re - Perl pragma to alter regular expression behaviour
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); # $x is not tainted hereno re 'eval'; # the default/foo${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 $^X in these examples because it's tainted by default.)
Whenuse re 'taint' is in effect, and a tainted string is the target of a regex, the regex memories (or values returned by the m// operator in list context) are tainted. This feature is useful when regex operations on tainted data aren't meant to extract safe substrings, but to perform other transformations.
Whenuse re 'eval' is in effect, a regex is allowed to contain(?{ ... }) zero-width assertions even if regular expression contains variable interpolation. That is normally disallowed, since it is a potential security risk. Note that this pragma is ignored when the regular expression is obtained from tainted data, i.e. evaluation is always disallowed with tainted regular expresssions. See"(?{ code })" in perlre.
For the purpose of this pragma, interpolation of precompiled regular expressions (i.e., the result ofqr//) isnot considered variable interpolation. Thus:
/foo${pat}bar/is allowed if $pat is a precompiled regular expression, even if $pat contains(?{ ... }) assertions.
Whenuse re 'debug' is in effect, perl emits debugging messages when compiling and using regular expressions. The output is the same as that obtained by running a-DDEBUGGING-enabled perl interpreter with the-Dr switch. It may be quite voluminous depending on the complexity of the match. Usingdebugcolor instead ofdebug enables a form of output that can be used to get a colorful display on terminals that understand termcap color sequences. Set$ENV{PERL_RE_TC} to a comma-separated list oftermcap properties to use for highlighting strings on/off, pre-point part on/off. See"Debugging regular expressions" in perldebug for additional info.
The directiveuse re 'debug' isnot lexically scoped, as the other directives are. It has both compile-time and run-time effects.
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