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pcreapi(3)                                                          pcreapi(3)




NAME

       PCRE - Perl-compatible regular expressions

       #include <pcre.h>


PCRE NATIVE API BASIC FUNCTIONS


       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);

       void pcre_free_study(pcre_extra *extra);

       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);


PCRE NATIVE API STRING EXTRACTION FUNCTIONS


       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);


PCRE NATIVE API AUXILIARY FUNCTIONS


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

       pcre_jit_stack *pcre_jit_stack_alloc(int startsize, int maxsize);

       void pcre_jit_stack_free(pcre_jit_stack *stack);

       void pcre_assign_jit_stack(pcre_extra *extra,
            pcre_jit_callback callback, void *data);

       const unsigned char *pcre_maketables(void);

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

       int pcre_refcount(pcre *code, int adjust);

       int pcre_config(int what, void *where);

       const char *pcre_version(void);

       int pcre_pattern_to_host_byte_order(pcre *code,
            pcre_extra *extra, const unsigned char *tables);


PCRE NATIVE API INDIRECTED FUNCTIONS


       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 *);

       int (*pcre_stack_guard)(void);


PCRE 8-BIT, 16-BIT, AND 32-BIT LIBRARIES


       As  well  as  support  for  8-bit character strings, PCRE also supports
       16-bit strings (from release 8.30) and  32-bit  strings  (from  release
       8.32),  by means of two additional libraries. They can be built as well
       as, or instead of, the 8-bit library. To avoid too  much  complication,
       this  document describes the 8-bit versions of the functions, with only
       occasional references to the 16-bit and 32-bit libraries.

       The 16-bit and 32-bit functions operate in the same way as their  8-bit
       counterparts;  they  just  use different data types for their arguments
       and results, and their names start with pcre16_ or pcre32_  instead  of
       pcre_.  For  every  option  that  has  UTF8  in  its name (for example,
       PCRE_UTF8), there are corresponding 16-bit and 32-bit names  with  UTF8
       replaced by UTF16 or UTF32, respectively. This facility is in fact just
       cosmetic; the 16-bit and 32-bit option names define the same  bit  val-
       ues.

       References to bytes and UTF-8 in this document should be read as refer-
       ences to 16-bit data units and UTF-16 when using the 16-bit library, or
       32-bit  data  units  and  UTF-32  when using the 32-bit library, unless
       specified otherwise.  More details of the specific differences for  the
       16-bit and 32-bit libraries are given in the pcre16 and pcre32 pages.


PCRE API OVERVIEW


       PCRE has its own native API, which is described in this document. There
       are also some wrapper functions (for the 8-bit library only) that  cor-
       respond  to  the  POSIX  regular  expression  API, but they do not give
       access to all the functionality. They are described  in  the  pcreposix
       documentation.  Both  of these APIs define a set of C function calls. A
       C++ wrapper (again for the 8-bit library only) is also 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-like systems the (8-bit) 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
       numbers 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.

       Just-in-time  compiler  support is an optional feature of PCRE that can
       be built in appropriate hardware environments. It greatly speeds up the
       matching  performance  of  many  patterns.  Simple  programs can easily
       request that it be used if available, by  setting  an  option  that  is
       ignored  when  it is not relevant. More complicated programs might need
       to    make    use    of    the    functions     pcre_jit_stack_alloc(),
       pcre_jit_stack_free(),  and pcre_assign_jit_stack() in order to control
       the JIT code's memory usage.

       From release 8.32 there is also a direct interface for  JIT  execution,
       which  gives  improved performance. The JIT-specific functions are dis-
       cussed in the pcrejit documentation.

       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. 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 always allocate 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.

       The global variable pcre_stack_guard initially contains NULL. It can be
       set by the caller to a function that is  called  by  PCRE  whenever  it
       starts  to  compile a parenthesized part of a pattern. When parentheses
       are nested, PCRE uses recursive function calls, which use up the system
       stack.  This  function is provided so that applications with restricted
       stacks can force a compilation error if the stack runs out.  The  func-
       tion  should return zero if all is well, or non-zero to force an error.


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 (form feed, 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 and stack-checking functions pointed  to  by  pcre_callout  and
       pcre_stack_guard, 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.

       If  the just-in-time optimization feature is being used, it needs sepa-
       rate memory stack areas for each thread. See the pcrejit  documentation
       for more details.


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,  which  includes  a  description  of  the
       pcre_pattern_to_host_byte_order()  function. However, compiling a regu-
       lar expression with one version of PCRE for use with a  different  ver-
       sion is not guaranteed 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 returned  value  is  zero  on
       success,  or  the negative error code PCRE_ERROR_BADOPTION if the value
       in the first argument is not recognized. 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. This value should normally be  given
       to the 8-bit version of this function, pcre_config(). If it is given to
       the  16-bit  or  32-bit  version  of  this  function,  the  result   is
       PCRE_ERROR_BADOPTION.

         PCRE_CONFIG_UTF16

       The output is an integer that is set to one if UTF-16 support is avail-
       able; otherwise it is set to zero. This value should normally be  given
       to the 16-bit version of this function, pcre16_config(). If it is given
       to the 8-bit  or  32-bit  version  of  this  function,  the  result  is
       PCRE_ERROR_BADOPTION.

         PCRE_CONFIG_UTF32

       The output is an integer that is set to one if UTF-32 support is avail-
       able; otherwise it is set to zero. This value should normally be  given
       to the 32-bit version of this function, pcre32_config(). If it is given
       to the 8-bit  or  16-bit  version  of  this  function,  the  result  is
       PCRE_ERROR_BADOPTION.

         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_JIT

       The output is an integer that is set to one if support for just-in-time
       compiling is available; otherwise it is set to zero.

         PCRE_CONFIG_JITTARGET

       The  output is a pointer to a zero-terminated "const char *" string. If
       JIT support is available, the string contains the name of the architec-
       ture  for  which the JIT compiler is configured, for example "x86 32bit
       (little endian + unaligned)". If JIT  support  is  not  available,  the
       result is NULL.

         PCRE_CONFIG_NEWLINE

       The  output  is  an integer whose value specifies the default character
       sequence that is recognized as meaning "newline". The values  that  are
       supported in ASCII/Unicode environments are: 10 for LF, 13 for CR, 3338
       for CRLF, -2 for ANYCRLF, and -1 for ANY. In EBCDIC  environments,  CR,
       ANYCRLF,  and  ANY  yield the same values. However, the value for LF is
       normally 21, though some EBCDIC environments use 37. The  corresponding
       values  for  CRLF are 3349 and 3365. 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.  For  the  8-bit
       library, the value can be 2, 3, or 4. For the 16-bit library, the value
       is  either  2  or  4  and  is  still  a number of bytes. For the 32-bit
       library, the value is either 2 or 4 and is still a number of bytes. 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.  Larger
       values  allow larger regular expressions to be compiled, at the expense
       of slower matching.

         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_PARENS_LIMIT

       The output is a long integer that gives the maximum depth of nesting of
       parentheses  (of  any  kind) in a pattern. This limit is imposed to cap
       the amount of system stack used when a pattern is compiled. It is spec-
       ified  when PCRE is built; the default is 250. This limit does not take
       into account the stack that may already be used by the calling applica-
       tion.  For  finer  control  over compilation stack usage, you can set a
       pointer to an external checking function in pcre_stack_guard.

         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_OPTIMIZE 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. Normally, the offset from the start of the pattern to
       the data unit 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). However, for an invalid  UTF-8
       or  UTF-16  string,  the  offset  is that of the first data unit of the
       failing character.

       Some errors are not detected until the whole pattern has been  scanned;
       in  these  cases,  the offset passed back is the length of the pattern.
       Note that the offset is in data units, not characters, even  in  a  UTF
       mode. It may sometimes point into the middle of a UTF-8 or UTF-16 char-
       acter.

       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() and pcre_dfa_exec()
       when the pattern is matched. 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, most white space  characters  in  the  pattern  are
       totally  ignored  except when escaped or inside a character class. How-
       ever, white space is not allowed within  sequences  such  as  (?>  that
       introduce  various  parenthesized  subpatterns,  nor within a numerical
       quantifier such as {1,3}.  However, ignorable white space is  permitted
       between an item and a following quantifier and between a quantifier and
       a following + that indicates possessiveness.

       White space did not used to include the VT character (code 11), because
       Perl did not treat this character as white space. However, Perl changed
       at release 5.18, so PCRE followed  at  release  8.34,  and  VT  is  now
       treated as white space.

       PCRE_EXTENDED  also  causes characters between an unescaped # outside a
       character class  and  the  next  newline,  inclusive,  to  be  ignored.
       PCRE_EXTENDED  is equivalent to Perl's /x option, and it can be changed
       within a pattern by a (?x) option setting.

       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.
       White  space  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.

       (3) \U matches an upper case "U" character; by default \U causes a com-
       pile time error (Perl uses \U to upper case subsequent characters).

       (4) \u matches a lower case "u" character unless it is followed by four
       hexadecimal  digits,  in  which case the hexadecimal number defines the
       code point to match. By default, \u causes a compile time  error  (Perl
       uses it to upper case the following character).

       (5)  \x matches a lower case "x" character unless it is followed by two
       hexadecimal digits, in which case the hexadecimal  number  defines  the
       code  point  to  match. By default, as in Perl, a hexadecimal number is
       always expected after \x, but it may have zero, one, or two digits (so,
       for example, \xz matches a binary zero character followed by z).

         PCRE_MULTILINE

       By  default,  for  the purposes of matching "start of line" and "end of
       line", 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, and the "end
       of  line"  metacharacter  ($) matches only at the end of the string, or
       before a terminating newline (except when PCRE_DOLLAR_ENDONLY is  set).
       Note,  however,  that  unless  PCRE_DOTALL  is set, the "any character"
       metacharacter (.) does not match at a newline. This behaviour  (for  ^,
       $, and dot) 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_NEVER_UTF

       This option locks out interpretation of the pattern as UTF-8 (or UTF-16
       or UTF-32 in the 16-bit and 32-bit libraries). In particular,  it  pre-
       vents  the  creator of the pattern from switching to UTF interpretation
       by starting the pattern with (*UTF). This may be useful in applications
       that  process  patterns  from  external  sources.  The  combination  of
       PCRE_UTF8 and PCRE_NEVER_UTF also causes an error.

         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.

       In  an ASCII/Unicode environment, the Unicode newline sequences are the
       three just mentioned, plus the  single  characters  VT  (vertical  tab,
       U+000B), FF (form feed, U+000C), NEL (next line, U+0085), LS (line sep-
       arator, U+2028), and PS (paragraph separator, U+2029).  For  the  8-bit
       library, the last two are recognized only in UTF-8 mode.

       When  PCRE is compiled to run in an EBCDIC (mainframe) environment, the
       code for CR is 0x0d, the same as ASCII. However, the character code for
       LF  is  normally 0x15, though in some EBCDIC environments 0x25 is used.
       Whichever of these is not LF is made to  correspond  to  Unicode's  NEL
       character.  EBCDIC  codes  are all less than 256. For more details, see
       the pcrebuild documentation.

       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 white space
       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.

         PCRE_NO_AUTO_POSSESS

       If  this option is set, it disables "auto-possessification". This is an
       optimization that, for example, turns a+b into a++b in order  to  avoid
       backtracks  into  a+ that can never be successful. However, if callouts
       are in use, auto-possessification means that some  of  them  are  never
       taken. You can set this option if you want the matching functions to do
       a full unoptimized search and run all the callouts, but  it  is  mainly
       provided for testing purposes.

         PCRE_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. This is necessary if you want to use JIT  execution,  because
       the  JIT  compiler needs to know whether or not this option is set. 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 strings. However, it
       is available only when PCRE is built to include UTF  support.  If  not,
       the  use  of  this option provokes an error. Details of how this option
       changes the behaviour of PCRE are given in the pcreunicode 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 pcreunicode page. If an invalid UTF-8 sequence  is
       found,  pcre_compile()  returns an error. If you already know that your
       pattern is valid, and you want to skip this check for performance  rea-
       sons,  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 or loop. Note that this option can also
       be passed to pcre_exec() and pcre_dfa_exec(), to suppress the  validity
       checking  of  subject strings only. If the same string is being matched
       many times, the option can be safely set for the second and  subsequent
       matchings to improve performance.


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.  Note  that error messages are always 8-bit
       ASCII strings, even in 16-bit or 32-bit mode. 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 compiled without UTF support
         33  [this code is not in use]
         34  character value in \x{} or \o{} is too large
         35  invalid condition (?(0)
         36  \C not allowed in lookbehind assertion
         37  PCRE does not support \L, \l, \N{name}, \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 (specifically UTF-8)
         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 in 8-bit non-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 or malformed
         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 Unicode property
               support
         68  \c must be followed by an ASCII character
         69  \k is not followed by a braced, angle-bracketed, or quoted name
         70  internal error: unknown opcode in find_fixedlength()
         71  \N is not supported in a class
         72  too many forward references
         73  disallowed Unicode code point (>= 0xd800 && <= 0xdfff)
         74  invalid UTF-16 string (specifically UTF-16)
         75  name is too long in (*MARK), (*PRUNE), (*SKIP), or (*THEN)
         76  character value in \u.... sequence is too large
         77  invalid UTF-32 string (specifically UTF-32)
         78  setting UTF is disabled by the application
         79  non-hex character in \x{} (closing brace missing?)
         80  non-octal character in \o{} (closing brace missing?)
         81  missing opening brace after \o
         82  parentheses are too deeply nested
         83  invalid range in character class
         84  group name must start with a non-digit
         85  parentheses are too deeply nested (stack check)

       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 by default.  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.  However,  if
       pcre_study()  is  called  with  the  PCRE_STUDY_EXTRA_NEEDED option, it
       returns a pcre_extra block even if studying did not find any additional
       information.  It  may still return NULL, however, if an error occurs in
       pcre_study().

       The second argument of pcre_study() contains  option  bits.  There  are
       three further options in addition to PCRE_STUDY_EXTRA_NEEDED:

         PCRE_STUDY_JIT_COMPILE
         PCRE_STUDY_JIT_PARTIAL_HARD_COMPILE
         PCRE_STUDY_JIT_PARTIAL_SOFT_COMPILE

       If  any  of  these are set, and the just-in-time compiler is available,
       the pattern is further compiled into machine code  that  executes  much
       faster  than  the  pcre_exec()  interpretive  matching function. If the
       just-in-time compiler is not available, these options are ignored.  All
       undefined bits in the options argument must be zero.

       JIT  compilation  is  a heavyweight optimization. It can take some time
       for patterns to be analyzed, and for one-off matches  and  simple  pat-
       terns  the benefit of faster execution might be offset by a much slower
       study time.  Not all patterns can be optimized by the JIT compiler. For
       those  that cannot be handled, matching automatically falls back to the
       pcre_exec() interpreter. For more details, see the  pcrejit  documenta-
       tion.

       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.

       When you are finished with a pattern, you can free the memory used  for
       the study data by calling pcre_free_study(). This function was added to
       the API for release 8.20. For earlier versions,  the  memory  could  be
       freed  with  pcre_free(), just like the pattern itself. This will still
       work in cases where JIT optimization is not used, but it  is  advisable
       to change to the new function when convenient.

       This  is  a typical way in which pcre_study() is used (except that in a
       real application there should be tests for errors):

         int rc;
         pcre *re;
         pcre_extra *sd;
         re = pcre_compile("pattern", 0, &error, &erroroffset, NULL);
         sd = pcre_study(
           re,             /* result of pcre_compile() */
           0,              /* no options */
           &error);        /* set to NULL or points to a message */
         rc = pcre_exec(   /* see below for details of pcre_exec() options */
           re, sd, "subject", 7, 0, 0, ovector, 30);
         ...
         pcre_free_study(sd);
         pcre_free(re);

       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 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. (In 16-bit mode, the bitmap is used for 16-bit
       values less than 256.  In 32-bit mode, the bitmap is  used  for  32-bit
       values less than 256.)

       These  two optimizations apply to both pcre_exec() and pcre_dfa_exec(),
       and the information is also used by the JIT  compiler.   The  optimiza-
       tions  can  be  disabled  by setting the PCRE_NO_START_OPTIMIZE option.
       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.

       PCRE_NO_START_OPTIMIZE can be specified at either compile time or  exe-
       cution   time.   However,   if   PCRE_NO_START_OPTIMIZE  is  passed  to
       pcre_exec(), (that is, after any JIT compilation has happened) JIT exe-
       cution  is disabled. For JIT execution to work with PCRE_NO_START_OPTI-
       MIZE, the option must be set at compile time.

       There is a longer discussion of PCRE_NO_START_OPTIMIZE 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 code point. When running in UTF-8 mode, or in the  16-  or
       32-bit libraries, this applies only to characters with code points less
       than 256. By default, higher-valued code  points  never  match  escapes
       such  as \w or \d. However, if PCRE is built with Unicode property sup-
       port, all characters can be tested with \p and \P,  or,  alternatively,
       the  PCRE_UCP option can be set when a pattern is compiled; this causes
       \w and friends to use Unicode property support instead of the  built-in
       tables.

       The  use  of  locales  with Unicode is discouraged. If you are handling
       characters with code points greater than 128,  you  should  either  use
       Unicode support, 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() 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 let-
       ters), 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 also by pcre_exec() and pcre_dfa_exec(). Thus, for any single  pat-
       tern, compilation, studying and matching all happen in the same locale,
       but different patterns can be processed in different locales.

       It is possible to pass a table pointer or NULL (indicating the  use  of
       the internal tables) to pcre_exec() or pcre_dfa_exec() (see the discus-
       sion below in the section on matching a pattern). This facility is pro-
       vided  for  use  with  pre-compiled  patterns  that have been saved and
       reloaded.  Character tables are not saved with patterns, so if  a  non-
       standard table was used at compile time, it must be provided again when
       the reloaded pattern is matched. Attempting to  use  this  facility  to
       match a pattern in a different locale from the one in which it was com-
       piled is likely to lead to anomalous (usually incorrect) results.


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 pcre_info() function, which was removed from the
       library at version 8.30, after more than 10 years of obsolescence.

       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_BADENDIANNESS  the pattern was compiled with different
                                   endianness
         PCRE_ERROR_BADOPTION      the value of what was invalid
         PCRE_ERROR_UNSET          the requested field is not set

       The  "magic  number" is placed at the start of each compiled pattern as
       an simple check against passing an arbitrary memory pointer. The  endi-
       anness error can occur if a compiled pattern is saved and reloaded on a
       different host. 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() */
           sd,               /* 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 (deprecated)

       Return information about the first data unit of any matched string, for
       a non-anchored pattern. The name of this option  refers  to  the  8-bit
       library,  where  data units are bytes. The fourth argument should point
       to an int variable. Negative values are used for  special  cases.  How-
       ever,  this  means  that when the 32-bit library is in non-UTF-32 mode,
       the full 32-bit range of characters cannot be returned. For  this  rea-
       son,  this  value  is deprecated; use PCRE_INFO_FIRSTCHARACTERFLAGS and
       PCRE_INFO_FIRSTCHARACTER instead.

       If there is a fixed first value, for example, the  letter  "c"  from  a
       pattern  such  as (cat|cow|coyote), its value is returned. In the 8-bit
       library, the value is always less than 256. In the 16-bit  library  the
       value can be up to 0xffff. In the 32-bit library the value can be up to
       0x10ffff.

       If there is no fixed first value, and 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_FIRSTCHARACTER

       Return the value of the first data  unit  (non-UTF  character)  of  any
       matched  string  in  the  situation where PCRE_INFO_FIRSTCHARACTERFLAGS
       returns 1; otherwise return 0. The fourth argument should point  to  an
       uint_t variable.

       In  the 8-bit library, the value is always less than 256. In the 16-bit
       library the value can be up to 0xffff. In the 32-bit library in  UTF-32
       mode  the  value  can  be up to 0x10ffff, and up to 0xffffffff when not
       using UTF-32 mode.

         PCRE_INFO_FIRSTCHARACTERFLAGS

       Return information about the first data unit of any matched string, for
       a  non-anchored  pattern.  The  fourth  argument should point to an int
       variable.

       If there is a fixed first value, for example, the  letter  "c"  from  a
       pattern  such  as  (cat|cow|coyote),  1  is returned, and the character
       value can be retrieved using PCRE_INFO_FIRSTCHARACTER. If there  is  no
       fixed first value, and 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),

       2 is returned, indicating that the pattern matches only at the start of
       a subject string or after any newline within the string. Otherwise 0 is
       returned. For anchored patterns, 0 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 values for the first data  unit
       in  any  matching string, a pointer to the table is returned. Otherwise
       NULL is returned. The fourth argument should point to an unsigned  char
       * variable.

         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_JIT

       Return 1 if the pattern was studied with one of the  JIT  options,  and
       just-in-time compiling was successful. The fourth argument should point
       to an int variable. A return value of 0 means that JIT support  is  not
       available  in this version of PCRE, or that the pattern was not studied
       with a JIT option, or that the JIT compiler could not handle this  par-
       ticular  pattern. See the pcrejit documentation for details of what can
       and cannot be handled.

         PCRE_INFO_JITSIZE

       If the pattern was successfully studied with a JIT option,  return  the
       size  of the JIT compiled code, otherwise return zero. The fourth argu-
       ment should point to a size_t variable.

         PCRE_INFO_LASTLITERAL

       Return the value of the rightmost literal data unit that must exist  in
       any  matched  string, other than at its start, if such a value has been
       recorded. The fourth argument should point to an int variable. If there
       is no such value, -1 is returned. For anchored patterns, a last literal
       value 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.

       Since for the 32-bit library using the non-UTF-32 mode,  this  function
       is  unable to return the full 32-bit range of characters, this value is
       deprecated;     instead     the     PCRE_INFO_REQUIREDCHARFLAGS     and
       PCRE_INFO_REQUIREDCHAR values should be used.

         PCRE_INFO_MATCH_EMPTY

       Return  1  if  the  pattern can match an empty string, otherwise 0. The
       fourth argument should point to an int variable.

         PCRE_INFO_MATCHLIMIT

       If the pattern set a match limit by  including  an  item  of  the  form
       (*LIMIT_MATCH=nnnn)  at  the  start,  the value is returned. The fourth
       argument should point to an unsigned 32-bit integer. If no  such  value
       has   been   set,   the  call  to  pcre_fullinfo()  returns  the  error
       PCRE_ERROR_UNSET.

         PCRE_INFO_MAXLOOKBEHIND

       Return the number of characters (NB not  data  units)  in  the  longest
       lookbehind  assertion  in  the pattern. This information is useful when
       doing multi-segment matching using  the  partial  matching  facilities.
       Note that the simple assertions \b and \B require a one-character look-
       behind. \A also registers a one-character lookbehind,  though  it  does
       not  actually inspect the previous character. This is to ensure that at
       least one character from the old segment is retained when a new segment
       is processed. Otherwise, if there are no lookbehinds in the pattern, \A
       might match incorrectly at the start of a new segment.

         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, which in UTF mode may
       be  different from the number of data units. 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. This is a pointer to char in
       the 8-bit library, where the first two bytes of each entry are the num-
       ber  of  the capturing parenthesis, most significant byte first. In the
       16-bit library, the pointer points to 16-bit data units, the  first  of
       which  contains  the  parenthesis  number.  In  the 32-bit library, the
       pointer points to 32-bit data units, the first of  which  contains  the
       parenthesis  number.  The  rest of the entry is the corresponding name,
       zero terminated.

       The names are in alphabetical order. If (?| is used to create  multiple
       groups  with  the same number, as described in the section on duplicate
       subpattern numbers in the pcrepattern page, the groups may be given the
       same  name,  but  there is only one entry in the table. Different names
       for groups of the same number are not permitted.  Duplicate  names  for
       subpatterns with different numbers are permitted, but only if PCRE_DUP-
       NAMES is set. They appear in the table in the order in which they  were
       found  in  the  pattern.  In  the  absence  of (?| this is the order of
       increasing number; when (?| is used this is not  necessarily  the  case
       because later subpatterns may have lower numbers.

       As  a  simple  example of the name/number table, consider the following
       pattern after compilation by the 8-bit library (assume PCRE_EXTENDED is
       set, so white space - including newlines - 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_RECURSIONLIMIT

       If the pattern set a recursion limit by including an item of  the  form
       (*LIMIT_RECURSION=nnnn) at the start, the value is returned. The fourth
       argument should point to an unsigned 32-bit integer. If no  such  value
       has   been   set,   the  call  to  pcre_fullinfo()  returns  the  error
       PCRE_ERROR_UNSET.

         PCRE_INFO_SIZE

       Return the size of  the  compiled  pattern  in  bytes  (for  all  three
       libraries). The fourth argument should point to a size_t variable. This
       value does not include the size of the pcre structure that is  returned
       by  pcre_compile().  The  value  that  is  passed  as  the  argument to
       pcre_malloc() when pcre_compile() is getting memory in which  to  place
       the compiled data is the value returned by this option plus the size of
       the pcre structure. Studying a compiled pattern, with or  without  JIT,
       does not alter the value returned by this option.

         PCRE_INFO_STUDYSIZE

       Return  the  size  in bytes (for all three libraries) of the data block
       pointed to by the study_data field in a pcre_extra block. If pcre_extra
       is  NULL, or there is no study data, zero is returned. The fourth argu-
       ment should point to a size_t variable. The study_data field is set  by
       pcre_study() to record information that will speed up matching (see the
       section entitled  "Studying  a  pattern"  above).  The  format  of  the
       study_data  block is private, but its length is made available via this
       option so that it can be saved and  restored  (see  the  pcreprecompile
       documentation for details).

         PCRE_INFO_REQUIREDCHARFLAGS

       Returns  1 if there is a rightmost literal data unit that must exist in
       any matched string, other than at its start. The fourth argument should
       point  to an int variable. If there is no such value, 0 is returned. If
       returning  1,  the  character  value  itself  can  be  retrieved  using
       PCRE_INFO_REQUIREDCHAR.

       For anchored patterns, a last literal value is recorded only if it fol-
       lows something  of  variable  length.  For  example,  for  the  pattern
       /^a\d+z\d+/   the   returned   value   1   (with   "z"   returned  from
       PCRE_INFO_REQUIREDCHAR), but for /^a\dz\d/ the returned value is 0.

         PCRE_INFO_REQUIREDCHAR

       Return the value of the rightmost literal data unit that must exist  in
       any  matched  string, other than at its start, if such a value has been
       recorded. The fourth argument should point to an uint32_t variable.  If
       there is no such value, 0 is returned.


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. You can call pcre_exec() with the same code and  extra  argu-
       ments  as  many  times as you like, in order to match different subject
       strings with the same pattern.

       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  section
       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;
         void *executable_jit;
         unsigned long int match_limit;
         unsigned long int match_limit_recursion;
         void *callout_data;
         const unsigned char *tables;
         unsigned char **mark;

       In  the  16-bit  version  of  this  structure,  the mark field has type
       "PCRE_UCHAR16 **".

       In the 32-bit version of  this  structure,  the  mark  field  has  type
       "PCRE_UCHAR32 **".

       The  flags  field is used to specify which of the other fields are set.
       The flag bits are:

         PCRE_EXTRA_CALLOUT_DATA
         PCRE_EXTRA_EXECUTABLE_JIT
         PCRE_EXTRA_MARK
         PCRE_EXTRA_MATCH_LIMIT
         PCRE_EXTRA_MATCH_LIMIT_RECURSION
         PCRE_EXTRA_STUDY_DATA
         PCRE_EXTRA_TABLES

       Other flag bits should be set to zero. The study_data field  and  some-
       times  the executable_jit field are set in the pcre_extra block that is
       returned by pcre_study(), together with the appropriate flag bits.  You
       should  not set these yourself, but you may add to the block by setting
       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_exec() uses a function called match(), which it  calls
       repeatedly  (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.

       When pcre_exec() is called with a pattern that was successfully studied
       with a JIT option, the way that the matching is  executed  is  entirely
       different.  However, there is still the possibility of runaway matching
       that goes on for a very long time, and so the match_limit value is also
       used in this case (but in a different way) to limit how long the match-
       ing can continue.

       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.

       A  value  for  the  match  limit may also be supplied by an item at the
       start of a pattern of the form

         (*LIMIT_MATCH=d)

       where d is a decimal number. However, such a setting is ignored  unless
       d  is  less  than  the limit set by the caller of pcre_exec() or, if no
       such limit is set, less than the default.

       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 machine 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. This
       limit is not relevant, and is ignored, when matching is done using  JIT
       compiled code.

       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.

       A value for the recursion limit may also be supplied by an item at  the
       start of a pattern of the form

         (*LIMIT_RECURSION=d)

       where  d is a decimal number. However, such a setting is ignored unless
       d is less than the limit set by the caller of  pcre_exec()  or,  if  no
       such limit is set, less than the default.

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

       The tables field is provided for use with patterns that have been  pre-
       compiled using custom character tables, saved to disc or elsewhere, and
       then reloaded, because the tables that were used to compile  a  pattern
       are  not saved with it. See the pcreprecompile documentation for a dis-
       cussion of saving compiled patterns for later use. If  NULL  is  passed
       using this mechanism, it forces PCRE's internal tables to be used.

       Warning:  The  tables  that  pcre_exec() uses must be the same as those
       that were used when the pattern was compiled. If this is not the  case,
       the behaviour of pcre_exec() is undefined. Therefore, when a pattern is
       compiled and matched in the same process, this field  should  never  be
       set. In this (the most common) case, the correct table pointer is auto-
       matically passed with  the  compiled  pattern  from  pcre_compile()  to
       pcre_exec().

       If  PCRE_EXTRA_MARK  is  set in the flags field, the mark field must be
       set to point to a suitable 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  is  set  to NULL. For details of the backtracking control verbs,
       see the section entitled "Backtracking control" in the pcrepattern doc-
       umentation.

   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_HARD,   and
       PCRE_PARTIAL_SOFT.

       If  the  pattern  was successfully studied with one of the just-in-time
       (JIT) compile options, the only supported options for JIT execution are
       PCRE_NO_UTF8_CHECK,     PCRE_NOTBOL,     PCRE_NOTEOL,    PCRE_NOTEMPTY,
       PCRE_NOTEMPTY_ATSTART, PCRE_PARTIAL_HARD, and PCRE_PARTIAL_SOFT. If  an
       unsupported  option  is  used, JIT execution is disabled and the normal
       interpretive code in pcre_exec() is run.

         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. Also, when callouts or (*MARK) items are in  use,
       these "start-up" optimizations can cause them to be skipped if the pat-
       tern 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.  The  use  of
       PCRE_NO_START_OPTIMIZE  at  matching  time  (that  is,  passing  it  to
       pcre_exec()) disables JIT execution; in  this  situation,  matching  is
       always done using interpretively.

       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 entire string is checked before any other processing takes
       place.  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 pcreunicode page. If an invalid
       sequence  of  bytes   is   found,   pcre_exec()   returns   the   error
       PCRE_ERROR_BADUTF8 or, if PCRE_PARTIAL_HARD is set and the problem is a
       truncated character at the end of the subject, PCRE_ERROR_SHORTUTF8. In
       both  cases, information about the precise nature of the error may also
       be returned (see the descriptions of these errors in the section  enti-
       tled  Error return values from pcre_exec() below).  If startoffset con-
       tains 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 character (or the end of the subject). When
       PCRE_NO_UTF8_CHECK is set, the effect of passing an invalid string as a
       subject  or  an invalid value of startoffset is undefined. Your program
       may crash or loop.

         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  length, and a starting offset in startoffset. The units for
       length and startoffset are bytes for the  8-bit  library,  16-bit  data
       items  for  the  16-bit  library,  and 32-bit data items for the 32-bit
       library.

       If startoffset 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 or UTF-16 mode, the
       offset must point to the start of a character, or the end of  the  sub-
       ject  (in  UTF-32 mode, one data unit equals one character, so all off-
       sets are valid). Unlike the pattern string,  the  subject  may  contain
       binary zeroes.

       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 offset of the first character in a
       substring, and the second is set to the offset of the  first  character
       after  the  end  of a substring. These values are always data unit off-
       sets, even in UTF mode. They are byte offsets  in  the  8-bit  library,
       16-bit  data  item  offsets in the 16-bit library, and 32-bit data item
       offsets in the 32-bit library. Note: 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 neither the actual string  matched
       nor  any captured substrings are of interest, pcre_exec() may be called
       with ovector passed as NULL and ovecsize as zero. However, if the  pat-
       tern  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 usually advisable to supply an ovector
       of reasonable size.

       There are some cases where zero is returned  (indicating  vector  over-
       flow)  when  in fact the vector is exactly the right size for the final
       match. For example, consider the pattern

         (a)(?:(b)c|bd)

       If a vector of 6 elements (allowing for only 1 captured  substring)  is
       given with subject string "abd", pcre_exec() will try to set the second
       captured string, thereby recording a vector overflow, before failing to
       match  "c"  and  backing  up  to  try  the second alternative. The zero
       return, however, does correctly indicate that  the  maximum  number  of
       slots (namely 2) have been filled. In similar cases where there is tem-
       porary overflow, but the final number of used slots  is  actually  less
       than the maximum, a non-zero value is returned.

       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  in  the first two-thirds of ovector that do not corre-
       spond to capturing parentheses in the pattern are never  changed.  That
       is,  if  a pattern contains n capturing parentheses, no more than ovec-
       tor[0] to ovector[2n+1] are set by pcre_exec(). The other elements  (in
       the first two-thirds) retain whatever values they previously 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,  and the PCRE_NO_UTF8_CHECK option was not set. If the size of
       the output vector (ovecsize) is at least 2,  the  byte  offset  to  the
       start  of  the  the invalid UTF-8 character is placed in the first ele-
       ment, and a reason code is placed in the  second  element.  The  reason
       codes are listed in the following section.  For backward compatibility,
       if PCRE_PARTIAL_HARD is set and the problem is a truncated UTF-8  char-
       acter   at   the   end   of   the   subject  (reason  codes  1  to  5),
       PCRE_ERROR_SHORTUTF8 is returned instead of PCRE_ERROR_BADUTF8.

         PCRE_ERROR_BADUTF8_OFFSET (-11)

       The UTF-8 byte sequence that was passed as a subject  was  checked  and
       found  to be valid (the PCRE_NO_UTF8_CHECK option was not set), 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)

       This error is returned instead of PCRE_ERROR_BADUTF8 when  the  subject
       string  ends with a truncated UTF-8 character and the PCRE_PARTIAL_HARD
       option is set.  Information  about  the  failure  is  returned  as  for
       PCRE_ERROR_BADUTF8.  It  is in fact sufficient to detect this case, but
       this special error code for PCRE_PARTIAL_HARD precedes the  implementa-
       tion  of returned information; it is retained for backwards compatibil-
       ity.

         PCRE_ERROR_RECURSELOOP    (-26)

       This error is returned when pcre_exec() detects a recursion loop within
       the  pattern. Specifically, it means that either the whole pattern or a
       subpattern has been called recursively for the second time at the  same
       position in the subject string. Some simple patterns that might do this
       are detected and faulted at compile time, but more  complicated  cases,
       in particular mutual recursions between two different subpatterns, can-
       not be detected until run time.

         PCRE_ERROR_JIT_STACKLIMIT (-27)

       This error is returned when a pattern  that  was  successfully  studied
       using  a  JIT compile option is being matched, but the memory available
       for the just-in-time processing stack is  not  large  enough.  See  the
       pcrejit documentation for more details.

         PCRE_ERROR_BADMODE        (-28)

       This error is given if a pattern that was compiled by the 8-bit library
       is passed to a 16-bit or 32-bit library function, or vice versa.

         PCRE_ERROR_BADENDIANNESS  (-29)

       This error is given if  a  pattern  that  was  compiled  and  saved  is
       reloaded  on  a  host  with  different endianness. The utility function
       pcre_pattern_to_host_byte_order() can be used to convert such a pattern
       so that it runs on the new host.

         PCRE_ERROR_JIT_BADOPTION

       This  error  is  returned  when a pattern that was successfully studied
       using a JIT compile option is being  matched,  but  the  matching  mode
       (partial  or complete match) does not correspond to any JIT compilation
       mode. When the JIT fast path function is used, this error may  be  also
       given  for  invalid  options.  See  the  pcrejit documentation for more
       details.

         PCRE_ERROR_BADLENGTH      (-32)

       This error is given if pcre_exec() is called with a negative value  for
       the length argument.

       Error numbers -16 to -20, -22, and 30 are not used by pcre_exec().

   Reason codes for invalid UTF-8 strings

       This  section  applies  only  to  the  8-bit library. The corresponding
       information for the 16-bit and 32-bit libraries is given in the  pcre16
       and pcre32 pages.

       When pcre_exec() returns either PCRE_ERROR_BADUTF8 or PCRE_ERROR_SHORT-
       UTF8, and the size of the output vector (ovecsize) is at least  2,  the
       offset  of  the  start  of the invalid UTF-8 character is placed in the
       first output vector element (ovector[0]) and a reason code is placed in
       the  second  element  (ovector[1]). The reason codes are given names in
       the pcre.h header file:

         PCRE_UTF8_ERR1
         PCRE_UTF8_ERR2
         PCRE_UTF8_ERR3
         PCRE_UTF8_ERR4
         PCRE_UTF8_ERR5

       The string ends with a truncated UTF-8 character;  the  code  specifies
       how  many bytes are missing (1 to 5). Although RFC 3629 restricts UTF-8
       characters to be no longer than 4 bytes, the  encoding  scheme  (origi-
       nally  defined  by  RFC  2279)  allows  for  up to 6 bytes, and this is
       checked first; hence the possibility of 4 or 5 missing bytes.

         PCRE_UTF8_ERR6
         PCRE_UTF8_ERR7
         PCRE_UTF8_ERR8
         PCRE_UTF8_ERR9
         PCRE_UTF8_ERR10

       The two most significant bits of the 2nd, 3rd, 4th, 5th, or 6th byte of
       the  character  do  not have the binary value 0b10 (that is, either the
       most significant bit is 0, or the next bit is 1).

         PCRE_UTF8_ERR11
         PCRE_UTF8_ERR12

       A character that is valid by the RFC 2279 rules is either 5 or 6  bytes
       long; these code points are excluded by RFC 3629.

         PCRE_UTF8_ERR13

       A  4-byte character has a value greater than 0x10fff; these code points
       are excluded by RFC 3629.

         PCRE_UTF8_ERR14

       A 3-byte character has a value in the  range  0xd800  to  0xdfff;  this
       range  of code points are reserved by RFC 3629 for use with UTF-16, and
       so are excluded from UTF-8.

         PCRE_UTF8_ERR15
         PCRE_UTF8_ERR16
         PCRE_UTF8_ERR17
         PCRE_UTF8_ERR18
         PCRE_UTF8_ERR19

       A 2-, 3-, 4-, 5-, or 6-byte character is "overlong", that is, it  codes
       for  a  value that can be represented by fewer bytes, which is invalid.
       For example, the two bytes 0xc0, 0xae give the value 0x2e,  whose  cor-
       rect coding uses just one byte.

         PCRE_UTF8_ERR20

       The two most significant bits of the first byte of a character have the
       binary value 0b10 (that is, the most significant bit is 1 and the  sec-
       ond  is  0). Such a byte can only validly occur as the second or subse-
       quent byte of a multi-byte character.

         PCRE_UTF8_ERR21

       The first byte of a character has the value 0xfe or 0xff. These  values
       can never occur in a valid UTF-8 string.

         PCRE_UTF8_ERR22

       This  error  code  was  formerly  used when the presence of a so-called
       "non-character" caused an error. Unicode corrigendum #9 makes it  clear
       that  such  characters should not cause a string to be rejected, and so
       this code is no longer in use and is never returned.


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 above.  Given all the rele-
       vant 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.


OBTAINING AN ESTIMATE OF STACK USAGE


       Matching certain patterns using pcre_exec() can use a  lot  of  process
       stack,  which  in  certain  environments can be rather limited in size.
       Some users find it helpful to have an estimate of the amount  of  stack
       that  is  used  by  pcre_exec(),  to help them set recursion limits, as
       described in the pcrestack documentation. The estimate that  is  output
       by pcretest when called with the -m and -C options is obtained by call-
       ing pcre_exec with the values NULL, NULL, NULL, -999, and -999 for  its
       first five arguments.

       Normally,  if  its  first  argument  is  NULL,  pcre_exec() immediately
       returns the negative error code PCRE_ERROR_NULL, but with this  special
       combination  of  arguments,  it returns instead a negative number whose
       absolute value is the approximate stack frame size in bytes.  (A  nega-
       tive  number  is  used so that it is clear that no match has happened.)
       The value is approximate because in  some  cases,  recursive  calls  to
       pcre_exec() occur when there are one or two additional variables on the
       stack.

       If PCRE has been compiled to use the heap  instead  of  the  stack  for
       recursion,  the  value  returned  is  the  size  of  each block that is
       obtained from the heap.


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.  Unlike  pcre_exec(),  pcre_dfa_exec()
       can use the entire ovector for returning matched strings.

       NOTE:  PCRE's  "auto-possessification"  optimization usually applies to
       character repeats at the end of a pattern (as well as internally).  For
       example,  the  pattern "a\d+" is compiled as if it were "a\d++" because
       there is no point even considering the possibility of backtracking into
       the  repeated digits. For DFA matching, this means that only one possi-
       ble match is found. If you really do  want  multiple  matches  in  such
       cases,   either   use   an   ungreedy   repeat  ("a\d+?")  or  set  the
       PCRE_NO_AUTO_POSSESS option when compiling.

   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  or  match_limit_recursion
       fields.  This  is  not  supported (these fields are meaningless for DFA
       matching).

         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.

         PCRE_ERROR_DFA_BADRESTART (-30)

       When pcre_dfa_exec() is called with the PCRE_DFA_RESTART  option,  some
       plausibility  checks  are  made on the contents of the workspace, which
       should contain data about the previous partial match. If any  of  these
       checks fail, this error is given.


SEE ALSO


       pcre16(3),   pcre32(3),  pcrebuild(3),  pcrecallout(3),  pcrecpp(3)(3),
       pcrematching(3), pcrepartial(3), pcreposix(3), pcreprecompile(3), pcre-
       sample(3), pcrestack(3).


AUTHOR


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


REVISION


       Last updated: 18 December 2015
       Copyright (c) 1997-2015 University of Cambridge.



PCRE 8.39                      18 December 2015                     pcreapi(3)

pcre 8.39 - Generated Mon Aug 8 19:58:02 CDT 2016
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