re(3pm) 						 Perl Programmers Reference Guide						   re(3pm)

NAME

       re - Perl pragma to alter regular expression behaviour

SYNOPSIS

	   use re 'taint';
	   ($x) = ($^X =~ /^(.*)$/s);	  # $x is tainted here

	   $pat = '(?{ $foo = 1 })';
	   use re 'eval';
	   /foo${pat}bar/;		  # won't fail (when not under -T switch)

	   {
	       no re 'taint';		  # the default
	       ($x) = ($^X =~ /^(.*)$/s); # $x is not tainted here

	       no re 'eval';		  # the default
	       /foo${pat}bar/;		  # disallowed (with or without -T switch)
	   }

	   use re 'debug';		  # NOT lexically scoped (as others are)
	   /^(.*)$/s;			  # output debugging info during
					  #	compile and run time

	   use re 'debugcolor'; 	  # same as 'debug', but with colored output
	   ...

       (We use $^X in these examples because it's tainted by default.)

DESCRIPTION

       When "use re 'taint'" is in effect, and a tainted string is the target of a regex, the regex memories (or values returned by the m// opera-
       tor in list context) are tainted.  This feature is useful when regex operations on tainted data aren't meant to extract safe substrings,
       but to perform other transformations.

       When "use re 'eval'" is in effect, a regex is allowed to contain "(?{ ... })" zero-width assertions even if regular expression contains
       variable interpolation.	That is normally disallowed, since it is a potential security risk.  Note that this pragma is ignored when the
       regular expression is obtained from tainted data, i.e.  evaluation is always disallowed with tainted regular expresssions.  See "(?{ code
       })" in perlre.

       For the purpose of this pragma, interpolation of precompiled regular expressions (i.e., the result of "qr//") is not considered variable
       interpolation.  Thus:

	   /foo${pat}bar/

       is allowed if $pat is a precompiled regular expression, even if $pat contains "(?{ ... })" assertions.

       When "use re 'debug'" is in effect, perl emits debugging messages when compiling and using regular expressions.	The output is the same as
       that obtained by running a "-DDEBUGGING"-enabled perl interpreter with the -Dr switch. It may be quite voluminous depending on the complex-
       ity of the match.  Using "debugcolor" instead of "debug" enables a form of output that can be used to get a colorful display on terminals
       that understand termcap color sequences.  Set $ENV{PERL_RE_TC} to a comma-separated list of "termcap" properties to use for highlighting
       strings on/off, pre-point part on/off.  See "Debugging regular expressions" in perldebug for additional info.

       The directive "use re 'debug'" is not lexically scoped, as the other directives are.  It has both compile-time and run-time effects.

       See "Pragmatic Modules" in perlmodlib.

perl v5.8.0							    2002-06-01								   re(3pm)