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 '/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);          # Finer tuned debugging options.
           use re qw(Debug More);
           no re qw(Debug ALL);           # Turn of 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.)

   'taint' mode
       When "use re 'taint'" is in effect, and a tainted string is the target
       of a regexp, the regexp memories (or values returned by the m//
       operator in list context) are tainted.  This feature is useful when
       regexp operations on tainted data aren't meant to extract safe
       substrings, but to perform other transformations.

   'eval' mode
       When "use re 'eval'" is in effect, a regexp is allowed to contain "(?{
       ... })" zero-width assertions and "(??{ ... })" postponed
       subexpressions, even if the regular expression contains variable
       is allowed if $pat is a precompiled regular expression, even if $pat
       contains "(?{ ... })" assertions or "(??{ ... })" subexpressions.

   '/flags' mode
       When "use re '/flags'" is specified, the given flags are automatically
       added to every regular expression till the end of the lexical scope.

       "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 /msx on
       by default, simply put

           use re '/msx';

       at the top of your code.

       The character set /adul flags cancel each other out. So, in this

           use re "/u";
           "ss" =~ /\xdf/;
           use re "/d";
           "ss" =~ /\xdf/;

       the second "use re" does an implicit "no re '/u'".

       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

   'debug' mode
       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.

       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.

               Turns on debug output related to the process of parsing the

               Enables output related to the optimisation phase of

               Detailed info about trie compilation.

               Dump the final program out after it is compiled and optimised.

       Execute related options
               Turns on all execute related debug options.

               Turns on debugging of the main matching loop.

               Extra debugging of how tries execute.

               Enable debugging of start point optimisations.

       Extra debugging options
               Turns on all "extra" debugging options.

               Enable debugging the capture group storage during match.
               Warning, this can potentially produce extremely large output.

               Enable enhanced TRIE debugging. Enhances both TRIEE and TRIEC.

               Enable debugging of states in the engine.

               Enable debugging of the recursion stack in the engine. Enabling
               or disabling this option automatically does the same for
               debugging states as well. This output from this can be quite

               Enable enhanced optimisation debugging and start point
               optimisations.  Probably not useful except when debugging the
               regexp engine itself.

               debug options.

               Almost definitely only useful to people hacking on the offsets
               part of the debug engine.

       Other useful flags
           These are useful shortcuts to save on the typing.

           ALL Enable all options at once except OFFSETS, OFFSETSDBG and

           All Enable DUMP and all execute options. Equivalent to:

                 use re 'debug';

               Enable TRIEM and all execute compile and execute options.

       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.

   Exportable Functions
       As of perl 5.9.5 're' debug contains a number of utility functions that
       may be optionally exported into the caller's namespace. They are listed

           Returns true if the argument is a compiled regular expression as
           returned by "qr//", false if it is not.

           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.

           If the argument is a compiled regular expression as returned by
           "qr//", then this function returns the pattern.

           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)')

           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


           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, prefering
           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.

           Returns the contents of a named buffer of the last successful
           match. If $all is true, then returns an array ref containing one
           entry per buffer, otherwise returns the first defined buffer.

           Returns a list of all of the named buffers defined in the last
           successful match. If $all is true, then it returns all names
           defined, if not it returns only names which were involved in the

           Returns the number of distinct names defined in the pattern used
           for the last successful match.

           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.

       "Pragmatic Modules" in perlmodlib.

perl v5.14.2                      2011-09-19                         re(3perl)
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