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 $^X in these examples because it's tainted by default.)
DESCRIPTION
When "use re 'taint'" is in effect, and a tainted string is the target of a regex, the regex memories
(or values returned by the m// operator in list context) are tainted. This feature is useful when
regex operations on tainted data aren't meant to extract safe substrings, but to perform other trans-formations. transformations.
formations.
When "use re 'eval'" is in effect, a regex is allowed to contain "(?{ ... })" zero-width assertions
even if regular expression contains variable interpolation. That is normally disallowed, since it is
a potential security risk. Note that this pragma is ignored when the regular expression is obtained
from tainted data, i.e. evaluation is always disallowed with tainted regular expressions. See "(?{
code })" in perlre.
For the purpose of this pragma, interpolation of precompiled regular expressions (i.e., the result of
"qr//") is not considered variable interpolation. Thus:
/foo${pat}bar/
is allowed if $pat is a precompiled regular expression, even if $pat contains "(?{ ... })" asser-tions. assertions.
tions.
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 inter-preter interpreter
preter 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-sepa-rated comma-separated
rated 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 v5.8.8 2001-09-21 re(3pm)
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