Check existing $^W functionality

__END__

# warnable code, warnings disabled
$a =+ 3 ;
EXPECT

########
-w
# warnable code, warnings enabled via command line switch
$a =+ 3 ;
EXPECT
Reversed += operator at - line 3.
Name "main::a" used only once: possible typo at - line 3.
########
#! perl -w
# warnable code, warnings enabled via #! line
$a =+ 3 ;
EXPECT
Reversed += operator at - line 3.
Name "main::a" used only once: possible typo at - line 3.
########

# warnable code, warnings enabled via compile time $^W
BEGIN { $^W = 1 }
$a =+ 3 ;
EXPECT
Reversed += operator at - line 4.
Name "main::a" used only once: possible typo at - line 4.
########

# compile-time warnable code, warnings enabled via runtime $^W
# so no warning printed.
$^W = 1 ;
$a =+ 3 ;
EXPECT

########

# warnable code, warnings enabled via runtime $^W
$^W = 1 ;
my $b ; chop $b ;
EXPECT
Use of uninitialized value at - line 4.
########

# warnings enabled at compile time, disabled at run time
BEGIN { $^W = 1 }
$^W = 0 ;
my $b ; chop $b ;
EXPECT

########

# warnings disabled at compile time, enabled at run time
BEGIN { $^W = 0 }
$^W = 1 ;
my $b ; chop $b ;
EXPECT
Use of uninitialized value at - line 5.
########
-w
--FILE-- abcd
my $b ; chop $b ;
1 ;
--FILE-- 
require "./abcd";
EXPECT
Use of uninitialized value at ./abcd line 1.
########

--FILE-- abcd
my $b ; chop $b ;
1 ;
--FILE-- 
#! perl -w
require "./abcd";
EXPECT
Use of uninitialized value at ./abcd line 1.
########

--FILE-- abcd
my $b ; chop $b ;
1 ;
--FILE-- 
$^W =1 ;
require "./abcd";
EXPECT
Use of uninitialized value at ./abcd line 1.
########

--FILE-- abcd
$^W = 0;
my $b ; chop $b ;
1 ;
--FILE-- 
$^W =1 ;
require "./abcd";
EXPECT

########

--FILE-- abcd
$^W = 1;
1 ;
--FILE-- 
$^W =0 ;
require "./abcd";
my $b ; chop $b ;
EXPECT
Use of uninitialized value at - line 3.
########

$^W = 1;
eval "my $b ; chop $b ;" ;
EXPECT
Use of uninitialized value at - line 3.
Use of uninitialized value at - line 3.
########

eval "$^W = 1;" ;
my $b ; chop $b ;
EXPECT

########

eval {$^W = 1;} ;
my $b ; chop $b ;
EXPECT
Use of uninitialized value at - line 3.
########

{
    local ($^W) = 1;
}
my $b ; chop $b ;
EXPECT

########

my $a ; chop $a ;
{
    local ($^W) = 1;
    my $b ; chop $b ;
}
my $c ; chop $c ;
EXPECT
Use of uninitialized value at - line 5.
########
-w
-e undef
EXPECT
Use of uninitialized value at - line 2.
########
BEGIN { $^W = 1 }
for (@{[0]}) { "$_" }		# check warning isn't duplicated
EXPECT
Useless use of string in void context at - line 2.