re(3) Perl Programmers Reference Guide re(3)NAMEre - 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 $^X in these examples because it's tainted by
default.)
DESCRIPTION
When "use re 'taint'" is in effect, and a tainted string
is the target of a regex, the regex memories (or values
returned by the m// operator in list context) are tainted.
This feature is useful when regex operations on tainted
data aren't meant to extract safe substrings, but to per
form other transformations.
When "use re 'eval'" is in effect, a regex is allowed to
contain "(?{ ... })" zero-width assertions even if regular
expression contains variable interpolation. That is nor
mally disallowed, since it is a potential security risk.
Note that this pragma is ignored when the regular expres
sion is obtained from tainted data, i.e. evaluation is
always disallowed with tainted regular expresssions. See
the section on "(?{ code })" in the perlre manpage.
For the purpose of this pragma, interpolation of precom
piled regular expressions (i.e., the result of "qr//") is
not considered variable interpolation. Thus:
/foo${pat}bar/
is allowed if $pat is a precompiled regular expression,
even if $pat contains "(?{ ... })" assertions.
When "use re 'debug'" is in effect, perl emits debugging
messages when compiling and using regular expressions.
The output is the same as that obtained by running a
"-DDEBUGGING"-enabled perl interpreter with the -Dr
switch. It may be quite voluminous depending on the com
plexity of the match. Using "debugcolor" instead of
"debug" enables a form of output that can be used to get a
colorful display on terminals that understand termcap
color sequences. Set "$ENV{PERL_RE_TC}" to a comma-sepa
rated 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.
2001-03-18 perl v5.6.1 re(3)
