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 'strict'; # Raise warnings for more conditions
use re '/ix';
"FOO" =~ / foo /; # /ix implied
no re '/x';
"FOO" =~ /foo/; # just /i implied
use re 'debug'; # output debugging info during
/^(.*)$/s; # compile and run time
use re 'debugcolor'; # same as 'debug', but with colored
# output
...
use re qw(Debug All); # Same as "use re 'debug'", but you
# can use "Debug" with things other
# than 'All'
use re qw(Debug More); # 'All' plus output more details
no re qw(Debug ALL); # Turn on (almost) all re debugging
# in this scope
use re qw(is_regexp regexp_pattern); # import utility functions
my ($pat,$mods)=regexp_pattern(qr/foo/i);
if (is_regexp($obj)) {
print "Got regexp: ",
scalar regexp_pattern($obj); # just as perl would stringify
} # it but no hassle with blessed
# re's.
(We use $^X in these examples because it's tainted by default.)
For the purpose of this pragma, interpolation of precompiled regular expressions (i.e., the result of "qr//") is not considered variable interpolation. Thus:
/foo${pat}bar/
is allowed if $pat is a precompiled regular expression, even if $pat contains "(?{ ... })" assertions or "(??{ ... })" subexpressions.
When "use re 'strict'" is in effect, stricter checks are applied than otherwise when compiling regular expressions patterns. These may cause more warnings to be raised than otherwise, and more things to be fatal instead of just warnings. The purpose of this is to find and report at compile time some things, which may be legal, but have a reasonable possibility of not being the programmer's actual intent. This automatically turns on the "regexp" warnings category (if not already on) within its scope.
As an example of something that is caught under ""strict'", but not otherwise, is the pattern
qr/\xABC/
The "\x" construct without curly braces should be followed by exactly two hex digits; this one is followed by three. This currently evaluates as equivalent to
qr/\x{AB}C/
that is, the character whose code point value is 0xAB, followed by the letter "C". But since "C" is a a hex digit, there is a reasonable chance that the intent was
qr/\x{ABC}/
that is the single character at 0xABC. Under 'strict' it is an error to not follow "\x" with exactly two hex digits. When not under 'strict' a warning is generated if there is only one hex digit, and no warning is raised if there are more than two.
It is expected that what exactly 'strict' does will evolve over time as we gain experience with it. This means that programs that compile under it in today's Perl may not compile, or may have more or fewer warnings, in future Perls. There is no backwards compatibility promises with regards to it. Also there are already proposals for an alternate syntax for enabling it. For these reasons, using it will raise a "experimental::re_strict" class warning, unless that category is turned off.
Note that if a pattern compiled within 'strict' is recompiled, say by interpolating into another pattern, outside of 'strict', it is not checked again for strictness. This is because if it works under strict it must work under non-strict.
"no re '/flags'" will turn off the effect of "use re '/flags'" for the given flags.
For example, if you want all your regular expressions to have /msxx on by default, simply put
use re '/msxx';
at the top of your code.
The character set "/adul" flags cancel each other out. So, in this example,
use re "/u";
"ss" =~ /\xdf/;
use re "/d";
"ss" =~ /\xdf/;
the second "use re" does an implicit "no re '/u'".
Similarly,
use re "/xx"; # Doubled-x
...
use re "/x"; # Single x from here on
...
Turning on one of the character set flags with "use re" takes precedence over the "locale" pragma and the 'unicode_strings' "feature", for regular expressions. Turning off one of these flags when it is active reverts to the behaviour specified by whatever other pragmata are in scope. For example:
use feature "unicode_strings";
no re "/u"; # does nothing
use re "/l";
no re "/l"; # reverts to unicode_strings behaviour
As of 5.9.5 the directive "use re 'debug'" and its equivalents are lexically scoped, as the other directives are. However they have both compile-time and run-time effects.
See ``Pragmatic Modules'' in perlmodlib.
NODENUM:POSITION[LENGTH]
Where 1 is the position of the first char in the string. Note that position can be 0, or larger than the actual length of the pattern, likewise length can be zero.
Almost definitely only useful to people hacking on the offsets part of the debug engine.
use re 'debug';
As of 5.9.5 the directive "use re 'debug'" and its equivalents are lexically scoped, as are the other directives. However they have both compile-time and run-time effects.
This function will not be confused by overloading or blessing. In internals terms, this extracts the regexp pointer out of the PERL_MAGIC_qr structure so it cannot be fooled.
In list context it returns a two element list, the first element containing the pattern and the second containing the modifiers used when the pattern was compiled.
my ($pat, $mods) = regexp_pattern($ref);
In scalar context it returns the same as perl would when stringifying a raw "qr//" with the same pattern inside. If the argument is not a compiled reference then this routine returns false but defined in scalar context, and the empty list in list context. Thus the following
if (regexp_pattern($ref) eq '(?^i:foo)')
will be warning free regardless of what $ref actually is.
Like "is_regexp" this function will not be confused by overloading or blessing of the object.
A fixed string is defined as being a substring that must appear for the pattern to match. An anchored fixed string is a fixed string that must appear at a particular offset from the beginning of the match. A floating fixed string is defined as a fixed string that can appear at any point in a range of positions relative to the start of the match. For example,
my $qr = qr/here .* there/x;
my ($anchored, $floating) = regmust($qr);
print "anchored:'$anchored'\nfloating:'$floating'\n";
results in
anchored:'here'
floating:'there'
Because the "here" is before the ".*" in the pattern, its position can be determined exactly. That's not true, however, for the "there"; it could appear at any point after where the anchored string appeared. Perl uses both for its optimisations, preferring the longer, or, if they are equal, the floating.
NOTE: This may not necessarily be the definitive longest anchored and floating string. This will be what the optimiser of the Perl that you are using thinks is the longest. If you believe that the result is wrong please report it via the perlbug utility.
Note: this result is always the actual number of distinct named buffers defined, it may not actually match that which is returned by "regnames()" and related routines when those routines have not been called with the $all parameter set.