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1 nigel 75 <html>
2     <head>
3     <title>pcrepartial specification</title>
4     </head>
5     <body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB">
6     <h1>pcrepartial man page</h1>
7     <p>
8     Return to the <a href="index.html">PCRE index page</a>.
9     </p>
10 ph10 111 <p>
11 nigel 75 This page is part of the PCRE HTML documentation. It was generated automatically
12     from the original man page. If there is any nonsense in it, please consult the
13     man page, in case the conversion went wrong.
14 ph10 111 <br>
15 nigel 75 <ul>
16     <li><a name="TOC1" href="#SEC1">PARTIAL MATCHING IN PCRE</a>
17 ph10 869 <li><a name="TOC2" href="#SEC2">PARTIAL MATCHING USING pcre_exec() OR pcre16_exec()</a>
18     <li><a name="TOC3" href="#SEC3">PARTIAL MATCHING USING pcre_dfa_exec() OR pcre16_dfa_exec()</a>
19 ph10 429 <li><a name="TOC4" href="#SEC4">PARTIAL MATCHING AND WORD BOUNDARIES</a>
20     <li><a name="TOC5" href="#SEC5">FORMERLY RESTRICTED PATTERNS</a>
22 ph10 869 <li><a name="TOC7" href="#SEC7">MULTI-SEGMENT MATCHING WITH pcre_dfa_exec() OR pcre16_dfa_exec()</a>
23     <li><a name="TOC8" href="#SEC8">MULTI-SEGMENT MATCHING WITH pcre_exec() OR pcre16_exec()</a>
24 ph10 429 <li><a name="TOC9" href="#SEC9">ISSUES WITH MULTI-SEGMENT MATCHING</a>
25     <li><a name="TOC10" href="#SEC10">AUTHOR</a>
26     <li><a name="TOC11" href="#SEC11">REVISION</a>
27 nigel 75 </ul>
28     <br><a name="SEC1" href="#TOC1">PARTIAL MATCHING IN PCRE</a><br>
29     <P>
30 ph10 869 In normal use of PCRE, if the subject string that is passed to a matching
31     function matches as far as it goes, but is too short to match the entire
32     pattern, PCRE_ERROR_NOMATCH is returned. There are circumstances where it might
33     be helpful to distinguish this case from other cases in which there is no
34     match.
35 nigel 75 </P>
36     <P>
37     Consider, for example, an application where a human is required to type in data
38     for a field with specific formatting requirements. An example might be a date
39     in the form <i>ddmmmyy</i>, defined by this pattern:
40     <pre>
41     ^\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d$
42     </pre>
43     If the application sees the user's keystrokes one by one, and can check that
44     what has been typed so far is potentially valid, it is able to raise an error
45 ph10 429 as soon as a mistake is made, by beeping and not reflecting the character that
46     has been typed, for example. This immediate feedback is likely to be a better
47 nigel 75 user interface than a check that is delayed until the entire string has been
48 ph10 567 entered. Partial matching can also be useful when the subject string is very
49     long and is not all available at once.
50 nigel 75 </P>
51     <P>
52 ph10 429 PCRE supports partial matching by means of the PCRE_PARTIAL_SOFT and
53 ph10 903 PCRE_PARTIAL_HARD options, which can be set when calling any of the matching
54 ph10 869 functions. For backwards compatibility, PCRE_PARTIAL is a synonym for
55     PCRE_PARTIAL_SOFT. The essential difference between the two options is whether
56     or not a partial match is preferred to an alternative complete match, though
57     the details differ between the two types of matching function. If both options
58 ph10 429 are set, PCRE_PARTIAL_HARD takes precedence.
59 nigel 75 </P>
60     <P>
61 ph10 975 If you want to use partial matching with just-in-time optimized code, you must
62 ph10 930 call <b>pcre_study()</b> or <b>pcre16_study()</b> with one or both of these
63     options:
64     <pre>
67     </pre>
68 ph10 975 PCRE_STUDY_JIT_COMPILE should also be set if you are going to run non-partial
69 ph10 930 matches on the same pattern. If the appropriate JIT study mode has not been set
70     for a match, the interpretive matching code is used.
71     </P>
72     <P>
73     Setting a partial matching option disables two of PCRE's standard
74 ph10 869 optimizations. PCRE remembers the last literal data unit in a pattern, and
75     abandons matching immediately if it is not present in the subject string. This
76 ph10 691 optimization cannot be used for a subject string that might match only
77     partially. If the pattern was studied, PCRE knows the minimum length of a
78     matching string, and does not bother to run the matching function on shorter
79     strings. This optimization is also disabled for partial matching.
80 nigel 77 </P>
81 ph10 869 <br><a name="SEC2" href="#TOC1">PARTIAL MATCHING USING pcre_exec() OR pcre16_exec()</a><br>
82 nigel 77 <P>
83 ph10 903 A partial match occurs during a call to <b>pcre_exec()</b> or
84 ph10 869 <b>pcre16_exec()</b> when the end of the subject string is reached successfully,
85     but matching cannot continue because more characters are needed. However, at
86     least one character in the subject must have been inspected. This character
87     need not form part of the final matched string; lookbehind assertions and the
88     \K escape sequence provide ways of inspecting characters before the start of a
89     matched substring. The requirement for inspecting at least one character exists
90     because an empty string can always be matched; without such a restriction there
91     would always be a partial match of an empty string at the end of the subject.
92 nigel 75 </P>
93     <P>
94 ph10 869 If there are at least two slots in the offsets vector when a partial match is
95     returned, the first slot is set to the offset of the earliest character that
96     was inspected. For convenience, the second offset points to the end of the
97     subject so that a substring can easily be identified.
98 ph10 453 </P>
99     <P>
100     For the majority of patterns, the first offset identifies the start of the
101     partially matched string. However, for patterns that contain lookbehind
102     assertions, or \K, or begin with \b or \B, earlier characters have been
103     inspected while carrying out the match. For example:
104 nigel 75 <pre>
105 ph10 453 /(?&#60;=abc)123/
106     </pre>
107     This pattern matches "123", but only if it is preceded by "abc". If the subject
108     string is "xyzabc12", the offsets after a partial match are for the substring
109     "abc12", because all these characters are needed if another match is tried
110 ph10 567 with extra characters added to the subject.
111 ph10 453 </P>
112     <P>
113 ph10 567 What happens when a partial match is identified depends on which of the two
114 ph10 579 partial matching options are set.
115 ph10 567 </P>
116     <br><b>
117 ph10 869 PCRE_PARTIAL_SOFT WITH pcre_exec() OR pcre16_exec()
118 ph10 567 </b><br>
119     <P>
120 ph10 869 If PCRE_PARTIAL_SOFT is set when <b>pcre_exec()</b> or <b>pcre16_exec()</b>
121     identifies a partial match, the partial match is remembered, but matching
122     continues as normal, and other alternatives in the pattern are tried. If no
123     complete match can be found, PCRE_ERROR_PARTIAL is returned instead of
125 ph10 567 </P>
126     <P>
127 ph10 579 This option is "soft" because it prefers a complete match over a partial match.
128     All the various matching items in a pattern behave as if the subject string is
129 ph10 567 potentially complete. For example, \z, \Z, and $ match at the end of the
130 ph10 579 subject, as normal, and for \b and \B the end of the subject is treated as a
131 ph10 567 non-alphanumeric.
132     </P>
133     <P>
134 ph10 453 If there is more than one partial match, the first one that was found provides
135     the data that is returned. Consider this pattern:
136     <pre>
137 ph10 429 /123\w+X|dogY/
138 nigel 75 </pre>
139 ph10 429 If this is matched against the subject string "abc123dog", both
140 ph10 453 alternatives fail to match, but the end of the subject is reached during
141 ph10 567 matching, so PCRE_ERROR_PARTIAL is returned. The offsets are set to 3 and 9,
142     identifying "123dog" as the first partial match that was found. (In this
143     example, there are two partial matches, because "dog" on its own partially
144     matches the second alternative.)
145 ph10 429 </P>
146 ph10 567 <br><b>
147 ph10 869 PCRE_PARTIAL_HARD WITH pcre_exec() OR pcre16_exec()
148 ph10 567 </b><br>
149 ph10 429 <P>
150 ph10 869 If PCRE_PARTIAL_HARD is set for <b>pcre_exec()</b> or <b>pcre16_exec()</b>,
151     PCRE_ERROR_PARTIAL is returned as soon as a partial match is found, without
152     continuing to search for possible complete matches. This option is "hard"
153     because it prefers an earlier partial match over a later complete match. For
154     this reason, the assumption is made that the end of the supplied subject string
155     may not be the true end of the available data, and so, if \z, \Z, \b, \B,
156     or $ are encountered at the end of the subject, the result is
157 ph10 903 PCRE_ERROR_PARTIAL, provided that at least one character in the subject has
158     been inspected.
159 ph10 567 </P>
160 ph10 572 <P>
161 ph10 869 Setting PCRE_PARTIAL_HARD also affects the way UTF-8 and UTF-16
162     subject strings are checked for validity. Normally, an invalid sequence
163     causes the error PCRE_ERROR_BADUTF8 or PCRE_ERROR_BADUTF16. However, in the
164     special case of a truncated character at the end of the subject,
165     PCRE_ERROR_SHORTUTF8 or PCRE_ERROR_SHORTUTF16 is returned when
166 ph10 572 PCRE_PARTIAL_HARD is set.
167     </P>
168 ph10 567 <br><b>
169     Comparing hard and soft partial matching
170     </b><br>
171     <P>
172     The difference between the two partial matching options can be illustrated by a
173     pattern such as:
174 nigel 75 <pre>
175 ph10 429 /dog(sbody)?/
176 nigel 75 </pre>
177 ph10 453 This matches either "dog" or "dogsbody", greedily (that is, it prefers the
178 ph10 429 longer string if possible). If it is matched against the string "dog" with
179 ph10 453 PCRE_PARTIAL_SOFT, it yields a complete match for "dog". However, if
180     PCRE_PARTIAL_HARD is set, the result is PCRE_ERROR_PARTIAL. On the other hand,
181 ph10 429 if the pattern is made ungreedy the result is different:
182 nigel 75 <pre>
183 ph10 429 /dog(sbody)??/
184 nigel 75 </pre>
185 ph10 869 In this case the result is always a complete match because that is found first,
186     and matching never continues after finding a complete match. It might be easier
187     to follow this explanation by thinking of the two patterns like this:
188 ph10 429 <pre>
189     /dog(sbody)?/ is the same as /dogsbody|dog/
190     /dog(sbody)??/ is the same as /dog|dogsbody/
191     </pre>
192 ph10 869 The second pattern will never match "dogsbody", because it will always find the
193     shorter match first.
194 nigel 75 </P>
195 ph10 869 <br><a name="SEC3" href="#TOC1">PARTIAL MATCHING USING pcre_dfa_exec() OR pcre16_dfa_exec()</a><br>
196 nigel 75 <P>
197 ph10 869 The DFA functions move along the subject string character by character, without
198     backtracking, searching for all possible matches simultaneously. If the end of
199     the subject is reached before the end of the pattern, there is the possibility
200     of a partial match, again provided that at least one character has been
201     inspected.
202 nigel 75 </P>
203     <P>
204 ph10 429 When PCRE_PARTIAL_SOFT is set, PCRE_ERROR_PARTIAL is returned only if there
205     have been no complete matches. Otherwise, the complete matches are returned.
206     However, if PCRE_PARTIAL_HARD is set, a partial match takes precedence over any
207 ph10 453 complete matches. The portion of the string that was inspected when the longest
208     partial match was found is set as the first matching string, provided there are
209     at least two slots in the offsets vector.
210 ph10 429 </P>
211     <P>
212 ph10 869 Because the DFA functions always search for all possible matches, and there is
213     no difference between greedy and ungreedy repetition, their behaviour is
214     different from the standard functions when PCRE_PARTIAL_HARD is set. Consider
215     the string "dog" matched against the ungreedy pattern shown above:
216 ph10 429 <pre>
217     /dog(sbody)??/
218     </pre>
219 ph10 869 Whereas the standard functions stop as soon as they find the complete match for
220     "dog", the DFA functions also find the partial match for "dogsbody", and so
221     return that when PCRE_PARTIAL_HARD is set.
222 ph10 429 </P>
223     <br><a name="SEC4" href="#TOC1">PARTIAL MATCHING AND WORD BOUNDARIES</a><br>
224     <P>
225 ph10 469 If a pattern ends with one of sequences \b or \B, which test for word
226 ph10 453 boundaries, partial matching with PCRE_PARTIAL_SOFT can give counter-intuitive
227 ph10 429 results. Consider this pattern:
228     <pre>
229     /\bcat\b/
230     </pre>
231     This matches "cat", provided there is a word boundary at either end. If the
232     subject string is "the cat", the comparison of the final "t" with a following
233 ph10 869 character cannot take place, so a partial match is found. However, normal
234     matching carries on, and \b matches at the end of the subject when the last
235     character is a letter, so a complete match is found. The result, therefore, is
236     <i>not</i> PCRE_ERROR_PARTIAL. Using PCRE_PARTIAL_HARD in this case does yield
237     PCRE_ERROR_PARTIAL, because then the partial match takes precedence.
238 ph10 429 </P>
239     <br><a name="SEC5" href="#TOC1">FORMERLY RESTRICTED PATTERNS</a><br>
240     <P>
241     For releases of PCRE prior to 8.00, because of the way certain internal
242     optimizations were implemented in the <b>pcre_exec()</b> function, the
243     PCRE_PARTIAL option (predecessor of PCRE_PARTIAL_SOFT) could not be used with
244     all patterns. From release 8.00 onwards, the restrictions no longer apply, and
245 ph10 869 partial matching with can be requested for any pattern.
246 ph10 429 </P>
247     <P>
248     Items that were formerly restricted were repeated single characters and
249     repeated metasequences. If PCRE_PARTIAL was set for a pattern that did not
250     conform to the restrictions, <b>pcre_exec()</b> returned the error code
251     PCRE_ERROR_BADPARTIAL (-13). This error code is no longer in use. The
252     PCRE_INFO_OKPARTIAL call to <b>pcre_fullinfo()</b> to find out if a compiled
253     pattern can be used for partial matching now always returns 1.
254     </P>
255     <br><a name="SEC6" href="#TOC1">EXAMPLE OF PARTIAL MATCHING USING PCRETEST</a><br>
256     <P>
257 nigel 75 If the escape sequence \P is present in a <b>pcretest</b> data line, the
258 ph10 429 PCRE_PARTIAL_SOFT option is used for the match. Here is a run of <b>pcretest</b>
259     that uses the date example quoted above:
260 nigel 75 <pre>
261     re&#62; /^\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d$/
262     data&#62; 25jun04\P
263     0: 25jun04
264     1: jun
265     data&#62; 25dec3\P
266 ph10 429 Partial match: 23dec3
267 nigel 75 data&#62; 3ju\P
268 ph10 429 Partial match: 3ju
269 nigel 75 data&#62; 3juj\P
270     No match
271     data&#62; j\P
272     No match
273     </pre>
274     The first data string is matched completely, so <b>pcretest</b> shows the
275     matched substrings. The remaining four strings do not match the complete
276 ph10 429 pattern, but the first two are partial matches. Similar output is obtained
277 ph10 869 if DFA matching is used.
278 nigel 75 </P>
279     <P>
280 ph10 429 If the escape sequence \P is present more than once in a <b>pcretest</b> data
281     line, the PCRE_PARTIAL_HARD option is set for the match.
282     </P>
283 ph10 869 <br><a name="SEC7" href="#TOC1">MULTI-SEGMENT MATCHING WITH pcre_dfa_exec() OR pcre16_dfa_exec()</a><br>
284 ph10 429 <P>
285 ph10 869 When a partial match has been found using a DFA matching function, it is
286     possible to continue the match by providing additional subject data and calling
287     the function again with the same compiled regular expression, this time setting
288     the PCRE_DFA_RESTART option. You must pass the same working space as before,
289     because this is where details of the previous partial match are stored. Here is
290     an example using <b>pcretest</b>, using the \R escape sequence to set the
291     PCRE_DFA_RESTART option (\D specifies the use of the DFA matching function):
292 nigel 77 <pre>
293     re&#62; /^\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d$/
294     data&#62; 23ja\P\D
295     Partial match: 23ja
296     data&#62; n05\R\D
297     0: n05
298     </pre>
299     The first call has "23ja" as the subject, and requests partial matching; the
300     second call has "n05" as the subject for the continued (restarted) match.
301     Notice that when the match is complete, only the last part is shown; PCRE does
302     not retain the previously partially-matched string. It is up to the calling
303     program to do that if it needs to.
304     </P>
305     <P>
306 ph10 429 You can set the PCRE_PARTIAL_SOFT or PCRE_PARTIAL_HARD options with
307     PCRE_DFA_RESTART to continue partial matching over multiple segments. This
308 ph10 903 facility can be used to pass very long subject strings to the DFA matching
309 ph10 869 functions.
310 nigel 77 </P>
311 ph10 869 <br><a name="SEC8" href="#TOC1">MULTI-SEGMENT MATCHING WITH pcre_exec() OR pcre16_exec()</a><br>
312 nigel 77 <P>
313 ph10 869 From release 8.00, the standard matching functions can also be used to do
314     multi-segment matching. Unlike the DFA functions, it is not possible to
315     restart the previous match with a new segment of data. Instead, new data must
316     be added to the previous subject string, and the entire match re-run, starting
317     from the point where the partial match occurred. Earlier data can be discarded.
318     </P>
319     <P>
320     It is best to use PCRE_PARTIAL_HARD in this situation, because it does not
321     treat the end of a segment as the end of the subject when matching \z, \Z,
322     \b, \B, and $. Consider an unanchored pattern that matches dates:
323 ph10 429 <pre>
324     re&#62; /\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d/
325 ph10 567 data&#62; The date is 23ja\P\P
326 ph10 429 Partial match: 23ja
327     </pre>
328 ph10 469 At this stage, an application could discard the text preceding "23ja", add on
329 ph10 869 text from the next segment, and call the matching function again. Unlike the
330 ph10 954 DFA matching functions, the entire matching string must always be available,
331     and the complete matching process occurs for each call, so more memory and more
332 ph10 429 processing time is needed.
333     </P>
334 ph10 453 <P>
335     <b>Note:</b> If the pattern contains lookbehind assertions, or \K, or starts
336 ph10 869 with \b or \B, the string that is returned for a partial match includes
337 ph10 453 characters that precede the partially matched string itself, because these must
338     be retained when adding on more characters for a subsequent matching attempt.
339 ph10 954 However, in some cases you may need to retain even earlier characters, as
340     discussed in the next section.
341 ph10 453 </P>
342 ph10 429 <br><a name="SEC9" href="#TOC1">ISSUES WITH MULTI-SEGMENT MATCHING</a><br>
343     <P>
344 ph10 453 Certain types of pattern may give problems with multi-segment matching,
345 ph10 429 whichever matching function is used.
346     </P>
347     <P>
348 ph10 567 1. If the pattern contains a test for the beginning of a line, you need to pass
349     the PCRE_NOTBOL option when the subject string for any call does start at the
350 ph10 579 beginning of a line. There is also a PCRE_NOTEOL option, but in practice when
351     doing multi-segment matching you should be using PCRE_PARTIAL_HARD, which
352 ph10 567 includes the effect of PCRE_NOTEOL.
353 nigel 77 </P>
354     <P>
355 ph10 954 2. Lookbehind assertions that have already been obeyed are catered for in the
356     offsets that are returned for a partial match. However a lookbehind assertion
357 ph10 975 later in the pattern could require even earlier characters to be inspected. You
358     can handle this case by using the PCRE_INFO_MAXLOOKBEHIND option of the
359 ph10 954 <b>pcre_fullinfo()</b> or <b>pcre16_fullinfo()</b> functions to obtain the length
360     of the largest lookbehind in the pattern. This length is given in characters,
361     not bytes. If you always retain at least that many characters before the
362     partially matched string, all should be well. (Of course, near the start of the
363     subject, fewer characters may be present; in that case all characters should be
364     retained.)
365 nigel 77 </P>
366     <P>
367 ph10 954 3. Because a partial match must always contain at least one character, what
368     might be considered a partial match of an empty string actually gives a "no
369     match" result. For example:
370     <pre>
371     re&#62; /c(?&#60;=abc)x/
372     data&#62; ab\P
373     No match
374     </pre>
375 ph10 975 If the next segment begins "cx", a match should be found, but this will only
376 ph10 954 happen if characters from the previous segment are retained. For this reason, a
377     "no match" result should be interpreted as "partial match of an empty string"
378     when the pattern contains lookbehinds.
379     </P>
380     <P>
381     4. Matching a subject string that is split into multiple segments may not
382 ph10 429 always produce exactly the same result as matching over one single long string,
383 ph10 453 especially when PCRE_PARTIAL_SOFT is used. The section "Partial Matching and
384     Word Boundaries" above describes an issue that arises if the pattern ends with
385 ph10 429 \b or \B. Another kind of difference may occur when there are multiple
386 ph10 567 matching possibilities, because (for PCRE_PARTIAL_SOFT) a partial match result
387     is given only when there are no completed matches. This means that as soon as
388     the shortest match has been found, continuation to a new subject segment is no
389     longer possible. Consider again this <b>pcretest</b> example:
390 nigel 77 <pre>
391     re&#62; /dog(sbody)?/
392 ph10 429 data&#62; dogsb\P
393 ph10 453 0: dog
394 nigel 77 data&#62; do\P\D
395     Partial match: do
396     data&#62; gsb\R\P\D
397     0: g
398     data&#62; dogsbody\D
399     0: dogsbody
400     1: dog
401     </pre>
402 ph10 869 The first data line passes the string "dogsb" to a standard matching function,
403     setting the PCRE_PARTIAL_SOFT option. Although the string is a partial match
404     for "dogsbody", the result is not PCRE_ERROR_PARTIAL, because the shorter
405     string "dog" is a complete match. Similarly, when the subject is presented to
406     a DFA matching function in several parts ("do" and "gsb" being the first two)
407     the match stops when "dog" has been found, and it is not possible to continue.
408     On the other hand, if "dogsbody" is presented as a single string, a DFA
409     matching function finds both matches.
410 nigel 77 </P>
411     <P>
412 ph10 567 Because of these problems, it is best to use PCRE_PARTIAL_HARD when matching
413     multi-segment data. The example above then behaves differently:
414 ph10 429 <pre>
415     re&#62; /dog(sbody)?/
416     data&#62; dogsb\P\P
417 ph10 453 Partial match: dogsb
418 ph10 429 data&#62; do\P\D
419     Partial match: do
420     data&#62; gsb\R\P\P\D
421 ph10 453 Partial match: gsb
422 ph10 572 </pre>
423 ph10 954 5. Patterns that contain alternatives at the top level which do not all start
424 ph10 869 with the same pattern item may not work as expected when PCRE_DFA_RESTART is
425     used. For example, consider this pattern:
426 nigel 87 <pre>
427     1234|3789
428     </pre>
429     If the first part of the subject is "ABC123", a partial match of the first
430     alternative is found at offset 3. There is no partial match for the second
431     alternative, because such a match does not start at the same point in the
432 ph10 429 subject string. Attempting to continue with the string "7890" does not yield a
433 nigel 87 match because only those alternatives that match at one point in the subject
434     are remembered. The problem arises because the start of the second alternative
435     matches within the first alternative. There is no problem with anchored
436     patterns or patterns such as:
437     <pre>
438     1234|ABCD
439     </pre>
440 ph10 429 where no string can be a partial match for both alternatives. This is not a
441 ph10 869 problem if a standard matching function is used, because the entire match has
442     to be rerun each time:
443 ph10 429 <pre>
444     re&#62; /1234|3789/
445 ph10 567 data&#62; ABC123\P\P
446 ph10 429 Partial match: 123
447     data&#62; 1237890
448     0: 3789
449 ph10 469 </pre>
450 ph10 567 Of course, instead of using PCRE_DFA_RESTART, the same technique of re-running
451 ph10 869 the entire match can also be used with the DFA matching functions. Another
452 ph10 469 possibility is to work with two buffers. If a partial match at offset <i>n</i>
453     in the first buffer is followed by "no match" when PCRE_DFA_RESTART is used on
454     the second buffer, you can then try a new match starting at offset <i>n+1</i> in
455     the first buffer.
456 nigel 87 </P>
457 ph10 429 <br><a name="SEC10" href="#TOC1">AUTHOR</a><br>
458 nigel 87 <P>
459 ph10 99 Philip Hazel
460 nigel 75 <br>
461 ph10 99 University Computing Service
462     <br>
463     Cambridge CB2 3QH, England.
464     <br>
465     </P>
466 ph10 429 <br><a name="SEC11" href="#TOC1">REVISION</a><br>
467 ph10 99 <P>
468 ph10 954 Last updated: 24 February 2012
469 ph10 99 <br>
470 ph10 869 Copyright &copy; 1997-2012 University of Cambridge.
471 ph10 99 <br>
472 nigel 75 <p>
473     Return to the <a href="index.html">PCRE index page</a>.
474     </p>


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