     \(dg Note the large, friendly letters.
     .ev

To copy an environment into the current one, use the evc request, which takes the name of the environment to copy from as an argument.

I/O
===

The so request will read in the file given as an argument and include it in place of the so request.  This is quite useful for large documents, i.e. keeping each chapter in a separate file. See gsoelim, for more information.

The mso request is the same as the so request except that the file is searched for in the same directories as tmac.NAME is searched for when the -mNAME option is specified.

The cf and trf requests are to include a file.  It will transparently output the contents of file filename.  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 will be 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, will embed in the diversion an object which, when reread, will cause 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.

The nx request will force gtroff to continue processing of the file specified as an argument.

The rd request will read from standard input, and include what is read as though it were part of the input file.  Text is read until a blank line is encountered.

Using these two 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

pi

The sy request will allow arbitrary system commands to be executed from within a gtroff document.  The output is not saved anyplace, so it is up to the user to do so.

For example, the following example will introduce 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 will set the number registers H, M and S, and then reads those commands in with the so request.

The systat number register contains the return value of the system() function executed by the last sy request.

The open request will open a file (specified as the second argument) for writing and associate the stream (specified as the first argument) with it.

The opena is like open, but if the file exists, append to it instead of truncating it.

The write request will write to the file associated with the stream specified by the first argument.  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 " will be stripped, and it will be read in copy-in mode.

The close request will close the stream specified by the first argument; stream will no longer be an acceptable argument to the write request.

The \V escape will interpolate the contents of the specified environment variable, as returned by the function getenv.  The argument to \V is specified 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 will allow information to be directly given to the postprocessor.  This is particularly useful for embedding POSTSCRIPT into the final document.

The \X escape will embed its argument into the gtroff output preceded with x X.

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 will confuse 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.

Line numbers can be printed in the left margin using the nm request.  The first argument is the line number of the next output line; this defaults to 1.  The second argument indicates on which lines numbers will be printed, i.e. 5 means put line numbers on every 5 lines; this defaults to 1.  The third argument 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.

The nn request will temporarily turn off line numbering.  The first argument is the number of lines not to be numbered; this defaults to 1.

Margin characters can be automatically printed to the right of the text with the mc request.  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 will be 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.

The primary reason for the existence of lf is to make debugging documents which are split into many files, which are then put together with soelim and other preprocessors.  The first argument is the name of the file and the second argument is the input line number in that file.  This way gtroff can produce error messages which are intelligible to the user.

Debugging
=========

gtroff is not easy to debug, but there are some useful features and strategies for debugging.

  * The tm request will send output to the standard error stream; this is very useful for printing debugging output.

  * 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

  * The ab request is similar to the tm request, except that it will cause gtroff to stop processing.  With no argument it will print User Abort.

  * The ex request will also cause gtroff to stop processing if encountered at the topmost level; see also I/O.

  * 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.

  * The pm request will dump out the entire symbol table.

  * The pnr request will print the names and contents of all currently defined number registers on stderr.

  * The ptr request will print 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.

  * The fl request instructs gtroff to flush its output immediately.  The intention is that this be used when using gtroff interactively.  There is little other use for it.  This request causes a line break.

  * The backtrace request will print 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.

  * The warn request controls the level of warnings checked for.  The only argument is the sum of the numbers associated with each warning that is to be enabled; all other warnings will be disabled.  The number associated with each warning is listed below.  For example, .warn 0 will disable all warnings, and .warn 1 will disable all warnings except that about missing characters.  If an argument is not given, all warnings will be enabled.  The 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 will be 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 will be 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 will be 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 will not be invoked.  When this warning is given, no macro is automatically defined.  This is enabled by default. This warning will never occur 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 will interpret

     .dsabcd

as defining a string ab with contents cd.  Normally, GNU troff will interpret this as a call of a macro named dsabcd.  Also UNIX troff will interpret \*[ or \n[ as references to a string or number register called [.  In GNU troff, however, this will normally be interpreted as the start of a long name.  In compatibility mode GNU troff will interpret these things in the traditional way.  In compatibility mode, however, long names are not recognized. 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

will set the point size to 10 points, whereas in GNU troff it will set 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 will be 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

will print \\ 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 will always print a single instance of the current escape character, regardless of whether or not it is used in a diversion; it will also work 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 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 will be only two characters long (as ditroff does).

When a character is to be printed, that character will always be 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!?

will produce

Drawing Functions
-----------------

The D drawing command has been extended.  These extensions will only be used by GNU pic 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 will be 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 will be 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.  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 N-th 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 will treat each of the x value as a horizontal quantity, and each of the y values as a vertical quantity and will assume that the width of the drawn object is sum if 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 will follow each newline in the argument with a + character (as usual, it will terminate 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 will be associated with styles S1 ... SM.

fonts N F1 F2 F3 ... FN
     Fonts F1 ... FN will be 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 will cause no font to be 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 will be 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 will be interpreted as octal; if it starts with 0x or 0X it will be interpreted as hexadecimal.

Anything on the line after the CODE field will be 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 kernpairs section will have a negative value for N.

Installation
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Request and Escape Index
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In this index, escapes are listed with a leading backslash (\) to distinguish them from requests which appear without the leading control character (normally either . or ').

Macro and String Index
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In this index, strings are listed with the calling escape sequence (\*) to distinguish them from macros which 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].