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re(3)
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// operator 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 the section on "(?{ code
  })" in the perlre manpage.

  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 complexity 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 the Debugging regular expressions entry in the perldebug
  manpage 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 the Pragmatic Modules entry in the perlmodlib manpage.

Index for Section 3

Alphabetical listing for R

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