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revision 43 by nigel, Sat Feb 24 21:39:21 2007 UTC revision 53 by nigel, Sat Feb 24 21:39:42 2007 UTC
# Line 44  pcre - Perl-compatible regular expressio Line 44  pcre - Perl-compatible regular expressio
44  .B int *\fIovector\fR, int \fIstringcount\fR, "const char ***\fIlistptr\fR);"  .B int *\fIovector\fR, int \fIstringcount\fR, "const char ***\fIlistptr\fR);"
45  .PP  .PP
46  .br  .br
47    .B void pcre_free_substring(const char *\fIstringptr\fR);
48    .PP
49    .br
50    .B void pcre_free_substring_list(const char **\fIstringptr\fR);
51    .PP
52    .br
53  .B const unsigned char *pcre_maketables(void);  .B const unsigned char *pcre_maketables(void);
54  .PP  .PP
55  .br  .br
# Line 70  pcre - Perl-compatible regular expressio Line 76  pcre - Perl-compatible regular expressio
76  The PCRE library is a set of functions that implement regular expression  The PCRE library is a set of functions that implement regular expression
77  pattern matching using the same syntax and semantics as Perl 5, with just a few  pattern matching using the same syntax and semantics as Perl 5, with just a few
78  differences (see below). The current implementation corresponds to Perl 5.005,  differences (see below). The current implementation corresponds to Perl 5.005,
79  with some additional features from the Perl development release.  with some additional features from later versions. This includes some
80    experimental, incomplete support for UTF-8 encoded strings. Details of exactly
81    what is and what is not supported are given below.
82    
83  PCRE has its own native API, which is described in this document. There is also  PCRE has its own native API, which is described in this document. There is also
84  a set of wrapper functions that correspond to the POSIX regular expression API.  a set of wrapper functions that correspond to the POSIX regular expression API.
# Line 84  contain the major and minor release numb Line 92  contain the major and minor release numb
92  use these to include support for different releases.  use these to include support for different releases.
93    
94  The functions \fBpcre_compile()\fR, \fBpcre_study()\fR, and \fBpcre_exec()\fR  The functions \fBpcre_compile()\fR, \fBpcre_study()\fR, and \fBpcre_exec()\fR
95  are used for compiling and matching regular expressions, while  are used for compiling and matching regular expressions. A sample program that
96  \fBpcre_copy_substring()\fR, \fBpcre_get_substring()\fR, and  demonstrates the simplest way of using them is given in the file
97    \fIpcredemo.c\fR. The last section of this man page describes how to run it.
98    
99    The functions \fBpcre_copy_substring()\fR, \fBpcre_get_substring()\fR, and
100  \fBpcre_get_substring_list()\fR are convenience functions for extracting  \fBpcre_get_substring_list()\fR are convenience functions for extracting
101  captured substrings from a matched subject string. The function  captured substrings from a matched subject string; \fBpcre_free_substring()\fR
102  \fBpcre_maketables()\fR is used (optionally) to build a set of character tables  and \fBpcre_free_substring_list()\fR are also provided, to free the memory used
103  in the current locale for passing to \fBpcre_compile()\fR.  for extracted strings.
104    
105    The function \fBpcre_maketables()\fR is used (optionally) to build a set of
106    character tables in the current locale for passing to \fBpcre_compile()\fR.
107    
108  The function \fBpcre_fullinfo()\fR is used to find out information about a  The function \fBpcre_fullinfo()\fR is used to find out information about a
109  compiled pattern; \fBpcre_info()\fR is an obsolete version which returns only  compiled pattern; \fBpcre_info()\fR is an obsolete version which returns only
# Line 117  the same compiled pattern can safely be Line 131  the same compiled pattern can safely be
131  The function \fBpcre_compile()\fR is called to compile a pattern into an  The function \fBpcre_compile()\fR is called to compile a pattern into an
132  internal form. The pattern is a C string terminated by a binary zero, and  internal form. The pattern is a C string terminated by a binary zero, and
133  is passed in the argument \fIpattern\fR. A pointer to a single block of memory  is passed in the argument \fIpattern\fR. A pointer to a single block of memory
134  that is obtained via \fBpcre_malloc\fR is returned. This contains the  that is obtained via \fBpcre_malloc\fR is returned. This contains the compiled
135  compiled code and related data. The \fBpcre\fR type is defined for this for  code and related data. The \fBpcre\fR type is defined for the returned block;
136  convenience, but in fact \fBpcre\fR is just a typedef for \fBvoid\fR, since the  this is a typedef for a structure whose contents are not externally defined. It
137  contents of the block are not externally defined. It is up to the caller to  is up to the caller to free the memory when it is no longer required.
138  free the memory when it is no longer required.  
139  .PP  Although the compiled code of a PCRE regex is relocatable, that is, it does not
140    depend on memory location, the complete \fBpcre\fR data block is not
141    fully relocatable, because it contains a copy of the \fItableptr\fR argument,
142    which is an address (see below).
143    
144  The size of a compiled pattern is roughly proportional to the length of the  The size of a compiled pattern is roughly proportional to the length of the
145  pattern string, except that each character class (other than those containing  pattern string, except that each character class (other than those containing
146  just a single character, negated or not) requires 33 bytes, and repeat  just a single character, negated or not) requires 33 bytes, and repeat
147  quantifiers with a minimum greater than one or a bounded maximum cause the  quantifiers with a minimum greater than one or a bounded maximum cause the
148  relevant portions of the compiled pattern to be replicated.  relevant portions of the compiled pattern to be replicated.
149  .PP  
150  The \fIoptions\fR argument contains independent bits that affect the  The \fIoptions\fR argument contains independent bits that affect the
151  compilation. It should be zero if no options are required. Some of the options,  compilation. It should be zero if no options are required. Some of the options,
152  in particular, those that are compatible with Perl, can also be set and unset  in particular, those that are compatible with Perl, can also be set and unset
# Line 137  below). For these options, the contents Line 155  below). For these options, the contents
155  their initial settings at the start of compilation and execution. The  their initial settings at the start of compilation and execution. The
156  PCRE_ANCHORED option can be set at the time of matching as well as at compile  PCRE_ANCHORED option can be set at the time of matching as well as at compile
157  time.  time.
158  .PP  
159  If \fIerrptr\fR is NULL, \fBpcre_compile()\fR returns NULL immediately.  If \fIerrptr\fR is NULL, \fBpcre_compile()\fR returns NULL immediately.
160  Otherwise, if compilation of a pattern fails, \fBpcre_compile()\fR returns  Otherwise, if compilation of a pattern fails, \fBpcre_compile()\fR returns
161  NULL, and sets the variable pointed to by \fIerrptr\fR to point to a textual  NULL, and sets the variable pointed to by \fIerrptr\fR to point to a textual
162  error message. The offset from the start of the pattern to the character where  error message. The offset from the start of the pattern to the character where
163  the error was discovered is placed in the variable pointed to by  the error was discovered is placed in the variable pointed to by
164  \fIerroffset\fR, which must not be NULL. If it is, an immediate error is given.  \fIerroffset\fR, which must not be NULL. If it is, an immediate error is given.
165  .PP  
166  If the final argument, \fItableptr\fR, is NULL, PCRE uses a default set of  If the final argument, \fItableptr\fR, is NULL, PCRE uses a default set of
167  character tables which are built when it is compiled, using the default C  character tables which are built when it is compiled, using the default C
168  locale. Otherwise, \fItableptr\fR must be the result of a call to  locale. Otherwise, \fItableptr\fR must be the result of a call to
169  \fBpcre_maketables()\fR. See the section on locale support below.  \fBpcre_maketables()\fR. See the section on locale support below.
170  .PP  
171    This code fragment shows a typical straightforward call to \fBpcre_compile()\fR:
172    
173      pcre *re;
174      const char *error;
175      int erroffset;
176      re = pcre_compile(
177        "^A.*Z",          /* the pattern */
178        0,                /* default options */
179        &error,           /* for error message */
180        &erroffset,       /* for error offset */
181        NULL);            /* use default character tables */
182    
183  The following option bits are defined in the header file:  The following option bits are defined in the header file:
184    
185    PCRE_ANCHORED    PCRE_ANCHORED
# Line 223  This option inverts the "greediness" of Line 253  This option inverts the "greediness" of
253  greedy by default, but become greedy if followed by "?". It is not compatible  greedy by default, but become greedy if followed by "?". It is not compatible
254  with Perl. It can also be set by a (?U) option setting within the pattern.  with Perl. It can also be set by a (?U) option setting within the pattern.
255    
256      PCRE_UTF8
257    
258    This option causes PCRE to regard both the pattern and the subject as strings
259    of UTF-8 characters instead of just byte strings. However, it is available only
260    if PCRE has been built to include UTF-8 support. If not, the use of this option
261    provokes an error. Support for UTF-8 is new, experimental, and incomplete.
262    Details of exactly what it entails are given below.
263    
264    
265  .SH STUDYING A PATTERN  .SH STUDYING A PATTERN
266  When a pattern is going to be used several times, it is worth spending more  When a pattern is going to be used several times, it is worth spending more
267  time analyzing it in order to speed up the time taken for matching. The  time analyzing it in order to speed up the time taken for matching. The
268  function \fBpcre_study()\fR takes a pointer to a compiled pattern as its first  function \fBpcre_study()\fR takes a pointer to a compiled pattern as its first
269  argument, and returns a pointer to a \fBpcre_extra\fR block (another \fBvoid\fR  argument, and returns a pointer to a \fBpcre_extra\fR block (another typedef
270  typedef) containing additional information about the pattern; this can be  for a structure with hidden contents) containing additional information about
271  passed to \fBpcre_exec()\fR. If no additional information is available, NULL  the pattern; this can be passed to \fBpcre_exec()\fR. If no additional
272  is returned.  information is available, NULL is returned.
273    
274  The second argument contains option bits. At present, no options are defined  The second argument contains option bits. At present, no options are defined
275  for \fBpcre_study()\fR, and this argument should always be zero.  for \fBpcre_study()\fR, and this argument should always be zero.
# Line 240  The third argument for \fBpcre_study()\f Line 278  The third argument for \fBpcre_study()\f
278  studying succeeds (even if no data is returned), the variable it points to is  studying succeeds (even if no data is returned), the variable it points to is
279  set to NULL. Otherwise it points to a textual error message.  set to NULL. Otherwise it points to a textual error message.
280    
281    This is a typical call to \fBpcre_study\fR():
282    
283      pcre_extra *pe;
284      pe = pcre_study(
285        re,             /* result of pcre_compile() */
286        0,              /* no options exist */
287        &error);        /* set to NULL or points to a message */
288    
289  At present, studying a pattern is useful only for non-anchored patterns that do  At present, studying a pattern is useful only for non-anchored patterns that do
290  not have a single fixed starting character. A bitmap of possible starting  not have a single fixed starting character. A bitmap of possible starting
291  characters is created.  characters is created.
# Line 289  the following negative numbers: Line 335  the following negative numbers:
335    PCRE_ERROR_BADMAGIC   the "magic number" was not found    PCRE_ERROR_BADMAGIC   the "magic number" was not found
336    PCRE_ERROR_BADOPTION  the value of \fIwhat\fR was invalid    PCRE_ERROR_BADOPTION  the value of \fIwhat\fR was invalid
337    
338    Here is a typical call of \fBpcre_fullinfo()\fR, to obtain the length of the
339    compiled pattern:
340    
341      int rc;
342      unsigned long int length;
343      rc = pcre_fullinfo(
344        re,               /* result of pcre_compile() */
345        pe,               /* result of pcre_study(), or NULL */
346        PCRE_INFO_SIZE,   /* what is required */
347        &length);         /* where to put the data */
348    
349  The possible values for the third argument are defined in \fBpcre.h\fR, and are  The possible values for the third argument are defined in \fBpcre.h\fR, and are
350  as follows:  as follows:
351    
352    PCRE_INFO_OPTIONS    PCRE_INFO_OPTIONS
353    
354  Return a copy of the options with which the pattern was compiled. The fourth  Return a copy of the options with which the pattern was compiled. The fourth
355  argument should point to au \fBunsigned long int\fR variable. These option bits  argument should point to an \fBunsigned long int\fR variable. These option bits
356  are those specified in the call to \fBpcre_compile()\fR, modified by any  are those specified in the call to \fBpcre_compile()\fR, modified by any
357  top-level option settings within the pattern itself, and with the PCRE_ANCHORED  top-level option settings within the pattern itself, and with the PCRE_ANCHORED
358  bit forcibly set if the form of the pattern implies that it can match only at  bit forcibly set if the form of the pattern implies that it can match only at
# Line 323  no back references. Line 380  no back references.
380    
381  Return information about the first character of any matched string, for a  Return information about the first character of any matched string, for a
382  non-anchored pattern. If there is a fixed first character, e.g. from a pattern  non-anchored pattern. If there is a fixed first character, e.g. from a pattern
383  such as (cat|cow|coyote), then it is returned in the integer pointed to by  such as (cat|cow|coyote), it is returned in the integer pointed to by
384  \fIwhere\fR. Otherwise, if either  \fIwhere\fR. Otherwise, if either
385    
386  (a) the pattern was compiled with the PCRE_MULTILINE option, and every branch  (a) the pattern was compiled with the PCRE_MULTILINE option, and every branch
# Line 332  starts with "^", or Line 389  starts with "^", or
389  (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not set  (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not set
390  (if it were set, the pattern would be anchored),  (if it were set, the pattern would be anchored),
391    
392  then -1 is returned, indicating that the pattern matches only at the  -1 is returned, indicating that the pattern matches only at the start of a
393  start of a subject string or after any "\\n" within the string. Otherwise -2 is  subject string or after any "\\n" within the string. Otherwise -2 is returned.
394  returned. For anchored patterns, -2 is returned.  For anchored patterns, -2 is returned.
395    
396    PCRE_INFO_FIRSTTABLE    PCRE_INFO_FIRSTTABLE
397    
# Line 376  pre-compiled pattern, which is passed in Line 433  pre-compiled pattern, which is passed in
433  pattern has been studied, the result of the study should be passed in the  pattern has been studied, the result of the study should be passed in the
434  \fIextra\fR argument. Otherwise this must be NULL.  \fIextra\fR argument. Otherwise this must be NULL.
435    
436    Here is an example of a simple call to \fBpcre_exec()\fR:
437    
438      int rc;
439      int ovector[30];
440      rc = pcre_exec(
441        re,             /* result of pcre_compile() */
442        NULL,           /* we didn't study the pattern */
443        "some string",  /* the subject string */
444        11,             /* the length of the subject string */
445        0,              /* start at offset 0 in the subject */
446        0,              /* default options */
447        ovector,        /* vector for substring information */
448        30);            /* number of elements in the vector */
449    
450  The PCRE_ANCHORED option can be passed in the \fIoptions\fR argument, whose  The PCRE_ANCHORED option can be passed in the \fIoptions\fR argument, whose
451  unused bits must be zero. However, if a pattern was compiled with  unused bits must be zero. However, if a pattern was compiled with
452  PCRE_ANCHORED, or turned out to be anchored by virtue of its contents, it  PCRE_ANCHORED, or turned out to be anchored by virtue of its contents, it
# Line 417  below) and trying an ordinary match agai Line 488  below) and trying an ordinary match agai
488    
489  The subject string is passed as a pointer in \fIsubject\fR, a length in  The subject string is passed as a pointer in \fIsubject\fR, a length in
490  \fIlength\fR, and a starting offset in \fIstartoffset\fR. Unlike the pattern  \fIlength\fR, and a starting offset in \fIstartoffset\fR. Unlike the pattern
491  string, it may contain binary zero characters. When the starting offset is  string, the subject may contain binary zero characters. When the starting
492  zero, the search for a match starts at the beginning of the subject, and this  offset is zero, the search for a match starts at the beginning of the subject,
493  is by far the most common case.  and this is by far the most common case.
494    
495  A non-zero starting offset is useful when searching for another match in the  A non-zero starting offset is useful when searching for another match in the
496  same subject by calling \fBpcre_exec()\fR again after a previous success.  same subject by calling \fBpcre_exec()\fR again after a previous success.
# Line 550  is a pointer to the vector of integer of Line 621  is a pointer to the vector of integer of
621  were captured by the match, including the substring that matched the entire  were captured by the match, including the substring that matched the entire
622  regular expression. This is the value returned by \fBpcre_exec\fR if it  regular expression. This is the value returned by \fBpcre_exec\fR if it
623  is greater than zero. If \fBpcre_exec()\fR returned zero, indicating that it  is greater than zero. If \fBpcre_exec()\fR returned zero, indicating that it
624  ran out of space in \fIovector\fR, then the value passed as  ran out of space in \fIovector\fR, the value passed as \fIstringcount\fR should
625  \fIstringcount\fR should be the size of the vector divided by three.  be the size of the vector divided by three.
626    
627  The functions \fBpcre_copy_substring()\fR and \fBpcre_get_substring()\fR  The functions \fBpcre_copy_substring()\fR and \fBpcre_get_substring()\fR
628  extract a single substring, whose number is given as \fIstringnumber\fR. A  extract a single substring, whose number is given as \fIstringnumber\fR. A
629  value of zero extracts the substring that matched the entire pattern, while  value of zero extracts the substring that matched the entire pattern, while
630  higher values extract the captured substrings. For \fBpcre_copy_substring()\fR,  higher values extract the captured substrings. For \fBpcre_copy_substring()\fR,
631  the string is placed in \fIbuffer\fR, whose length is given by  the string is placed in \fIbuffer\fR, whose length is given by
632  \fIbuffersize\fR, while for \fBpcre_get_substring()\fR a new block of store is  \fIbuffersize\fR, while for \fBpcre_get_substring()\fR a new block of memory is
633  obtained via \fBpcre_malloc\fR, and its address is returned via  obtained via \fBpcre_malloc\fR, and its address is returned via
634  \fIstringptr\fR. The yield of the function is the length of the string, not  \fIstringptr\fR. The yield of the function is the length of the string, not
635  including the terminating zero, or one of  including the terminating zero, or one of
# Line 590  string. This can be distinguished from a Line 661  string. This can be distinguished from a
661  inspecting the appropriate offset in \fIovector\fR, which is negative for unset  inspecting the appropriate offset in \fIovector\fR, which is negative for unset
662  substrings.  substrings.
663    
664    The two convenience functions \fBpcre_free_substring()\fR and
665    \fBpcre_free_substring_list()\fR can be used to free the memory returned by
666    a previous call of \fBpcre_get_substring()\fR or
667    \fBpcre_get_substring_list()\fR, respectively. They do nothing more than call
668    the function pointed to by \fBpcre_free\fR, which of course could be called
669    directly from a C program. However, PCRE is used in some situations where it is
670    linked via a special interface to another programming language which cannot use
671    \fBpcre_free\fR directly; it is for these cases that the functions are
672    provided.
673    
674    
675  .SH LIMITATIONS  .SH LIMITATIONS
# Line 597  There are some size limitations in PCRE Line 677  There are some size limitations in PCRE
677  practice be relevant.  practice be relevant.
678  The maximum length of a compiled pattern is 65539 (sic) bytes.  The maximum length of a compiled pattern is 65539 (sic) bytes.
679  All values in repeating quantifiers must be less than 65536.  All values in repeating quantifiers must be less than 65536.
680  The maximum number of capturing subpatterns is 99.  There maximum number of capturing subpatterns is 65535.
681  The maximum number of all parenthesized subpatterns, including capturing  There is no limit to the number of non-capturing subpatterns, but the maximum
682    depth of nesting of all kinds of parenthesized subpattern, including capturing
683  subpatterns, assertions, and other types of subpattern, is 200.  subpatterns, assertions, and other types of subpattern, is 200.
684    
685  The maximum length of a subject string is the largest positive number that an  The maximum length of a subject string is the largest positive number that an
# Line 650  patterns using the non-Perl item (?R). Line 731  patterns using the non-Perl item (?R).
731  with the settings of captured strings when part of a pattern is repeated. For  with the settings of captured strings when part of a pattern is repeated. For
732  example, matching "aba" against the pattern /^(a(b)?)+$/ sets $2 to the value  example, matching "aba" against the pattern /^(a(b)?)+$/ sets $2 to the value
733  "b", but matching "aabbaa" against /^(aa(bb)?)+$/ leaves $2 unset. However, if  "b", but matching "aabbaa" against /^(aa(bb)?)+$/ leaves $2 unset. However, if
734  the pattern is changed to /^(aa(b(b))?)+$/ then $2 (and $3) get set.  the pattern is changed to /^(aa(b(b))?)+$/ then $2 (and $3) are set.
735    
736  In Perl 5.004 $2 is set in both cases, and that is also true of PCRE. If in the  In Perl 5.004 $2 is set in both cases, and that is also true of PCRE. If in the
737  future Perl changes to a consistent state that is different, PCRE may change to  future Perl changes to a consistent state that is different, PCRE may change to
# Line 691  The syntax and semantics of the regular Line 772  The syntax and semantics of the regular
772  described below. Regular expressions are also described in the Perl  described below. Regular expressions are also described in the Perl
773  documentation and in a number of other books, some of which have copious  documentation and in a number of other books, some of which have copious
774  examples. Jeffrey Friedl's "Mastering Regular Expressions", published by  examples. Jeffrey Friedl's "Mastering Regular Expressions", published by
775  O'Reilly (ISBN 1-56592-257), covers them in great detail. The description  O'Reilly (ISBN 1-56592-257), covers them in great detail.
776  here is intended as reference documentation.  
777    The description here is intended as reference documentation. The basic
778    operation of PCRE is on strings of bytes. However, there is the beginnings of
779    some support for UTF-8 character strings. To use this support you must
780    configure PCRE to include it, and then call \fBpcre_compile()\fR with the
781    PCRE_UTF8 option. How this affects the pattern matching is described in the
782    final section of this document.
783    
784  A regular expression is a pattern that is matched against a subject string from  A regular expression is a pattern that is matched against a subject string from
785  left to right. Most characters stand for themselves in a pattern, and match the  left to right. Most characters stand for themselves in a pattern, and match the
# Line 914  PCRE_MULTILINE is set. Line 1001  PCRE_MULTILINE is set.
1001    
1002  Note that the sequences \\A, \\Z, and \\z can be used to match the start and  Note that the sequences \\A, \\Z, and \\z can be used to match the start and
1003  end of the subject in both modes, and if all branches of a pattern start with  end of the subject in both modes, and if all branches of a pattern start with
1004  \\A is it always anchored, whether PCRE_MULTILINE is set or not.  \\A it is always anchored, whether PCRE_MULTILINE is set or not.
1005    
1006    
1007  .SH FULL STOP (PERIOD, DOT)  .SH FULL STOP (PERIOD, DOT)
1008  Outside a character class, a dot in the pattern matches any one character in  Outside a character class, a dot in the pattern matches any one character in
1009  the subject, including a non-printing character, but not (by default) newline.  the subject, including a non-printing character, but not (by default) newline.
1010  If the PCRE_DOTALL option is set, then dots match newlines as well. The  If the PCRE_DOTALL option is set, dots match newlines as well. The handling of
1011  handling of dot is entirely independent of the handling of circumflex and  dot is entirely independent of the handling of circumflex and dollar, the only
1012  dollar, the only relationship being that they both involve newline characters.  relationship being that they both involve newline characters. Dot has no
1013  Dot has no special meaning in a character class.  special meaning in a character class.
1014    
1015    
1016  .SH SQUARE BRACKETS  .SH SQUARE BRACKETS
# Line 1018  negation, which is indicated by a ^ char Line 1105  negation, which is indicated by a ^ char
1105    
1106    [12[:^digit:]]    [12[:^digit:]]
1107    
1108  matches "1", "2", or any non-digit. PCRE (and Perl) also recogize the POSIX  matches "1", "2", or any non-digit. PCRE (and Perl) also recognize the POSIX
1109  syntax [.ch.] and [=ch=] where "ch" is a "collating element", but these are not  syntax [.ch.] and [=ch=] where "ch" is a "collating element", but these are not
1110  supported, and an error is given if they are encountered.  supported, and an error is given if they are encountered.
1111    
# Line 1116  For example, if the string "the red king Line 1203  For example, if the string "the red king
1203    the ((red|white) (king|queen))    the ((red|white) (king|queen))
1204    
1205  the captured substrings are "red king", "red", and "king", and are numbered 1,  the captured substrings are "red king", "red", and "king", and are numbered 1,
1206  2, and 3.  2, and 3, respectively.
1207    
1208  The fact that plain parentheses fulfil two functions is not always helpful.  The fact that plain parentheses fulfil two functions is not always helpful.
1209  There are often times when a grouping subpattern is required without a  There are often times when a grouping subpattern is required without a
# Line 1210  to the string Line 1297  to the string
1297    
1298    /* first command */  not comment  /* second comment */    /* first command */  not comment  /* second comment */
1299    
1300  fails, because it matches the entire string due to the greediness of the .*  fails, because it matches the entire string owing to the greediness of the .*
1301  item.  item.
1302    
1303  However, if a quantifier is followed by a question mark, then it ceases to be  However, if a quantifier is followed by a question mark, it ceases to be
1304  greedy, and instead matches the minimum number of times possible, so the  greedy, and instead matches the minimum number of times possible, so the
1305  pattern  pattern
1306    
# Line 1229  own right. Because it has two uses, it c Line 1316  own right. Because it has two uses, it c
1316  which matches one digit by preference, but can match two if that is the only  which matches one digit by preference, but can match two if that is the only
1317  way the rest of the pattern matches.  way the rest of the pattern matches.
1318    
1319  If the PCRE_UNGREEDY option is set (an option which is not available in Perl)  If the PCRE_UNGREEDY option is set (an option which is not available in Perl),
1320  then the quantifiers are not greedy by default, but individual ones can be made  the quantifiers are not greedy by default, but individual ones can be made
1321  greedy by following them with a question mark. In other words, it inverts the  greedy by following them with a question mark. In other words, it inverts the
1322  default behaviour.  default behaviour.
1323    
# Line 1239  is greater than 1 or with a limited maxi Line 1326  is greater than 1 or with a limited maxi
1326  compiled pattern, in proportion to the size of the minimum or maximum.  compiled pattern, in proportion to the size of the minimum or maximum.
1327    
1328  If a pattern starts with .* or .{0,} and the PCRE_DOTALL option (equivalent  If a pattern starts with .* or .{0,} and the PCRE_DOTALL option (equivalent
1329  to Perl's /s) is set, thus allowing the . to match newlines, then the pattern  to Perl's /s) is set, thus allowing the . to match newlines, the pattern is
1330  is implicitly anchored, because whatever follows will be tried against every  implicitly anchored, because whatever follows will be tried against every
1331  character position in the subject string, so there is no point in retrying the  character position in the subject string, so there is no point in retrying the
1332  overall match at any position after the first. PCRE treats such a pattern as  overall match at any position after the first. PCRE treats such a pattern as
1333  though it were preceded by \\A. In cases where it is known that the subject  though it were preceded by \\A. In cases where it is known that the subject
# Line 1284  itself. So the pattern Line 1371  itself. So the pattern
1371    
1372  matches "sense and sensibility" and "response and responsibility", but not  matches "sense and sensibility" and "response and responsibility", but not
1373  "sense and responsibility". If caseful matching is in force at the time of the  "sense and responsibility". If caseful matching is in force at the time of the
1374  back reference, then the case of letters is relevant. For example,  back reference, the case of letters is relevant. For example,
1375    
1376    ((?i)rah)\\s+\\1    ((?i)rah)\\s+\\1
1377    
# Line 1292  matches "rah rah" and "RAH RAH", but not Line 1379  matches "rah rah" and "RAH RAH", but not
1379  capturing subpattern is matched caselessly.  capturing subpattern is matched caselessly.
1380    
1381  There may be more than one back reference to the same subpattern. If a  There may be more than one back reference to the same subpattern. If a
1382  subpattern has not actually been used in a particular match, then any back  subpattern has not actually been used in a particular match, any back
1383  references to it always fail. For example, the pattern  references to it always fail. For example, the pattern
1384    
1385    (a|(bc))\\2    (a|(bc))\\2
# Line 1300  references to it always fail. For exampl Line 1387  references to it always fail. For exampl
1387  always fails if it starts to match "a" rather than "bc". Because there may be  always fails if it starts to match "a" rather than "bc". Because there may be
1388  up to 99 back references, all digits following the backslash are taken  up to 99 back references, all digits following the backslash are taken
1389  as part of a potential back reference number. If the pattern continues with a  as part of a potential back reference number. If the pattern continues with a
1390  digit character, then some delimiter must be used to terminate the back  digit character, some delimiter must be used to terminate the back reference.
1391  reference. If the PCRE_EXTENDED option is set, this can be whitespace.  If the PCRE_EXTENDED option is set, this can be whitespace. Otherwise an empty
1392  Otherwise an empty comment can be used.  comment can be used.
1393    
1394  A back reference that occurs inside the parentheses to which it refers fails  A back reference that occurs inside the parentheses to which it refers fails
1395  when the subpattern is first used, so, for example, (a\\1) never matches.  when the subpattern is first used, so, for example, (a\\1) never matches.
# Line 1311  example, the pattern Line 1398  example, the pattern
1398    
1399    (a|b\\1)+    (a|b\\1)+
1400    
1401  matches any number of "a"s and also "aba", "ababaa" etc. At each iteration of  matches any number of "a"s and also "aba", "ababbaa" etc. At each iteration of
1402  the subpattern, the back reference matches the character string corresponding  the subpattern, the back reference matches the character string corresponding
1403  to the previous iteration. In order for this to work, the pattern must be such  to the previous iteration. In order for this to work, the pattern must be such
1404  that the first iteration does not need to match the back reference. This can be  that the first iteration does not need to match the back reference. This can be
# Line 1390  Several assertions (of any sort) may occ Line 1477  Several assertions (of any sort) may occ
1477  matches "foo" preceded by three digits that are not "999". Notice that each of  matches "foo" preceded by three digits that are not "999". Notice that each of
1478  the assertions is applied independently at the same point in the subject  the assertions is applied independently at the same point in the subject
1479  string. First there is a check that the previous three characters are all  string. First there is a check that the previous three characters are all
1480  digits, then there is a check that the same three characters are not "999".  digits, and then there is a check that the same three characters are not "999".
1481  This pattern does \fInot\fR match "foo" preceded by six characters, the first  This pattern does \fInot\fR match "foo" preceded by six characters, the first
1482  of which are digits and the last three of which are not "999". For example, it  of which are digits and the last three of which are not "999". For example, it
1483  doesn't match "123abcfoo". A pattern to do that is  doesn't match "123abcfoo". A pattern to do that is
# Line 1475  what follows matches the rest of the pat Line 1562  what follows matches the rest of the pat
1562    
1563    ^.*abcd$    ^.*abcd$
1564    
1565  then the initial .* matches the entire string at first, but when this fails  the initial .* matches the entire string at first, but when this fails (because
1566  (because there is no following "a"), it backtracks to match all but the last  there is no following "a"), it backtracks to match all but the last character,
1567  character, then all but the last two characters, and so on. Once again the  then all but the last two characters, and so on. Once again the search for "a"
1568  search for "a" covers the entire string, from right to left, so we are no  covers the entire string, from right to left, so we are no better off. However,
1569  better off. However, if the pattern is written as  if the pattern is written as
1570    
1571    ^(?>.*)(?<=abcd)    ^(?>.*)(?<=abcd)
1572    
1573  then there can be no backtracking for the .* item; it can match only the entire  there can be no backtracking for the .* item; it can match only the entire
1574  string. The subsequent lookbehind assertion does a single test on the last four  string. The subsequent lookbehind assertion does a single test on the last four
1575  characters. If it fails, the match fails immediately. For long strings, this  characters. If it fails, the match fails immediately. For long strings, this
1576  approach makes a significant difference to the processing time.  approach makes a significant difference to the processing time.
# Line 1528  no-pattern (if present) is used. If ther Line 1615  no-pattern (if present) is used. If ther
1615  subpattern, a compile-time error occurs.  subpattern, a compile-time error occurs.
1616    
1617  There are two kinds of condition. If the text between the parentheses consists  There are two kinds of condition. If the text between the parentheses consists
1618  of a sequence of digits, then the condition is satisfied if the capturing  of a sequence of digits, the condition is satisfied if the capturing subpattern
1619  subpattern of that number has previously matched. Consider the following  of that number has previously matched. The number must be greater than zero.
1620  pattern, which contains non-significant white space to make it more readable  Consider the following pattern, which contains non-significant white space to
1621  (assume the PCRE_EXTENDED option) and to divide it into three parts for ease  make it more readable (assume the PCRE_EXTENDED option) and to divide it into
1622  of discussion:  three parts for ease of discussion:
1623    
1624    ( \\( )?    [^()]+    (?(1) \\) )    ( \\( )?    [^()]+    (?(1) \\) )
1625    
# Line 1622  on at the top level. If additional paren Line 1709  on at the top level. If additional paren
1709    \\( ( ( (?>[^()]+) | (?R) )* ) \\)    \\( ( ( (?>[^()]+) | (?R) )* ) \\)
1710       ^                        ^       ^                        ^
1711       ^                        ^       ^                        ^
1712  then the string they capture is "ab(cd)ef", the contents of the top level  the string they capture is "ab(cd)ef", the contents of the top level
1713  parentheses. If there are more than 15 capturing parentheses in a pattern, PCRE  parentheses. If there are more than 15 capturing parentheses in a pattern, PCRE
1714  has to obtain extra memory to store data during a recursion, which it does by  has to obtain extra memory to store data during a recursion, which it does by
1715  using \fBpcre_malloc\fR, freeing it via \fBpcre_free\fR afterwards. If no  using \fBpcre_malloc\fR, freeing it via \fBpcre_free\fR afterwards. If no
# Line 1686  with the pattern above. The former gives Line 1773  with the pattern above. The former gives
1773  applied to a whole line of "a" characters, whereas the latter takes an  applied to a whole line of "a" characters, whereas the latter takes an
1774  appreciable time with strings longer than about 20 characters.  appreciable time with strings longer than about 20 characters.
1775    
1776    
1777    .SH UTF-8 SUPPORT
1778    Starting at release 3.3, PCRE has some support for character strings encoded
1779    in the UTF-8 format. This is incomplete, and is regarded as experimental. In
1780    order to use it, you must configure PCRE to include UTF-8 support in the code,
1781    and, in addition, you must call \fBpcre_compile()\fR with the PCRE_UTF8 option
1782    flag. When you do this, both the pattern and any subject strings that are
1783    matched against it are treated as UTF-8 strings instead of just strings of
1784    bytes, but only in the cases that are mentioned below.
1785    
1786    If you compile PCRE with UTF-8 support, but do not use it at run time, the
1787    library will be a bit bigger, but the additional run time overhead is limited
1788    to testing the PCRE_UTF8 flag in several places, so should not be very large.
1789    
1790    PCRE assumes that the strings it is given contain valid UTF-8 codes. It does
1791    not diagnose invalid UTF-8 strings. If you pass invalid UTF-8 strings to PCRE,
1792    the results are undefined.
1793    
1794    Running with PCRE_UTF8 set causes these changes in the way PCRE works:
1795    
1796    1. In a pattern, the escape sequence \\x{...}, where the contents of the braces
1797    is a string of hexadecimal digits, is interpreted as a UTF-8 character whose
1798    code number is the given hexadecimal number, for example: \\x{1234}. This
1799    inserts from one to six literal bytes into the pattern, using the UTF-8
1800    encoding. If a non-hexadecimal digit appears between the braces, the item is
1801    not recognized.
1802    
1803    2. The original hexadecimal escape sequence, \\xhh, generates a two-byte UTF-8
1804    character if its value is greater than 127.
1805    
1806    3. Repeat quantifiers are NOT correctly handled if they follow a multibyte
1807    character. For example, \\x{100}* and \\xc3+ do not work. If you want to
1808    repeat such characters, you must enclose them in non-capturing parentheses,
1809    for example (?:\\x{100}), at present.
1810    
1811    4. The dot metacharacter matches one UTF-8 character instead of a single byte.
1812    
1813    5. Unlike literal UTF-8 characters, the dot metacharacter followed by a
1814    repeat quantifier does operate correctly on UTF-8 characters instead of
1815    single bytes.
1816    
1817    4. Although the \\x{...} escape is permitted in a character class, characters
1818    whose values are greater than 255 cannot be included in a class.
1819    
1820    5. A class is matched against a UTF-8 character instead of just a single byte,
1821    but it can match only characters whose values are less than 256. Characters
1822    with greater values always fail to match a class.
1823    
1824    6. Repeated classes work correctly on multiple characters.
1825    
1826    7. Classes containing just a single character whose value is greater than 127
1827    (but less than 256), for example, [\\x80] or [^\\x{93}], do not work because
1828    these are optimized into single byte matches. In the first case, of course,
1829    the class brackets are just redundant.
1830    
1831    8. Lookbehind assertions move backwards in the subject by a fixed number of
1832    characters instead of a fixed number of bytes. Simple cases have been tested
1833    to work correctly, but there may be hidden gotchas herein.
1834    
1835    9. The character types such as \\d and \\w do not work correctly with UTF-8
1836    characters. They continue to test a single byte.
1837    
1838    10. Anything not explicitly mentioned here continues to work in bytes rather
1839    than in characters.
1840    
1841    The following UTF-8 features of Perl 5.6 are not implemented:
1842    
1843    1. The escape sequence \\C to match a single byte.
1844    
1845    2. The use of Unicode tables and properties and escapes \\p, \\P, and \\X.
1846    
1847    
1848    .SH SAMPLE PROGRAM
1849    The code below is a simple, complete demonstration program, to get you started
1850    with using PCRE. This code is also supplied in the file \fIpcredemo.c\fR in the
1851    PCRE distribution.
1852    
1853    The program compiles the regular expression that is its first argument, and
1854    matches it against the subject string in its second argument. No options are
1855    set, and default character tables are used. If matching succeeds, the program
1856    outputs the portion of the subject that matched, together with the contents of
1857    any captured substrings.
1858    
1859    On a Unix system that has PCRE installed in \fI/usr/local\fR, you can compile
1860    the demonstration program using a command like this:
1861    
1862      gcc -o pcredemo pcredemo.c -I/usr/local/include -L/usr/local/lib -lpcre
1863    
1864    Then you can run simple tests like this:
1865    
1866      ./pcredemo 'cat|dog' 'the cat sat on the mat'
1867    
1868    Note that there is a much more comprehensive test program, called
1869    \fBpcretest\fR, which supports many more facilities for testing regular
1870    expressions. The \fBpcredemo\fR program is provided as a simple coding example.
1871    
1872    On some operating systems (e.g. Solaris) you may get an error like this when
1873    you try to run \fBpcredemo\fR:
1874    
1875      ld.so.1: a.out: fatal: libpcre.so.0: open failed: No such file or directory
1876    
1877    This is caused by the way shared library support works on those systems. You
1878    need to add
1879    
1880      -R/usr/local/lib
1881    
1882    to the compile command to get round this problem. Here's the code:
1883    
1884      #include <stdio.h>
1885      #include <string.h>
1886      #include <pcre.h>
1887    
1888      #define OVECCOUNT 30    /* should be a multiple of 3 */
1889    
1890      int main(int argc, char **argv)
1891      {
1892      pcre *re;
1893      const char *error;
1894      int erroffset;
1895      int ovector[OVECCOUNT];
1896      int rc, i;
1897    
1898      if (argc != 3)
1899        {
1900        printf("Two arguments required: a regex and a "
1901          "subject string\\n");
1902        return 1;
1903        }
1904    
1905      /* Compile the regular expression in the first argument */
1906    
1907      re = pcre_compile(
1908        argv[1],     /* the pattern */
1909        0,           /* default options */
1910        &error,      /* for error message */
1911        &erroffset,  /* for error offset */
1912        NULL);       /* use default character tables */
1913    
1914      /* Compilation failed: print the error message and exit */
1915    
1916      if (re == NULL)
1917        {
1918        printf("PCRE compilation failed at offset %d: %s\\n",
1919          erroffset, error);
1920        return 1;
1921        }
1922    
1923      /* Compilation succeeded: match the subject in the second
1924         argument */
1925    
1926      rc = pcre_exec(
1927        re,          /* the compiled pattern */
1928        NULL,        /* we didn't study the pattern */
1929        argv[2],     /* the subject string */
1930        (int)strlen(argv[2]), /* the length of the subject */
1931        0,           /* start at offset 0 in the subject */
1932        0,           /* default options */
1933        ovector,     /* vector for substring information */
1934        OVECCOUNT);  /* number of elements in the vector */
1935    
1936      /* Matching failed: handle error cases */
1937    
1938      if (rc < 0)
1939        {
1940        switch(rc)
1941          {
1942          case PCRE_ERROR_NOMATCH: printf("No match\\n"); break;
1943          /*
1944          Handle other special cases if you like
1945          */
1946          default: printf("Matching error %d\\n", rc); break;
1947          }
1948        return 1;
1949        }
1950    
1951      /* Match succeded */
1952    
1953      printf("Match succeeded\\n");
1954    
1955      /* The output vector wasn't big enough */
1956    
1957      if (rc == 0)
1958        {
1959        rc = OVECCOUNT/3;
1960        printf("ovector only has room for %d captured "
1961          substrings\\n", rc - 1);
1962        }
1963    
1964      /* Show substrings stored in the output vector */
1965    
1966      for (i = 0; i < rc; i++)
1967        {
1968        char *substring_start = argv[2] + ovector[2*i];
1969        int substring_length = ovector[2*i+1] - ovector[2*i];
1970        printf("%2d: %.*s\\n", i, substring_length,
1971          substring_start);
1972        }
1973    
1974      return 0;
1975      }
1976    
1977    
1978  .SH AUTHOR  .SH AUTHOR
1979  Philip Hazel <ph10@cam.ac.uk>  Philip Hazel <ph10@cam.ac.uk>
1980  .br  .br
# Line 1697  Cambridge CB2 3QG, England. Line 1986  Cambridge CB2 3QG, England.
1986  .br  .br
1987  Phone: +44 1223 334714  Phone: +44 1223 334714
1988    
1989  Last updated: 27 January 2000  Last updated: 15 August 2001
1990  .br  .br
1991  Copyright (c) 1997-2000 University of Cambridge.  Copyright (c) 1997-2001 University of Cambridge.
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