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