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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 '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 expressions. 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 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 ``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.

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