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PCREAPI(3)							    PCREAPI(3)

NAME
       PCRE - Perl-compatible regular expressions

PCRE NATIVE API

       #include <pcre.h>

       pcre *pcre_compile(const char *pattern, int options,
	    const char **errptr, int *erroffset,
	    const unsigned char *tableptr);

       pcre *pcre_compile2(const char *pattern, int options,
	    int *errorcodeptr,
	    const char **errptr, int *erroffset,
	    const unsigned char *tableptr);

       pcre_extra *pcre_study(const pcre *code, int options,
	    const char **errptr);

       int pcre_exec(const pcre *code, const pcre_extra *extra,
	    const char *subject, int length, int startoffset,
	    int options, int *ovector, int ovecsize);

       int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
	    const char *subject, int length, int startoffset,
	    int options, int *ovector, int ovecsize,
	    int *workspace, int wscount);

       int pcre_copy_named_substring(const pcre *code,
	    const char *subject, int *ovector,
	    int stringcount, const char *stringname,
	    char *buffer, int buffersize);

       int pcre_copy_substring(const char *subject, int *ovector,
	    int stringcount, int stringnumber, char *buffer,
	    int buffersize);

       int pcre_get_named_substring(const pcre *code,
	    const char *subject, int *ovector,
	    int stringcount, const char *stringname,
	    const char **stringptr);

       int pcre_get_stringnumber(const pcre *code,
	    const char *name);

       int pcre_get_stringtable_entries(const pcre *code,
	    const char *name, char **first, char **last);

       int pcre_get_substring(const char *subject, int *ovector,
	    int stringcount, int stringnumber,
	    const char **stringptr);

       int pcre_get_substring_list(const char *subject,
	    int *ovector, int stringcount, const char ***listptr);

       void pcre_free_substring(const char *stringptr);

       void pcre_free_substring_list(const char **stringptr);

       const unsigned char *pcre_maketables(void);

       int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
	    int what, void *where);

       int pcre_info(const pcre *code, int *optptr, int *firstcharptr);

       int pcre_refcount(pcre *code, int adjust);

       int pcre_config(int what, void *where);

       char *pcre_version(void);

       void *(*pcre_malloc)(size_t);

       void (*pcre_free)(void *);

       void *(*pcre_stack_malloc)(size_t);

       void (*pcre_stack_free)(void *);

       int (*pcre_callout)(pcre_callout_block *);

PCRE API OVERVIEW

       PCRE has its own native API, which is described in this document. There
       are also some wrapper functions that correspond to  the	POSIX  regular
       expression  API.	 These	are  described in the pcreposix documentation.
       Both of these APIs define a set of C function calls. A C++  wrapper  is
       distributed with PCRE. It is documented in the pcrecpp page.

       The  native  API	 C  function prototypes are defined in the header file
       pcre.h, and on Unix systems the library itself is called	 libpcre.   It
       can normally be accessed by adding -lpcre to the command for linking an
       application  that  uses	PCRE.  The  header  file  defines  the	macros
       PCRE_MAJOR  and	PCRE_MINOR to contain the major and minor release num‐
       bers for the library.  Applications can use these  to  include  support
       for different releases of PCRE.

       In a Windows environment, if you want to statically link an application
       program against a non-dll pcre.a	 file,	you  must  define  PCRE_STATIC
       before  including  pcre.h or pcrecpp.h, because otherwise the pcre_mal‐
       loc()   and   pcre_free()   exported   functions	  will	 be   declared
       __declspec(dllimport), with unwanted results.

       The   functions	 pcre_compile(),  pcre_compile2(),  pcre_study(),  and
       pcre_exec() are used for compiling and matching regular expressions  in
       a  Perl-compatible  manner. A sample program that demonstrates the sim‐
       plest way of using them is provided in the file	called	pcredemo.c  in
       the PCRE source distribution. A listing of this program is given in the
       pcredemo documentation, and the pcresample documentation describes  how
       to compile and run it.

       A second matching function, pcre_dfa_exec(), which is not Perl-compati‐
       ble, is also provided. This uses a different algorithm for  the	match‐
       ing.  The  alternative algorithm finds all possible matches (at a given
       point in the subject), and scans the subject just  once	(unless	 there
       are  lookbehind	assertions).  However,	this algorithm does not return
       captured substrings. A description of the two matching  algorithms  and
       their  advantages  and disadvantages is given in the pcrematching docu‐
       mentation.

       In addition to the main compiling and  matching	functions,  there  are
       convenience functions for extracting captured substrings from a subject
       string that is matched by pcre_exec(). They are:

	 pcre_copy_substring()
	 pcre_copy_named_substring()
	 pcre_get_substring()
	 pcre_get_named_substring()
	 pcre_get_substring_list()
	 pcre_get_stringnumber()
	 pcre_get_stringtable_entries()

       pcre_free_substring() and pcre_free_substring_list() are also provided,
       to free the memory used for extracted strings.

       The  function  pcre_maketables()	 is  used  to build a set of character
       tables  in  the	current	 locale	  for	passing	  to   pcre_compile(),
       pcre_exec(),  or	 pcre_dfa_exec(). This is an optional facility that is
       provided for specialist use.  Most  commonly,  no  special  tables  are
       passed,	in  which case internal tables that are generated when PCRE is
       built are used.

       The function pcre_fullinfo() is used to find out	 information  about  a
       compiled	 pattern; pcre_info() is an obsolete version that returns only
       some of the available information, but is retained for  backwards  com‐
       patibility.   The function pcre_version() returns a pointer to a string
       containing the version of PCRE and its date of release.

       The function pcre_refcount() maintains a	 reference  count  in  a  data
       block  containing  a compiled pattern. This is provided for the benefit
       of object-oriented applications.

       The global variables pcre_malloc and pcre_free  initially  contain  the
       entry  points  of  the  standard malloc() and free() functions, respec‐
       tively. PCRE calls the memory management functions via these variables,
       so  a  calling  program	can replace them if it wishes to intercept the
       calls. This should be done before calling any PCRE functions.

       The global variables pcre_stack_malloc  and  pcre_stack_free  are  also
       indirections  to	 memory	 management functions. These special functions
       are used only when PCRE is compiled to use  the	heap  for  remembering
       data, instead of recursive function calls, when running the pcre_exec()
       function. See the pcrebuild documentation for  details  of  how	to  do
       this.  It  is  a non-standard way of building PCRE, for use in environ‐
       ments that have limited stacks. Because of the greater  use  of	memory
       management,  it	runs  more  slowly. Separate functions are provided so
       that special-purpose external code can be  used	for  this  case.  When
       used,  these  functions	are always called in a stack-like manner (last
       obtained, first freed), and always for memory blocks of the same	 size.
       There  is  a discussion about PCRE's stack usage in the pcrestack docu‐
       mentation.

       The global variable pcre_callout initially contains NULL. It can be set
       by  the	caller	to  a "callout" function, which PCRE will then call at
       specified points during a matching operation. Details are given in  the
       pcrecallout documentation.

NEWLINES

       PCRE  supports five different conventions for indicating line breaks in
       strings: a single CR (carriage return) character, a  single  LF	(line‐
       feed) character, the two-character sequence CRLF, any of the three pre‐
       ceding, or any Unicode newline sequence. The Unicode newline  sequences
       are  the	 three just mentioned, plus the single characters VT (vertical
       tab, U+000B), FF (formfeed, U+000C), NEL (next line, U+0085), LS	 (line
       separator, U+2028), and PS (paragraph separator, U+2029).

       Each  of	 the first three conventions is used by at least one operating
       system as its standard newline sequence. When PCRE is built, a  default
       can  be	specified.  The default default is LF, which is the Unix stan‐
       dard. When PCRE is run, the default can be overridden,  either  when  a
       pattern is compiled, or when it is matched.

       At compile time, the newline convention can be specified by the options
       argument of pcre_compile(), or it can be specified by special  text  at
       the start of the pattern itself; this overrides any other settings. See
       the pcrepattern page for details of the special character sequences.

       In the PCRE documentation the word "newline" is used to mean "the char‐
       acter  or pair of characters that indicate a line break". The choice of
       newline convention affects the handling of  the	dot,  circumflex,  and
       dollar metacharacters, the handling of #-comments in /x mode, and, when
       CRLF is a recognized line ending sequence, the match position  advance‐
       ment for a non-anchored pattern. There is more detail about this in the
       section on pcre_exec() options below.

       The choice of newline convention does not affect the interpretation  of
       the  \n	or  \r	escape	sequences, nor does it affect what \R matches,
       which is controlled in a similar way, but by separate options.

MULTITHREADING

       The PCRE functions can be used in  multi-threading  applications,  with
       the  proviso  that  the	memory	management  functions  pointed	to  by
       pcre_malloc, pcre_free, pcre_stack_malloc, and pcre_stack_free, and the
       callout function pointed to by pcre_callout, are shared by all threads.

       The  compiled form of a regular expression is not altered during match‐
       ing, so the same compiled pattern can safely be used by several threads
       at once.

SAVING PRECOMPILED PATTERNS FOR LATER USE

       The compiled form of a regular expression can be saved and re-used at a
       later time, possibly by a different program, and even on a  host	 other
       than  the  one  on  which  it  was  compiled.  Details are given in the
       pcreprecompile documentation. However, compiling a  regular  expression
       with  one version of PCRE for use with a different version is not guar‐
       anteed to work and may cause crashes.

CHECKING BUILD-TIME OPTIONS

       int pcre_config(int what, void *where);

       The function pcre_config() makes it possible for a PCRE client to  dis‐
       cover which optional features have been compiled into the PCRE library.
       The pcrebuild documentation has more details about these optional  fea‐
       tures.

       The  first  argument  for pcre_config() is an integer, specifying which
       information is required; the second argument is a pointer to a variable
       into  which  the	 information  is  placed. The following information is
       available:

	 PCRE_CONFIG_UTF8

       The output is an integer that is set to one if UTF-8 support is	avail‐
       able; otherwise it is set to zero.

	 PCRE_CONFIG_UNICODE_PROPERTIES

       The  output  is	an  integer  that is set to one if support for Unicode
       character properties is available; otherwise it is set to zero.

	 PCRE_CONFIG_NEWLINE

       The output is an integer whose value specifies  the  default  character
       sequence	 that is recognized as meaning "newline". The four values that
       are supported are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for ANYCRLF,
       and  -1	for  ANY.  Though they are derived from ASCII, the same values
       are returned in EBCDIC environments. The default should normally corre‐
       spond to the standard sequence for your operating system.

	 PCRE_CONFIG_BSR

       The output is an integer whose value indicates what character sequences
       the \R escape sequence matches by default. A value of 0 means  that  \R
       matches	any  Unicode  line ending sequence; a value of 1 means that \R
       matches only CR, LF, or CRLF. The default can be overridden when a pat‐
       tern is compiled or matched.

	 PCRE_CONFIG_LINK_SIZE

       The  output  is	an  integer that contains the number of bytes used for
       internal linkage in compiled regular expressions. The value is 2, 3, or
       4.  Larger  values  allow larger regular expressions to be compiled, at
       the expense of slower matching. The default value of  2	is  sufficient
       for  all	 but  the  most massive patterns, since it allows the compiled
       pattern to be up to 64K in size.

	 PCRE_CONFIG_POSIX_MALLOC_THRESHOLD

       The output is an integer that contains the threshold  above  which  the
       POSIX  interface	 uses malloc() for output vectors. Further details are
       given in the pcreposix documentation.

	 PCRE_CONFIG_MATCH_LIMIT

       The output is a long integer that gives the default limit for the  num‐
       ber  of	internal  matching  function calls in a pcre_exec() execution.
       Further details are given with pcre_exec() below.

	 PCRE_CONFIG_MATCH_LIMIT_RECURSION

       The output is a long integer that gives the default limit for the depth
       of   recursion  when  calling  the  internal  matching  function	 in  a
       pcre_exec() execution.  Further	details	 are  given  with  pcre_exec()
       below.

	 PCRE_CONFIG_STACKRECURSE

       The  output is an integer that is set to one if internal recursion when
       running pcre_exec() is implemented by recursive function calls that use
       the  stack  to remember their state. This is the usual way that PCRE is
       compiled. The output is zero if PCRE was compiled to use blocks of data
       on  the	heap  instead  of  recursive  function	calls.	In  this case,
       pcre_stack_malloc and  pcre_stack_free  are  called  to	manage	memory
       blocks on the heap, thus avoiding the use of the stack.

COMPILING A PATTERN

       pcre *pcre_compile(const char *pattern, int options,
	    const char **errptr, int *erroffset,
	    const unsigned char *tableptr);

       pcre *pcre_compile2(const char *pattern, int options,
	    int *errorcodeptr,
	    const char **errptr, int *erroffset,
	    const unsigned char *tableptr);

       Either of the functions pcre_compile() or pcre_compile2() can be called
       to compile a pattern into an internal form. The only difference between
       the  two interfaces is that pcre_compile2() has an additional argument,
       errorcodeptr, via which a numerical error  code	can  be	 returned.  To
       avoid  too  much repetition, we refer just to pcre_compile() below, but
       the information applies equally to pcre_compile2().

       The pattern is a C string terminated by a binary zero, and is passed in
       the  pattern  argument.	A  pointer to a single block of memory that is
       obtained via pcre_malloc is returned. This contains the	compiled  code
       and related data. The pcre type is defined for the returned block; this
       is a typedef for a structure whose contents are not externally defined.
       It is up to the caller to free the memory (via pcre_free) when it is no
       longer required.

       Although the compiled code of a PCRE regex is relocatable, that is,  it
       does not depend on memory location, the complete pcre data block is not
       fully relocatable, because it may contain a copy of the tableptr	 argu‐
       ment, which is an address (see below).

       The options argument contains various bit settings that affect the com‐
       pilation. It should be zero if no options are required.	The  available
       options	are  described	below. Some of them (in particular, those that
       are compatible with Perl, but some others as well) can also be set  and
       unset  from  within  the	 pattern  (see the detailed description in the
       pcrepattern documentation). For those options that can be different  in
       different  parts	 of  the pattern, the contents of the options argument
       specifies their settings at the start of compilation and execution. The
       PCRE_ANCHORED,  PCRE_BSR_xxx, PCRE_NEWLINE_xxx, PCRE_NO_UTF8_CHECK, and
       PCRE_NO_START_OPT options can be set at the time of matching as well as
       at compile time.

       If errptr is NULL, pcre_compile() returns NULL immediately.  Otherwise,
       if compilation of a pattern fails,  pcre_compile()  returns  NULL,  and
       sets the variable pointed to by errptr to point to a textual error mes‐
       sage. This is a static string that is part of the library. You must not
       try  to	free  it. The offset from the start of the pattern to the byte
       that was being processed when the error was discovered is placed in the
       variable	 pointed to by erroffset, which must not be NULL. If it is, an
       immediate error is given. Some errors are not detected until checks are
       carried	out  when the whole pattern has been scanned; in this case the
       offset is set to the end of the pattern.

       Note that the offset is in bytes, not characters, even in  UTF-8	 mode.
       It  may	point  into the middle of a UTF-8 character (for example, when
       PCRE_ERROR_BADUTF8 is returned for an invalid UTF-8 string).

       If pcre_compile2() is used instead of pcre_compile(),  and  the	error‐
       codeptr	argument is not NULL, a non-zero error code number is returned
       via this argument in the event of an error. This is in addition to  the
       textual error message. Error codes and messages are listed below.

       If  the	final  argument, tableptr, is NULL, PCRE uses a default set of
       character tables that are  built	 when  PCRE  is	 compiled,  using  the
       default	C  locale.  Otherwise, tableptr must be an address that is the
       result of a call to pcre_maketables(). This value is  stored  with  the
       compiled	 pattern,  and used again by pcre_exec(), unless another table
       pointer is passed to it. For more discussion, see the section on locale
       support below.

       This  code  fragment  shows a typical straightforward call to pcre_com‐
       pile():

	 pcre *re;
	 const char *error;
	 int erroffset;
	 re = pcre_compile(
	   "^A.*Z",	     /* the pattern */
	   0,		     /* default options */
	   &error,	     /* for error message */
	   &erroffset,	     /* for error offset */
	   NULL);	     /* use default character tables */

       The following names for option bits are defined in  the	pcre.h	header
       file:

	 PCRE_ANCHORED

       If this bit is set, the pattern is forced to be "anchored", that is, it
       is constrained to match only at the first matching point in the	string
       that  is being searched (the "subject string"). This effect can also be
       achieved by appropriate constructs in the pattern itself, which is  the
       only way to do it in Perl.

	 PCRE_AUTO_CALLOUT

       If this bit is set, pcre_compile() automatically inserts callout items,
       all with number 255, before each pattern item. For  discussion  of  the
       callout facility, see the pcrecallout documentation.

	 PCRE_BSR_ANYCRLF
	 PCRE_BSR_UNICODE

       These options (which are mutually exclusive) control what the \R escape
       sequence matches. The choice is either to match only CR, LF,  or	 CRLF,
       or to match any Unicode newline sequence. The default is specified when
       PCRE is built. It can be overridden from within the pattern, or by set‐
       ting an option when a compiled pattern is matched.

	 PCRE_CASELESS

       If  this	 bit is set, letters in the pattern match both upper and lower
       case letters. It is equivalent to Perl's	 /i  option,  and  it  can  be
       changed	within a pattern by a (?i) option setting. In UTF-8 mode, PCRE
       always understands the concept of case for characters whose values  are
       less  than 128, so caseless matching is always possible. For characters
       with higher values, the concept of case is supported if	PCRE  is  com‐
       piled  with Unicode property support, but not otherwise. If you want to
       use caseless matching for characters 128 and  above,  you  must	ensure
       that  PCRE  is  compiled	 with Unicode property support as well as with
       UTF-8 support.

	 PCRE_DOLLAR_ENDONLY

       If this bit is set, a dollar metacharacter in the pattern matches  only
       at  the	end  of the subject string. Without this option, a dollar also
       matches immediately before a newline at the end of the string (but  not
       before  any  other newlines). The PCRE_DOLLAR_ENDONLY option is ignored
       if PCRE_MULTILINE is set.  There is no equivalent  to  this  option  in
       Perl, and no way to set it within a pattern.

	 PCRE_DOTALL

       If  this bit is set, a dot metacharacter in the pattern matches a char‐
       acter of any value, including one that indicates a newline. However, it
       only  ever  matches  one character, even if newlines are coded as CRLF.
       Without this option, a dot does not match when the current position  is
       at a newline. This option is equivalent to Perl's /s option, and it can
       be changed within a pattern by a (?s) option setting. A negative	 class
       such as [^a] always matches newline characters, independent of the set‐
       ting of this option.

	 PCRE_DUPNAMES

       If this bit is set, names used to identify capturing  subpatterns  need
       not be unique. This can be helpful for certain types of pattern when it
       is known that only one instance of the named  subpattern	 can  ever  be
       matched.	 There	are  more details of named subpatterns below; see also
       the pcrepattern documentation.

	 PCRE_EXTENDED

       If this bit is set, whitespace  data  characters	 in  the  pattern  are
       totally ignored except when escaped or inside a character class. White‐
       space does not include the VT character (code 11). In addition, charac‐
       ters between an unescaped # outside a character class and the next new‐
       line, inclusive, are also ignored. This	is  equivalent	to  Perl's  /x
       option,	and  it	 can be changed within a pattern by a (?x) option set‐
       ting.

       Which characters are interpreted	 as  newlines  is  controlled  by  the
       options	passed to pcre_compile() or by a special sequence at the start
       of the pattern, as described in the section entitled  "Newline  conven‐
       tions" in the pcrepattern documentation. Note that the end of this type
       of comment is  a	 literal  newline  sequence  in	 the  pattern;	escape
       sequences that happen to represent a newline do not count.

       This  option  makes  it possible to include comments inside complicated
       patterns.  Note, however, that this applies only	 to  data  characters.
       Whitespace   characters	may  never  appear  within  special  character
       sequences in a pattern, for example within the sequence (?( that intro‐
       duces a conditional subpattern.

	 PCRE_EXTRA

       This  option  was invented in order to turn on additional functionality
       of PCRE that is incompatible with Perl, but it  is  currently  of  very
       little  use. When set, any backslash in a pattern that is followed by a
       letter that has no special meaning  causes  an  error,  thus  reserving
       these  combinations  for	 future	 expansion.  By default, as in Perl, a
       backslash followed by a letter with no special meaning is treated as  a
       literal. (Perl can, however, be persuaded to give an error for this, by
       running it with the -w option.) There are at present no other  features
       controlled  by this option. It can also be set by a (?X) option setting
       within a pattern.

	 PCRE_FIRSTLINE

       If this option is set, an  unanchored  pattern  is  required  to	 match
       before  or  at  the  first  newline  in	the subject string, though the
       matched text may continue over the newline.

	 PCRE_JAVASCRIPT_COMPAT

       If this option is set, PCRE's behaviour is changed in some ways so that
       it  is  compatible with JavaScript rather than Perl. The changes are as
       follows:

       (1) A lone closing square bracket in a pattern  causes  a  compile-time
       error,  because this is illegal in JavaScript (by default it is treated
       as a data character). Thus, the pattern AB]CD becomes illegal when this
       option is set.

       (2)  At run time, a back reference to an unset subpattern group matches
       an empty string (by default this causes the current  matching  alterna‐
       tive  to	 fail). A pattern such as (\1)(a) succeeds when this option is
       set (assuming it can find an "a" in the subject), whereas it  fails  by
       default, for Perl compatibility.

	 PCRE_MULTILINE

       By  default,  PCRE  treats the subject string as consisting of a single
       line of characters (even if it actually contains newlines). The	"start
       of  line"  metacharacter	 (^)  matches only at the start of the string,
       while the "end of line" metacharacter ($) matches only at  the  end  of
       the string, or before a terminating newline (unless PCRE_DOLLAR_ENDONLY
       is set). This is the same as Perl.

       When PCRE_MULTILINE it is set, the "start of line" and  "end  of	 line"
       constructs  match  immediately following or immediately before internal
       newlines in the subject string, respectively, as well as	 at  the  very
       start  and  end.	 This is equivalent to Perl's /m option, and it can be
       changed within a pattern by a (?m) option setting. If there are no new‐
       lines  in  a  subject string, or no occurrences of ^ or $ in a pattern,
       setting PCRE_MULTILINE has no effect.

	 PCRE_NEWLINE_CR
	 PCRE_NEWLINE_LF
	 PCRE_NEWLINE_CRLF
	 PCRE_NEWLINE_ANYCRLF
	 PCRE_NEWLINE_ANY

       These options override the default newline definition that  was	chosen
       when  PCRE  was built. Setting the first or the second specifies that a
       newline is indicated by a single character (CR  or  LF,	respectively).
       Setting	PCRE_NEWLINE_CRLF specifies that a newline is indicated by the
       two-character CRLF  sequence.  Setting  PCRE_NEWLINE_ANYCRLF  specifies
       that any of the three preceding sequences should be recognized. Setting
       PCRE_NEWLINE_ANY specifies that any Unicode newline sequence should  be
       recognized. The Unicode newline sequences are the three just mentioned,
       plus the single characters VT (vertical	tab,  U+000B),	FF  (formfeed,
       U+000C),	 NEL  (next line, U+0085), LS (line separator, U+2028), and PS
       (paragraph separator, U+2029). The last	two  are  recognized  only  in
       UTF-8 mode.

       The  newline  setting  in  the  options	word  uses three bits that are
       treated as a number, giving eight possibilities. Currently only six are
       used  (default  plus the five values above). This means that if you set
       more than one newline option, the combination may or may not be	sensi‐
       ble. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to
       PCRE_NEWLINE_CRLF, but other combinations may yield unused numbers  and
       cause an error.

       The  only  time	that a line break in a pattern is specially recognized
       when compiling is when PCRE_EXTENDED is set. CR and LF  are  whitespace
       characters,  and so are ignored in this mode. Also, an unescaped # out‐
       side a character class indicates a comment that lasts until  after  the
       next  line break sequence. In other circumstances, line break sequences
       in patterns are treated as literal data.

       The newline option that is set at compile time becomes the default that
       is used for pcre_exec() and pcre_dfa_exec(), but it can be overridden.

	 PCRE_NO_AUTO_CAPTURE

       If this option is set, it disables the use of numbered capturing paren‐
       theses in the pattern. Any opening parenthesis that is not followed  by
       ?  behaves as if it were followed by ?: but named parentheses can still
       be used for capturing (and they acquire	numbers	 in  the  usual	 way).
       There is no equivalent of this option in Perl.

	 NO_START_OPTIMIZE

       This  is an option that acts at matching time; that is, it is really an
       option for pcre_exec() or pcre_dfa_exec(). If  it  is  set  at  compile
       time,  it is remembered with the compiled pattern and assumed at match‐
       ing time. For details  see  the	discussion  of	PCRE_NO_START_OPTIMIZE
       below.

	 PCRE_UCP

       This  option changes the way PCRE processes \B, \b, \D, \d, \S, \s, \W,
       \w, and some of the POSIX character classes.  By	 default,  only	 ASCII
       characters  are	recognized, but if PCRE_UCP is set, Unicode properties
       are used instead to classify characters. More details are given in  the
       section	on generic character types in the pcrepattern page. If you set
       PCRE_UCP, matching one of the items it affects takes much  longer.  The
       option  is  available only if PCRE has been compiled with Unicode prop‐
       erty support.

	 PCRE_UNGREEDY

       This option inverts the "greediness" of the quantifiers	so  that  they
       are  not greedy by default, but become greedy if followed by "?". It is
       not compatible with Perl. It can also be set by a (?U)  option  setting
       within the pattern.

	 PCRE_UTF8

       This  option  causes PCRE to regard both the pattern and the subject as
       strings of UTF-8 characters instead of single-byte  character  strings.
       However,	 it is available only when PCRE is built to include UTF-8 sup‐
       port. If not, the use of this option provokes an error. Details of  how
       this  option  changes the behaviour of PCRE are given in the section on
       UTF-8 support in the main pcre page.

	 PCRE_NO_UTF8_CHECK

       When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
       automatically  checked.	There  is  a  discussion about the validity of
       UTF-8 strings in the main pcre page. If an invalid  UTF-8  sequence  of
       bytes  is  found,  pcre_compile() returns an error. If you already know
       that your pattern is valid, and you want to skip this check for perfor‐
       mance  reasons,	you  can set the PCRE_NO_UTF8_CHECK option. When it is
       set, the effect of passing an invalid UTF-8  string  as	a  pattern  is
       undefined.  It  may  cause your program to crash. Note that this option
       can also be passed to pcre_exec() and pcre_dfa_exec(), to suppress  the
       UTF-8 validity checking of subject strings.

COMPILATION ERROR CODES

       The  following  table  lists  the  error	 codes than may be returned by
       pcre_compile2(), along with the error messages that may be returned  by
       both  compiling functions. As PCRE has developed, some error codes have
       fallen out of use. To avoid confusion, they have not been re-used.

	  0  no error
	  1  \ at end of pattern
	  2  \c at end of pattern
	  3  unrecognized character follows \
	  4  numbers out of order in {} quantifier
	  5  number too big in {} quantifier
	  6  missing terminating ] for character class
	  7  invalid escape sequence in character class
	  8  range out of order in character class
	  9  nothing to repeat
	 10  [this code is not in use]
	 11  internal error: unexpected repeat
	 12  unrecognized character after (? or (?-
	 13  POSIX named classes are supported only within a class
	 14  missing )
	 15  reference to non-existent subpattern
	 16  erroffset passed as NULL
	 17  unknown option bit(s) set
	 18  missing ) after comment
	 19  [this code is not in use]
	 20  regular expression is too large
	 21  failed to get memory
	 22  unmatched parentheses
	 23  internal error: code overflow
	 24  unrecognized character after (?<
	 25  lookbehind assertion is not fixed length
	 26  malformed number or name after (?(
	 27  conditional group contains more than two branches
	 28  assertion expected after (?(
	 29  (?R or (?[+-]digits must be followed by )
	 30  unknown POSIX class name
	 31  POSIX collating elements are not supported
	 32  this version of PCRE is not compiled with PCRE_UTF8 support
	 33  [this code is not in use]
	 34  character value in \x{...} sequence is too large
	 35  invalid condition (?(0)
	 36  \C not allowed in lookbehind assertion
	 37  PCRE does not support \L, \l, \N, \U, or \u
	 38  number after (?C is > 255
	 39  closing ) for (?C expected
	 40  recursive call could loop indefinitely
	 41  unrecognized character after (?P
	 42  syntax error in subpattern name (missing terminator)
	 43  two named subpatterns have the same name
	 44  invalid UTF-8 string
	 45  support for \P, \p, and \X has not been compiled
	 46  malformed \P or \p sequence
	 47  unknown property name after \P or \p
	 48  subpattern name is too long (maximum 32 characters)
	 49  too many named subpatterns (maximum 10000)
	 50  [this code is not in use]
	 51  octal value is greater than \377 (not in UTF-8 mode)
	 52  internal error: overran compiling workspace
	 53  internal error: previously-checked referenced subpattern
	       not found
	 54  DEFINE group contains more than one branch
	 55  repeating a DEFINE group is not allowed
	 56  inconsistent NEWLINE options
	 57  \g is not followed by a braced, angle-bracketed, or quoted
	       name/number or by a plain number
	 58  a numbered reference must not be zero
	 59  an argument is not allowed for (*ACCEPT), (*FAIL), or (*COMMIT)
	 60  (*VERB) not recognized
	 61  number is too big
	 62  subpattern name expected
	 63  digit expected after (?+
	 64  ] is an invalid data character in JavaScript compatibility mode
	 65  different names for subpatterns of the same number are
	       not allowed
	 66  (*MARK) must have an argument
	 67  this version of PCRE is not compiled with PCRE_UCP support

       The numbers 32 and 10000 in errors 48 and 49  are  defaults;  different
       values may be used if the limits were changed when PCRE was built.

STUDYING A PATTERN

       pcre_extra *pcre_study(const pcre *code, int options
	    const char **errptr);

       If  a  compiled	pattern is going to be used several times, it is worth
       spending more time analyzing it in order to speed up the time taken for
       matching.  The function pcre_study() takes a pointer to a compiled pat‐
       tern as its first argument. If studying the pattern produces additional
       information  that  will	help speed up matching, pcre_study() returns a
       pointer to a pcre_extra block, in which the study_data field points  to
       the results of the study.

       The  returned  value  from  pcre_study()	 can  be  passed  directly  to
       pcre_exec() or pcre_dfa_exec(). However, a pcre_extra block  also  con‐
       tains  other  fields  that can be set by the caller before the block is
       passed; these are described below in the section on matching a pattern.

       If studying the	pattern	 does  not  produce  any  useful  information,
       pcre_study() returns NULL. In that circumstance, if the calling program
       wants  to  pass	any  of	  the	other	fields	 to   pcre_exec()   or
       pcre_dfa_exec(), it must set up its own pcre_extra block.

       The  second  argument of pcre_study() contains option bits. At present,
       no options are defined, and this argument should always be zero.

       The third argument for pcre_study() is a pointer for an error  message.
       If  studying  succeeds  (even  if no data is returned), the variable it
       points to is set to NULL. Otherwise it is set to	 point	to  a  textual
       error message. This is a static string that is part of the library. You
       must not try to free it. You should test the  error  pointer  for  NULL
       after calling pcre_study(), to be sure that it has run successfully.

       This is a typical call to pcre_study():

	 pcre_extra *pe;
	 pe = pcre_study(
	   re,		   /* result of pcre_compile() */
	   0,		   /* no options exist */
	   &error);	   /* set to NULL or points to a message */

       Studying a pattern does two things: first, a lower bound for the length
       of subject string that is needed to match the pattern is computed. This
       does not mean that there are any strings of that length that match, but
       it does guarantee that no shorter strings match. The value is  used  by
       pcre_exec()  and	 pcre_dfa_exec()  to  avoid  wasting time by trying to
       match strings that are shorter than the lower bound. You can  find  out
       the value in a calling program via the pcre_fullinfo() function.

       Studying a pattern is also useful for non-anchored patterns that do not
       have a single fixed starting character. A bitmap of  possible  starting
       bytes  is  created. This speeds up finding a position in the subject at
       which to start matching.

       The two optimizations just described can be  disabled  by  setting  the
       PCRE_NO_START_OPTIMIZE	 option	   when	   calling    pcre_exec()   or
       pcre_dfa_exec(). You might want to do this  if  your  pattern  contains
       callouts	 or  (*MARK),  and you want to make use of these facilities in
       cases where matching fails. See the discussion  of  PCRE_NO_START_OPTI‐
       MIZE below.

LOCALE SUPPORT

       PCRE  handles  caseless matching, and determines whether characters are
       letters, digits, or whatever, by reference to a set of tables,  indexed
       by  character  value.  When running in UTF-8 mode, this applies only to
       characters with codes less than 128. By	default,  higher-valued	 codes
       never match escapes such as \w or \d, but they can be tested with \p if
       PCRE is built with Unicode character property  support.	Alternatively,
       the  PCRE_UCP  option  can  be  set at compile time; this causes \w and
       friends to use Unicode property support instead of built-in tables. The
       use of locales with Unicode is discouraged. If you are handling charac‐
       ters with codes greater than 128, you should either use UTF-8 and  Uni‐
       code, or use locales, but not try to mix the two.

       PCRE  contains  an  internal set of tables that are used when the final
       argument of pcre_compile() is  NULL.  These  are	 sufficient  for  many
       applications.  Normally, the internal tables recognize only ASCII char‐
       acters. However, when PCRE is built, it is possible to cause the inter‐
       nal tables to be rebuilt in the default "C" locale of the local system,
       which may cause them to be different.

       The internal tables can always be overridden by tables supplied by  the
       application that calls PCRE. These may be created in a different locale
       from the default. As more and more applications change  to  using  Uni‐
       code, the need for this locale support is expected to die away.

       External	 tables	 are  built by calling the pcre_maketables() function,
       which has no arguments, in the relevant locale. The result can then  be
       passed  to  pcre_compile()  or  pcre_exec()  as often as necessary. For
       example, to build and use tables that are appropriate  for  the	French
       locale  (where  accented	 characters  with  values greater than 128 are
       treated as letters), the following code could be used:

	 setlocale(LC_CTYPE, "fr_FR");
	 tables = pcre_maketables();
	 re = pcre_compile(..., tables);

       The locale name "fr_FR" is used on Linux and other  Unix-like  systems;
       if you are using Windows, the name for the French locale is "french".

       When  pcre_maketables()	runs,  the  tables are built in memory that is
       obtained via pcre_malloc. It is the caller's responsibility  to	ensure
       that  the memory containing the tables remains available for as long as
       it is needed.

       The pointer that is passed to pcre_compile() is saved with the compiled
       pattern,	 and the same tables are used via this pointer by pcre_study()
       and normally also by pcre_exec(). Thus, by default, for any single pat‐
       tern, compilation, studying and matching all happen in the same locale,
       but different patterns can be compiled in different locales.

       It is possible to pass a table pointer or NULL (indicating the  use  of
       the  internal  tables)  to  pcre_exec(). Although not intended for this
       purpose, this facility could be used to match a pattern in a  different
       locale from the one in which it was compiled. Passing table pointers at
       run time is discussed below in the section on matching a pattern.

INFORMATION ABOUT A PATTERN

       int pcre_fullinfo(const pcre *code, const pcre_extra *extra,
	    int what, void *where);

       The pcre_fullinfo() function returns information about a compiled  pat‐
       tern. It replaces the obsolete pcre_info() function, which is neverthe‐
       less retained for backwards compability (and is documented below).

       The first argument for pcre_fullinfo() is a  pointer  to	 the  compiled
       pattern.	 The second argument is the result of pcre_study(), or NULL if
       the pattern was not studied. The third argument specifies  which	 piece
       of  information	is required, and the fourth argument is a pointer to a
       variable to receive the data. The yield of the  function	 is  zero  for
       success, or one of the following negative numbers:

	 PCRE_ERROR_NULL       the argument code was NULL
			       the argument where was NULL
	 PCRE_ERROR_BADMAGIC   the "magic number" was not found
	 PCRE_ERROR_BADOPTION  the value of what was invalid

       The  "magic  number" is placed at the start of each compiled pattern as
       an simple check against passing an arbitrary memory pointer. Here is  a
       typical	call  of pcre_fullinfo(), to obtain the length of the compiled
       pattern:

	 int rc;
	 size_t length;
	 rc = pcre_fullinfo(
	   re,		     /* result of pcre_compile() */
	   pe,		     /* result of pcre_study(), or NULL */
	   PCRE_INFO_SIZE,   /* what is required */
	   &length);	     /* where to put the data */

       The possible values for the third argument are defined in  pcre.h,  and
       are as follows:

	 PCRE_INFO_BACKREFMAX

       Return  the  number  of	the highest back reference in the pattern. The
       fourth argument should point to an int variable. Zero  is  returned  if
       there are no back references.

	 PCRE_INFO_CAPTURECOUNT

       Return  the  number of capturing subpatterns in the pattern. The fourth
       argument should point to an int variable.

	 PCRE_INFO_DEFAULT_TABLES

       Return a pointer to the internal default character tables within	 PCRE.
       The  fourth  argument should point to an unsigned char * variable. This
       information call is provided for internal use by the pcre_study() func‐
       tion.  External	callers	 can  cause PCRE to use its internal tables by
       passing a NULL table pointer.

	 PCRE_INFO_FIRSTBYTE

       Return information about the first byte of any matched  string,	for  a
       non-anchored  pattern. The fourth argument should point to an int vari‐
       able. (This option used to be called PCRE_INFO_FIRSTCHAR; the old  name
       is still recognized for backwards compatibility.)

       If  there  is  a	 fixed first byte, for example, from a pattern such as
       (cat|cow|coyote), its value is returned. Otherwise, if either

       (a) the pattern was compiled with the PCRE_MULTILINE option, and	 every
       branch starts with "^", or

       (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not
       set (if it were set, the pattern would be anchored),

       -1 is returned, indicating that the pattern matches only at  the	 start
       of  a  subject string or after any newline within the string. Otherwise
       -2 is returned. For anchored patterns, -2 is returned.

	 PCRE_INFO_FIRSTTABLE

       If the pattern was studied, and this resulted in the construction of  a
       256-bit table indicating a fixed set of bytes for the first byte in any
       matching string, a pointer to the table is returned. Otherwise NULL  is
       returned.  The fourth argument should point to an unsigned char * vari‐
       able.

	 PCRE_INFO_HASCRORLF

       Return 1 if the pattern contains any explicit  matches  for  CR	or  LF
       characters,  otherwise  0.  The	fourth argument should point to an int
       variable. An explicit match is either a literal CR or LF character,  or
       \r or \n.

	 PCRE_INFO_JCHANGED

       Return  1  if  the (?J) or (?-J) option setting is used in the pattern,
       otherwise 0. The fourth argument should point to an int variable.  (?J)
       and (?-J) set and unset the local PCRE_DUPNAMES option, respectively.

	 PCRE_INFO_LASTLITERAL

       Return  the  value of the rightmost literal byte that must exist in any
       matched string, other than at its  start,  if  such  a  byte  has  been
       recorded. The fourth argument should point to an int variable. If there
       is no such byte, -1 is returned. For anchored patterns, a last  literal
       byte  is	 recorded only if it follows something of variable length. For
       example, for the pattern /^a\d+z\d+/ the returned value is "z", but for
       /^a\dz\d/ the returned value is -1.

	 PCRE_INFO_MINLENGTH

       If  the	pattern	 was studied and a minimum length for matching subject
       strings was computed, its value is  returned.  Otherwise	 the  returned
       value  is  -1. The value is a number of characters, not bytes (this may
       be relevant in UTF-8 mode). The fourth argument should point to an  int
       variable.  A  non-negative  value is a lower bound to the length of any
       matching string. There may not be any strings of that  length  that  do
       actually match, but every string that does match is at least that long.

	 PCRE_INFO_NAMECOUNT
	 PCRE_INFO_NAMEENTRYSIZE
	 PCRE_INFO_NAMETABLE

       PCRE  supports the use of named as well as numbered capturing parenthe‐
       ses. The names are just an additional way of identifying the  parenthe‐
       ses, which still acquire numbers. Several convenience functions such as
       pcre_get_named_substring() are provided for  extracting	captured  sub‐
       strings	by  name. It is also possible to extract the data directly, by
       first converting the name to a number in order to  access  the  correct
       pointers in the output vector (described with pcre_exec() below). To do
       the conversion, you need	 to  use  the  name-to-number  map,  which  is
       described by these three values.

       The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT
       gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size
       of  each	 entry;	 both  of  these  return  an int value. The entry size
       depends on the length of the longest name. PCRE_INFO_NAMETABLE  returns
       a  pointer  to  the  first  entry of the table (a pointer to char). The
       first two bytes of each entry are the number of the capturing parenthe‐
       sis,  most  significant byte first. The rest of the entry is the corre‐
       sponding name, zero terminated.

       The names are in alphabetical order. Duplicate names may appear if  (?|
       is used to create multiple groups with the same number, as described in
       the section on duplicate subpattern numbers in  the  pcrepattern	 page.
       Duplicate  names	 for  subpatterns with different numbers are permitted
       only if PCRE_DUPNAMES is set. In all cases  of  duplicate  names,  they
       appear  in  the table in the order in which they were found in the pat‐
       tern. In the absence of (?| this is the	order  of  increasing  number;
       when (?| is used this is not necessarily the case because later subpat‐
       terns may have lower numbers.

       As a simple example of the name/number table,  consider	the  following
       pattern	(assume	 PCRE_EXTENDED is set, so white space - including new‐
       lines - is ignored):

	 (?<date> (?<year>(\d\d)?\d\d) -
	 (?<month>\d\d) - (?<day>\d\d) )

       There are four named subpatterns, so the table has  four	 entries,  and
       each  entry  in the table is eight bytes long. The table is as follows,
       with non-printing bytes shows in hexadecimal, and undefined bytes shown
       as ??:

	 00 01 d  a  t	e  00 ??
	 00 05 d  a  y	00 ?? ??
	 00 04 m  o  n	t  h  00
	 00 02 y  e  a	r  00 ??

       When  writing  code  to	extract	 data from named subpatterns using the
       name-to-number map, remember that the length of the entries  is	likely
       to be different for each compiled pattern.

	 PCRE_INFO_OKPARTIAL

       Return  1  if  the  pattern  can	 be  used  for	partial	 matching with
       pcre_exec(), otherwise 0. The fourth argument should point  to  an  int
       variable.  From	release	 8.00,	this  always  returns  1,  because the
       restrictions that previously applied  to	 partial  matching  have  been
       lifted.	The  pcrepartial documentation gives details of partial match‐
       ing.

	 PCRE_INFO_OPTIONS

       Return a copy of the options with which the pattern was	compiled.  The
       fourth  argument	 should	 point to an unsigned long int variable. These
       option bits are those specified in the call to pcre_compile(), modified
       by any top-level option settings at the start of the pattern itself. In
       other words, they are the options that will be in force	when  matching
       starts.	For  example, if the pattern /(?im)abc(?-i)d/ is compiled with
       the PCRE_EXTENDED option, the result is PCRE_CASELESS,  PCRE_MULTILINE,
       and PCRE_EXTENDED.

       A  pattern  is  automatically  anchored by PCRE if all of its top-level
       alternatives begin with one of the following:

	 ^     unless PCRE_MULTILINE is set
	 \A    always
	 \G    always
	 .*    if PCRE_DOTALL is set and there are no back
		 references to the subpattern in which .* appears

       For such patterns, the PCRE_ANCHORED bit is set in the options returned
       by pcre_fullinfo().

	 PCRE_INFO_SIZE

       Return  the  size  of the compiled pattern, that is, the value that was
       passed as the argument to pcre_malloc() when PCRE was getting memory in
       which to place the compiled data. The fourth argument should point to a
       size_t variable.

	 PCRE_INFO_STUDYSIZE

       Return the size of the data block pointed to by the study_data field in
       a  pcre_extra  block.  That  is,	 it  is	 the  value that was passed to
       pcre_malloc() when PCRE was getting memory into which to place the data
       created	by  pcre_study().  If pcre_extra is NULL, or there is no study
       data, zero is returned. The fourth argument should point	 to  a	size_t
       variable.

OBSOLETE INFO FUNCTION

       int pcre_info(const pcre *code, int *optptr, int *firstcharptr);

       The  pcre_info()	 function is now obsolete because its interface is too
       restrictive to return all the available data about a compiled  pattern.
       New   programs	should	use  pcre_fullinfo()  instead.	The  yield  of
       pcre_info() is the number of capturing subpatterns, or one of the  fol‐
       lowing negative numbers:

	 PCRE_ERROR_NULL       the argument code was NULL
	 PCRE_ERROR_BADMAGIC   the "magic number" was not found

       If  the	optptr	argument is not NULL, a copy of the options with which
       the pattern was compiled is placed in the integer  it  points  to  (see
       PCRE_INFO_OPTIONS above).

       If  the	pattern	 is  not anchored and the firstcharptr argument is not
       NULL, it is used to pass back information about the first character  of
       any matched string (see PCRE_INFO_FIRSTBYTE above).

REFERENCE COUNTS

       int pcre_refcount(pcre *code, int adjust);

       The  pcre_refcount()  function is used to maintain a reference count in
       the data block that contains a compiled pattern. It is provided for the
       benefit	of  applications  that	operate	 in an object-oriented manner,
       where different parts of the application may be using the same compiled
       pattern, but you want to free the block when they are all done.

       When a pattern is compiled, the reference count field is initialized to
       zero.  It is changed only by calling this function, whose action is  to
       add  the	 adjust	 value	(which may be positive or negative) to it. The
       yield of the function is the new value. However, the value of the count
       is  constrained to lie between 0 and 65535, inclusive. If the new value
       is outside these limits, it is forced to the appropriate limit value.

       Except when it is zero, the reference count is not correctly  preserved
       if  a  pattern  is  compiled on one host and then transferred to a host
       whose byte-order is different. (This seems a highly unlikely scenario.)

MATCHING A PATTERN: THE TRADITIONAL FUNCTION

       int pcre_exec(const pcre *code, const pcre_extra *extra,
	    const char *subject, int length, int startoffset,
	    int options, int *ovector, int ovecsize);

       The function pcre_exec() is called to match a subject string against  a
       compiled	 pattern, which is passed in the code argument. If the pattern
       was studied, the result of the study should  be	passed	in  the	 extra
       argument.  This	function is the main matching facility of the library,
       and it operates in a Perl-like manner. For specialist use there is also
       an  alternative matching function, which is described below in the sec‐
       tion about the pcre_dfa_exec() function.

       In most applications, the pattern will have been compiled (and  option‐
       ally  studied)  in the same process that calls pcre_exec(). However, it
       is possible to save compiled patterns and study data, and then use them
       later  in  different processes, possibly even on different hosts. For a
       discussion about this, see the pcreprecompile documentation.

       Here is an example of a simple call to pcre_exec():

	 int rc;
	 int ovector[30];
	 rc = pcre_exec(
	   re,		   /* result of pcre_compile() */
	   NULL,	   /* we didn't study the pattern */
	   "some string",  /* the subject string */
	   11,		   /* the length of the subject string */
	   0,		   /* start at offset 0 in the subject */
	   0,		   /* default options */
	   ovector,	   /* vector of integers for substring information */
	   30);		   /* number of elements (NOT size in bytes) */

   Extra data for pcre_exec()

       If the extra argument is not NULL, it must point to a  pcre_extra  data
       block.  The pcre_study() function returns such a block (when it doesn't
       return NULL), but you can also create one for yourself, and pass	 addi‐
       tional  information  in it. The pcre_extra block contains the following
       fields (not necessarily in this order):

	 unsigned long int flags;
	 void *study_data;
	 unsigned long int match_limit;
	 unsigned long int match_limit_recursion;
	 void *callout_data;
	 const unsigned char *tables;
	 unsigned char **mark;

       The flags field is a bitmap that specifies which of  the	 other	fields
       are set. The flag bits are:

	 PCRE_EXTRA_STUDY_DATA
	 PCRE_EXTRA_MATCH_LIMIT
	 PCRE_EXTRA_MATCH_LIMIT_RECURSION
	 PCRE_EXTRA_CALLOUT_DATA
	 PCRE_EXTRA_TABLES
	 PCRE_EXTRA_MARK

       Other  flag  bits should be set to zero. The study_data field is set in
       the pcre_extra block that is returned by	 pcre_study(),	together  with
       the appropriate flag bit. You should not set this yourself, but you may
       add to the block by setting the other fields  and  their	 corresponding
       flag bits.

       The match_limit field provides a means of preventing PCRE from using up
       a vast amount of resources when running patterns that are not going  to
       match,  but  which  have	 a very large number of possibilities in their
       search trees. The classic example is a pattern that uses nested	unlim‐
       ited repeats.

       Internally,  PCRE uses a function called match() which it calls repeat‐
       edly (sometimes recursively). The limit set by match_limit  is  imposed
       on  the	number	of times this function is called during a match, which
       has the effect of limiting the amount of	 backtracking  that  can  take
       place. For patterns that are not anchored, the count restarts from zero
       for each position in the subject string.

       The default value for the limit can be set  when	 PCRE  is  built;  the
       default	default	 is 10 million, which handles all but the most extreme
       cases. You can override the default  by	suppling  pcre_exec()  with  a
       pcre_extra     block    in    which    match_limit    is	   set,	   and
       PCRE_EXTRA_MATCH_LIMIT is set in the  flags  field.  If	the  limit  is
       exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.

       The  match_limit_recursion field is similar to match_limit, but instead
       of limiting the total number of times that match() is called, it limits
       the  depth  of  recursion. The recursion depth is a smaller number than
       the total number of calls, because not all calls to match() are	recur‐
       sive.  This limit is of use only if it is set smaller than match_limit.

       Limiting	 the  recursion	 depth	limits the amount of stack that can be
       used, or, when PCRE has been compiled to use memory on the heap instead
       of the stack, the amount of heap memory that can be used.

       The  default  value  for	 match_limit_recursion can be set when PCRE is
       built; the default default  is  the  same  value	 as  the  default  for
       match_limit.  You can override the default by suppling pcre_exec() with
       a  pcre_extra  block  in	 which	match_limit_recursion  is   set,   and
       PCRE_EXTRA_MATCH_LIMIT_RECURSION	 is  set  in  the  flags field. If the
       limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.

       The callout_data field is used in conjunction with the  "callout"  fea‐
       ture, and is described in the pcrecallout documentation.

       The  tables  field  is  used  to	 pass  a  character  tables pointer to
       pcre_exec(); this overrides the value that is stored with the  compiled
       pattern.	 A  non-NULL value is stored with the compiled pattern only if
       custom tables were supplied to pcre_compile() via  its  tableptr	 argu‐
       ment.  If NULL is passed to pcre_exec() using this mechanism, it forces
       PCRE's internal tables to be used. This facility is  helpful  when  re-
       using  patterns	that  have been saved after compiling with an external
       set of tables, because the external tables  might  be  at  a  different
       address	when  pcre_exec() is called. See the pcreprecompile documenta‐
       tion for a discussion of saving compiled patterns for later use.

       If PCRE_EXTRA_MARK is set in the flags field, the mark  field  must  be
       set  to	point  to a char * variable. If the pattern contains any back‐
       tracking control verbs such as (*MARK:NAME), and the execution ends  up
       with  a	name  to  pass back, a pointer to the name string (zero termi‐
       nated) is placed in the variable pointed to  by	the  mark  field.  The
       names  are  within  the	compiled pattern; if you wish to retain such a
       name you must copy it before freeing the memory of a compiled  pattern.
       If  there  is no name to pass back, the variable pointed to by the mark
       field set to NULL. For details of the backtracking control  verbs,  see
       the section entitled "Backtracking control" in the pcrepattern documen‐
       tation.

   Option bits for pcre_exec()

       The unused bits of the options argument for pcre_exec() must  be	 zero.
       The  only  bits	that  may  be set are PCRE_ANCHORED, PCRE_NEWLINE_xxx,
       PCRE_NOTBOL,   PCRE_NOTEOL,    PCRE_NOTEMPTY,	PCRE_NOTEMPTY_ATSTART,
       PCRE_NO_START_OPTIMIZE,	 PCRE_NO_UTF8_CHECK,   PCRE_PARTIAL_SOFT,  and
       PCRE_PARTIAL_HARD.

	 PCRE_ANCHORED

       The PCRE_ANCHORED option limits pcre_exec() to matching	at  the	 first
       matching	 position.  If	a  pattern was compiled with PCRE_ANCHORED, or
       turned out to be anchored by virtue of its contents, it cannot be  made
       unachored at matching time.

	 PCRE_BSR_ANYCRLF
	 PCRE_BSR_UNICODE

       These options (which are mutually exclusive) control what the \R escape
       sequence matches. The choice is either to match only CR, LF,  or	 CRLF,
       or  to  match  any Unicode newline sequence. These options override the
       choice that was made or defaulted when the pattern was compiled.

	 PCRE_NEWLINE_CR
	 PCRE_NEWLINE_LF
	 PCRE_NEWLINE_CRLF
	 PCRE_NEWLINE_ANYCRLF
	 PCRE_NEWLINE_ANY

       These options override  the  newline  definition	 that  was  chosen  or
       defaulted  when the pattern was compiled. For details, see the descrip‐
       tion of pcre_compile()  above.  During  matching,  the  newline	choice
       affects	the  behaviour	of the dot, circumflex, and dollar metacharac‐
       ters. It may also alter the way the match position is advanced after  a
       match failure for an unanchored pattern.

       When  PCRE_NEWLINE_CRLF,	 PCRE_NEWLINE_ANYCRLF,	or PCRE_NEWLINE_ANY is
       set, and a match attempt for an unanchored pattern fails when the  cur‐
       rent  position  is  at  a  CRLF	sequence,  and the pattern contains no
       explicit matches for  CR	 or  LF	 characters,  the  match  position  is
       advanced by two characters instead of one, in other words, to after the
       CRLF.

       The above rule is a compromise that makes the most common cases work as
       expected.  For  example,	 if  the  pattern  is .+A (and the PCRE_DOTALL
       option is not set), it does not match the string "\r\nA" because, after
       failing	at the start, it skips both the CR and the LF before retrying.
       However, the pattern [\r\n]A does match that string,  because  it  con‐
       tains an explicit CR or LF reference, and so advances only by one char‐
       acter after the first failure.

       An explicit match for CR of LF is either a literal appearance of one of
       those  characters,  or  one  of the \r or \n escape sequences. Implicit
       matches such as [^X] do not count, nor does \s (which includes  CR  and
       LF in the characters that it matches).

       Notwithstanding	the above, anomalous effects may still occur when CRLF
       is a valid newline sequence and explicit \r or \n escapes appear in the
       pattern.

	 PCRE_NOTBOL

       This option specifies that first character of the subject string is not
       the beginning of a line, so the	circumflex  metacharacter  should  not
       match  before it. Setting this without PCRE_MULTILINE (at compile time)
       causes circumflex never to match. This option affects only  the	behav‐
       iour of the circumflex metacharacter. It does not affect \A.

	 PCRE_NOTEOL

       This option specifies that the end of the subject string is not the end
       of a line, so the dollar metacharacter should not match it nor  (except
       in  multiline mode) a newline immediately before it. Setting this with‐
       out PCRE_MULTILINE (at compile time) causes dollar never to match. This
       option  affects only the behaviour of the dollar metacharacter. It does
       not affect \Z or \z.

	 PCRE_NOTEMPTY

       An empty string is not considered to be a valid match if this option is
       set.  If	 there are alternatives in the pattern, they are tried. If all
       the alternatives match the empty string, the entire  match  fails.  For
       example, if the pattern

	 a?b?

       is  applied  to	a  string not beginning with "a" or "b", it matches an
       empty string at the start of the subject. With PCRE_NOTEMPTY set,  this
       match is not valid, so PCRE searches further into the string for occur‐
       rences of "a" or "b".

	 PCRE_NOTEMPTY_ATSTART

       This is like PCRE_NOTEMPTY, except that an empty string match  that  is
       not  at	the  start  of	the  subject  is  permitted. If the pattern is
       anchored, such a match can occur only if the pattern contains \K.

       Perl    has    no    direct    equivalent    of	  PCRE_NOTEMPTY	    or
       PCRE_NOTEMPTY_ATSTART,  but  it	does  make a special case of a pattern
       match of the empty string within its split() function, and  when	 using
       the  /g	modifier.  It  is  possible  to emulate Perl's behaviour after
       matching a null string by first trying the match again at the same off‐
       set  with  PCRE_NOTEMPTY_ATSTART	 and  PCRE_ANCHORED,  and then if that
       fails, by advancing the starting offset (see below) and trying an ordi‐
       nary  match  again. There is some code that demonstrates how to do this
       in the pcredemo sample program. In the most general case, you  have  to
       check  to  see  if the newline convention recognizes CRLF as a newline,
       and if so, and the current character is CR followed by LF, advance  the
       starting offset by two characters instead of one.

	 PCRE_NO_START_OPTIMIZE

       There  are a number of optimizations that pcre_exec() uses at the start
       of a match, in order to speed up the process. For  example,  if	it  is
       known that an unanchored match must start with a specific character, it
       searches the subject for that character, and fails  immediately	if  it
       cannot  find  it,  without actually running the main matching function.
       This means that a special item such as (*COMMIT) at the start of a pat‐
       tern  is	 not  considered until after a suitable starting point for the
       match has been found. When callouts or (*MARK) items are in use,	 these
       "start-up" optimizations can cause them to be skipped if the pattern is
       never actually used. The start-up optimizations are in  effect  a  pre-
       scan of the subject that takes place before the pattern is run.

       The  PCRE_NO_START_OPTIMIZE option disables the start-up optimizations,
       possibly causing performance to suffer,	but  ensuring  that  in	 cases
       where  the  result is "no match", the callouts do occur, and that items
       such as (*COMMIT) and (*MARK) are considered at every possible starting
       position	 in  the  subject  string. If PCRE_NO_START_OPTIMIZE is set at
       compile time, it cannot be unset at matching time.

       Setting PCRE_NO_START_OPTIMIZE can change the  outcome  of  a  matching
       operation.  Consider the pattern

	 (*COMMIT)ABC

       When  this  is  compiled, PCRE records the fact that a match must start
       with the character "A". Suppose the subject  string  is	"DEFABC".  The
       start-up	 optimization  scans along the subject, finds "A" and runs the
       first match attempt from there. The (*COMMIT) item means that the  pat‐
       tern  must  match the current starting position, which in this case, it
       does. However, if the same match	 is  run  with	PCRE_NO_START_OPTIMIZE
       set,  the  initial  scan	 along the subject string does not happen. The
       first match attempt is run starting  from  "D"  and  when  this	fails,
       (*COMMIT)  prevents  any	 further  matches  being tried, so the overall
       result is "no match". If the pattern is studied,	 more  start-up	 opti‐
       mizations  may  be  used. For example, a minimum length for the subject
       may be recorded. Consider the pattern

	 (*MARK:A)(X|Y)

       The minimum length for a match is one  character.  If  the  subject  is
       "ABC",  there  will  be	attempts  to  match "ABC", "BC", "C", and then
       finally an empty string.	 If the pattern is studied, the final  attempt
       does  not take place, because PCRE knows that the subject is too short,
       and so the (*MARK) is never encountered.	 In this  case,	 studying  the
       pattern	does  not  affect the overall match result, which is still "no
       match", but it does affect the auxiliary information that is returned.

	 PCRE_NO_UTF8_CHECK

       When PCRE_UTF8 is set at compile time, the validity of the subject as a
       UTF-8  string is automatically checked when pcre_exec() is subsequently
       called.	The value of startoffset is also checked  to  ensure  that  it
       points  to  the start of a UTF-8 character. There is a discussion about
       the validity of UTF-8 strings in the section on UTF-8  support  in  the
       main  pcre  page.  If  an  invalid  UTF-8  sequence  of bytes is found,
       pcre_exec() returns  the	 error	PCRE_ERROR_BADUTF8  or,	 if  PCRE_PAR‐
       TIAL_HARD  is set and the problem is a truncated UTF-8 character at the
       end of the subject, PCRE_ERROR_SHORTUTF8.  If  startoffset  contains  a
       value  that does not point to the start of a UTF-8 character (or to the
       end of the subject), PCRE_ERROR_BADUTF8_OFFSET is returned.

       If you already know that your subject is valid, and you	want  to  skip
       these	checks	  for	performance   reasons,	 you   can   set   the
       PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might  want  to
       do  this	 for the second and subsequent calls to pcre_exec() if you are
       making repeated calls to find all  the  matches	in  a  single  subject
       string.	However,  you  should  be  sure	 that the value of startoffset
       points to the start of a UTF-8 character (or the end of	the  subject).
       When  PCRE_NO_UTF8_CHECK is set, the effect of passing an invalid UTF-8
       string as a subject or an invalid value of  startoffset	is  undefined.
       Your program may crash.

	 PCRE_PARTIAL_HARD
	 PCRE_PARTIAL_SOFT

       These  options turn on the partial matching feature. For backwards com‐
       patibility, PCRE_PARTIAL is a synonym for PCRE_PARTIAL_SOFT. A  partial
       match  occurs if the end of the subject string is reached successfully,
       but there are not enough subject characters to complete the  match.  If
       this happens when PCRE_PARTIAL_SOFT (but not PCRE_PARTIAL_HARD) is set,
       matching continues by testing any remaining alternatives.  Only	if  no
       complete	 match	can be found is PCRE_ERROR_PARTIAL returned instead of
       PCRE_ERROR_NOMATCH. In other words,  PCRE_PARTIAL_SOFT  says  that  the
       caller  is  prepared to handle a partial match, but only if no complete
       match can be found.

       If PCRE_PARTIAL_HARD is set, it overrides  PCRE_PARTIAL_SOFT.  In  this
       case,  if  a  partial  match  is found, pcre_exec() immediately returns
       PCRE_ERROR_PARTIAL, without  considering	 any  other  alternatives.  In
       other  words, when PCRE_PARTIAL_HARD is set, a partial match is consid‐
       ered to be more important that an alternative complete match.

       In both cases, the portion of the string that was  inspected  when  the
       partial match was found is set as the first matching string. There is a
       more detailed discussion of partial and	multi-segment  matching,  with
       examples, in the pcrepartial documentation.

   The string to be matched by pcre_exec()

       The  subject string is passed to pcre_exec() as a pointer in subject, a
       length (in bytes) in length, and a starting byte offset in startoffset.
       If  this	 is  negative  or  greater  than  the  length  of the subject,
       pcre_exec() returns PCRE_ERROR_BADOFFSET. When the starting  offset  is
       zero,  the  search  for a match starts at the beginning of the subject,
       and this is by far the most common case. In UTF-8 mode, the byte offset
       must  point  to	the start of a UTF-8 character (or the end of the sub‐
       ject). Unlike the pattern string, the subject may contain  binary  zero
       bytes.

       A  non-zero  starting offset is useful when searching for another match
       in the same subject by calling pcre_exec() again after a previous  suc‐
       cess.   Setting	startoffset differs from just passing over a shortened
       string and setting PCRE_NOTBOL in the case of  a	 pattern  that	begins
       with any kind of lookbehind. For example, consider the pattern

	 \Biss\B

       which  finds  occurrences  of "iss" in the middle of words. (\B matches
       only if the current position in the subject is not  a  word  boundary.)
       When  applied  to the string "Mississipi" the first call to pcre_exec()
       finds the first occurrence. If pcre_exec() is called  again  with  just
       the  remainder  of  the	subject,  namely  "issipi", it does not match,
       because \B is always false at the start of the subject, which is deemed
       to  be  a  word	boundary. However, if pcre_exec() is passed the entire
       string again, but with startoffset set to 4, it finds the second occur‐
       rence  of "iss" because it is able to look behind the starting point to
       discover that it is preceded by a letter.

       Finding all the matches in a subject is tricky  when  the  pattern  can
       match an empty string. It is possible to emulate Perl's /g behaviour by
       first  trying  the  match  again	 at  the   same	  offset,   with   the
       PCRE_NOTEMPTY_ATSTART  and  PCRE_ANCHORED  options,  and	 then  if that
       fails, advancing the starting  offset  and  trying  an  ordinary	 match
       again. There is some code that demonstrates how to do this in the pcre‐
       demo sample program. In the most general case, you have to check to see
       if  the newline convention recognizes CRLF as a newline, and if so, and
       the current character is CR followed by LF, advance the starting offset
       by two characters instead of one.

       If  a  non-zero starting offset is passed when the pattern is anchored,
       one attempt to match at the given offset is made. This can only succeed
       if  the	pattern	 does  not require the match to be at the start of the
       subject.

   How pcre_exec() returns captured substrings

       In general, a pattern matches a certain portion of the subject, and  in
       addition,  further  substrings  from  the  subject may be picked out by
       parts of the pattern. Following the usage  in  Jeffrey  Friedl's	 book,
       this  is	 called "capturing" in what follows, and the phrase "capturing
       subpattern" is used for a fragment of a pattern that picks out  a  sub‐
       string.	PCRE  supports several other kinds of parenthesized subpattern
       that do not cause substrings to be captured.

       Captured substrings are returned to the caller via a vector of integers
       whose  address is passed in ovector. The number of elements in the vec‐
       tor is passed in ovecsize, which must be a non-negative	number.	 Note:
       this argument is NOT the size of ovector in bytes.

       The  first  two-thirds of the vector is used to pass back captured sub‐
       strings, each substring using a pair of integers. The  remaining	 third
       of  the	vector is used as workspace by pcre_exec() while matching cap‐
       turing subpatterns, and is not available for passing back  information.
       The  number passed in ovecsize should always be a multiple of three. If
       it is not, it is rounded down.

       When a match is successful, information about  captured	substrings  is
       returned	 in  pairs  of integers, starting at the beginning of ovector,
       and continuing up to two-thirds of its length at the  most.  The	 first
       element	of  each pair is set to the byte offset of the first character
       in a substring, and the second is set to the byte offset of  the	 first
       character  after	 the end of a substring. Note: these values are always
       byte offsets, even in UTF-8 mode. They are not character counts.

       The first pair of integers, ovector[0]  and  ovector[1],	 identify  the
       portion	of  the subject string matched by the entire pattern. The next
       pair is used for the first capturing subpattern, and so on.  The	 value
       returned by pcre_exec() is one more than the highest numbered pair that
       has been set.  For example, if two substrings have been	captured,  the
       returned	 value is 3. If there are no capturing subpatterns, the return
       value from a successful match is 1, indicating that just the first pair
       of offsets has been set.

       If a capturing subpattern is matched repeatedly, it is the last portion
       of the string that it matched that is returned.

       If the vector is too small to hold all the captured substring  offsets,
       it is used as far as possible (up to two-thirds of its length), and the
       function returns a value of zero. If the substring offsets are  not  of
       interest,  pcre_exec()  may  be	called with ovector passed as NULL and
       ovecsize as zero. However, if the pattern contains back references  and
       the  ovector is not big enough to remember the related substrings, PCRE
       has to get additional memory for use during matching. Thus it  is  usu‐
       ally advisable to supply an ovector.

       The pcre_fullinfo() function can be used to find out how many capturing
       subpatterns there are in a compiled  pattern.  The  smallest  size  for
       ovector	that  will allow for n captured substrings, in addition to the
       offsets of the substring matched by the whole pattern, is (n+1)*3.

       It is possible for capturing subpattern number n+1 to match  some  part
       of the subject when subpattern n has not been used at all. For example,
       if the string "abc" is matched  against	the  pattern  (a|(z))(bc)  the
       return from the function is 4, and subpatterns 1 and 3 are matched, but
       2 is not. When this happens, both values in  the	 offset	 pairs	corre‐
       sponding to unused subpatterns are set to -1.

       Offset  values  that correspond to unused subpatterns at the end of the
       expression are also set to -1. For example,  if	the  string  "abc"  is
       matched	against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not
       matched. The return from the function is 2, because  the	 highest  used
       capturing  subpattern  number  is 1, and the offsets for for the second
       and third capturing subpatterns (assuming the vector is	large  enough,
       of course) are set to -1.

       Note: Elements of ovector that do not correspond to capturing parenthe‐
       ses in the pattern are never changed. That is, if a pattern contains  n
       capturing parentheses, no more than ovector[0] to ovector[2n+1] are set
       by pcre_exec(). The other elements retain whatever values  they	previ‐
       ously had.

       Some  convenience  functions  are  provided for extracting the captured
       substrings as separate strings. These are described below.

   Error return values from pcre_exec()

       If pcre_exec() fails, it returns a negative number. The	following  are
       defined in the header file:

	 PCRE_ERROR_NOMATCH	   (-1)

       The subject string did not match the pattern.

	 PCRE_ERROR_NULL	   (-2)

       Either  code  or	 subject  was  passed as NULL, or ovector was NULL and
       ovecsize was not zero.

	 PCRE_ERROR_BADOPTION	   (-3)

       An unrecognized bit was set in the options argument.

	 PCRE_ERROR_BADMAGIC	   (-4)

       PCRE stores a 4-byte "magic number" at the start of the compiled	 code,
       to catch the case when it is passed a junk pointer and to detect when a
       pattern that was compiled in an environment of one endianness is run in
       an  environment	with the other endianness. This is the error that PCRE
       gives when the magic number is not present.

	 PCRE_ERROR_UNKNOWN_OPCODE (-5)

       While running the pattern match, an unknown item was encountered in the
       compiled	 pattern.  This	 error	could be caused by a bug in PCRE or by
       overwriting of the compiled pattern.

	 PCRE_ERROR_NOMEMORY	   (-6)

       If a pattern contains back references, but the ovector that  is	passed
       to pcre_exec() is not big enough to remember the referenced substrings,
       PCRE gets a block of memory at the start of matching to	use  for  this
       purpose.	 If the call via pcre_malloc() fails, this error is given. The
       memory is automatically freed at the end of matching.

       This error is also given if pcre_stack_malloc() fails  in  pcre_exec().
       This  can happen only when PCRE has been compiled with --disable-stack-
       for-recursion.

	 PCRE_ERROR_NOSUBSTRING	   (-7)

       This error is used by the pcre_copy_substring(),	 pcre_get_substring(),
       and  pcre_get_substring_list()  functions  (see	below).	 It  is	 never
       returned by pcre_exec().

	 PCRE_ERROR_MATCHLIMIT	   (-8)

       The backtracking limit, as specified by	the  match_limit  field	 in  a
       pcre_extra  structure  (or  defaulted) was reached. See the description
       above.

	 PCRE_ERROR_CALLOUT	   (-9)

       This error is never generated by pcre_exec() itself. It is provided for
       use  by	callout functions that want to yield a distinctive error code.
       See the pcrecallout documentation for details.

	 PCRE_ERROR_BADUTF8	   (-10)

       A string that contains an invalid UTF-8 byte sequence was passed	 as  a
       subject.	  However,  if	PCRE_PARTIAL_HARD  is set and the problem is a
       truncated UTF-8 character at the end of the subject,  PCRE_ERROR_SHORT‐
       UTF8 is used instead.

	 PCRE_ERROR_BADUTF8_OFFSET (-11)

       The UTF-8 byte sequence that was passed as a subject was valid, but the
       value of startoffset did not point to the beginning of a UTF-8  charac‐
       ter or the end of the subject.

	 PCRE_ERROR_PARTIAL	   (-12)

       The  subject  string did not match, but it did match partially. See the
       pcrepartial documentation for details of partial matching.

	 PCRE_ERROR_BADPARTIAL	   (-13)

       This code is no longer in  use.	It  was	 formerly  returned  when  the
       PCRE_PARTIAL  option  was used with a compiled pattern containing items
       that were  not  supported  for  partial	matching.  From	 release  8.00
       onwards, there are no restrictions on partial matching.

	 PCRE_ERROR_INTERNAL	   (-14)

       An  unexpected  internal error has occurred. This error could be caused
       by a bug in PCRE or by overwriting of the compiled pattern.

	 PCRE_ERROR_BADCOUNT	   (-15)

       This error is given if the value of the ovecsize argument is negative.

	 PCRE_ERROR_RECURSIONLIMIT (-21)

       The internal recursion limit, as specified by the match_limit_recursion
       field  in  a  pcre_extra	 structure (or defaulted) was reached. See the
       description above.

	 PCRE_ERROR_BADNEWLINE	   (-23)

       An invalid combination of PCRE_NEWLINE_xxx options was given.

	 PCRE_ERROR_BADOFFSET	   (-24)

       The value of startoffset was negative or greater than the length of the
       subject, that is, the value in length.

	 PCRE_ERROR_SHORTUTF8	   (-25)

       The  subject  string ended with an incomplete (truncated) UTF-8 charac‐
       ter, and the PCRE_PARTIAL_HARD option was  set.	Without	 this  option,
       PCRE_ERROR_BADUTF8 is returned in this situation.

       Error numbers -16 to -20 and -22 are not used by pcre_exec().

EXTRACTING CAPTURED SUBSTRINGS BY NUMBER

       int pcre_copy_substring(const char *subject, int *ovector,
	    int stringcount, int stringnumber, char *buffer,
	    int buffersize);

       int pcre_get_substring(const char *subject, int *ovector,
	    int stringcount, int stringnumber,
	    const char **stringptr);

       int pcre_get_substring_list(const char *subject,
	    int *ovector, int stringcount, const char ***listptr);

       Captured	 substrings  can  be  accessed	directly  by using the offsets
       returned by pcre_exec() in  ovector.  For  convenience,	the  functions
       pcre_copy_substring(),	 pcre_get_substring(),	  and	 pcre_get_sub‐
       string_list() are provided for extracting captured substrings  as  new,
       separate,  zero-terminated strings. These functions identify substrings
       by number. The next section describes functions	for  extracting	 named
       substrings.

       A  substring that contains a binary zero is correctly extracted and has
       a further zero added on the end, but the result is not, of course, a  C
       string.	 However,  you	can  process such a string by referring to the
       length that is  returned	 by  pcre_copy_substring()  and	 pcre_get_sub‐
       string().  Unfortunately, the interface to pcre_get_substring_list() is
       not adequate for handling strings containing binary zeros, because  the
       end of the final string is not independently indicated.

       The  first  three  arguments  are the same for all three of these func‐
       tions: subject is the subject string that has  just  been  successfully
       matched, ovector is a pointer to the vector of integer offsets that was
       passed to pcre_exec(), and stringcount is the number of substrings that
       were  captured  by  the match, including the substring that matched the
       entire regular expression. This is the value returned by pcre_exec() if
       it  is greater than zero. If pcre_exec() returned zero, indicating that
       it ran out of space in ovector, the value passed as stringcount	should
       be the number of elements in the vector divided by three.

       The  functions pcre_copy_substring() and pcre_get_substring() extract a
       single substring, whose number is given as  stringnumber.  A  value  of
       zero  extracts  the  substring that matched the entire pattern, whereas
       higher values  extract  the  captured  substrings.  For	pcre_copy_sub‐
       string(),  the  string  is  placed  in buffer, whose length is given by
       buffersize, while for pcre_get_substring() a new	 block	of  memory  is
       obtained	 via  pcre_malloc,  and its address is returned via stringptr.
       The yield of the function is the length of the  string,	not  including
       the terminating zero, or one of these error codes:

	 PCRE_ERROR_NOMEMORY	   (-6)

       The  buffer  was too small for pcre_copy_substring(), or the attempt to
       get memory failed for pcre_get_substring().

	 PCRE_ERROR_NOSUBSTRING	   (-7)

       There is no substring whose number is stringnumber.

       The pcre_get_substring_list()  function	extracts  all  available  sub‐
       strings	and  builds  a list of pointers to them. All this is done in a
       single block of memory that is obtained via pcre_malloc. The address of
       the  memory  block  is returned via listptr, which is also the start of
       the list of string pointers. The end of the list is marked  by  a  NULL
       pointer.	 The  yield  of	 the function is zero if all went well, or the
       error code

	 PCRE_ERROR_NOMEMORY	   (-6)

       if the attempt to get the memory block failed.

       When any of these functions encounter a substring that is unset,	 which
       can  happen  when  capturing subpattern number n+1 matches some part of
       the subject, but subpattern n has not been used at all, they return  an
       empty string. This can be distinguished from a genuine zero-length sub‐
       string by inspecting the appropriate offset in ovector, which is	 nega‐
       tive for unset substrings.

       The  two convenience functions pcre_free_substring() and pcre_free_sub‐
       string_list() can be used to free the memory  returned  by  a  previous
       call  of	 pcre_get_substring()  or  pcre_get_substring_list(),  respec‐
       tively. They do nothing more than  call	the  function  pointed	to  by
       pcre_free,  which  of course could be called directly from a C program.
       However, PCRE is used in some situations where it is linked via a  spe‐
       cial   interface	 to  another  programming  language  that  cannot  use
       pcre_free directly; it is for these cases that the functions  are  pro‐
       vided.

EXTRACTING CAPTURED SUBSTRINGS BY NAME

       int pcre_get_stringnumber(const pcre *code,
	    const char *name);

       int pcre_copy_named_substring(const pcre *code,
	    const char *subject, int *ovector,
	    int stringcount, const char *stringname,
	    char *buffer, int buffersize);

       int pcre_get_named_substring(const pcre *code,
	    const char *subject, int *ovector,
	    int stringcount, const char *stringname,
	    const char **stringptr);

       To  extract a substring by name, you first have to find associated num‐
       ber.  For example, for this pattern

	 (a+)b(?<xxx>\d+)...

       the number of the subpattern called "xxx" is 2. If the name is known to
       be unique (PCRE_DUPNAMES was not set), you can find the number from the
       name by calling pcre_get_stringnumber(). The first argument is the com‐
       piled pattern, and the second is the name. The yield of the function is
       the subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if	 there	is  no
       subpattern of that name.

       Given the number, you can extract the substring directly, or use one of
       the functions described in the previous section. For convenience, there
       are also two functions that do the whole job.

       Most    of    the    arguments	of   pcre_copy_named_substring()   and
       pcre_get_named_substring() are the same	as  those  for	the  similarly
       named  functions	 that extract by number. As these are described in the
       previous section, they are not re-described here. There	are  just  two
       differences:

       First,  instead	of a substring number, a substring name is given. Sec‐
       ond, there is an extra argument, given at the start, which is a pointer
       to  the compiled pattern. This is needed in order to gain access to the
       name-to-number translation table.

       These functions call pcre_get_stringnumber(), and if it succeeds,  they
       then  call  pcre_copy_substring() or pcre_get_substring(), as appropri‐
       ate. NOTE: If PCRE_DUPNAMES is set and there are duplicate  names,  the
       behaviour may not be what you want (see the next section).

       Warning: If the pattern uses the (?| feature to set up multiple subpat‐
       terns with the same number, as described in the	section	 on  duplicate
       subpattern  numbers  in	the  pcrepattern page, you cannot use names to
       distinguish the different subpatterns, because names are	 not  included
       in  the compiled code. The matching process uses only numbers. For this
       reason, the use of different names for subpatterns of the  same	number
       causes an error at compile time.

DUPLICATE SUBPATTERN NAMES

       int pcre_get_stringtable_entries(const pcre *code,
	    const char *name, char **first, char **last);

       When  a	pattern	 is  compiled with the PCRE_DUPNAMES option, names for
       subpatterns are not required to be unique. (Duplicate names are	always
       allowed	for subpatterns with the same number, created by using the (?|
       feature. Indeed, if such subpatterns are named, they  are  required  to
       use the same names.)

       Normally, patterns with duplicate names are such that in any one match,
       only one of the named subpatterns participates. An example is shown  in
       the pcrepattern documentation.

       When    duplicates   are	  present,   pcre_copy_named_substring()   and
       pcre_get_named_substring() return the first substring corresponding  to
       the  given  name	 that  is set. If none are set, PCRE_ERROR_NOSUBSTRING
       (-7) is returned; no  data  is  returned.  The  pcre_get_stringnumber()
       function	 returns one of the numbers that are associated with the name,
       but it is not defined which it is.

       If you want to get full details of all captured substrings for a	 given
       name,  you  must	 use  the pcre_get_stringtable_entries() function. The
       first argument is the compiled pattern, and the second is the name. The
       third  and  fourth  are	pointers to variables which are updated by the
       function. After it has run, they point to the first and last entries in
       the  name-to-number  table  for	the  given  name.  The function itself
       returns the length of each entry,  or  PCRE_ERROR_NOSUBSTRING  (-7)  if
       there  are none. The format of the table is described above in the sec‐
       tion entitled Information about a  pattern.   Given  all	 the  relevant
       entries	for the name, you can extract each of their numbers, and hence
       the captured data, if any.

FINDING ALL POSSIBLE MATCHES

       The traditional matching function uses a	 similar  algorithm  to	 Perl,
       which stops when it finds the first match, starting at a given point in
       the subject. If you want to find all possible matches, or  the  longest
       possible	 match,	 consider using the alternative matching function (see
       below) instead. If you cannot use the alternative function,  but	 still
       need  to	 find all possible matches, you can kludge it up by making use
       of the callout facility, which is described in the pcrecallout documen‐
       tation.

       What you have to do is to insert a callout right at the end of the pat‐
       tern.  When your callout function is called, extract and save the  cur‐
       rent  matched  substring.  Then	return	1, which forces pcre_exec() to
       backtrack and try other alternatives. Ultimately, when it runs  out  of
       matches, pcre_exec() will yield PCRE_ERROR_NOMATCH.

MATCHING A PATTERN: THE ALTERNATIVE FUNCTION

       int pcre_dfa_exec(const pcre *code, const pcre_extra *extra,
	    const char *subject, int length, int startoffset,
	    int options, int *ovector, int ovecsize,
	    int *workspace, int wscount);

       The  function  pcre_dfa_exec()  is  called  to  match  a subject string
       against a compiled pattern, using a matching algorithm that  scans  the
       subject	string	just  once, and does not backtrack. This has different
       characteristics to the normal algorithm, and  is	 not  compatible  with
       Perl.  Some  of the features of PCRE patterns are not supported. Never‐
       theless, there are times when this kind of matching can be useful.  For
       a  discussion  of  the  two matching algorithms, and a list of features
       that pcre_dfa_exec() does not support, see the pcrematching  documenta‐
       tion.

       The  arguments  for  the	 pcre_dfa_exec()  function are the same as for
       pcre_exec(), plus two extras. The ovector argument is used in a differ‐
       ent  way,  and  this is described below. The other common arguments are
       used in the same way as for pcre_exec(), so their  description  is  not
       repeated here.

       The  two	 additional  arguments provide workspace for the function. The
       workspace vector should contain at least 20 elements. It	 is  used  for
       keeping	track  of  multiple  paths  through  the  pattern  tree.  More
       workspace will be needed for patterns and subjects where	 there	are  a
       lot of potential matches.

       Here is an example of a simple call to pcre_dfa_exec():

	 int rc;
	 int ovector[10];
	 int wspace[20];
	 rc = pcre_dfa_exec(
	   re,		   /* result of pcre_compile() */
	   NULL,	   /* we didn't study the pattern */
	   "some string",  /* the subject string */
	   11,		   /* the length of the subject string */
	   0,		   /* start at offset 0 in the subject */
	   0,		   /* default options */
	   ovector,	   /* vector of integers for substring information */
	   10,		   /* number of elements (NOT size in bytes) */
	   wspace,	   /* working space vector */
	   20);		   /* number of elements (NOT size in bytes) */

   Option bits for pcre_dfa_exec()

       The  unused  bits  of  the options argument for pcre_dfa_exec() must be
       zero. The only bits  that  may  be  set	are  PCRE_ANCHORED,  PCRE_NEW‐
       LINE_xxx,	PCRE_NOTBOL,	    PCRE_NOTEOL,	PCRE_NOTEMPTY,
       PCRE_NOTEMPTY_ATSTART,	   PCRE_NO_UTF8_CHECK,	     PCRE_BSR_ANYCRLF,
       PCRE_BSR_UNICODE,  PCRE_NO_START_OPTIMIZE, PCRE_PARTIAL_HARD, PCRE_PAR‐
       TIAL_SOFT, PCRE_DFA_SHORTEST, and PCRE_DFA_RESTART.  All but  the  last
       four  of	 these	are  exactly  the  same	 as  for pcre_exec(), so their
       description is not repeated here.

	 PCRE_PARTIAL_HARD
	 PCRE_PARTIAL_SOFT

       These have the same general effect as they do for pcre_exec(), but  the
       details	are  slightly  different.  When	 PCRE_PARTIAL_HARD  is set for
       pcre_dfa_exec(), it returns PCRE_ERROR_PARTIAL if the end of  the  sub‐
       ject  is	 reached  and there is still at least one matching possibility
       that requires additional characters. This happens even if some complete
       matches have also been found. When PCRE_PARTIAL_SOFT is set, the return
       code PCRE_ERROR_NOMATCH is converted into PCRE_ERROR_PARTIAL if the end
       of  the	subject	 is  reached, there have been no complete matches, but
       there is still at least one matching possibility. The  portion  of  the
       string  that  was inspected when the longest partial match was found is
       set as the first matching string	 in  both  cases.   There  is  a  more
       detailed	 discussion  of partial and multi-segment matching, with exam‐
       ples, in the pcrepartial documentation.

	 PCRE_DFA_SHORTEST

       Setting the PCRE_DFA_SHORTEST option causes the matching	 algorithm  to
       stop as soon as it has found one match. Because of the way the alterna‐
       tive algorithm works, this is necessarily the shortest  possible	 match
       at the first possible matching point in the subject string.

	 PCRE_DFA_RESTART

       When pcre_dfa_exec() returns a partial match, it is possible to call it
       again, with additional subject characters, and have  it	continue  with
       the  same match. The PCRE_DFA_RESTART option requests this action; when
       it is set, the workspace and wscount options must  reference  the  same
       vector  as  before  because data about the match so far is left in them
       after a partial match. There is more discussion of this facility in the
       pcrepartial documentation.

   Successful returns from pcre_dfa_exec()

       When  pcre_dfa_exec()  succeeds, it may have matched more than one sub‐
       string in the subject. Note, however, that all the matches from one run
       of  the	function  start	 at the same point in the subject. The shorter
       matches are all initial substrings of the longer matches. For  example,
       if the pattern

	 <.*>

       is matched against the string

	 This is <something> <something else> <something further> no more

       the three matched strings are

	 <something>
	 <something> <something else>
	 <something> <something else> <something further>

       On  success,  the  yield of the function is a number greater than zero,
       which is the number of matched substrings.  The	substrings  themselves
       are  returned  in  ovector. Each string uses two elements; the first is
       the offset to the start, and the second is the offset to	 the  end.  In
       fact,  all  the	strings	 have the same start offset. (Space could have
       been saved by giving this only once, but it was decided to retain  some
       compatibility  with  the	 way pcre_exec() returns data, even though the
       meaning of the strings is different.)

       The strings are returned in reverse order of length; that is, the long‐
       est  matching  string is given first. If there were too many matches to
       fit into ovector, the yield of the function is zero, and the vector  is
       filled with the longest matches.

   Error returns from pcre_dfa_exec()

       The  pcre_dfa_exec()  function returns a negative number when it fails.
       Many of the errors are the same	as  for	 pcre_exec(),  and  these  are
       described  above.   There are in addition the following errors that are
       specific to pcre_dfa_exec():

	 PCRE_ERROR_DFA_UITEM	   (-16)

       This return is given if pcre_dfa_exec() encounters an item in the  pat‐
       tern  that  it  does not support, for instance, the use of \C or a back
       reference.

	 PCRE_ERROR_DFA_UCOND	   (-17)

       This return is given if pcre_dfa_exec()	encounters  a  condition  item
       that  uses  a back reference for the condition, or a test for recursion
       in a specific group. These are not supported.

	 PCRE_ERROR_DFA_UMLIMIT	   (-18)

       This return is given if pcre_dfa_exec() is called with an  extra	 block
       that contains a setting of the match_limit field. This is not supported
       (it is meaningless).

	 PCRE_ERROR_DFA_WSSIZE	   (-19)

       This return is given if	pcre_dfa_exec()	 runs  out  of	space  in  the
       workspace vector.

	 PCRE_ERROR_DFA_RECURSE	   (-20)

       When  a	recursive subpattern is processed, the matching function calls
       itself recursively, using private vectors for  ovector  and  workspace.
       This  error  is	given  if  the output vector is not large enough. This
       should be extremely rare, as a vector of size 1000 is used.

SEE ALSO

       pcrebuild(3), pcrecallout(3), pcrecpp(3)(3), pcrematching(3),  pcrepar‐
       tial(3), pcreposix(3), pcreprecompile(3), pcresample(3), pcrestack(3).

AUTHOR

       Philip Hazel
       University Computing Service
       Cambridge CB2 3QH, England.

REVISION

       Last updated: 21 November 2010
       Copyright (c) 1997-2010 University of Cambridge.

								    PCREAPI(3)
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