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Balanced.pm @ 2566

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Revision 2566, 66.1 kB (checked in by fumiakiy, 18 months ago)
Added Text::Balanced which is required in Lucene::QueryParser but not included in Perl 5.6.1. BugId:80080

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1	# EXTRACT VARIOUSLY DELIMITED TEXT SEQUENCES FROM STRINGS.
2	# FOR FULL DOCUMENTATION SEE Balanced.pod
3
4	use 5.005;
5	use strict;
6
7	package Text::Balanced;
8
9	use Exporter;
10	use SelfLoader;
11	use vars qw { $VERSION @ISA %EXPORT_TAGS };
12
13	use version; $VERSION = qv('2.0.0');
14	@ISA = qw ( Exporter );
15
16	%EXPORT_TAGS = ( ALL => [ qw(
17	&extract_delimited
18	&extract_bracketed
19	&extract_quotelike
20	&extract_codeblock
21	&extract_variable
22	&extract_tagged
23	&extract_multiple
24
25	&gen_delimited_pat
26	&gen_extract_tagged
27
28	&delimited_pat
29	) ] );
30
31	Exporter::export_ok_tags('ALL');
32
33	# PROTOTYPES
34
35	sub _match_bracketed($$$$$$);
36	sub _match_variable($$);
37	sub _match_codeblock($$$$$$$);
38	sub _match_quotelike($$$$);
39
40	# HANDLE RETURN VALUES IN VARIOUS CONTEXTS
41
42	sub _failmsg {
43	my ($message, $pos) = @_;
44	$@ = bless { error=>$message, pos=>$pos }, "Text::Balanced::ErrorMsg";
45	}
46
47	sub _fail
48	{
49	my ($wantarray, $textref, $message, $pos) = @_;
50	_failmsg $message, $pos if $message;
51	return (undef,$$textref,undef) if $wantarray;
52	return undef;
53	}
54
55	sub _succeed
56	{
57	$@ = undef;
58	my ($wantarray,$textref) = splice @_, 0, 2;
59	my ($extrapos, $extralen) = @_>18 ? splice(@_, -2, 2) : (0,0);
60	my ($startlen, $oppos) = @_[5,6];
61	my $remainderpos = $_[2];
62	if ($wantarray)
63	{
64	my @res;
65	while (my ($from, $len) = splice @_, 0, 2)
66	{
67	push @res, substr($$textref,$from,$len);
68	}
69	if ($extralen) { # CORRECT FILLET
70	my $extra = substr($res[0], $extrapos-$oppos, $extralen, "\n");
71	$res[1] = "$extra$res[1]";
72	eval { substr($$textref,$remainderpos,0) = $extra;
73	substr($$textref,$extrapos,$extralen,"\n")} ;
74	#REARRANGE HERE DOC AND FILLET IF POSSIBLE
75	pos($$textref) = $remainderpos-$extralen+1; # RESET \G
76	}
77	else {
78	pos($$textref) = $remainderpos; # RESET \G
79	}
80	return @res;
81	}
82	else
83	{
84	my $match = substr($$textref,$_[0],$_[1]);
85	substr($match,$extrapos-$_[0]-$startlen,$extralen,"") if $extralen;
86	my $extra = $extralen
87	? substr($$textref, $extrapos, $extralen)."\n" : "";
88	eval {substr($$textref,$_[4],$_[1]+$_[5])=$extra} ; #CHOP OUT PREFIX & MATCH, IF POSSIBLE
89	pos($$textref) = $_[4]; # RESET \G
90	return $match;
91	}
92	}
93
94	# BUILD A PATTERN MATCHING A SIMPLE DELIMITED STRING
95
96	sub gen_delimited_pat($;$) # ($delimiters;$escapes)
97	{
98	my ($dels, $escs) = @_;
99	return "" unless $dels =~ /\S/;
100	$escs = '\\' unless $escs;
101	$escs .= substr($escs,-1) x (length($dels)-length($escs));
102	my @pat = ();
103	my $i;
104	for ($i=0; $i<length $dels; $i++)
105	{
106	my $del = quotemeta substr($dels,$i,1);
107	my $esc = quotemeta substr($escs,$i,1);
108	if ($del eq $esc)
109	{
110	push @pat, "$del(?:[^$del](?:(?:$del$del)[^$del])*)$del";
111	}
112	else
113	{
114	push @pat, "$del(?:[^$esc$del](?:$esc.[^$esc$del])*)$del";
115	}
116	}
117	my $pat = join '\|', @pat;
118	return "(?:$pat)";
119	}
120
121	*delimited_pat = \&gen_delimited_pat;
122
123
124	# THE EXTRACTION FUNCTIONS
125
126	sub extract_delimited (;$$$$)
127	{
128	my $textref = defined $_[0] ? \$_[0] : \$_;
129	my $wantarray = wantarray;
130	my $del = defined $_[1] ? $_[1] : qq{\'\"\`};
131	my $pre = defined $_[2] ? $_[2] : '\s*';
132	my $esc = defined $_[3] ? $_[3] : qq{\\};
133	my $pat = gen_delimited_pat($del, $esc);
134	my $startpos = pos $$textref \|\| 0;
135	return _fail($wantarray, $textref, "Not a delimited pattern", 0)
136	unless $$textref =~ m/\G($pre)($pat)/gc;
137	my $prelen = length($1);
138	my $matchpos = $startpos+$prelen;
139	my $endpos = pos $$textref;
140	return _succeed $wantarray, $textref,
141	$matchpos, $endpos-$matchpos, # MATCH
142	$endpos, length($$textref)-$endpos, # REMAINDER
143	$startpos, $prelen; # PREFIX
144	}
145
146	sub extract_bracketed (;$$$)
147	{
148	my $textref = defined $_[0] ? \$_[0] : \$_;
149	my $ldel = defined $_[1] ? $_[1] : '{([<';
150	my $pre = defined $_[2] ? $_[2] : '\s*';
151	my $wantarray = wantarray;
152	my $qdel = "";
153	my $quotelike;
154	$ldel =~ s/'//g and $qdel .= q{'};
155	$ldel =~ s/"//g and $qdel .= q{"};
156	$ldel =~ s/`//g and $qdel .= q{`};
157	$ldel =~ s/q//g and $quotelike = 1;
158	$ldel =~ tr/[](){}<>\0-\377/[[(({{<</ds;
159	my $rdel = $ldel;
160	unless ($rdel =~ tr/[({</])}>/)
161	{
162	return _fail $wantarray, $textref,
163	"Did not find a suitable bracket in delimiter: \"$_[1]\"",
164	0;
165	}
166	my $posbug = pos;
167	$ldel = join('\|', map { quotemeta $_ } split('', $ldel));
168	$rdel = join('\|', map { quotemeta $_ } split('', $rdel));
169	pos = $posbug;
170
171	my $startpos = pos $$textref \|\| 0;
172	my @match = _match_bracketed($textref,$pre, $ldel, $qdel, $quotelike, $rdel);
173
174	return _fail ($wantarray, $textref) unless @match;
175
176	return _succeed ( $wantarray, $textref,
177	$match[2], $match[5]+2, # MATCH
178	@match[8,9], # REMAINDER
179	@match[0,1], # PREFIX
180	);
181	}
182
183	sub _match_bracketed($$$$$$) # $textref, $pre, $ldel, $qdel, $quotelike, $rdel
184	{
185	my ($textref, $pre, $ldel, $qdel, $quotelike, $rdel) = @_;
186	my ($startpos, $ldelpos, $endpos) = (pos $$textref = pos $$textref\|\|0);
187	unless ($$textref =~ m/\G$pre/gc)
188	{
189	_failmsg "Did not find prefix: /$pre/", $startpos;
190	return;
191	}
192
193	$ldelpos = pos $$textref;
194
195	unless ($$textref =~ m/\G($ldel)/gc)
196	{
197	_failmsg "Did not find opening bracket after prefix: \"$pre\"",
198	pos $$textref;
199	pos $$textref = $startpos;
200	return;
201	}
202
203	my @nesting = ( $1 );
204	my $textlen = length $$textref;
205	while (pos $$textref < $textlen)
206	{
207	next if $$textref =~ m/\G\\./gcs;
208
209	if ($$textref =~ m/\G($ldel)/gc)
210	{
211	push @nesting, $1;
212	}
213	elsif ($$textref =~ m/\G($rdel)/gc)
214	{
215	my ($found, $brackettype) = ($1, $1);
216	if ($#nesting < 0)
217	{
218	_failmsg "Unmatched closing bracket: \"$found\"",
219	pos $$textref;
220	pos $$textref = $startpos;
221	return;
222	}
223	my $expected = pop(@nesting);
224	$expected =~ tr/({[</)}]>/;
225	if ($expected ne $brackettype)
226	{
227	_failmsg qq{Mismatched closing bracket: expected "$expected" but found "$found"},
228	pos $$textref;
229	pos $$textref = $startpos;
230	return;
231	}
232	last if $#nesting < 0;
233	}
234	elsif ($qdel && $$textref =~ m/\G([$qdel])/gc)
235	{
236	$$textref =~ m/\G[^\\$1](?:\\.[^\\$1])*(\Q$1\E)/gsc and next;
237	_failmsg "Unmatched embedded quote ($1)",
238	pos $$textref;
239	pos $$textref = $startpos;
240	return;
241	}
242	elsif ($quotelike && _match_quotelike($textref,"",1,0))
243	{
244	next;
245	}
246
247	else { $$textref =~ m/\G(?:[a-zA-Z0-9]+\|.)/gcs }
248	}
249	if ($#nesting>=0)
250	{
251	_failmsg "Unmatched opening bracket(s): "
252	. join("..",@nesting)."..",
253	pos $$textref;
254	pos $$textref = $startpos;
255	return;
256	}
257
258	$endpos = pos $$textref;
259
260	return (
261	$startpos, $ldelpos-$startpos, # PREFIX
262	$ldelpos, 1, # OPENING BRACKET
263	$ldelpos+1, $endpos-$ldelpos-2, # CONTENTS
264	$endpos-1, 1, # CLOSING BRACKET
265	$endpos, length($$textref)-$endpos, # REMAINDER
266	);
267	}
268
269	sub _revbracket($)
270	{
271	my $brack = reverse $_[0];
272	$brack =~ tr/[({</])}>/;
273	return $brack;
274	}
275
276	my $XMLNAME = q{[a-zA-Z_:][a-zA-Z0-9_:.-]*};
277
278	sub extract_tagged (;$$$$$) # ($text, $opentag, $closetag, $pre, \%options)
279	{
280	my $textref = defined $_[0] ? \$_[0] : \$_;
281	my $ldel = $_[1];
282	my $rdel = $_[2];
283	my $pre = defined $_[3] ? $_[3] : '\s*';
284	my %options = defined $_[4] ? %{$_[4]} : ();
285	my $omode = defined $options{fail} ? $options{fail} : '';
286	my $bad = ref($options{reject}) eq 'ARRAY' ? join('\|', @{$options{reject}})
287	: defined($options{reject}) ? $options{reject}
288	: ''
289	;
290	my $ignore = ref($options{ignore}) eq 'ARRAY' ? join('\|', @{$options{ignore}})
291	: defined($options{ignore}) ? $options{ignore}
292	: ''
293	;
294
295	if (!defined $ldel) { $ldel = '<\w+(?:' . gen_delimited_pat(q{'"}) . '\|[^>])*>'; }
296	$@ = undef;
297
298	my @match = _match_tagged($textref, $pre, $ldel, $rdel, $omode, $bad, $ignore);
299
300	return _fail(wantarray, $textref) unless @match;
301	return _succeed wantarray, $textref,
302	$match[2], $match[3]+$match[5]+$match[7], # MATCH
303	@match[8..9,0..1,2..7]; # REM, PRE, BITS
304	}
305
306	sub _match_tagged # ($$$$$$$)
307	{
308	my ($textref, $pre, $ldel, $rdel, $omode, $bad, $ignore) = @_;
309	my $rdelspec;
310
311	my ($startpos, $opentagpos, $textpos, $parapos, $closetagpos, $endpos) = ( pos($$textref) = pos($$textref)\|\|0 );
312
313	unless ($$textref =~ m/\G($pre)/gc)
314	{
315	_failmsg "Did not find prefix: /$pre/", pos $$textref;
316	goto failed;
317	}
318
319	$opentagpos = pos($$textref);
320
321	unless ($$textref =~ m/\G$ldel/gc)
322	{
323	_failmsg "Did not find opening tag: /$ldel/", pos $$textref;
324	goto failed;
325	}
326
327	$textpos = pos($$textref);
328
329	if (!defined $rdel)
330	{
331	$rdelspec = substr($$textref, $-[0], $+[0] - $-[0]);
332	unless ($rdelspec =~ s/\A([[(<{]+)($XMLNAME).*/ quotemeta "$1\/$2". _revbracket($1) /oes)
333	{
334	_failmsg "Unable to construct closing tag to match: $rdel",
335	pos $$textref;
336	goto failed;
337	}
338	}
339	else
340	{
341	$rdelspec = eval "qq{$rdel}" \|\| do {
342	my $del;
343	for (qw,~ ! ^ & * ) _ + - = } ] : " ; ' > . ? / \| ',)
344	{ next if $rdel =~ /\Q$_/; $del = $_; last }
345	unless ($del) {
346	use Carp;
347	croak "Can't interpolate right delimiter $rdel"
348	}
349	eval "qq$del$rdel$del";
350	};
351	}
352
353	while (pos($$textref) < length($$textref))
354	{
355	next if $$textref =~ m/\G\\./gc;
356
357	if ($$textref =~ m/\G(\n[ \t]*\n)/gc )
358	{
359	$parapos = pos($$textref) - length($1)
360	unless defined $parapos;
361	}
362	elsif ($$textref =~ m/\G($rdelspec)/gc )
363	{
364	$closetagpos = pos($$textref)-length($1);
365	goto matched;
366	}
367	elsif ($ignore && $$textref =~ m/\G(?:$ignore)/gc)
368	{
369	next;
370	}
371	elsif ($bad && $$textref =~ m/\G($bad)/gcs)
372	{
373	pos($$textref) -= length($1); # CUT OFF WHATEVER CAUSED THE SHORTNESS
374	goto short if ($omode eq 'PARA' \|\| $omode eq 'MAX');
375	_failmsg "Found invalid nested tag: $1", pos $$textref;
376	goto failed;
377	}
378	elsif ($$textref =~ m/\G($ldel)/gc)
379	{
380	my $tag = $1;
381	pos($$textref) -= length($tag); # REWIND TO NESTED TAG
382	unless (_match_tagged(@_)) # MATCH NESTED TAG
383	{
384	goto short if $omode eq 'PARA' \|\| $omode eq 'MAX';
385	_failmsg "Found unbalanced nested tag: $tag",
386	pos $$textref;
387	goto failed;
388	}
389	}
390	else { $$textref =~ m/./gcs }
391	}
392
393	short:
394	$closetagpos = pos($$textref);
395	goto matched if $omode eq 'MAX';
396	goto failed unless $omode eq 'PARA';
397
398	if (defined $parapos) { pos($$textref) = $parapos }
399	else { $parapos = pos($$textref) }
400
401	return (
402	$startpos, $opentagpos-$startpos, # PREFIX
403	$opentagpos, $textpos-$opentagpos, # OPENING TAG
404	$textpos, $parapos-$textpos, # TEXT
405	$parapos, 0, # NO CLOSING TAG
406	$parapos, length($$textref)-$parapos, # REMAINDER
407	);
408
409	matched:
410	$endpos = pos($$textref);
411	return (
412	$startpos, $opentagpos-$startpos, # PREFIX
413	$opentagpos, $textpos-$opentagpos, # OPENING TAG
414	$textpos, $closetagpos-$textpos, # TEXT
415	$closetagpos, $endpos-$closetagpos, # CLOSING TAG
416	$endpos, length($$textref)-$endpos, # REMAINDER
417	);
418
419	failed:
420	_failmsg "Did not find closing tag", pos $$textref unless $@;
421	pos($$textref) = $startpos;
422	return;
423	}
424
425	sub extract_variable (;$$)
426	{
427	my $textref = defined $_[0] ? \$_[0] : \$_;
428	return ("","","") unless defined $$textref;
429	my $pre = defined $_[1] ? $_[1] : '\s*';
430
431	my @match = _match_variable($textref,$pre);
432
433	return _fail wantarray, $textref unless @match;
434
435	return _succeed wantarray, $textref,
436	@match[2..3,4..5,0..1]; # MATCH, REMAINDER, PREFIX
437	}
438
439	sub _match_variable($$)
440	{
441	# $#
442	# $^
443	# $$
444	my ($textref, $pre) = @_;
445	my $startpos = pos($$textref) = pos($$textref)\|\|0;
446	unless ($$textref =~ m/\G($pre)/gc)
447	{
448	_failmsg "Did not find prefix: /$pre/", pos $$textref;
449	return;
450	}
451	my $varpos = pos($$textref);
452	unless ($$textref =~ m{\G\$\s(?!::)(\d+\|[][&`'+./\|,";%=~:?!\@<>()-]\|\^[a-z]?)}gci)
453	{
454	unless ($$textref =~ m/\G((\$#?\|[*\@\%]\|\\&)+)/gc)
455	{
456	_failmsg "Did not find leading dereferencer", pos $$textref;
457	pos $$textref = $startpos;
458	return;
459	}
460	my $deref = $1;
461
462	unless ($$textref =~ m/\G\s(?:::\|')?(?:[_a-z]\w(?:::\|'))[_a-z]\w/gci
463	or _match_codeblock($textref, "", '\{', '\}', '\{', '\}', 0)
464	or $deref eq '$#' or $deref eq '$$' )
465	{
466	_failmsg "Bad identifier after dereferencer", pos $$textref;
467	pos $$textref = $startpos;
468	return;
469	}
470	}
471
472	while (1)
473	{
474	next if $$textref =~ m/\G\s(?:->)?\s[{]\w+[}]/gc;
475	next if _match_codeblock($textref,
476	qr/\s->\s(?:[_a-zA-Z]\w+\s*)?/,
477	qr/[({[]/, qr/[)}\]]/,
478	qr/[({[]/, qr/[)}\]]/, 0);
479	next if _match_codeblock($textref,
480	qr/\s*/, qr/[{[]/, qr/[}\]]/,
481	qr/[{[]/, qr/[}\]]/, 0);
482	next if _match_variable($textref,'\s->\s');
483	next if $$textref =~ m/\G\s->\s\w+(?![{([])/gc;
484	last;
485	}
486
487	my $endpos = pos($$textref);
488	return ($startpos, $varpos-$startpos,
489	$varpos, $endpos-$varpos,
490	$endpos, length($$textref)-$endpos
491	);
492	}
493
494	sub extract_codeblock (;$$$$$)
495	{
496	my $textref = defined $_[0] ? \$_[0] : \$_;
497	my $wantarray = wantarray;
498	my $ldel_inner = defined $_[1] ? $_[1] : '{';
499	my $pre = defined $_[2] ? $_[2] : '\s*';
500	my $ldel_outer = defined $_[3] ? $_[3] : $ldel_inner;
501	my $rd = $_[4];
502	my $rdel_inner = $ldel_inner;
503	my $rdel_outer = $ldel_outer;
504	my $posbug = pos;
505	for ($ldel_inner, $ldel_outer) { tr/[]()<>{}\0-\377/[[((<<{{/ds }
506	for ($rdel_inner, $rdel_outer) { tr/[]()<>{}\0-\377/]]))>>}}/ds }
507	for ($ldel_inner, $ldel_outer, $rdel_inner, $rdel_outer)
508	{
509	$_ = '('.join('\|',map { quotemeta $_ } split('',$_)).')'
510	}
511	pos = $posbug;
512
513	my @match = _match_codeblock($textref, $pre,
514	$ldel_outer, $rdel_outer,
515	$ldel_inner, $rdel_inner,
516	$rd);
517	return _fail($wantarray, $textref) unless @match;
518	return _succeed($wantarray, $textref,
519	@match[2..3,4..5,0..1] # MATCH, REMAINDER, PREFIX
520	);
521
522	}
523
524	sub _match_codeblock($$$$$$$)
525	{
526	my ($textref, $pre, $ldel_outer, $rdel_outer, $ldel_inner, $rdel_inner, $rd) = @_;
527	my $startpos = pos($$textref) = pos($$textref) \|\| 0;
528	unless ($$textref =~ m/\G($pre)/gc)
529	{
530	_failmsg qq{Did not match prefix /$pre/ at"} .
531	substr($$textref,pos($$textref),20) .
532	q{..."},
533	pos $$textref;
534	return;
535	}
536	my $codepos = pos($$textref);
537	unless ($$textref =~ m/\G($ldel_outer)/gc) # OUTERMOST DELIMITER
538	{
539	_failmsg qq{Did not find expected opening bracket at "} .
540	substr($$textref,pos($$textref),20) .
541	q{..."},
542	pos $$textref;
543	pos $$textref = $startpos;
544	return;
545	}
546	my $closing = $1;
547	$closing =~ tr/([<{/)]>}/;
548	my $matched;
549	my $patvalid = 1;
550	while (pos($$textref) < length($$textref))
551	{
552	$matched = '';
553	if ($rd && $$textref =~ m#\G(\Q(?)\E\|\Q(s?)\E\|\Q(s)\E)#gc)
554	{
555	$patvalid = 0;
556	next;
557	}
558
559	if ($$textref =~ m/\G\s#./gc)
560	{
561	next;
562	}
563
564	if ($$textref =~ m/\G\s*($rdel_outer)/gc)
565	{
566	unless ($matched = ($closing && $1 eq $closing) )
567	{
568	next if $1 eq '>'; # MIGHT BE A "LESS THAN"
569	_failmsg q{Mismatched closing bracket at "} .
570	substr($$textref,pos($$textref),20) .
571	qq{...". Expected '$closing'},
572	pos $$textref;
573	}
574	last;
575	}
576
577	if (_match_variable($textref,'\s*') \|\|
578	_match_quotelike($textref,'\s*',$patvalid,$patvalid) )
579	{
580	$patvalid = 0;
581	next;
582	}
583
584
585	# NEED TO COVER MANY MORE CASES HERE!!!
586	if ($$textref =~ m#\G\s*(?!$ldel_inner)
587	( [-+*x/%^&\|.]=?
588	\| [!=]~
589	\| =(?!>)
590	\| (\\\|&&\|\\|\\|\|<<\|>>)=?
591	\| split\|grep\|map\|return
592	\| [([]
593	)#gcx)
594	{
595	$patvalid = 1;
596	next;
597	}
598
599	if ( _match_codeblock($textref, '\s*', $ldel_inner, $rdel_inner, $ldel_inner, $rdel_inner, $rd) )
600	{
601	$patvalid = 1;
602	next;
603	}
604
605	if ($$textref =~ m/\G\s*$ldel_outer/gc)
606	{
607	_failmsg q{Improperly nested codeblock at "} .
608	substr($$textref,pos($$textref),20) .
609	q{..."},
610	pos $$textref;
611	last;
612	}
613
614	$patvalid = 0;
615	$$textref =~ m/\G\s*(\w+\|[-=>]>\|.\|\Z)/gc;
616	}
617	continue { $@ = undef }
618
619	unless ($matched)
620	{
621	_failmsg 'No match found for opening bracket', pos $$textref
622	unless $@;
623	return;
624	}
625
626	my $endpos = pos($$textref);
627	return ( $startpos, $codepos-$startpos,
628	$codepos, $endpos-$codepos,
629	$endpos, length($$textref)-$endpos,
630	);
631	}
632
633
634	my %mods = (
635	'none' => '[cgimsox]*',
636	'm' => '[cgimsox]*',
637	's' => '[cegimsox]*',
638	'tr' => '[cds]*',
639	'y' => '[cds]*',
640	'qq' => '',
641	'qx' => '',
642	'qw' => '',
643	'qr' => '[imsx]*',
644	'q' => '',
645	);
646
647	sub extract_quotelike (;$$)
648	{
649	my $textref = $_[0] ? \$_[0] : \$_;
650	my $wantarray = wantarray;
651	my $pre = defined $_[1] ? $_[1] : '\s*';
652
653	my @match = _match_quotelike($textref,$pre,1,0);
654	return _fail($wantarray, $textref) unless @match;
655	return _succeed($wantarray, $textref,
656	$match[2], $match[18]-$match[2], # MATCH
657	@match[18,19], # REMAINDER
658	@match[0,1], # PREFIX
659	@match[2..17], # THE BITS
660	@match[20,21], # ANY FILLET?
661	);
662	};
663
664	sub _match_quotelike($$$$) # ($textref, $prepat, $allow_raw_match)
665	{
666	my ($textref, $pre, $rawmatch, $qmark) = @_;
667
668	my ($textlen,$startpos,
669	$oppos,
670	$preld1pos,$ld1pos,$str1pos,$rd1pos,
671	$preld2pos,$ld2pos,$str2pos,$rd2pos,
672	$modpos) = ( length($$textref), pos($$textref) = pos($$textref) \|\| 0 );
673
674	unless ($$textref =~ m/\G($pre)/gc)
675	{
676	_failmsg qq{Did not find prefix /$pre/ at "} .
677	substr($$textref, pos($$textref), 20) .
678	q{..."},
679	pos $$textref;
680	return;
681	}
682	$oppos = pos($$textref);
683
684	my $initial = substr($$textref,$oppos,1);
685
686	if ($initial && $initial =~ m\|^[\"\'\`]\|
687	\|\| $rawmatch && $initial =~ m\|^/\|
688	\|\| $qmark && $initial =~ m\|^\?\|)
689	{
690	unless ($$textref =~ m/ \Q$initial\E [^\\$initial]* (\\.[^\\$initial]) \Q$initial\E /gcsx)
691	{
692	_failmsg qq{Did not find closing delimiter to match '$initial' at "} .
693	substr($$textref, $oppos, 20) .
694	q{..."},
695	pos $$textref;
696	pos $$textref = $startpos;
697	return;
698	}
699	$modpos= pos($$textref);
700	$rd1pos = $modpos-1;
701
702	if ($initial eq '/' \|\| $initial eq '?')
703	{
704	$$textref =~ m/\G$mods{none}/gc
705	}
706
707	my $endpos = pos($$textref);
708	return (
709	$startpos, $oppos-$startpos, # PREFIX
710	$oppos, 0, # NO OPERATOR
711	$oppos, 1, # LEFT DEL
712	$oppos+1, $rd1pos-$oppos-1, # STR/PAT
713	$rd1pos, 1, # RIGHT DEL
714	$modpos, 0, # NO 2ND LDEL
715	$modpos, 0, # NO 2ND STR
716	$modpos, 0, # NO 2ND RDEL
717	$modpos, $endpos-$modpos, # MODIFIERS
718	$endpos, $textlen-$endpos, # REMAINDER
719	);
720	}
721
722	unless ($$textref =~ m{\G(\b(?:m\|s\|qq\|qx\|qw\|q\|qr\|tr\|y)\b(?=\s*\S)\|<<)}gc)
723	{
724	_failmsg q{No quotelike operator found after prefix at "} .
725	substr($$textref, pos($$textref), 20) .
726	q{..."},
727	pos $$textref;
728	pos $$textref = $startpos;
729	return;
730	}
731
732	my $op = $1;
733	$preld1pos = pos($$textref);
734	if ($op eq '<<') {
735	$ld1pos = pos($$textref);
736	my $label;
737	if ($$textref =~ m{\G([A-Za-z_]\w*)}gc) {
738	$label = $1;
739	}
740	elsif ($$textref =~ m{ \G ' ([^'\\]* (?:\\.[^'\\])) '
741	\| \G " ([^"\\]* (?:\\.[^"\\])) "
742	\| \G ` ([^`\\]* (?:\\.[^`\\])) `
743	}gcsx) {
744	$label = $+;
745	}
746	else {
747	$label = "";
748	}
749	my $extrapos = pos($$textref);
750	$$textref =~ m{.*\n}gc;
751	$str1pos = pos($$textref)--;
752	unless ($$textref =~ m{.*?\n(?=\Q$label\E\n)}gc) {
753	_failmsg qq{Missing here doc terminator ('$label') after "} .
754	substr($$textref, $startpos, 20) .
755	q{..."},
756	pos $$textref;
757	pos $$textref = $startpos;
758	return;
759	}
760	$rd1pos = pos($$textref);
761	$$textref =~ m{\Q$label\E\n}gc;
762	$ld2pos = pos($$textref);
763	return (
764	$startpos, $oppos-$startpos, # PREFIX
765	$oppos, length($op), # OPERATOR
766	$ld1pos, $extrapos-$ld1pos, # LEFT DEL
767	$str1pos, $rd1pos-$str1pos, # STR/PAT
768	$rd1pos, $ld2pos-$rd1pos, # RIGHT DEL
769	$ld2pos, 0, # NO 2ND LDEL
770	$ld2pos, 0, # NO 2ND STR
771	$ld2pos, 0, # NO 2ND RDEL
772	$ld2pos, 0, # NO MODIFIERS
773	$ld2pos, $textlen-$ld2pos, # REMAINDER
774	$extrapos, $str1pos-$extrapos, # FILLETED BIT
775	);
776	}
777
778	$$textref =~ m/\G\s*/gc;
779	$ld1pos = pos($$textref);
780	$str1pos = $ld1pos+1;
781
782	unless ($$textref =~ m/\G(\S)/gc) # SHOULD USE LOOKAHEAD
783	{
784	_failmsg "No block delimiter found after quotelike $op",
785	pos $$textref;
786	pos $$textref = $startpos;
787	return;
788	}
789	pos($$textref) = $ld1pos; # HAVE TO DO THIS BECAUSE LOOKAHEAD BROKEN
790	my ($ldel1, $rdel1) = ("\Q$1","\Q$1");
791	if ($ldel1 =~ /[[(<{]/)
792	{
793	$rdel1 =~ tr/[({</])}>/;
794	defined(_match_bracketed($textref,"",$ldel1,"","",$rdel1))
795	\|\| do { pos $$textref = $startpos; return };
796	$ld2pos = pos($$textref);
797	$rd1pos = $ld2pos-1;
798	}
799	else
800	{
801	$$textref =~ /\G$ldel1[^\\$ldel1](\\.[^\\$ldel1])*$ldel1/gcs
802	\|\| do { pos $$textref = $startpos; return };
803	$ld2pos = $rd1pos = pos($$textref)-1;
804	}
805
806	my $second_arg = $op =~ /s\|tr\|y/ ? 1 : 0;
807	if ($second_arg)
808	{
809	my ($ldel2, $rdel2);
810	if ($ldel1 =~ /[[(<{]/)
811	{
812	unless ($$textref =~ /\G\s*(\S)/gc) # SHOULD USE LOOKAHEAD
813	{
814	_failmsg "Missing second block for quotelike $op",
815	pos $$textref;
816	pos $$textref = $startpos;
817	return;
818	}
819	$ldel2 = $rdel2 = "\Q$1";
820	$rdel2 =~ tr/[({</])}>/;
821	}
822	else
823	{
824	$ldel2 = $rdel2 = $ldel1;
825	}
826	$str2pos = $ld2pos+1;
827
828	if ($ldel2 =~ /[[(<{]/)
829	{
830	pos($$textref)--; # OVERCOME BROKEN LOOKAHEAD
831	defined(_match_bracketed($textref,"",$ldel2,"","",$rdel2))
832	\|\| do { pos $$textref = $startpos; return };
833	}
834	else
835	{
836	$$textref =~ /[^\\$ldel2](\\.[^\\$ldel2])*$ldel2/gcs
837	\|\| do { pos $$textref = $startpos; return };
838	}
839	$rd2pos = pos($$textref)-1;
840	}
841	else
842	{
843	$ld2pos = $str2pos = $rd2pos = $rd1pos;
844	}
845
846	$modpos = pos $$textref;
847
848	$$textref =~ m/\G($mods{$op})/gc;
849	my $endpos = pos $$textref;
850
851	return (
852	$startpos, $oppos-$startpos, # PREFIX
853	$oppos, length($op), # OPERATOR
854	$ld1pos, 1, # LEFT DEL
855	$str1pos, $rd1pos-$str1pos, # STR/PAT
856	$rd1pos, 1, # RIGHT DEL
857	$ld2pos, $second_arg, # 2ND LDEL (MAYBE)
858	$str2pos, $rd2pos-$str2pos, # 2ND STR (MAYBE)
859	$rd2pos, $second_arg, # 2ND RDEL (MAYBE)
860	$modpos, $endpos-$modpos, # MODIFIERS
861	$endpos, $textlen-$endpos, # REMAINDER
862	);
863	}
864
865	my $def_func =
866	[
867	sub { extract_variable($_[0], '') },
868	sub { extract_quotelike($_[0],'') },
869	sub { extract_codeblock($_[0],'{}','') },
870	];
871
872	sub extract_multiple (;$$$$) # ($text, $functions_ref, $max_fields, $ignoreunknown)
873	{
874	my $textref = defined($_[0]) ? \$_[0] : \$_;
875	my $posbug = pos;
876	my ($lastpos, $firstpos);
877	my @fields = ();
878
879	#for ($$textref)
880	{
881	my @func = defined $_[1] ? @{$_[1]} : @{$def_func};
882	my $max = defined $_[2] && $_[2]>0 ? $_[2] : 1_000_000_000;
883	my $igunk = $_[3];
884
885	pos $$textref \|\|= 0;
886
887	unless (wantarray)
888	{
889	use Carp;
890	carp "extract_multiple reset maximal count to 1 in scalar context"
891	if $^W && defined($_[2]) && $max > 1;
892	$max = 1
893	}
894
895	my $unkpos;
896	my $func;
897	my $class;
898
899	my @class;
900	foreach $func ( @func )
901	{
902	if (ref($func) eq 'HASH')
903	{
904	push @class, (keys %$func)[0];
905	$func = (values %$func)[0];
906	}
907	else
908	{
909	push @class, undef;
910	}
911	}
912
913	FIELD: while (pos($$textref) < length($$textref))
914	{
915	my ($field, $rem);
916	my @bits;
917	foreach my $i ( 0..$#func )
918	{
919	my $pref;
920	$func = $func[$i];
921	$class = $class[$i];
922	$lastpos = pos $$textref;
923	if (ref($func) eq 'CODE')
924	{ ($field,$rem,$pref) = @bits = $func->($$textref) }
925	elsif (ref($func) eq 'Text::Balanced::Extractor')
926	{ @bits = $field = $func->extract($$textref) }
927	elsif( $$textref =~ m/\G$func/gc )
928	{ @bits = $field = defined($1)
929	? $1
930	: substr($$textref, $-[0], $+[0] - $-[0])
931	}
932	$pref \|\|= "";
933	if (defined($field) && length($field))
934	{
935	if (!$igunk) {
936	$unkpos = $lastpos
937	if length($pref) && !defined($unkpos);
938	if (defined $unkpos)
939	{
940	push @fields, substr($$textref, $unkpos, $lastpos-$unkpos).$pref;
941	$firstpos = $unkpos unless defined $firstpos;
942	undef $unkpos;
943	last FIELD if @fields == $max;
944	}
945	}
946	push @fields, $class
947	? bless (\$field, $class)
948	: $field;
949	$firstpos = $lastpos unless defined $firstpos;
950	$lastpos = pos $$textref;
951	last FIELD if @fields == $max;
952	next FIELD;
953	}
954	}
955	if ($$textref =~ /\G(.)/gcs)
956	{
957	$unkpos = pos($$textref)-1
958	unless $igunk \|\| defined $unkpos;
959	}
960	}
961
962	if (defined $unkpos)
963	{
964	push @fields, substr($$textref, $unkpos);
965	$firstpos = $unkpos unless defined $firstpos;
966	$lastpos = length $$textref;
967	}
968	last;
969	}
970
971	pos $$textref = $lastpos;
972	return @fields if wantarray;
973
974	$firstpos \|\|= 0;
975	eval { substr($$textref,$firstpos,$lastpos-$firstpos)="";
976	pos $$textref = $firstpos };
977	return $fields[0];
978	}
979
980
981	sub gen_extract_tagged # ($opentag, $closetag, $pre, \%options)
982	{
983	my $ldel = $_[0];
984	my $rdel = $_[1];
985	my $pre = defined $_[2] ? $_[2] : '\s*';
986	my %options = defined $_[3] ? %{$_[3]} : ();
987	my $omode = defined $options{fail} ? $options{fail} : '';
988	my $bad = ref($options{reject}) eq 'ARRAY' ? join('\|', @{$options{reject}})
989	: defined($options{reject}) ? $options{reject}
990	: ''
991	;
992	my $ignore = ref($options{ignore}) eq 'ARRAY' ? join('\|', @{$options{ignore}})
993	: defined($options{ignore}) ? $options{ignore}
994	: ''
995	;
996
997	if (!defined $ldel) { $ldel = '<\w+(?:' . gen_delimited_pat(q{'"}) . '\|[^>])*>'; }
998
999	my $posbug = pos;
1000	for ($ldel, $pre, $bad, $ignore) { $_ = qr/$_/ if $_ }
1001	pos = $posbug;
1002
1003	my $closure = sub
1004	{
1005	my $textref = defined $_[0] ? \$_[0] : \$_;
1006	my @match = Text::Balanced::_match_tagged($textref, $pre, $ldel, $rdel, $omode, $bad, $ignore);
1007
1008	return _fail(wantarray, $textref) unless @match;
1009	return _succeed wantarray, $textref,
1010	$match[2], $match[3]+$match[5]+$match[7], # MATCH
1011	@match[8..9,0..1,2..7]; # REM, PRE, BITS
1012	};
1013
1014	bless $closure, 'Text::Balanced::Extractor';
1015	}
1016
1017	package Text::Balanced::Extractor;
1018
1019	sub extract($$) # ($self, $text)
1020	{
1021	&{$_[0]}($_[1]);
1022	}
1023
1024	package Text::Balanced::ErrorMsg;
1025
1026	use overload '""' => sub { "$_[0]->{error}, detected at offset $_[0]->{pos}" };
1027
1028	1;
1029
1030	__END__
1031
1032	=head1 NAME
1033
1034	Text::Balanced - Extract delimited text sequences from strings.
1035
1036
1037	=head1 SYNOPSIS
1038
1039	use Text::Balanced qw (
1040	extract_delimited
1041	extract_bracketed
1042	extract_quotelike
1043	extract_codeblock
1044	extract_variable
1045	extract_tagged
1046	extract_multiple
1047
1048	gen_delimited_pat
1049	gen_extract_tagged
1050	);
1051
1052	# Extract the initial substring of $text that is delimited by
1053	# two (unescaped) instances of the first character in $delim.
1054
1055	($extracted, $remainder) = extract_delimited($text,$delim);
1056
1057
1058	# Extract the initial substring of $text that is bracketed
1059	# with a delimiter(s) specified by $delim (where the string
1060	# in $delim contains one or more of '(){}[]<>').
1061
1062	($extracted, $remainder) = extract_bracketed($text,$delim);
1063
1064
1065	# Extract the initial substring of $text that is bounded by
1066	# an XML tag.
1067
1068	($extracted, $remainder) = extract_tagged($text);
1069
1070
1071	# Extract the initial substring of $text that is bounded by
1072	# a C<BEGIN>...C<END> pair. Don't allow nested C<BEGIN> tags
1073
1074	($extracted, $remainder) =
1075	extract_tagged($text,"BEGIN","END",undef,{bad=>["BEGIN"]});
1076
1077
1078	# Extract the initial substring of $text that represents a
1079	# Perl "quote or quote-like operation"
1080
1081	($extracted, $remainder) = extract_quotelike($text);
1082
1083
1084	# Extract the initial substring of $text that represents a block
1085	# of Perl code, bracketed by any of character(s) specified by $delim
1086	# (where the string $delim contains one or more of '(){}[]<>').
1087
1088	($extracted, $remainder) = extract_codeblock($text,$delim);
1089
1090
1091	# Extract the initial substrings of $text that would be extracted by
1092	# one or more sequential applications of the specified functions
1093	# or regular expressions
1094
1095	@extracted = extract_multiple($text,
1096	[ \&extract_bracketed,
1097	\&extract_quotelike,
1098	\&some_other_extractor_sub,
1099	qr/[xyz]*/,
1100	'literal',
1101	]);
1102
1103	# Create a string representing an optimized pattern (a la Friedl)
1104	# that matches a substring delimited by any of the specified characters
1105	# (in this case: any type of quote or a slash)
1106
1107	$patstring = gen_delimited_pat(q{'"`/});
1108
1109
1110	# Generate a reference to an anonymous sub that is just like extract_tagged
1111	# but pre-compiled and optimized for a specific pair of tags, and consequently
1112	# much faster (i.e. 3 times faster). It uses qr// for better performance on
1113	# repeated calls, so it only works under Perl 5.005 or later.
1114
1115	$extract_head = gen_extract_tagged('<HEAD>','</HEAD>');
1116
1117	($extracted, $remainder) = $extract_head->($text);
1118
1119
1120	=head1 DESCRIPTION
1121
1122	The various C<extract_...> subroutines may be used to
1123	extract a delimited substring, possibly after skipping a
1124	specified prefix string. By default, that prefix is
1125	optional whitespace (C</\s*/>), but you can change it to whatever
1126	you wish (see below).
1127
1128	The substring to be extracted must appear at the
1129	current C<pos> location of the string's variable
1130	(or at index zero, if no C<pos> position is defined).
1131	In other words, the C<extract_...> subroutines I<don't>
1132	extract the first occurrence of a substring anywhere
1133	in a string (like an unanchored regex would). Rather,
1134	they extract an occurrence of the substring appearing
1135	immediately at the current matching position in the
1136	string (like a C<\G>-anchored regex would).
1137
1138
1139
1140	=head2 General behaviour in list contexts
1141
1142	In a list context, all the subroutines return a list, the first three
1143	elements of which are always:
1144
1145	=over 4
1146
1147	=item [0]
1148
1149	The extracted string, including the specified delimiters.
1150	If the extraction fails C<undef> is returned.
1151
1152	=item [1]
1153
1154	The remainder of the input string (i.e. the characters after the
1155	extracted string). On failure, the entire string is returned.
1156
1157	=item [2]
1158
1159	The skipped prefix (i.e. the characters before the extracted string).
1160	On failure, C<undef> is returned.
1161
1162	=back
1163
1164	Note that in a list context, the contents of the original input text (the first
1165	argument) are not modified in any way.
1166
1167	However, if the input text was passed in a variable, that variable's
1168	C<pos> value is updated to point at the first character after the
1169	extracted text. That means that in a list context the various
1170	subroutines can be used much like regular expressions. For example:
1171
1172	while ( $next = (extract_quotelike($text))[0] )
1173	{
1174	# process next quote-like (in $next)
1175	}
1176
1177
1178	=head2 General behaviour in scalar and void contexts
1179
1180	In a scalar context, the extracted string is returned, having first been
1181	removed from the input text. Thus, the following code also processes
1182	each quote-like operation, but actually removes them from $text:
1183
1184	while ( $next = extract_quotelike($text) )
1185	{
1186	# process next quote-like (in $next)
1187	}
1188
1189	Note that if the input text is a read-only string (i.e. a literal),
1190	no attempt is made to remove the extracted text.
1191
1192	In a void context the behaviour of the extraction subroutines is
1193	exactly the same as in a scalar context, except (of course) that the
1194	extracted substring is not returned.
1195
1196	=head2 A note about prefixes
1197
1198	Prefix patterns are matched without any trailing modifiers (C</gimsox> etc.)
1199	This can bite you if you're expecting a prefix specification like
1200	'.*?(?=<H1>)' to skip everything up to the first <H1> tag. Such a prefix
1201	pattern will only succeed if the <H1> tag is on the current line, since
1202	. normally doesn't match newlines.
1203
1204	To overcome this limitation, you need to turn on /s matching within
1205	the prefix pattern, using the C<(?s)> directive: '(?s).*?(?=<H1>)'
1206
1207
1208	=head2 C<extract_delimited>
1209
1210	The C<extract_delimited> function formalizes the common idiom
1211	of extracting a single-character-delimited substring from the start of
1212	a string. For example, to extract a single-quote delimited string, the
1213	following code is typically used:
1214
1215	($remainder = $text) =~ s/\A('(\\.\|[^'])*')//s;
1216	$extracted = $1;
1217
1218	but with C<extract_delimited> it can be simplified to:
1219
1220	($extracted,$remainder) = extract_delimited($text, "'");
1221
1222	C<extract_delimited> takes up to four scalars (the input text, the
1223	delimiters, a prefix pattern to be skipped, and any escape characters)
1224	and extracts the initial substring of the text that
1225	is appropriately delimited. If the delimiter string has multiple
1226	characters, the first one encountered in the text is taken to delimit
1227	the substring.
1228	The third argument specifies a prefix pattern that is to be skipped
1229	(but must be present!) before the substring is extracted.
1230	The final argument specifies the escape character to be used for each
1231	delimiter.
1232
1233	All arguments are optional. If the escape characters are not specified,
1234	every delimiter is escaped with a backslash (C<\>).
1235	If the prefix is not specified, the
1236	pattern C<'\s*'> - optional whitespace - is used. If the delimiter set
1237	is also not specified, the set C</["'`]/> is used. If the text to be processed
1238	is not specified either, C<$_> is used.
1239
1240	In list context, C<extract_delimited> returns a array of three
1241	elements, the extracted substring (I<including the surrounding
1242	delimiters>), the remainder of the text, and the skipped prefix (if
1243	any). If a suitable delimited substring is not found, the first
1244	element of the array is the empty string, the second is the complete
1245	original text, and the prefix returned in the third element is an
1246	empty string.
1247
1248	In a scalar context, just the extracted substring is returned. In
1249	a void context, the extracted substring (and any prefix) are simply
1250	removed from the beginning of the first argument.
1251
1252	Examples:
1253
1254	# Remove a single-quoted substring from the very beginning of $text:
1255
1256	$substring = extract_delimited($text, "'", '');
1257
1258	# Remove a single-quoted Pascalish substring (i.e. one in which
1259	# doubling the quote character escapes it) from the very
1260	# beginning of $text:
1261
1262	$substring = extract_delimited($text, "'", '', "'");
1263
1264	# Extract a single- or double- quoted substring from the
1265	# beginning of $text, optionally after some whitespace
1266	# (note the list context to protect $text from modification):
1267
1268	($substring) = extract_delimited $text, q{"'};
1269
1270
1271	# Delete the substring delimited by the first '/' in $text:
1272
1273	$text = join '', (extract_delimited($text,'/','[^/]*')[2,1];
1274
1275	Note that this last example is I<not> the same as deleting the first
1276	quote-like pattern. For instance, if C<$text> contained the string:
1277
1278	"if ('./cmd' =~ m/$UNIXCMD/s) { $cmd = $1; }"
1279
1280	then after the deletion it would contain:
1281
1282	"if ('.$UNIXCMD/s) { $cmd = $1; }"
1283
1284	not:
1285
1286	"if ('./cmd' =~ ms) { $cmd = $1; }"
1287
1288
1289	See L<"extract_quotelike"> for a (partial) solution to this problem.
1290
1291
1292	=head2 C<extract_bracketed>
1293
1294	Like C<"extract_delimited">, the C<extract_bracketed> function takes
1295	up to three optional scalar arguments: a string to extract from, a delimiter
1296	specifier, and a prefix pattern. As before, a missing prefix defaults to
1297	optional whitespace and a missing text defaults to C<$_>. However, a missing
1298	delimiter specifier defaults to C<'{}()[]E<lt>E<gt>'> (see below).
1299
1300	C<extract_bracketed> extracts a balanced-bracket-delimited
1301	substring (using any one (or more) of the user-specified delimiter
1302	brackets: '(..)', '{..}', '[..]', or '<..>'). Optionally it will also
1303	respect quoted unbalanced brackets (see below).
1304
1305	A "delimiter bracket" is a bracket in list of delimiters passed as
1306	C<extract_bracketed>'s second argument. Delimiter brackets are
1307	specified by giving either the left or right (or both!) versions
1308	of the required bracket(s). Note that the order in which
1309	two or more delimiter brackets are specified is not significant.
1310
1311	A "balanced-bracket-delimited substring" is a substring bounded by
1312	matched brackets, such that any other (left or right) delimiter
1313	bracket I<within> the substring is also matched by an opposite
1314	(right or left) delimiter bracket I<at the same level of nesting>. Any
1315	type of bracket not in the delimiter list is treated as an ordinary
1316	character.
1317
1318	In other words, each type of bracket specified as a delimiter must be
1319	balanced and correctly nested within the substring, and any other kind of
1320	("non-delimiter") bracket in the substring is ignored.
1321
1322	For example, given the string:
1323
1324	$text = "{ an '[irregularly :-(] {} parenthesized >:-)' string }";
1325
1326	then a call to C<extract_bracketed> in a list context:
1327
1328	@result = extract_bracketed( $text, '{}' );
1329
1330	would return:
1331
1332	( "{ an '[irregularly :-(] {} parenthesized >:-)' string }" , "" , "" )
1333
1334	since both sets of C<'{..}'> brackets are properly nested and evenly balanced.
1335	(In a scalar context just the first element of the array would be returned. In
1336	a void context, C<$text> would be replaced by an empty string.)
1337
1338	Likewise the call in:
1339
1340	@result = extract_bracketed( $text, '{[' );
1341
1342	would return the same result, since all sets of both types of specified
1343	delimiter brackets are correctly nested and balanced.
1344
1345	However, the call in:
1346
1347	@result = extract_bracketed( $text, '{([<' );
1348
1349	would fail, returning:
1350
1351	( undef , "{ an '[irregularly :-(] {} parenthesized >:-)' string }" );
1352
1353	because the embedded pairs of C<'(..)'>s and C<'[..]'>s are "cross-nested" and
1354	the embedded C<'E<gt>'> is unbalanced. (In a scalar context, this call would
1355	return an empty string. In a void context, C<$text> would be unchanged.)
1356
1357	Note that the embedded single-quotes in the string don't help in this
1358	case, since they have not been specified as acceptable delimiters and are
1359	therefore treated as non-delimiter characters (and ignored).
1360
1361	However, if a particular species of quote character is included in the
1362	delimiter specification, then that type of quote will be correctly handled.
1363	for example, if C<$text> is:
1364
1365	$text = '<A HREF=">>>>">link</A>';
1366
1367	then
1368
1369	@result = extract_bracketed( $text, '<">' );
1370
1371	returns:
1372
1373	( '<A HREF=">>>>">', 'link</A>', "" )
1374
1375	as expected. Without the specification of C<"> as an embedded quoter:
1376
1377	@result = extract_bracketed( $text, '<>' );
1378
1379	the result would be:
1380
1381	( '<A HREF=">', '>>>">link</A>', "" )
1382
1383	In addition to the quote delimiters C<'>, C<">, and C<`>, full Perl quote-like
1384	quoting (i.e. q{string}, qq{string}, etc) can be specified by including the
1385	letter 'q' as a delimiter. Hence:
1386
1387	@result = extract_bracketed( $text, '<q>' );
1388
1389	would correctly match something like this:
1390
1391	$text = '<leftop: conj /and/ conj>';
1392
1393	See also: C<"extract_quotelike"> and C<"extract_codeblock">.
1394
1395
1396	=head2 C<extract_variable>
1397
1398	C<extract_variable> extracts any valid Perl variable or
1399	variable-involved expression, including scalars, arrays, hashes, array
1400	accesses, hash look-ups, method calls through objects, subroutine calls
1401	through subroutine references, etc.
1402
1403	The subroutine takes up to two optional arguments:
1404
1405	=over 4
1406
1407	=item 1.
1408
1409	A string to be processed (C<$_> if the string is omitted or C<undef>)
1410
1411	=item 2.
1412
1413	A string specifying a pattern to be matched as a prefix (which is to be
1414	skipped). If omitted, optional whitespace is skipped.
1415
1416	=back
1417
1418	On success in a list context, an array of 3 elements is returned. The
1419	elements are:
1420
1421	=over 4
1422
1423	=item [0]
1424
1425	the extracted variable, or variablish expression
1426
1427	=item [1]
1428
1429	the remainder of the input text,
1430
1431	=item [2]
1432
1433	the prefix substring (if any),
1434
1435	=back
1436
1437	On failure, all of these values (except the remaining text) are C<undef>.
1438
1439	In a scalar context, C<extract_variable> returns just the complete
1440	substring that matched a variablish expression. C<undef> is returned on
1441	failure. In addition, the original input text has the returned substring
1442	(and any prefix) removed from it.
1443
1444	In a void context, the input text just has the matched substring (and
1445	any specified prefix) removed.
1446
1447
1448	=head2 C<extract_tagged>
1449
1450	C<extract_tagged> extracts and segments text between (balanced)
1451	specified tags.
1452
1453	The subroutine takes up to five optional arguments:
1454
1455	=over 4
1456
1457	=item 1.
1458
1459	A string to be processed (C<$_> if the string is omitted or C<undef>)
1460
1461	=item 2.
1462
1463	A string specifying a pattern to be matched as the opening tag.
1464	If the pattern string is omitted (or C<undef>) then a pattern
1465	that matches any standard XML tag is used.
1466
1467	=item 3.
1468
1469	A string specifying a pattern to be matched at the closing tag.
1470	If the pattern string is omitted (or C<undef>) then the closing
1471	tag is constructed by inserting a C</> after any leading bracket
1472	characters in the actual opening tag that was matched (I<not> the pattern
1473	that matched the tag). For example, if the opening tag pattern
1474	is specified as C<'{{\w+}}'> and actually matched the opening tag
1475	C<"{{DATA}}">, then the constructed closing tag would be C<"{{/DATA}}">.
1476
1477	=item 4.
1478
1479	A string specifying a pattern to be matched as a prefix (which is to be
1480	skipped). If omitted, optional whitespace is skipped.
1481
1482	=item 5.
1483
1484	A hash reference containing various parsing options (see below)
1485
1486	=back
1487
1488	The various options that can be specified are:
1489
1490	=over 4
1491
1492	=item C<reject =E<gt> $listref>
1493
1494	The list reference contains one or more strings specifying patterns
1495	that must I<not> appear within the tagged text.
1496
1497	For example, to extract
1498	an HTML link (which should not contain nested links) use:
1499
1500	extract_tagged($text, '<A>', '</A>', undef, {reject => ['<A>']} );
1501
1502	=item C<ignore =E<gt> $listref>
1503
1504	The list reference contains one or more strings specifying patterns
1505	that are I<not> be be treated as nested tags within the tagged text
1506	(even if they would match the start tag pattern).
1507
1508	For example, to extract an arbitrary XML tag, but ignore "empty" elements:
1509
1510	extract_tagged($text, undef, undef, undef, {ignore => ['<[^>]*/>']} );
1511
1512	(also see L<"gen_delimited_pat"> below).
1513
1514
1515	=item C<fail =E<gt> $str>
1516
1517	The C<fail> option indicates the action to be taken if a matching end
1518	tag is not encountered (i.e. before the end of the string or some
1519	C<reject> pattern matches). By default, a failure to match a closing
1520	tag causes C<extract_tagged> to immediately fail.
1521
1522	However, if the string value associated with <reject> is "MAX", then
1523	C<extract_tagged> returns the complete text up to the point of failure.
1524	If the string is "PARA", C<extract_tagged> returns only the first paragraph
1525	after the tag (up to the first line that is either empty or contains
1526	only whitespace characters).
1527	If the string is "", the the default behaviour (i.e. failure) is reinstated.
1528
1529	For example, suppose the start tag "/para" introduces a paragraph, which then
1530	continues until the next "/endpara" tag or until another "/para" tag is
1531	encountered:
1532
1533	$text = "/para line 1\n\nline 3\n/para line 4";
1534
1535	extract_tagged($text, '/para', '/endpara', undef,
1536	{reject => '/para', fail => MAX );
1537
1538	# EXTRACTED: "/para line 1\n\nline 3\n"
1539
1540	Suppose instead, that if no matching "/endpara" tag is found, the "/para"
1541	tag refers only to the immediately following paragraph:
1542
1543	$text = "/para line 1\n\nline 3\n/para line 4";
1544
1545	extract_tagged($text, '/para', '/endpara', undef,
1546	{reject => '/para', fail => MAX );
1547
1548	# EXTRACTED: "/para line 1\n"
1549
1550	Note that the specified C<fail> behaviour applies to nested tags as well.
1551
1552	=back
1553
1554	On success in a list context, an array of 6 elements is returned. The elements are:
1555
1556	=over 4
1557
1558	=item [0]
1559
1560	the extracted tagged substring (including the outermost tags),
1561
1562	=item [1]
1563
1564	the remainder of the input text,
1565
1566	=item [2]
1567
1568	the prefix substring (if any),
1569
1570	=item [3]
1571
1572	the opening tag
1573
1574	=item [4]
1575
1576	the text between the opening and closing tags
1577
1578	=item [5]
1579
1580	the closing tag (or "" if no closing tag was found)
1581
1582	=back
1583
1584	On failure, all of these values (except the remaining text) are C<undef>.
1585
1586	In a scalar context, C<extract_tagged> returns just the complete
1587	substring that matched a tagged text (including the start and end
1588	tags). C<undef> is returned on failure. In addition, the original input
1589	text has the returned substring (and any prefix) removed from it.
1590
1591	In a void context, the input text just has the matched substring (and
1592	any specified prefix) removed.
1593
1594
1595	=head2 C<gen_extract_tagged>
1596
1597	(Note: This subroutine is only available under Perl5.005)
1598
1599	C<gen_extract_tagged> generates a new anonymous subroutine which
1600	extracts text between (balanced) specified tags. In other words,
1601	it generates a function identical in function to C<extract_tagged>.
1602
1603	The difference between C<extract_tagged> and the anonymous
1604	subroutines generated by
1605	C<gen_extract_tagged>, is that those generated subroutines:
1606
1607	=over 4
1608
1609	=item *
1610
1611	do not have to reparse tag specification or parsing options every time
1612	they are called (whereas C<extract_tagged> has to effectively rebuild
1613	its tag parser on every call);
1614
1615	=item *
1616
1617	make use of the new qr// construct to pre-compile the regexes they use
1618	(whereas C<extract_tagged> uses standard string variable interpolation
1619	to create tag-matching patterns).
1620
1621	=back
1622
1623	The subroutine takes up to four optional arguments (the same set as
1624	C<extract_tagged> except for the string to be processed). It returns
1625	a reference to a subroutine which in turn takes a single argument (the text to
1626	be extracted from).
1627
1628	In other words, the implementation of C<extract_tagged> is exactly
1629	equivalent to:
1630
1631	sub extract_tagged
1632	{
1633	my $text = shift;
1634	$extractor = gen_extract_tagged(@_);
1635	return $extractor->($text);
1636	}
1637
1638	(although C<extract_tagged> is not currently implemented that way, in order
1639	to preserve pre-5.005 compatibility).
1640
1641	Using C<gen_extract_tagged> to create extraction functions for specific tags
1642	is a good idea if those functions are going to be called more than once, since
1643	their performance is typically twice as good as the more general-purpose
1644	C<extract_tagged>.
1645
1646
1647	=head2 C<extract_quotelike>
1648
1649	C<extract_quotelike> attempts to recognize, extract, and segment any
1650	one of the various Perl quotes and quotelike operators (see
1651	L<perlop(3)>) Nested backslashed delimiters, embedded balanced bracket
1652	delimiters (for the quotelike operators), and trailing modifiers are
1653	all caught. For example, in:
1654
1655	extract_quotelike 'q # an octothorpe: \# (not the end of the q!) #'
1656
1657	extract_quotelike ' "You said, \"Use sed\"." '
1658
1659	extract_quotelike ' s{([A-Z]{1,8}\.[A-Z]{3})} /\L$1\E/; '
1660
1661	extract_quotelike ' tr/\\\/\\\\/\\\//ds; '
1662
1663	the full Perl quotelike operations are all extracted correctly.
1664
1665	Note too that, when using the /x modifier on a regex, any comment
1666	containing the current pattern delimiter will cause the regex to be
1667	immediately terminated. In other words:
1668
1669	'm /
1670	(?i) # CASE INSENSITIVE
1671	[a-z_] # LEADING ALPHABETIC/UNDERSCORE
1672	[a-z0-9]* # FOLLOWED BY ANY NUMBER OF ALPHANUMERICS
1673	/x'
1674
1675	will be extracted as if it were:
1676
1677	'm /
1678	(?i) # CASE INSENSITIVE
1679	[a-z_] # LEADING ALPHABETIC/'
1680
1681	This behaviour is identical to that of the actual compiler.
1682
1683	C<extract_quotelike> takes two arguments: the text to be processed and
1684	a prefix to be matched at the very beginning of the text. If no prefix
1685	is specified, optional whitespace is the default. If no text is given,
1686	C<$_> is used.
1687
1688	In a list context, an array of 11 elements is returned. The elements are:
1689
1690	=over 4
1691
1692	=item [0]
1693
1694	the extracted quotelike substring (including trailing modifiers),
1695
1696	=item [1]
1697
1698	the remainder of the input text,
1699
1700	=item [2]
1701
1702	the prefix substring (if any),
1703
1704	=item [3]
1705
1706	the name of the quotelike operator (if any),
1707
1708	=item [4]
1709
1710	the left delimiter of the first block of the operation,
1711
1712	=item [5]
1713
1714	the text of the first block of the operation
1715	(that is, the contents of
1716	a quote, the regex of a match or substitution or the target list of a
1717	translation),
1718
1719	=item [6]
1720
1721	the right delimiter of the first block of the operation,
1722
1723	=item [7]
1724
1725	the left delimiter of the second block of the operation
1726	(that is, if it is a C<s>, C<tr>, or C<y>),
1727
1728	=item [8]
1729
1730	the text of the second block of the operation
1731	(that is, the replacement of a substitution or the translation list
1732	of a translation),
1733
1734	=item [9]
1735
1736	the right delimiter of the second block of the operation (if any),
1737
1738	=item [10]
1739
1740	the trailing modifiers on the operation (if any).
1741
1742	=back
1743
1744	For each of the fields marked "(if any)" the default value on success is
1745	an empty string.
1746	On failure, all of these values (except the remaining text) are C<undef>.
1747
1748
1749	In a scalar context, C<extract_quotelike> returns just the complete substring
1750	that matched a quotelike operation (or C<undef> on failure). In a scalar or
1751	void context, the input text has the same substring (and any specified
1752	prefix) removed.
1753
1754	Examples:
1755
1756	# Remove the first quotelike literal that appears in text
1757
1758	$quotelike = extract_quotelike($text,'.*?');
1759
1760	# Replace one or more leading whitespace-separated quotelike
1761	# literals in $_ with "<QLL>"
1762
1763	do { $_ = join '<QLL>', (extract_quotelike)[2,1] } until $@;
1764
1765
1766	# Isolate the search pattern in a quotelike operation from $text
1767
1768	($op,$pat) = (extract_quotelike $text)[3,5];
1769	if ($op =~ /[ms]/)
1770	{
1771	print "search pattern: $pat\n";
1772	}
1773	else
1774	{
1775	print "$op is not a pattern matching operation\n";
1776	}
1777
1778
1779	=head2 C<extract_quotelike> and "here documents"
1780
1781	C<extract_quotelike> can successfully extract "here documents" from an input
1782	string, but with an important caveat in list contexts.
1783
1784	Unlike other types of quote-like literals, a here document is rarely
1785	a contiguous substring. For example, a typical piece of code using
1786	here document might look like this:
1787
1788	<<'EOMSG' \|\| die;
1789	This is the message.
1790	EOMSG
1791	exit;
1792
1793	Given this as an input string in a scalar context, C<extract_quotelike>
1794	would correctly return the string "<<'EOMSG'\nThis is the message.\nEOMSG",
1795	leaving the string " \|\| die;\nexit;" in the original variable. In other words,
1796	the two separate pieces of the here document are successfully extracted and
1797	concatenated.
1798
1799	In a list context, C<extract_quotelike> would return the list
1800
1801	=over 4
1802
1803	=item [0]
1804
1805	"<<'EOMSG'\nThis is the message.\nEOMSG\n" (i.e. the full extracted here document,
1806	including fore and aft delimiters),
1807
1808	=item [1]
1809
1810	" \|\| die;\nexit;" (i.e. the remainder of the input text, concatenated),
1811
1812	=item [2]
1813
1814	"" (i.e. the prefix substring -- trivial in this case),
1815
1816	=item [3]
1817
1818	"<<" (i.e. the "name" of the quotelike operator)
1819
1820	=item [4]
1821
1822	"'EOMSG'" (i.e. the left delimiter of the here document, including any quotes),
1823
1824	=item [5]
1825
1826	"This is the message.\n" (i.e. the text of the here document),
1827
1828	=item [6]
1829
1830	"EOMSG" (i.e. the right delimiter of the here document),
1831
1832	=item [7..10]
1833
1834	"" (a here document has no second left delimiter, second text, second right
1835	delimiter, or trailing modifiers).
1836
1837	=back
1838
1839	However, the matching position of the input variable would be set to
1840	"exit;" (i.e. I<after> the closing delimiter of the here document),
1841	which would cause the earlier " \|\| die;\nexit;" to be skipped in any
1842	sequence of code fragment extractions.
1843
1844	To avoid this problem, when it encounters a here document whilst
1845	extracting from a modifiable string, C<extract_quotelike> silently
1846	rearranges the string to an equivalent piece of Perl:
1847
1848	<<'EOMSG'
1849	This is the message.
1850	EOMSG
1851	\|\| die;
1852	exit;
1853
1854	in which the here document I<is> contiguous. It still leaves the
1855	matching position after the here document, but now the rest of the line
1856	on which the here document starts is not skipped.
1857
1858	To prevent <extract_quotelike> from mucking about with the input in this way
1859	(this is the only case where a list-context C<extract_quotelike> does so),
1860	you can pass the input variable as an interpolated literal:
1861
1862	$quotelike = extract_quotelike("$var");
1863
1864
1865	=head2 C<extract_codeblock>
1866
1867	C<extract_codeblock> attempts to recognize and extract a balanced
1868	bracket delimited substring that may contain unbalanced brackets
1869	inside Perl quotes or quotelike operations. That is, C<extract_codeblock>
1870	is like a combination of C<"extract_bracketed"> and
1871	C<"extract_quotelike">.
1872
1873	C<extract_codeblock> takes the same initial three parameters as C<extract_bracketed>:
1874	a text to process, a set of delimiter brackets to look for, and a prefix to
1875	match first. It also takes an optional fourth parameter, which allows the
1876	outermost delimiter brackets to be specified separately (see below).
1877
1878	Omitting the first argument (input text) means process C<$_> instead.
1879	Omitting the second argument (delimiter brackets) indicates that only C<'{'> is to be used.
1880	Omitting the third argument (prefix argument) implies optional whitespace at the start.
1881	Omitting the fourth argument (outermost delimiter brackets) indicates that the
1882	value of the second argument is to be used for the outermost delimiters.
1883
1884	Once the prefix an dthe outermost opening delimiter bracket have been
1885	recognized, code blocks are extracted by stepping through the input text and
1886	trying the following alternatives in sequence:
1887
1888	=over 4
1889
1890	=item 1.
1891
1892	Try and match a closing delimiter bracket. If the bracket was the same
1893	species as the last opening bracket, return the substring to that
1894	point. If the bracket was mismatched, return an error.
1895
1896	=item 2.
1897
1898	Try to match a quote or quotelike operator. If found, call
1899	C<extract_quotelike> to eat it. If C<extract_quotelike> fails, return
1900	the error it returned. Otherwise go back to step 1.
1901
1902	=item 3.
1903
1904	Try to match an opening delimiter bracket. If found, call
1905	C<extract_codeblock> recursively to eat the embedded block. If the
1906	recursive call fails, return an error. Otherwise, go back to step 1.
1907
1908	=item 4.
1909
1910	Unconditionally match a bareword or any other single character, and
1911	then go back to step 1.
1912
1913	=back
1914
1915
1916	Examples:
1917
1918	# Find a while loop in the text
1919
1920	if ($text =~ s/.?while\s\{/{/)
1921	{
1922	$loop = "while " . extract_codeblock($text);
1923	}
1924
1925	# Remove the first round-bracketed list (which may include
1926	# round- or curly-bracketed code blocks or quotelike operators)
1927
1928	extract_codeblock $text, "(){}", '[^(]*';
1929
1930
1931	The ability to specify a different outermost delimiter bracket is useful
1932	in some circumstances. For example, in the Parse::RecDescent module,
1933	parser actions which are to be performed only on a successful parse
1934	are specified using a C<E<lt>defer:...E<gt>> directive. For example:
1935
1936	sentence: subject verb object
1937	<defer: {$::theVerb = $item{verb}} >
1938
1939	Parse::RecDescent uses C<extract_codeblock($text, '{}E<lt>E<gt>')> to extract the code
1940	within the C<E<lt>defer:...E<gt>> directive, but there's a problem.
1941
1942	A deferred action like this:
1943
1944	<defer: {if ($count>10) {$count--}} >
1945
1946	will be incorrectly parsed as:
1947
1948	<defer: {if ($count>
1949
1950	because the "less than" operator is interpreted as a closing delimiter.
1951
1952	But, by extracting the directive using
1953	S<C<extract_codeblock($text, '{}', undef, 'E<lt>E<gt>')>>
1954	the '>' character is only treated as a delimited at the outermost
1955	level of the code block, so the directive is parsed correctly.
1956
1957	=head2 C<extract_multiple>
1958
1959	The C<extract_multiple> subroutine takes a string to be processed and a
1960	list of extractors (subroutines or regular expressions) to apply to that string.
1961
1962	In an array context C<extract_multiple> returns an array of substrings
1963	of the original string, as extracted by the specified extractors.
1964	In a scalar context, C<extract_multiple> returns the first
1965	substring successfully extracted from the original string. In both
1966	scalar and void contexts the original string has the first successfully
1967	extracted substring removed from it. In all contexts
1968	C<extract_multiple> starts at the current C<pos> of the string, and
1969	sets that C<pos> appropriately after it matches.
1970
1971	Hence, the aim of of a call to C<extract_multiple> in a list context
1972	is to split the processed string into as many non-overlapping fields as
1973	possible, by repeatedly applying each of the specified extractors
1974	to the remainder of the string. Thus C<extract_multiple> is
1975	a generalized form of Perl's C<split> subroutine.
1976
1977	The subroutine takes up to four optional arguments:
1978
1979	=over 4
1980
1981	=item 1.
1982
1983	A string to be processed (C<$_> if the string is omitted or C<undef>)
1984
1985	=item 2.
1986
1987	A reference to a list of subroutine references and/or qr// objects and/or
1988	literal strings and/or hash references, specifying the extractors
1989	to be used to split the string. If this argument is omitted (or
1990	C<undef>) the list:
1991
1992	[
1993	sub { extract_variable($_[0], '') },
1994	sub { extract_quotelike($_[0],'') },
1995	sub { extract_codeblock($_[0],'{}','') },
1996	]
1997
1998	is used.
1999
2000
2001	=item 3.
2002
2003	An number specifying the maximum number of fields to return. If this
2004	argument is omitted (or C<undef>), split continues as long as possible.
2005
2006	If the third argument is I<N>, then extraction continues until I<N> fields
2007	have been successfully extracted, or until the string has been completely
2008	processed.
2009
2010	Note that in scalar and void contexts the value of this argument is
2011	automatically reset to 1 (under C<-w>, a warning is issued if the argument
2012	has to be reset).
2013
2014	=item 4.
2015
2016	A value indicating whether unmatched substrings (see below) within the
2017	text should be skipped or returned as fields. If the value is true,
2018	such substrings are skipped. Otherwise, they are returned.
2019
2020	=back
2021
2022	The extraction process works by applying each extractor in
2023	sequence to the text string.
2024
2025	If the extractor is a subroutine it is called in a list context and is
2026	expected to return a list of a single element, namely the extracted
2027	text. It may optionally also return two further arguments: a string
2028	representing the text left after extraction (like $' for a pattern
2029	match), and a string representing any prefix skipped before the
2030	extraction (like $` in a pattern match). Note that this is designed
2031	to facilitate the use of other Text::Balanced subroutines with
2032	C<extract_multiple>. Note too that the value returned by an extractor
2033	subroutine need not bear any relationship to the corresponding substring
2034	of the original text (see examples below).
2035
2036	If the extractor is a precompiled regular expression or a string,
2037	it is matched against the text in a scalar context with a leading
2038	'\G' and the gc modifiers enabled. The extracted value is either
2039	$1 if that variable is defined after the match, or else the
2040	complete match (i.e. $&).
2041
2042	If the extractor is a hash reference, it must contain exactly one element.
2043	The value of that element is one of the
2044	above extractor types (subroutine reference, regular expression, or string).
2045	The key of that element is the name of a class into which the successful
2046	return value of the extractor will be blessed.
2047
2048	If an extractor returns a defined value, that value is immediately
2049	treated as the next extracted field and pushed onto the list of fields.
2050	If the extractor was specified in a hash reference, the field is also
2051	blessed into the appropriate class,
2052
2053	If the extractor fails to match (in the case of a regex extractor), or returns an empty list or an undefined value (in the case of a subroutine extractor), it is
2054	assumed to have failed to extract.
2055	If none of the extractor subroutines succeeds, then one
2056	character is extracted from the start of the text and the extraction
2057	subroutines reapplied. Characters which are thus removed are accumulated and
2058	eventually become the next field (unless the fourth argument is true, in which
2059	case they are discarded).
2060
2061	For example, the following extracts substrings that are valid Perl variables:
2062
2063	@fields = extract_multiple($text,
2064	[ sub { extract_variable($_[0]) } ],
2065	undef, 1);
2066
2067	This example separates a text into fields which are quote delimited,
2068	curly bracketed, and anything else. The delimited and bracketed
2069	parts are also blessed to identify them (the "anything else" is unblessed):
2070
2071	@fields = extract_multiple($text,
2072	[
2073	{ Delim => sub { extract_delimited($_[0],q{'"}) } },
2074	{ Brack => sub { extract_bracketed($_[0],'{}') } },
2075	]);
2076
2077	This call extracts the next single substring that is a valid Perl quotelike
2078	operator (and removes it from $text):
2079
2080	$quotelike = extract_multiple($text,
2081	[
2082	sub { extract_quotelike($_[0]) },
2083	], undef, 1);
2084
2085	Finally, here is yet another way to do comma-separated value parsing:
2086
2087	@fields = extract_multiple($csv_text,
2088	[
2089	sub { extract_delimited($_[0],q{'"}) },
2090	qr/([^,]+)(.*)/,
2091	],
2092	undef,1);
2093
2094	The list in the second argument means:
2095	I<"Try and extract a ' or " delimited string, otherwise extract anything up to a comma...">.
2096	The undef third argument means:
2097	I<"...as many times as possible...">,
2098	and the true value in the fourth argument means
2099	I<"...discarding anything else that appears (i.e. the commas)">.
2100
2101	If you wanted the commas preserved as separate fields (i.e. like split
2102	does if your split pattern has capturing parentheses), you would
2103	just make the last parameter undefined (or remove it).
2104
2105
2106	=head2 C<gen_delimited_pat>
2107
2108	The C<gen_delimited_pat> subroutine takes a single (string) argument and
2109	> builds a Friedl-style optimized regex that matches a string delimited
2110	by any one of the characters in the single argument. For example:
2111
2112	gen_delimited_pat(q{'"})
2113
2114	returns the regex:
2115
2116	(?:\"(?:\\\"\|(?!\").)\"\|\'(?:\\\'\|(?!\').)\')
2117
2118	Note that the specified delimiters are automatically quotemeta'd.
2119
2120	A typical use of C<gen_delimited_pat> would be to build special purpose tags
2121	for C<extract_tagged>. For example, to properly ignore "empty" XML elements
2122	(which might contain quoted strings):
2123
2124	my $empty_tag = '<(' . gen_delimited_pat(q{'"}) . '\|.)+/>';
2125
2126	extract_tagged($text, undef, undef, undef, {ignore => [$empty_tag]} );
2127
2128
2129	C<gen_delimited_pat> may also be called with an optional second argument,
2130	which specifies the "escape" character(s) to be used for each delimiter.
2131	For example to match a Pascal-style string (where ' is the delimiter
2132	and '' is a literal ' within the string):
2133
2134	gen_delimited_pat(q{'},q{'});
2135
2136	Different escape characters can be specified for different delimiters.
2137	For example, to specify that '/' is the escape for single quotes
2138	and '%' is the escape for double quotes:
2139
2140	gen_delimited_pat(q{'"},q{/%});
2141
2142	If more delimiters than escape chars are specified, the last escape char
2143	is used for the remaining delimiters.
2144	If no escape char is specified for a given specified delimiter, '\' is used.
2145
2146	=head2 C<delimited_pat>
2147
2148	Note that C<gen_delimited_pat> was previously called C<delimited_pat>.
2149	That name may still be used, but is now deprecated.
2150
2151
2152	=head1 DIAGNOSTICS
2153
2154	In a list context, all the functions return C<(undef,$original_text)>
2155	on failure. In a scalar context, failure is indicated by returning C<undef>
2156	(in this case the input text is not modified in any way).
2157
2158	In addition, on failure in I<any> context, the C<$@> variable is set.
2159	Accessing C<$@-E<gt>{error}> returns one of the error diagnostics listed
2160	below.
2161	Accessing C<$@-E<gt>{pos}> returns the offset into the original string at
2162	which the error was detected (although not necessarily where it occurred!)
2163	Printing C<$@> directly produces the error message, with the offset appended.
2164	On success, the C<$@> variable is guaranteed to be C<undef>.
2165
2166	The available diagnostics are:
2167
2168	=over 4
2169
2170	=item C<Did not find a suitable bracket: "%s">
2171
2172	The delimiter provided to C<extract_bracketed> was not one of
2173	C<'()[]E<lt>E<gt>{}'>.
2174
2175	=item C<Did not find prefix: /%s/>
2176
2177	A non-optional prefix was specified but wasn't found at the start of the text.
2178
2179	=item C<Did not find opening bracket after prefix: "%s">
2180
2181	C<extract_bracketed> or C<extract_codeblock> was expecting a
2182	particular kind of bracket at the start of the text, and didn't find it.
2183
2184	=item C<No quotelike operator found after prefix: "%s">
2185
2186	C<extract_quotelike> didn't find one of the quotelike operators C<q>,
2187	C<qq>, C<qw>, C<qx>, C<s>, C<tr> or C<y> at the start of the substring
2188	it was extracting.
2189
2190	=item C<Unmatched closing bracket: "%c">
2191
2192	C<extract_bracketed>, C<extract_quotelike> or C<extract_codeblock> encountered
2193	a closing bracket where none was expected.
2194
2195	=item C<Unmatched opening bracket(s): "%s">
2196
2197	C<extract_bracketed>, C<extract_quotelike> or C<extract_codeblock> ran
2198	out of characters in the text before closing one or more levels of nested
2199	brackets.
2200
2201	=item C<Unmatched embedded quote (%s)>
2202
2203	C<extract_bracketed> attempted to match an embedded quoted substring, but
2204	failed to find a closing quote to match it.
2205
2206	=item C<Did not find closing delimiter to match '%s'>
2207
2208	C<extract_quotelike> was unable to find a closing delimiter to match the
2209	one that opened the quote-like operation.
2210
2211	=item C<Mismatched closing bracket: expected "%c" but found "%s">
2212
2213	C<extract_bracketed>, C<extract_quotelike> or C<extract_codeblock> found
2214	a valid bracket delimiter, but it was the wrong species. This usually
2215	indicates a nesting error, but may indicate incorrect quoting or escaping.
2216
2217	=item C<No block delimiter found after quotelike "%s">
2218
2219	C<extract_quotelike> or C<extract_codeblock> found one of the
2220	quotelike operators C<q>, C<qq>, C<qw>, C<qx>, C<s>, C<tr> or C<y>
2221	without a suitable block after it.
2222
2223	=item C<Did not find leading dereferencer>
2224
2225	C<extract_variable> was expecting one of '$', '@', or '%' at the start of
2226	a variable, but didn't find any of them.
2227
2228	=item C<Bad identifier after dereferencer>
2229
2230	C<extract_variable> found a '$', '@', or '%' indicating a variable, but that
2231	character was not followed by a legal Perl identifier.
2232
2233	=item C<Did not find expected opening bracket at %s>
2234
2235	C<extract_codeblock> failed to find any of the outermost opening brackets
2236	that were specified.
2237
2238	=item C<Improperly nested codeblock at %s>
2239
2240	A nested code block was found that started with a delimiter that was specified
2241	as being only to be used as an outermost bracket.
2242
2243	=item C<Missing second block for quotelike "%s">
2244
2245	C<extract_codeblock> or C<extract_quotelike> found one of the
2246	quotelike operators C<s>, C<tr> or C<y> followed by only one block.
2247
2248	=item C<No match found for opening bracket>
2249
2250	C<extract_codeblock> failed to find a closing bracket to match the outermost
2251	opening bracket.
2252
2253	=item C<Did not find opening tag: /%s/>
2254
2255	C<extract_tagged> did not find a suitable opening tag (after any specified
2256	prefix was removed).
2257
2258	=item C<Unable to construct closing tag to match: /%s/>
2259
2260	C<extract_tagged> matched the specified opening tag and tried to
2261	modify the matched text to produce a matching closing tag (because
2262	none was specified). It failed to generate the closing tag, almost
2263	certainly because the opening tag did not start with a
2264	bracket of some kind.
2265
2266	=item C<Found invalid nested tag: %s>
2267
2268	C<extract_tagged> found a nested tag that appeared in the "reject" list
2269	(and the failure mode was not "MAX" or "PARA").
2270
2271	=item C<Found unbalanced nested tag: %s>
2272
2273	C<extract_tagged> found a nested opening tag that was not matched by a
2274	corresponding nested closing tag (and the failure mode was not "MAX" or "PARA").
2275
2276	=item C<Did not find closing tag>
2277
2278	C<extract_tagged> reached the end of the text without finding a closing tag
2279	to match the original opening tag (and the failure mode was not
2280	"MAX" or "PARA").
2281
2282
2283
2284
2285	=back
2286
2287
2288	=head1 AUTHOR
2289
2290	Damian Conway (damian@conway.org)
2291
2292
2293	=head1 BUGS AND IRRITATIONS
2294
2295	There are undoubtedly serious bugs lurking somewhere in this code, if
2296	only because parts of it give the impression of understanding a great deal
2297	more about Perl than they really do.
2298
2299	Bug reports and other feedback are most welcome.
2300
2301
2302	=head1 COPYRIGHT
2303
2304	Copyright (c) 1997-2001, Damian Conway. All Rights Reserved.
2305	This module is free software. It may be used, redistributed
2306	and/or modified under the same terms as Perl itself.

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