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    1 package re;
    2 
    3 # pragma for controlling the regexp engine
    4 use strict;
    5 use warnings;
    6 
    7 our $VERSION     = "0.37";
    8 our @ISA         = qw(Exporter);
    9 our @EXPORT_OK   = ('regmust',
   10                     qw(is_regexp regexp_pattern
   11                        regname regnames regnames_count));
   12 our %EXPORT_OK = map { $_ => 1 } @EXPORT_OK;
   13 
   14 my %bitmask = (
   15     taint   => 0x00100000, # HINT_RE_TAINT
   16     eval    => 0x00200000, # HINT_RE_EVAL
   17 );
   18 
   19 my $flags_hint = 0x02000000; # HINT_RE_FLAGS
   20 my $PMMOD_SHIFT = 0;
   21 my %reflags = (
   22     m => 1 << ($PMMOD_SHIFT + 0),
   23     s => 1 << ($PMMOD_SHIFT + 1),
   24     i => 1 << ($PMMOD_SHIFT + 2),
   25     x => 1 << ($PMMOD_SHIFT + 3),
   26    xx => 1 << ($PMMOD_SHIFT + 4),
   27     n => 1 << ($PMMOD_SHIFT + 5),
   28     p => 1 << ($PMMOD_SHIFT + 6),
   29     strict => 1 << ($PMMOD_SHIFT + 10),
   30 # special cases:
   31     d => 0,
   32     l => 1,
   33     u => 2,
   34     a => 3,
   35     aa => 4,
   36 );
   37 
   38 sub setcolor {
   39  eval {             # Ignore errors
   40   require Term::Cap;
   41 
   42   my $terminal = Tgetent Term::Cap ({OSPEED => 9600}); # Avoid warning.
   43   my $props = $ENV{PERL_RE_TC} || 'md,me,so,se,us,ue';
   44   my @props = split /,/, $props;
   45   my $colors = join "\t", map {$terminal->Tputs($_,1)} @props;
   46 
   47   $colors =~ s/\0//g;
   48   $ENV{PERL_RE_COLORS} = $colors;
   49  };
   50  if ($@) {
   51     $ENV{PERL_RE_COLORS} ||= qq'\t\t> <\t> <\t\t';
   52  }
   53 
   54 }
   55 
   56 my %flags = (
   57     COMPILE         => 0x0000FF,
   58     PARSE           => 0x000001,
   59     OPTIMISE        => 0x000002,
   60     TRIEC           => 0x000004,
   61     DUMP            => 0x000008,
   62     FLAGS           => 0x000010,
   63     TEST            => 0x000020,
   64 
   65     EXECUTE         => 0x00FF00,
   66     INTUIT          => 0x000100,
   67     MATCH           => 0x000200,
   68     TRIEE           => 0x000400,
   69 
   70     EXTRA           => 0xFF0000,
   71     TRIEM           => 0x010000,
   72     OFFSETS         => 0x020000,
   73     OFFSETSDBG      => 0x040000,
   74     STATE           => 0x080000,
   75     OPTIMISEM       => 0x100000,
   76     STACK           => 0x280000,
   77     BUFFERS         => 0x400000,
   78     GPOS            => 0x800000,
   79 );
   80 $flags{ALL} = -1 & ~($flags{OFFSETS}|$flags{OFFSETSDBG}|$flags{BUFFERS});
   81 $flags{All} = $flags{all} = $flags{DUMP} | $flags{EXECUTE};
   82 $flags{Extra} = $flags{EXECUTE} | $flags{COMPILE} | $flags{GPOS};
   83 $flags{More} = $flags{MORE} = $flags{All} | $flags{TRIEC} | $flags{TRIEM} | $flags{STATE};
   84 $flags{State} = $flags{DUMP} | $flags{EXECUTE} | $flags{STATE};
   85 $flags{TRIE} = $flags{DUMP} | $flags{EXECUTE} | $flags{TRIEC};
   86 
   87 if (defined &DynaLoader::boot_DynaLoader) {
   88     require XSLoader;
   89     XSLoader::load();
   90 }
   91 # else we're miniperl
   92 # We need to work for miniperl, because the XS toolchain uses Text::Wrap, which
   93 # uses re 'taint'.
   94 
   95 sub _load_unload {
   96     my ($on)= @_;
   97     if ($on) {
   98     # We call install() every time, as if we didn't, we wouldn't
   99     # "see" any changes to the color environment var since
  100     # the last time it was called.
  101 
  102     # install() returns an integer, which if casted properly
  103     # in C resolves to a structure containing the regexp
  104     # hooks. Setting it to a random integer will guarantee
  105     # segfaults.
  106     $^H{regcomp} = install();
  107     } else {
  108         delete $^H{regcomp};
  109     }
  110 }
  111 
  112 sub bits {
  113     my $on = shift;
  114     my $bits = 0;
  115     my $turning_all_off = ! @_ && ! $on;
  116     if ($turning_all_off) {
  117 
  118         # Pretend were called with certain parameters, which are best dealt
  119         # with that way.
  120         push @_, keys %bitmask; # taint and eval
  121         push @_, 'strict';
  122     }
  123 
  124     # Process each subpragma parameter
  125    ARG:
  126     foreach my $idx (0..$#_){
  127         my $s=$_[$idx];
  128         if ($s eq 'Debug' or $s eq 'Debugcolor') {
  129             setcolor() if $s =~/color/i;
  130             ${^RE_DEBUG_FLAGS} = 0 unless defined ${^RE_DEBUG_FLAGS};
  131             for my $idx ($idx+1..$#_) {
  132                 if ($flags{$_[$idx]}) {
  133                     if ($on) {
  134                         ${^RE_DEBUG_FLAGS} |= $flags{$_[$idx]};
  135                     } else {
  136                         ${^RE_DEBUG_FLAGS} &= ~ $flags{$_[$idx]};
  137                     }
  138                 } else {
  139                     require Carp;
  140                     Carp::carp("Unknown \"re\" Debug flag '$_[$idx]', possible flags: ",
  141                                join(", ",sort keys %flags ) );
  142                 }
  143             }
  144             _load_unload($on ? 1 : ${^RE_DEBUG_FLAGS});
  145             last;
  146         } elsif ($s eq 'debug' or $s eq 'debugcolor') {
  147         setcolor() if $s =~/color/i;
  148         _load_unload($on);
  149         last;
  150         } elsif (exists $bitmask{$s}) {
  151         $bits |= $bitmask{$s};
  152     } elsif ($EXPORT_OK{$s}) {
  153         require Exporter;
  154         re->export_to_level(2, 're', $s);
  155         } elsif ($s eq 'strict') {
  156             if ($on) {
  157                 $^H{reflags} |= $reflags{$s};
  158                 warnings::warnif('experimental::re_strict',
  159                                  "\"use re 'strict'\" is experimental");
  160 
  161                 # Turn on warnings if not already done.
  162                 if (! warnings::enabled('regexp')) {
  163                     require warnings;
  164                     warnings->import('regexp');
  165                     $^H{re_strict} = 1;
  166                 }
  167             }
  168             else {
  169                 $^H{reflags} &= ~$reflags{$s} if $^H{reflags};
  170 
  171                 # Turn off warnings if we turned them on.
  172                 warnings->unimport('regexp') if $^H{re_strict};
  173             }
  174         if ($^H{reflags}) {
  175                 $^H |= $flags_hint;
  176             }
  177             else {
  178                 $^H &= ~$flags_hint;
  179             }
  180     } elsif ($s =~ s/^\///) {
  181         my $reflags = $^H{reflags} || 0;
  182         my $seen_charset;
  183             my $x_count = 0;
  184         while ($s =~ m/( . )/gx) {
  185                 local $_ = $1;
  186         if (/[adul]/) {
  187                     # The 'a' may be repeated; hide this from the rest of the
  188                     # code by counting and getting rid of all of them, then
  189                     # changing to 'aa' if there is a repeat.
  190                     if ($_ eq 'a') {
  191                         my $sav_pos = pos $s;
  192                         my $a_count = $s =~ s/a//g;
  193                         pos $s = $sav_pos - 1;  # -1 because got rid of the 'a'
  194                         if ($a_count > 2) {
  195                 require Carp;
  196                             Carp::carp(
  197                             qq 'The "a" flag may only appear a maximum of twice'
  198                             );
  199                         }
  200                         elsif ($a_count == 2) {
  201                             $_ = 'aa';
  202                         }
  203                     }
  204             if ($on) {
  205             if ($seen_charset) {
  206                 require Carp;
  207                             if ($seen_charset ne $_) {
  208                                 Carp::carp(
  209                                 qq 'The "$seen_charset" and "$_" flags '
  210                                 .qq 'are exclusive'
  211                                 );
  212                             }
  213                             else {
  214                                 Carp::carp(
  215                                 qq 'The "$seen_charset" flag may not appear '
  216                                 .qq 'twice'
  217                                 );
  218                             }
  219             }
  220             $^H{reflags_charset} = $reflags{$_};
  221             $seen_charset = $_;
  222             }
  223             else {
  224             delete $^H{reflags_charset}
  225                                      if defined $^H{reflags_charset}
  226                                         && $^H{reflags_charset} == $reflags{$_};
  227             }
  228         } elsif (exists $reflags{$_}) {
  229                     if ($_ eq 'x') {
  230                         $x_count++;
  231                         if ($x_count > 2) {
  232                 require Carp;
  233                             Carp::carp(
  234                             qq 'The "x" flag may only appear a maximum of twice'
  235                             );
  236                         }
  237                         elsif ($x_count == 2) {
  238                             $_ = 'xx';  # First time through got the /x
  239                         }
  240                     }
  241 
  242                     $on
  243               ? $reflags |= $reflags{$_}
  244               : ($reflags &= ~$reflags{$_});
  245         } else {
  246             require Carp;
  247             Carp::carp(
  248              qq'Unknown regular expression flag "$_"'
  249             );
  250             next ARG;
  251         }
  252         }
  253         ($^H{reflags} = $reflags or defined $^H{reflags_charset})
  254                         ? $^H |= $flags_hint
  255                         : ($^H &= ~$flags_hint);
  256     } else {
  257         require Carp;
  258         Carp::carp("Unknown \"re\" subpragma '$s' (known ones are: ",
  259                        join(', ', map {qq('$_')} 'debug', 'debugcolor', sort keys %bitmask),
  260                        ")");
  261     }
  262     }
  263 
  264     if ($turning_all_off) {
  265         _load_unload(0);
  266         $^H{reflags} = 0;
  267         $^H{reflags_charset} = 0;
  268         $^H &= ~$flags_hint;
  269     }
  270 
  271     $bits;
  272 }
  273 
  274 sub import {
  275     shift;
  276     $^H |= bits(1, @_);
  277 }
  278 
  279 sub unimport {
  280     shift;
  281     $^H &= ~ bits(0, @_);
  282 }
  283 
  284 1;
  285 
  286 __END__
  287 
  288 =head1 NAME
  289 
  290 re - Perl pragma to alter regular expression behaviour
  291 
  292 =head1 SYNOPSIS
  293 
  294     use re 'taint';
  295     ($x) = ($^X =~ /^(.*)$/s);     # $x is tainted here
  296 
  297     $pat = '(?{ $foo = 1 })';
  298     use re 'eval';
  299     /foo${pat}bar/;        # won't fail (when not under -T
  300                                    # switch)
  301 
  302     {
  303     no re 'taint';         # the default
  304     ($x) = ($^X =~ /^(.*)$/s); # $x is not tainted here
  305 
  306     no re 'eval';          # the default
  307     /foo${pat}bar/;        # disallowed (with or without -T
  308                                    # switch)
  309     }
  310 
  311     use re 'strict';               # Raise warnings for more conditions
  312 
  313     use re '/ix';
  314     "FOO" =~ / foo /; # /ix implied
  315     no re '/x';
  316     "FOO" =~ /foo/; # just /i implied
  317 
  318     use re 'debug';        # output debugging info during
  319     /^(.*)$/s;             # compile and run time
  320 
  321 
  322     use re 'debugcolor';       # same as 'debug', but with colored
  323                                    # output
  324     ...
  325 
  326     use re qw(Debug All);          # Same as "use re 'debug'", but you
  327                                    # can use "Debug" with things other
  328                                    # than 'All'
  329     use re qw(Debug More);         # 'All' plus output more details
  330     no re qw(Debug ALL);           # Turn on (almost) all re debugging
  331                                    # in this scope
  332 
  333     use re qw(is_regexp regexp_pattern); # import utility functions
  334     my ($pat,$mods)=regexp_pattern(qr/foo/i);
  335     if (is_regexp($obj)) {
  336         print "Got regexp: ",
  337             scalar regexp_pattern($obj); # just as perl would stringify
  338     }                                    # it but no hassle with blessed
  339                                          # re's.
  340 
  341 (We use $^X in these examples because it's tainted by default.)
  342 
  343 =head1 DESCRIPTION
  344 
  345 =head2 'taint' mode
  346 
  347 When C<use re 'taint'> is in effect, and a tainted string is the target
  348 of a regexp, the regexp memories (or values returned by the m// operator
  349 in list context) are tainted.  This feature is useful when regexp operations
  350 on tainted data aren't meant to extract safe substrings, but to perform
  351 other transformations.
  352 
  353 =head2 'eval' mode
  354 
  355 When C<use re 'eval'> is in effect, a regexp is allowed to contain
  356 C<(?{ ... })> zero-width assertions and C<(??{ ... })> postponed
  357 subexpressions that are derived from variable interpolation, rather than
  358 appearing literally within the regexp.  That is normally disallowed, since
  359 it is a
  360 potential security risk.  Note that this pragma is ignored when the regular
  361 expression is obtained from tainted data, i.e.  evaluation is always
  362 disallowed with tainted regular expressions.  See L<perlre/(?{ code })> 
  363 and L<perlre/(??{ code })>.
  364 
  365 For the purpose of this pragma, interpolation of precompiled regular
  366 expressions (i.e., the result of C<qr//>) is I<not> considered variable
  367 interpolation.  Thus:
  368 
  369     /foo${pat}bar/
  370 
  371 I<is> allowed if $pat is a precompiled regular expression, even
  372 if $pat contains C<(?{ ... })> assertions or C<(??{ ... })> subexpressions.
  373 
  374 =head2 'strict' mode
  375 
  376 Note that this is an experimental feature which may be changed or removed in a
  377 future Perl release.
  378 
  379 When C<use re 'strict'> is in effect, stricter checks are applied than
  380 otherwise when compiling regular expressions patterns.  These may cause more
  381 warnings to be raised than otherwise, and more things to be fatal instead of
  382 just warnings.  The purpose of this is to find and report at compile time some
  383 things, which may be legal, but have a reasonable possibility of not being the
  384 programmer's actual intent.  This automatically turns on the C<"regexp">
  385 warnings category (if not already on) within its scope.
  386 
  387 As an example of something that is caught under C<"strict'>, but not
  388 otherwise, is the pattern
  389 
  390  qr/\xABC/
  391 
  392 The C<"\x"> construct without curly braces should be followed by exactly two
  393 hex digits; this one is followed by three.  This currently evaluates as
  394 equivalent to
  395 
  396  qr/\x{AB}C/
  397 
  398 that is, the character whose code point value is C<0xAB>, followed by the
  399 letter C<C>.  But since C<C> is a a hex digit, there is a reasonable chance
  400 that the intent was
  401 
  402  qr/\x{ABC}/
  403 
  404 that is the single character at C<0xABC>.  Under C<'strict'> it is an error to
  405 not follow C<\x> with exactly two hex digits.  When not under C<'strict'> a
  406 warning is generated if there is only one hex digit, and no warning is raised
  407 if there are more than two.
  408 
  409 It is expected that what exactly C<'strict'> does will evolve over time as we
  410 gain experience with it.  This means that programs that compile under it in
  411 today's Perl may not compile, or may have more or fewer warnings, in future
  412 Perls.  There is no backwards compatibility promises with regards to it.  Also
  413 there are already proposals for an alternate syntax for enabling it.  For
  414 these reasons, using it will raise a C<experimental::re_strict> class warning,
  415 unless that category is turned off.
  416 
  417 Note that if a pattern compiled within C<'strict'> is recompiled, say by
  418 interpolating into another pattern, outside of C<'strict'>, it is not checked
  419 again for strictness.  This is because if it works under strict it must work
  420 under non-strict.
  421 
  422 =head2 '/flags' mode
  423 
  424 When C<use re '/I<flags>'> is specified, the given I<flags> are automatically
  425 added to every regular expression till the end of the lexical scope.
  426 I<flags> can be any combination of
  427 C<'a'>,
  428 C<'aa'>,
  429 C<'d'>,
  430 C<'i'>,
  431 C<'l'>,
  432 C<'m'>,
  433 C<'n'>,
  434 C<'p'>,
  435 C<'s'>,
  436 C<'u'>,
  437 C<'x'>,
  438 and/or
  439 C<'xx'>.
  440 
  441 C<no re '/I<flags>'> will turn off the effect of C<use re '/I<flags>'> for the
  442 given flags.
  443 
  444 For example, if you want all your regular expressions to have /msxx on by
  445 default, simply put
  446 
  447     use re '/msxx';
  448 
  449 at the top of your code.
  450 
  451 The character set C</adul> flags cancel each other out. So, in this example,
  452 
  453     use re "/u";
  454     "ss" =~ /\xdf/;
  455     use re "/d";
  456     "ss" =~ /\xdf/;
  457 
  458 the second C<use re> does an implicit C<no re '/u'>.
  459 
  460 Similarly,
  461 
  462     use re "/xx";   # Doubled-x
  463     ...
  464     use re "/x";    # Single x from here on
  465     ...
  466 
  467 Turning on one of the character set flags with C<use re> takes precedence over the
  468 C<locale> pragma and the 'unicode_strings' C<feature>, for regular
  469 expressions. Turning off one of these flags when it is active reverts to
  470 the behaviour specified by whatever other pragmata are in scope. For
  471 example:
  472 
  473     use feature "unicode_strings";
  474     no re "/u"; # does nothing
  475     use re "/l";
  476     no re "/l"; # reverts to unicode_strings behaviour
  477 
  478 =head2 'debug' mode
  479 
  480 When C<use re 'debug'> is in effect, perl emits debugging messages when
  481 compiling and using regular expressions.  The output is the same as that
  482 obtained by running a C<-DDEBUGGING>-enabled perl interpreter with the
  483 B<-Dr> switch. It may be quite voluminous depending on the complexity
  484 of the match.  Using C<debugcolor> instead of C<debug> enables a
  485 form of output that can be used to get a colorful display on terminals
  486 that understand termcap color sequences.  Set C<$ENV{PERL_RE_TC}> to a
  487 comma-separated list of C<termcap> properties to use for highlighting
  488 strings on/off, pre-point part on/off.
  489 See L<perldebug/"Debugging Regular Expressions"> for additional info.
  490 
  491 As of 5.9.5 the directive C<use re 'debug'> and its equivalents are
  492 lexically scoped, as the other directives are.  However they have both
  493 compile-time and run-time effects.
  494 
  495 See L<perlmodlib/Pragmatic Modules>.
  496 
  497 =head2 'Debug' mode
  498 
  499 Similarly C<use re 'Debug'> produces debugging output, the difference
  500 being that it allows the fine tuning of what debugging output will be
  501 emitted. Options are divided into three groups, those related to
  502 compilation, those related to execution and those related to special
  503 purposes. The options are as follows:
  504 
  505 =over 4
  506 
  507 =item Compile related options
  508 
  509 =over 4
  510 
  511 =item COMPILE
  512 
  513 Turns on all compile related debug options.
  514 
  515 =item PARSE
  516 
  517 Turns on debug output related to the process of parsing the pattern.
  518 
  519 =item OPTIMISE
  520 
  521 Enables output related to the optimisation phase of compilation.
  522 
  523 =item TRIEC
  524 
  525 Detailed info about trie compilation.
  526 
  527 =item DUMP
  528 
  529 Dump the final program out after it is compiled and optimised.
  530 
  531 =item FLAGS
  532 
  533 Dump the flags associated with the program
  534 
  535 =item TEST
  536 
  537 Print output intended for testing the internals of the compile process
  538 
  539 =back
  540 
  541 =item Execute related options
  542 
  543 =over 4
  544 
  545 =item EXECUTE
  546 
  547 Turns on all execute related debug options.
  548 
  549 =item MATCH
  550 
  551 Turns on debugging of the main matching loop.
  552 
  553 =item TRIEE
  554 
  555 Extra debugging of how tries execute.
  556 
  557 =item INTUIT
  558 
  559 Enable debugging of start-point optimisations.
  560 
  561 =back
  562 
  563 =item Extra debugging options
  564 
  565 =over 4
  566 
  567 =item EXTRA
  568 
  569 Turns on all "extra" debugging options.
  570 
  571 =item BUFFERS
  572 
  573 Enable debugging the capture group storage during match. Warning,
  574 this can potentially produce extremely large output.
  575 
  576 =item TRIEM
  577 
  578 Enable enhanced TRIE debugging. Enhances both TRIEE
  579 and TRIEC.
  580 
  581 =item STATE
  582 
  583 Enable debugging of states in the engine.
  584 
  585 =item STACK
  586 
  587 Enable debugging of the recursion stack in the engine. Enabling
  588 or disabling this option automatically does the same for debugging
  589 states as well. This output from this can be quite large.
  590 
  591 =item GPOS
  592 
  593 Enable debugging of the \G modifier.
  594 
  595 =item OPTIMISEM
  596 
  597 Enable enhanced optimisation debugging and start-point optimisations.
  598 Probably not useful except when debugging the regexp engine itself.
  599 
  600 =item OFFSETS
  601 
  602 Dump offset information. This can be used to see how regops correlate
  603 to the pattern. Output format is
  604 
  605    NODENUM:POSITION[LENGTH]
  606 
  607 Where 1 is the position of the first char in the string. Note that position
  608 can be 0, or larger than the actual length of the pattern, likewise length
  609 can be zero.
  610 
  611 =item OFFSETSDBG
  612 
  613 Enable debugging of offsets information. This emits copious
  614 amounts of trace information and doesn't mesh well with other
  615 debug options.
  616 
  617 Almost definitely only useful to people hacking
  618 on the offsets part of the debug engine.
  619 
  620 
  621 =back
  622 
  623 =item Other useful flags
  624 
  625 These are useful shortcuts to save on the typing.
  626 
  627 =over 4
  628 
  629 =item ALL
  630 
  631 Enable all options at once except OFFSETS, OFFSETSDBG and BUFFERS.
  632 (To get every single option without exception, use both ALL and EXTRA, or
  633 starting in 5.30 on a C<-DDEBUGGING>-enabled perl interpreter, use
  634 the B<-Drv> command-line switches.)
  635 
  636 =item All
  637 
  638 Enable DUMP and all execute options. Equivalent to:
  639 
  640   use re 'debug';
  641 
  642 =item MORE
  643 
  644 =item More
  645 
  646 Enable the options enabled by "All", plus STATE, TRIEC, and TRIEM.
  647 
  648 =back
  649 
  650 =back
  651 
  652 As of 5.9.5 the directive C<use re 'debug'> and its equivalents are
  653 lexically scoped, as are the other directives.  However they have both
  654 compile-time and run-time effects.
  655 
  656 =head2 Exportable Functions
  657 
  658 As of perl 5.9.5 're' debug contains a number of utility functions that
  659 may be optionally exported into the caller's namespace. They are listed
  660 below.
  661 
  662 =over 4
  663 
  664 =item is_regexp($ref)
  665 
  666 Returns true if the argument is a compiled regular expression as returned
  667 by C<qr//>, false if it is not.
  668 
  669 This function will not be confused by overloading or blessing. In
  670 internals terms, this extracts the regexp pointer out of the
  671 PERL_MAGIC_qr structure so it cannot be fooled.
  672 
  673 =item regexp_pattern($ref)
  674 
  675 If the argument is a compiled regular expression as returned by C<qr//>,
  676 then this function returns the pattern.
  677 
  678 In list context it returns a two element list, the first element
  679 containing the pattern and the second containing the modifiers used when
  680 the pattern was compiled.
  681 
  682   my ($pat, $mods) = regexp_pattern($ref);
  683 
  684 In scalar context it returns the same as perl would when stringifying a raw
  685 C<qr//> with the same pattern inside.  If the argument is not a compiled
  686 reference then this routine returns false but defined in scalar context,
  687 and the empty list in list context. Thus the following
  688 
  689     if (regexp_pattern($ref) eq '(?^i:foo)')
  690 
  691 will be warning free regardless of what $ref actually is.
  692 
  693 Like C<is_regexp> this function will not be confused by overloading
  694 or blessing of the object.
  695 
  696 =item regmust($ref)
  697 
  698 If the argument is a compiled regular expression as returned by C<qr//>,
  699 then this function returns what the optimiser considers to be the longest
  700 anchored fixed string and longest floating fixed string in the pattern.
  701 
  702 A I<fixed string> is defined as being a substring that must appear for the
  703 pattern to match. An I<anchored fixed string> is a fixed string that must
  704 appear at a particular offset from the beginning of the match. A I<floating
  705 fixed string> is defined as a fixed string that can appear at any point in
  706 a range of positions relative to the start of the match. For example,
  707 
  708     my $qr = qr/here .* there/x;
  709     my ($anchored, $floating) = regmust($qr);
  710     print "anchored:'$anchored'\nfloating:'$floating'\n";
  711 
  712 results in
  713 
  714     anchored:'here'
  715     floating:'there'
  716 
  717 Because the C<here> is before the C<.*> in the pattern, its position
  718 can be determined exactly. That's not true, however, for the C<there>;
  719 it could appear at any point after where the anchored string appeared.
  720 Perl uses both for its optimisations, preferring the longer, or, if they are
  721 equal, the floating.
  722 
  723 B<NOTE:> This may not necessarily be the definitive longest anchored and
  724 floating string. This will be what the optimiser of the Perl that you
  725 are using thinks is the longest. If you believe that the result is wrong
  726 please report it via the L<perlbug> utility.
  727 
  728 =item regname($name,$all)
  729 
  730 Returns the contents of a named buffer of the last successful match. If
  731 $all is true, then returns an array ref containing one entry per buffer,
  732 otherwise returns the first defined buffer.
  733 
  734 =item regnames($all)
  735 
  736 Returns a list of all of the named buffers defined in the last successful
  737 match. If $all is true, then it returns all names defined, if not it returns
  738 only names which were involved in the match.
  739 
  740 =item regnames_count()
  741 
  742 Returns the number of distinct names defined in the pattern used
  743 for the last successful match.
  744 
  745 B<Note:> this result is always the actual number of distinct
  746 named buffers defined, it may not actually match that which is
  747 returned by C<regnames()> and related routines when those routines
  748 have not been called with the $all parameter set.
  749 
  750 =back
  751 
  752 =head1 SEE ALSO
  753 
  754 L<perlmodlib/Pragmatic Modules>.
  755 
  756 =cut