xref: /aosp_15_r20/external/pcre/doc/pcre2test.txt (revision 22dc650d8ae982c6770746019a6f94af92b0f024)

PCRE2TEST(1)                General Commands Manual               PCRE2TEST(1)


NAME
       pcre2test - a program for testing Perl-compatible regular expressions.


SYNOPSIS

       pcre2test [options] [input file [output file]]

       pcre2test is a test program for the PCRE2 regular expression libraries,
       but  it  can  also  be used for experimenting with regular expressions.
       This document describes the features of the test program;  for  details
       of  the regular expressions themselves, see the pcre2pattern documenta-
       tion. For details of the PCRE2 library function  calls  and  their  op-
       tions, see the pcre2api documentation.

       The  input  for  pcre2test is a sequence of regular expression patterns
       and subject strings to be matched. There are  also  command  lines  for
       setting defaults and controlling some special actions. The output shows
       the  result  of  each  match attempt. Modifiers on external or internal
       command lines, the patterns, and the subject lines specify PCRE2  func-
       tion  options, control how the subject is processed, and what output is
       produced.

       There are many obscure modifiers, some of which  are  specifically  de-
       signed  for use in conjunction with the test script and data files that
       are distributed as part of PCRE2.  All  the  modifiers  are  documented
       here, some without much justification, but many of them are unlikely to
       be of use except when testing the libraries.


PCRE2's 8-BIT, 16-BIT AND 32-BIT LIBRARIES

       Different versions of the PCRE2 library can be built to support charac-
       ter  strings  that  are encoded in 8-bit, 16-bit, or 32-bit code units.
       One, two, or all three of these libraries  may  be  simultaneously  in-
       stalled.  The  pcre2test program can be used to test all the libraries.
       However, its own input and output are  always  in  8-bit  format.  When
       testing  the  16-bit  or 32-bit libraries, patterns and subject strings
       are converted to 16-bit or 32-bit format before being passed to the li-
       brary functions. Results are converted back to  8-bit  code  units  for
       output.

       In the rest of this document, the names of library functions and struc-
       tures  are given in generic form, for example, pcre2_compile(). The ac-
       tual names used in the libraries have a suffix _8, _16, or _32, as  ap-
       propriate.


INPUT ENCODING

       Input  to  pcre2test is processed line by line, either by calling the C
       library's fgets() function, or via the libreadline or libedit  library.
       In  some Windows environments character 26 (hex 1A) causes an immediate
       end of file, and no further data is read, so this character  should  be
       avoided unless you really want that action.

       The  input is processed using C's string functions, so must not contain
       binary zeros, even though in Unix-like environments, fgets() treats any
       bytes other than newline as data characters. An error is generated if a
       binary zero is encountered. By default subject lines are processed  for
       backslash escapes, which makes it possible to include any data value in
       strings  that  are  passed  to  the library for matching. For patterns,
       there is a facility for specifying some or all of the 8-bit input char-
       acters as hexadecimal pairs, which makes it possible to include  binary
       zeros.

   Input for the 16-bit and 32-bit libraries

       When testing the 16-bit or 32-bit libraries, there is a need to be able
       to  generate character code points greater than 255 in the strings that
       are passed to the library. For subject lines, backslash escapes can  be
       used.  In addition, when the utf modifier (see "Setting compilation op-
       tions" below) is set, the pattern and any following subject  lines  are
       interpreted  as UTF-8 strings and translated to UTF-16 or UTF-32 as ap-
       propriate.

       For non-UTF testing of wide characters, the utf8_input modifier can  be
       used.  This  is  mutually  exclusive  with  utf, and is allowed only in
       16-bit or 32-bit mode. It causes  the  pattern  and  following  subject
       lines  to be treated as UTF-8 according to the original definition (RFC
       2279), which allows for character values up to 0x7fffffff. Each charac-
       ter is placed in one 16-bit or 32-bit code unit (in  the  16-bit  case,
       values greater than 0xffff cause an error to occur).

       UTF-8  (in  its  original definition) is not capable of encoding values
       greater than 0x7fffffff, but such values can be handled by  the  32-bit
       library. When testing this library in non-UTF mode with utf8_input set,
       if any character is preceded by the byte 0xff (which is an invalid byte
       in  UTF-8)  0x80000000  is  added to the character's value. This is the
       only way of passing such code points in a pattern string.  For  subject
       strings, using an escape sequence is preferable.


COMMAND LINE OPTIONS

       -8        If the 8-bit library has been built, this option causes it to
                 be  used  (this is the default). If the 8-bit library has not
                 been built, this option causes an error.

       -16       If the 16-bit library has been built, this option  causes  it
                 to  be used. If the 8-bit library has not been built, this is
                 the default. If the 16-bit library has not been  built,  this
                 option causes an error.

       -32       If  the  32-bit library has been built, this option causes it
                 to be used. If no other library has been built, this  is  the
                 default.  If  the 32-bit library has not been built, this op-
                 tion causes an error.

       -ac       Behave as if each pattern has the auto_callout modifier, that
                 is, insert automatic callouts into every pattern that is com-
                 piled.

       -AC       As for -ac, but in addition behave as if  each  subject  line
                 has  the callout_extra modifier, that is, show additional in-
                 formation from callouts.

       -b        Behave as if each pattern has the fullbincode  modifier;  the
                 full internal binary form of the pattern is output after com-
                 pilation.

       -C        Output  the  version  number  of  the  PCRE2 library, and all
                 available information about the optional  features  that  are
                 included,  and  then  exit with zero exit code. All other op-
                 tions are ignored. If both -C and -LM are present,  whichever
                 is first is recognized.

       -C option Output  information  about a specific build-time option, then
                 exit. This functionality is intended for use in scripts  such
                 as  RunTest.  The  following options output the value and set
                 the exit code as indicated:

                   ebcdic-nl  the code for LF (= NL) in an EBCDIC environment:
                                0x15 or 0x25
                                0 if used in an ASCII environment
                                exit code is always 0
                   linksize   the configured internal link size (2, 3, or 4)
                                exit code is set to the link size
                   newline    the default newline setting:
                                CR, LF, CRLF, ANYCRLF, ANY, or NUL
                                exit code is always 0
                   bsr        the default setting for what \R matches:
                                ANYCRLF or ANY
                                exit code is always 0

                 The following options output 1 for true or 0 for  false,  and
                 set the exit code to the same value:

                   backslash-C  \C is supported (not locked out)
                   ebcdic       compiled for an EBCDIC environment
                   jit          just-in-time support is available
                   pcre2-16     the 16-bit library was built
                   pcre2-32     the 32-bit library was built
                   pcre2-8      the 8-bit library was built
                   unicode      Unicode support is available

                 If  an  unknown  option is given, an error message is output;
                 the exit code is 0.

       -d        Behave as if each pattern has the debug modifier; the  inter-
                 nal form and information about the compiled pattern is output
                 after compilation; -d is equivalent to -b -i.

       -dfa      Behave as if each subject line has the dfa modifier; matching
                 is  done  using the pcre2_dfa_match() function instead of the
                 default pcre2_match().

       -error number[,number,...]
                 Call pcre2_get_error_message() for each of the error  numbers
                 in  the  comma-separated list, display the resulting messages
                 on the standard output, then exit with zero  exit  code.  The
                 numbers  may  be  positive or negative. This is a convenience
                 facility for PCRE2 maintainers.

       -help     Output a brief summary these options and then exit.

       -i        Behave as if each pattern has the info modifier;  information
                 about the compiled pattern is given after compilation.

       -jit      Behave  as  if  each pattern line has the jit modifier; after
                 successful compilation, each pattern is passed to  the  just-
                 in-time compiler, if available.

       -jitfast  Behave  as if each pattern line has the jitfast modifier; af-
                 ter successful compilation, each pattern  is  passed  to  the
                 just-in-time compiler, if available, and each subject line is
                 passed directly to the JIT matcher via its "fast path".

       -jitverify
                 Behave  as  if  each pattern line has the jitverify modifier;
                 after successful compilation, each pattern is passed  to  the
                 just-in-time  compiler,  if available, and the use of JIT for
                 matching is verified.

       -LM       List modifiers: write a list of available pattern and subject
                 modifiers to the standard output, then exit  with  zero  exit
                 code.  All other options are ignored.  If both -C and any -Lx
                 options are present, whichever is first is recognized.

       -LP       List properties: write a list of recognized  Unicode  proper-
                 ties  to  the standard output, then exit with zero exit code.
                 All other options are ignored. If both -C and any -Lx options
                 are present, whichever is first is recognized.

       -LS       List scripts: write a list of recognized Unicode script names
                 to the standard output, then exit with zero  exit  code.  All
                 other options are ignored. If both -C and any -Lx options are
                 present, whichever is first is recognized.

       -pattern modifier-list
                 Behave as if each pattern line contains the given modifiers.

       -q        Do not output the version number of pcre2test at the start of
                 execution.

       -S size   On  Unix-like  systems, set the size of the run-time stack to
                 size mebibytes (units of 1024*1024 bytes).

       -subject modifier-list
                 Behave as if each subject line contains the given modifiers.

       -t        Run each compile and match many times with a timer, and  out-
                 put  the  resulting  times  per compile or match. When JIT is
                 used, separate times are given for the  initial  compile  and
                 the  JIT  compile.  You  can control the number of iterations
                 that are used for timing by following -t with a number (as  a
                 separate  item  on  the command line). For example, "-t 1000"
                 iterates 1000 times. The default is to iterate 500,000 times.

       -tm       This is like -t except that it times only the matching phase,
                 not the compile phase.

       -T -TM    These behave like -t and -tm, but in addition, at the end  of
                 a  run, the total times for all compiles and matches are out-
                 put.

       -version  Output the PCRE2 version number and then exit.


DESCRIPTION

       If pcre2test is given two filename arguments, it reads from  the  first
       and writes to the second. If the first name is "-", input is taken from
       the  standard  input. If pcre2test is given only one argument, it reads
       from that file and writes to stdout. Otherwise, it reads from stdin and
       writes to stdout.

       When pcre2test is built, a configuration option  can  specify  that  it
       should  be linked with the libreadline or libedit library. When this is
       done, if the input is from a terminal, it is read using the  readline()
       function. This provides line-editing and history facilities. The output
       from the -help option states whether or not readline() will be used.

       The  program  handles  any number of tests, each of which consists of a
       set of input lines. Each set starts with a regular expression  pattern,
       followed by any number of subject lines to be matched against that pat-
       tern. In between sets of test data, command lines that begin with # may
       appear. This file format, with some restrictions, can also be processed
       by  the perltest.sh script that is distributed with PCRE2 as a means of
       checking that the behaviour of PCRE2 and Perl is the same. For a speci-
       fication of perltest.sh, see the comments near its beginning. See  also
       the #perltest command below.

       When the input is a terminal, pcre2test prompts for each line of input,
       using  "re>"  to prompt for regular expression patterns, and "data>" to
       prompt for subject lines. Command lines starting with # can be  entered
       only in response to the "re>" prompt.

       Each  subject line is matched separately and independently. If you want
       to do multi-line matches, you have to use the \n escape sequence (or \r
       or \r\n, etc., depending on the newline setting) in a  single  line  of
       input  to encode the newline sequences. There is no limit on the length
       of subject lines; the input buffer is automatically extended if  it  is
       too  small.  There  are  replication features that makes it possible to
       generate long repetitive pattern or subject  lines  without  having  to
       supply them explicitly.

       An  empty  line  or  the end of the file signals the end of the subject
       lines for a test, at which point a new pattern or command line  is  ex-
       pected if there is still input to be read.


COMMAND LINES

       In  between sets of test data, a line that begins with # is interpreted
       as a command line. If the first character is followed by white space or
       an exclamation mark, the line is treated as  a  comment,  and  ignored.
       Otherwise, the following commands are recognized:

         #forbid_utf

       Subsequent   patterns   automatically   have  the  PCRE2_NEVER_UTF  and
       PCRE2_NEVER_UCP options set, which locks out the use of  the  PCRE2_UTF
       and  PCRE2_UCP options and the use of (*UTF) and (*UCP) at the start of
       patterns. This command also forces an error  if  a  subsequent  pattern
       contains  any  occurrences  of \P, \p, or \X, which are still supported
       when PCRE2_UTF is not set, but which require Unicode  property  support
       to be included in the library.

       This  is  a trigger guard that is used in test files to ensure that UTF
       or Unicode property tests are not accidentally added to files that  are
       used  when  Unicode  support  is  not  included in the library. Setting
       PCRE2_NEVER_UTF and PCRE2_NEVER_UCP as a default can also  be  obtained
       by  the  use  of #pattern; the difference is that #forbid_utf cannot be
       unset, and the automatic options are not displayed in pattern  informa-
       tion, to avoid cluttering up test output.

         #load <filename>

       This command is used to load a set of precompiled patterns from a file,
       as  described  in  the  section entitled "Saving and restoring compiled
       patterns" below.

         #loadtables <filename>

       This command is used to load a set of binary character tables that  can
       be  accessed  by  the tables=3 qualifier. Such tables can be created by
       the pcre2_dftables program with the -b option.

         #newline_default [<newline-list>]

       When PCRE2 is built, a default newline  convention  can  be  specified.
       This  determines which characters and/or character pairs are recognized
       as indicating a newline in a pattern or subject string. The default can
       be overridden when a pattern is compiled. The standard test files  con-
       tain  tests  of  various  newline  conventions, but the majority of the
       tests expect a single linefeed to be recognized as  a  newline  by  de-
       fault.  Without  special action the tests would fail when PCRE2 is com-
       piled with either CR or CRLF as the default newline.

       The #newline_default command specifies a list of newline types that are
       acceptable as the default. The types must be one of CR, LF, CRLF,  ANY-
       CRLF, ANY, or NUL (in upper or lower case), for example:

         #newline_default LF Any anyCRLF

       If the default newline is in the list, this command has no effect. Oth-
       erwise,  except  when  testing  the  POSIX API, a newline modifier that
       specifies the first newline convention in the list (LF in the above ex-
       ample) is added to any pattern that does not  already  have  a  newline
       modifier. If the newline list is empty, the feature is turned off. This
       command is present in a number of the standard test input files.

       When  the POSIX API is being tested there is no way to override the de-
       fault newline convention, though it is possible to set the newline con-
       vention from within the pattern. A warning is given  if  the  posix  or
       posix_nosub  modifier is used when #newline_default would set a default
       for the non-POSIX API.

         #pattern <modifier-list>

       This command sets a default modifier list that applies  to  all  subse-
       quent patterns. Modifiers on a pattern can change these settings.

         #perltest

       This  line  is  used  in test files that can also be processed by perl-
       test.sh to confirm that Perl gives the same results  as  PCRE2.  Subse-
       quent  tests are checked for the use of pcre2test features that are in-
       compatible with the perltest.sh script.

       Patterns must use '/' as their delimiter, and  only  certain  modifiers
       are  supported. Comment lines, #pattern commands, and #subject commands
       that set or unset "mark" are recognized and acted  on.  The  #perltest,
       #forbid_utf,  and  #newline_default  commands,  which are needed in the
       relevant pcre2test files, are silently ignored. All other command lines
       are ignored, but give a warning message. The  #perltest  command  helps
       detect  tests  that  are  accidentally put in the wrong file or use the
       wrong delimiter. For more details of the  perltest.sh  script  see  the
       comments it contains.

         #pop [<modifiers>]
         #popcopy [<modifiers>]

       These  commands  are used to manipulate the stack of compiled patterns,
       as described in the section entitled  "Saving  and  restoring  compiled
       patterns" below.

         #save <filename>

       This  command  is used to save a set of compiled patterns to a file, as
       described in the section entitled "Saving and restoring  compiled  pat-
       terns" below.

         #subject <modifier-list>

       This  command  sets  a default modifier list that applies to all subse-
       quent subject lines. Modifiers on a subject line can change these  set-
       tings.


MODIFIER SYNTAX

       Modifier lists are used with both pattern and subject lines. Items in a
       list are separated by commas followed by optional white space. Trailing
       whitespace  in  a modifier list is ignored. Some modifiers may be given
       for both patterns and subject lines, whereas others are valid only  for
       one  or  the  other.  Each  modifier  has a long name, for example "an-
       chored", and some of them must be followed by  an  equals  sign  and  a
       value,  for  example,  "offset=12". Values cannot contain comma charac-
       ters, but may contain spaces. Modifiers that do not take values may  be
       preceded by a minus sign to turn off a previous setting.

       A few of the more common modifiers can also be specified as single let-
       ters,  for  example "i" for "caseless". In documentation, following the
       Perl convention, these are written with a slash ("the /i modifier") for
       clarity. Abbreviated modifiers must all be concatenated  in  the  first
       item  of a modifier list. If the first item is not recognized as a long
       modifier name, it is interpreted as a sequence of these  abbreviations.
       For example:

         /abc/ig,newline=cr,jit=3

       This  is  a pattern line whose modifier list starts with two one-letter
       modifiers (/i and /g). The lower-case  abbreviated  modifiers  are  the
       same as used in Perl.


PATTERN SYNTAX

       A  pattern line must start with one of the following characters (common
       symbols, excluding pattern meta-characters):

         / ! " ' ` - = _ : ; , % & @ ~

       This is interpreted as the pattern's delimiter.  A  regular  expression
       may  be  continued  over several input lines, in which case the newline
       characters are included within it. It is possible to include the delim-
       iter as a literal within the pattern by escaping it with  a  backslash,
       for example

         /abc\/def/

       If  you do this, the escape and the delimiter form part of the pattern,
       but since the delimiters are all non-alphanumeric, the inclusion of the
       backslash does not affect the pattern's interpretation. Note,  however,
       that this trick does not work within \Q...\E literal bracketing because
       the backslash will itself be interpreted as a literal. If the terminat-
       ing delimiter is immediately followed by a backslash, for example,

         /abc/\

       a backslash is added to the end of the pattern. This is done to provide
       a  way of testing the error condition that arises if a pattern finishes
       with a backslash, because

         /abc\/

       is interpreted as the first line of a pattern that starts with  "abc/",
       causing  pcre2test to read the next line as a continuation of the regu-
       lar expression.

       A pattern can be followed by a modifier list (details below).


SUBJECT LINE SYNTAX

       Before each subject line is passed to pcre2_match(), pcre2_dfa_match(),
       or pcre2_jit_match(), leading and trailing white space is removed,  and
       the  line  is scanned for backslash escapes, unless the subject_literal
       modifier was set for the pattern. The following provide a means of  en-
       coding non-printing characters in a visible way:

         \a         alarm (BEL, \x07)
         \b         backspace (\x08)
         \e         escape (\x27)
         \f         form feed (\x0c)
         \n         newline (\x0a)
         \r         carriage return (\x0d)
         \t         tab (\x09)
         \v         vertical tab (\x0b)
         \nnn       octal character (up to 3 octal digits); always
                      a byte unless > 255 in UTF-8 or 16-bit or 32-bit mode
         \o{dd...}  octal character (any number of octal digits}
         \xhh       hexadecimal byte (up to 2 hex digits)
         \x{hh...}  hexadecimal character (any number of hex digits)

       The use of \x{hh...} is not dependent on the use of the utf modifier on
       the  pattern. It is recognized always. There may be any number of hexa-
       decimal digits inside the braces; invalid  values  provoke  error  mes-
       sages.

       Note  that  \xhh  specifies one byte rather than one character in UTF-8
       mode; this makes it possible to construct invalid UTF-8  sequences  for
       testing  purposes.  On the other hand, \x{hh} is interpreted as a UTF-8
       character in UTF-8 mode, generating more than one byte if the value  is
       greater  than  127.   When testing the 8-bit library not in UTF-8 mode,
       \x{hh} generates one byte for values less than 256, and causes an error
       for greater values.

       In UTF-16 mode, all 4-digit \x{hhhh} values are accepted. This makes it
       possible to construct invalid UTF-16 sequences for testing purposes.

       In UTF-32 mode, all 4- to 8-digit \x{...}  values  are  accepted.  This
       makes  it  possible  to  construct invalid UTF-32 sequences for testing
       purposes.

       There is a special backslash sequence that specifies replication of one
       or more characters:

         \[<characters>]{<count>}

       This makes it possible to test long strings without having  to  provide
       them as part of the file. For example:

         \[abc]{4}

       is  converted to "abcabcabcabc". This feature does not support nesting.
       To include a closing square bracket in the characters, code it as \x5D.

       A backslash followed by an equals sign marks the  end  of  the  subject
       string and the start of a modifier list. For example:

         abc\=notbol,notempty

       If  the  subject  string is empty and \= is followed by whitespace, the
       line is treated as a comment line, and is not used  for  matching.  For
       example:

         \= This is a comment.
         abc\= This is an invalid modifier list.

       A  backslash  followed by any other non-alphanumeric character just es-
       capes that character. A backslash followed by anything else  causes  an
       error.  However,  if the very last character in the line is a backslash
       (and there is no modifier list), it is ignored. This  gives  a  way  of
       passing  an  empty line as data, since a real empty line terminates the
       data input.

       If the subject_literal modifier is set for a pattern, all subject lines
       that follow are treated as literals, with no special treatment of back-
       slashes.  No replication is possible, and any subject modifiers must be
       set as defaults by a #subject command.


PATTERN MODIFIERS

       There are several types of modifier that can appear in  pattern  lines.
       Except where noted below, they may also be used in #pattern commands. A
       pattern's  modifier  list can add to or override default modifiers that
       were set by a previous #pattern command.

   Setting compilation options

       The following modifiers set options for pcre2_compile(). Most  of  them
       set  bits  in  the  options  argument of that function, but those whose
       names start with PCRE2_EXTRA are additional options that are set in the
       compile context.  Some of these options  have  single-letter  abbrevia-
       tions.  There  is  special  handling  for /x: if a second x is present,
       PCRE2_EXTENDED is converted into  PCRE2_EXTENDED_MORE  as  in  Perl.  A
       third appearance adds PCRE2_EXTENDED as well, though this makes no dif-
       ference to the way pcre2_compile() behaves. See pcre2api for a descrip-
       tion of the effects of these options.

             allow_empty_class         set PCRE2_ALLOW_EMPTY_CLASS
             allow_lookaround_bsk      set PCRE2_EXTRA_ALLOW_LOOKAROUND_BSK
             allow_surrogate_escapes   set PCRE2_EXTRA_ALLOW_SURROGATE_ESCAPES
             alt_bsux                  set PCRE2_ALT_BSUX
             alt_circumflex            set PCRE2_ALT_CIRCUMFLEX
             alt_verbnames             set PCRE2_ALT_VERBNAMES
             anchored                  set PCRE2_ANCHORED
         /a  ascii_all                 set all ASCII options
             ascii_bsd                 set PCRE2_EXTRA_ASCII_BSD
             ascii_bss                 set PCRE2_EXTRA_ASCII_BSS
             ascii_bsw                 set PCRE2_EXTRA_ASCII_BSW
             ascii_digit               set PCRE2_EXTRA_ASCII_DIGIT
             ascii_posix               set PCRE2_EXTRA_ASCII_POSIX
             auto_callout              set PCRE2_AUTO_CALLOUT
             bad_escape_is_literal     set PCRE2_EXTRA_BAD_ESCAPE_IS_LITERAL
         /i  caseless                  set PCRE2_CASELESS
         /r  caseless_restrict         set PCRE2_EXTRA_CASELESS_RESTRICT
             dollar_endonly            set PCRE2_DOLLAR_ENDONLY
         /s  dotall                    set PCRE2_DOTALL
             dupnames                  set PCRE2_DUPNAMES
             endanchored               set PCRE2_ENDANCHORED
             escaped_cr_is_lf          set PCRE2_EXTRA_ESCAPED_CR_IS_LF
         /x  extended                  set PCRE2_EXTENDED
         /xx extended_more             set PCRE2_EXTENDED_MORE
             extra_alt_bsux            set PCRE2_EXTRA_ALT_BSUX
             firstline                 set PCRE2_FIRSTLINE
             literal                   set PCRE2_LITERAL
             match_line                set PCRE2_EXTRA_MATCH_LINE
             match_invalid_utf         set PCRE2_MATCH_INVALID_UTF
             match_unset_backref       set PCRE2_MATCH_UNSET_BACKREF
             match_word                set PCRE2_EXTRA_MATCH_WORD
         /m  multiline                 set PCRE2_MULTILINE
             never_backslash_c         set PCRE2_NEVER_BACKSLASH_C
             never_ucp                 set PCRE2_NEVER_UCP
             never_utf                 set PCRE2_NEVER_UTF
         /n  no_auto_capture           set PCRE2_NO_AUTO_CAPTURE
             no_auto_possess           set PCRE2_NO_AUTO_POSSESS
             no_dotstar_anchor         set PCRE2_NO_DOTSTAR_ANCHOR
             no_start_optimize         set PCRE2_NO_START_OPTIMIZE
             no_utf_check              set PCRE2_NO_UTF_CHECK
             ucp                       set PCRE2_UCP
             ungreedy                  set PCRE2_UNGREEDY
             use_offset_limit          set PCRE2_USE_OFFSET_LIMIT
             utf                       set PCRE2_UTF

       As well as turning on the PCRE2_UTF option, the utf modifier causes all
       non-printing  characters  in  output  strings  to  be printed using the
       \x{hh...} notation. Otherwise, those less than 0x100 are output in  hex
       without  the  curly brackets. Setting utf in 16-bit or 32-bit mode also
       causes pattern and subject  strings  to  be  translated  to  UTF-16  or
       UTF-32, respectively, before being passed to library functions.

   Setting compilation controls

       The  following  modifiers affect the compilation process or request in-
       formation about the pattern. There are single-letter abbreviations  for
       some that are heavily used in the test files.

             bsr=[anycrlf|unicode]     specify \R handling
         /B  bincode                   show binary code without lengths
             callout_info              show callout information
             convert=<options>         request foreign pattern conversion
             convert_glob_escape=c     set glob escape character
             convert_glob_separator=c  set glob separator character
             convert_length            set convert buffer length
             debug                     same as info,fullbincode
             framesize                 show matching frame size
             fullbincode               show binary code with lengths
         /I  info                      show info about compiled pattern
             hex                       unquoted characters are hexadecimal
             jit[=<number>]            use JIT
             jitfast                   use JIT fast path
             jitverify                 verify JIT use
             locale=<name>             use this locale
             max_pattern_compiled      ) set maximum compiled pattern
                        _length=<n>    )   length (bytes)
             max_pattern_length=<n>    set maximum pattern length (code units)
             max_varlookbehind=<n>     set maximum variable lookbehind length
             memory                    show memory used
             newline=<type>            set newline type
             null_context              compile with a NULL context
             null_pattern              pass pattern as NULL
             parens_nest_limit=<n>     set maximum parentheses depth
             posix                     use the POSIX API
             posix_nosub               use the POSIX API with REG_NOSUB
             push                      push compiled pattern onto the stack
             pushcopy                  push a copy onto the stack
             stackguard=<number>       test the stackguard feature
             subject_literal           treat all subject lines as literal
             tables=[0|1|2|3]          select internal tables
             use_length                do not zero-terminate the pattern
             utf8_input                treat input as UTF-8

       The effects of these modifiers are described in the following sections.

   Newline and \R handling

       The  bsr modifier specifies what \R in a pattern should match. If it is
       set to "anycrlf", \R matches CR, LF, or CRLF only.  If  it  is  set  to
       "unicode",  \R matches any Unicode newline sequence. The default can be
       specified when PCRE2 is built; if it is not, the default is set to Uni-
       code.

       The newline modifier specifies which characters are to  be  interpreted
       as newlines, both in the pattern and in subject lines. The type must be
       one of CR, LF, CRLF, ANYCRLF, ANY, or NUL (in upper or lower case).

   Information about a pattern

       The  debug modifier is a shorthand for info,fullbincode, requesting all
       available information.

       The bincode modifier causes a representation of the compiled code to be
       output after compilation. This information does not contain length  and
       offset values, which ensures that the same output is generated for dif-
       ferent  internal  link  sizes  and different code unit widths. By using
       bincode, the same regression tests can be used  in  different  environ-
       ments.

       The  fullbincode  modifier, by contrast, does include length and offset
       values. This is used in a few special tests that run only for  specific
       code unit widths and link sizes, and is also useful for one-off tests.

       The  info  modifier  requests  information  about  the compiled pattern
       (whether it is anchored, has a fixed first character, and so  on).  The
       information  is  obtained  from the pcre2_pattern_info() function. Here
       are some typical examples:

           re> /(?i)(^a|^b)/m,info
         Capture group count = 1
         Compile options: multiline
         Overall options: caseless multiline
         First code unit at start or follows newline
         Subject length lower bound = 1

           re> /(?i)abc/info
         Capture group count = 0
         Compile options: <none>
         Overall options: caseless
         First code unit = 'a' (caseless)
         Last code unit = 'c' (caseless)
         Subject length lower bound = 3

       "Compile options" are those specified by modifiers;  "overall  options"
       have  added options that are taken or deduced from the pattern. If both
       sets of options are the same, just a single "options" line  is  output;
       if  there  are  no  options,  the line is omitted. "First code unit" is
       where any match must start; if there is more than one they  are  listed
       as  "starting  code  units".  "Last code unit" is the last literal code
       unit that must be present in any match. This  is  not  necessarily  the
       last  character.  These lines are omitted if no starting or ending code
       units  are  recorded.  The  subject  length  line   is   omitted   when
       no_start_optimize  is  set because the minimum length is not calculated
       when it can never be used.

       The framesize modifier shows the size, in bytes, of each storage  frame
       used  by  pcre2_match()  for handling backtracking. The size depends on
       the number of capturing parentheses in the pattern. A vector  of  these
       frames  is  used  at  matching time; its overall size is shown when the
       heaframes_size subject modifier is set.

       The callout_info modifier requests information about all  the  callouts
       in the pattern. A list of them is output at the end of any other infor-
       mation that is requested. For each callout, either its number or string
       is given, followed by the item that follows it in the pattern.

   Passing a NULL context

       Normally,  pcre2test  passes a context block to pcre2_compile(). If the
       null_context modifier is set, however, NULL  is  passed.  This  is  for
       testing  that  pcre2_compile()  behaves correctly in this case (it uses
       default values).

   Passing a NULL pattern

       The null_pattern modifier is for testing the  behaviour  of  pcre2_com-
       pile()  when  the  pattern argument is NULL. The length value passed is
       the default PCRE2_ZERO_TERMINATED unless use_length is set.  Any length
       other than zero causes an error.

   Specifying pattern characters in hexadecimal

       The hex modifier specifies that the characters of the  pattern,  except
       for  substrings  enclosed  in single or double quotes, are to be inter-
       preted as pairs of hexadecimal digits. This feature is  provided  as  a
       way of creating patterns that contain binary zeros and other non-print-
       ing  characters.  White space is permitted between pairs of digits. For
       example, this pattern contains three characters:

         /ab 32 59/hex

       Parts of such a pattern are taken literally  if  quoted.  This  pattern
       contains  nine characters, only two of which are specified in hexadeci-
       mal:

         /ab "literal" 32/hex

       Either single or double quotes may be used. There is no way of  includ-
       ing  the delimiter within a substring. The hex and expand modifiers are
       mutually exclusive.

   Specifying the pattern's length

       By default, patterns are passed to the compiling functions as zero-ter-
       minated strings but can be passed by length instead of being  zero-ter-
       minated.  The use_length modifier causes this to happen. Using a length
       happens automatically (whether or not use_length is set)  when  hex  is
       set,  because  patterns specified in hexadecimal may contain binary ze-
       ros.

       If hex or use_length is used with the POSIX wrapper API (see "Using the
       POSIX wrapper API" below), the REG_PEND extension is used to  pass  the
       pattern's length.

   Specifying a maximum for variable lookbehinds

       Variable  lookbehind  assertions  are  supported only if, for each one,
       there is a maximum length (in characters) that it can match. There is a
       limit on this, whose default can be set at build time, with an ultimate
       default   of   255.   The   max_varlookbehind   modifier    uses    the
       pcre2_set_max_varlookbehind() function to change the limit. Lookbehinds
       whose  branches  each match a fixed length are limited to 65535 charac-
       ters per branch.

   Specifying wide characters in 16-bit and 32-bit modes

       In 16-bit and 32-bit modes, all input is automatically treated as UTF-8
       and translated to UTF-16 or UTF-32 when the utf modifier  is  set.  For
       testing the 16-bit and 32-bit libraries in non-UTF mode, the utf8_input
       modifier  can  be  used. It is mutually exclusive with utf. Input lines
       are interpreted as UTF-8 as a means of specifying wide characters. More
       details are given in "Input encoding" above.

   Generating long repetitive patterns

       Some tests use long patterns that are very repetitive. Instead of  cre-
       ating  a very long input line for such a pattern, you can use a special
       repetition feature, similar to the  one  described  for  subject  lines
       above.  If  the  expand  modifier is present on a pattern, parts of the
       pattern that have the form

         \[<characters>]{<count>}

       are expanded before the pattern is passed to pcre2_compile(). For exam-
       ple, \[AB]{6000} is expanded to "ABAB..." 6000 times. This construction
       cannot be nested. An initial "\[" sequence is recognized only  if  "]{"
       followed  by  decimal  digits and "}" is found later in the pattern. If
       not, the characters remain in the pattern unaltered. The expand and hex
       modifiers are mutually exclusive.

       If part of an expanded pattern looks like an expansion, but  is  really
       part of the actual pattern, unwanted expansion can be avoided by giving
       two values in the quantifier. For example, \[AB]{6000,6000} is not rec-
       ognized as an expansion item.

       If  the  info modifier is set on an expanded pattern, the result of the
       expansion is included in the information that is output.

   JIT compilation

       Just-in-time (JIT) compiling is a  heavyweight  optimization  that  can
       greatly  speed  up pattern matching. See the pcre2jit documentation for
       details. JIT compiling happens, optionally, after a  pattern  has  been
       successfully  compiled into an internal form. The JIT compiler converts
       this to optimized machine code. It needs to know whether the match-time
       options PCRE2_PARTIAL_HARD and PCRE2_PARTIAL_SOFT are going to be used,
       because different code is generated for the different  cases.  See  the
       partial  modifier in "Subject Modifiers" below for details of how these
       options are specified for each match attempt.

       JIT compilation is requested by the jit pattern modifier, which may op-
       tionally be followed by an equals sign and a number in the range  0  to
       7.   The  three bits that make up the number specify which of the three
       JIT operating modes are to be compiled:

         1  compile JIT code for non-partial matching
         2  compile JIT code for soft partial matching
         4  compile JIT code for hard partial matching

       The possible values for the jit modifier are therefore:

         0  disable JIT
         1  normal matching only
         2  soft partial matching only
         3  normal and soft partial matching
         4  hard partial matching only
         6  soft and hard partial matching only
         7  all three modes

       If no number is given, 7 is  assumed.  The  phrase  "partial  matching"
       means a call to pcre2_match() with either the PCRE2_PARTIAL_SOFT or the
       PCRE2_PARTIAL_HARD  option set. Note that such a call may return a com-
       plete match; the options enable the possibility of a partial match, but
       do not require it. Note also that if you request JIT  compilation  only
       for  partial  matching  (for example, jit=2) but do not set the partial
       modifier on a subject line, that match will not use  JIT  code  because
       none was compiled for non-partial matching.

       If  JIT compilation is successful, the compiled JIT code will automati-
       cally be used when an appropriate type of match is run, except when in-
       compatible run-time options are specified. For more  details,  see  the
       pcre2jit  documentation. See also the jitstack modifier below for a way
       of setting the size of the JIT stack.

       If the jitfast modifier is specified, matching is done  using  the  JIT
       "fast  path" interface, pcre2_jit_match(), which skips some of the san-
       ity checks that are done by pcre2_match(), and of course does not  work
       when  JIT  is not supported. If jitfast is specified without jit, jit=7
       is assumed.

       If the jitverify modifier is specified, information about the  compiled
       pattern  shows  whether  JIT  compilation was or was not successful. If
       jitverify is specified without jit, jit=7 is assumed. If  JIT  compila-
       tion  is successful when jitverify is set, the text "(JIT)" is added to
       the first output line after a match or non match when JIT-compiled code
       was actually used in the match.

   Setting a locale

       The locale modifier must specify the name of a locale, for example:

         /pattern/locale=fr_FR

       The given locale is set, pcre2_maketables() is called to build a set of
       character tables for the locale, and this is then passed to  pcre2_com-
       pile()  when compiling the regular expression. The same tables are used
       when matching the following subject lines. The locale modifier  applies
       only to the pattern on which it appears, but can be given in a #pattern
       command  if a default is needed. Setting a locale and alternate charac-
       ter tables are mutually exclusive.

   Showing pattern memory

       The memory modifier causes the size in bytes of the memory used to hold
       the compiled pattern to be output. This does not include  the  size  of
       the  pcre2_code block; it is just the actual compiled data. If the pat-
       tern is subsequently passed to the JIT compiler, the size  of  the  JIT
       compiled code is also output. Here is an example:

           re> /a(b)c/jit,memory
         Memory allocation (code space): 21
         Memory allocation (JIT code): 1910


   Limiting nested parentheses

       The  parens_nest_limit  modifier  sets  a  limit on the depth of nested
       parentheses in a pattern. Breaching the limit causes a compilation  er-
       ror.   The  default  for  the  library  is set when PCRE2 is built, but
       pcre2test sets its own default of 220, which is  required  for  running
       the standard test suite.

   Limiting the pattern length

       The  max_pattern_length  modifier  sets  a limit, in code units, to the
       length of pattern that pcre2_compile() will accept. Breaching the limit
       causes a compilation  error.  The  default  is  the  largest  number  a
       PCRE2_SIZE variable can hold (essentially unlimited).

   Limiting the size of a compiled pattern

       The max_pattern_compiled_length modifier sets a limit, in bytes, to the
       amount of memory used by a compiled pattern. Breaching the limit causes
       a  compilation  error.  The  default is the largest number a PCRE2_SIZE
       variable can hold (essentially unlimited).

   Using the POSIX wrapper API

       The posix and posix_nosub modifiers cause pcre2test to call  PCRE2  via
       the  POSIX  wrapper API rather than its native API. When posix_nosub is
       used, the POSIX option REG_NOSUB is  passed  to  regcomp().  The  POSIX
       wrapper  supports  only  the 8-bit library. Note that it does not imply
       POSIX matching semantics; for more detail see the pcre2posix documenta-
       tion. The following pattern modifiers set  options  for  the  regcomp()
       function:

         caseless           REG_ICASE
         multiline          REG_NEWLINE
         dotall             REG_DOTALL     )
         ungreedy           REG_UNGREEDY   ) These options are not part of
         ucp                REG_UCP        )   the POSIX standard
         utf                REG_UTF8       )

       The  regerror_buffsize  modifier  specifies a size for the error buffer
       that is passed to regerror() in the event of a compilation  error.  For
       example:

         /abc/posix,regerror_buffsize=20

       This  provides  a means of testing the behaviour of regerror() when the
       buffer is too small for the error message. If  this  modifier  has  not
       been set, a large buffer is used.

       The  aftertext and allaftertext subject modifiers work as described be-
       low. All other modifiers are either ignored, with a warning message, or
       cause an error.

       The pattern is passed to regcomp() as a zero-terminated string  by  de-
       fault, but if the use_length or hex modifiers are set, the REG_PEND ex-
       tension is used to pass it by length.

   Testing the stack guard feature

       The  stackguard  modifier  is  used  to  test the use of pcre2_set_com-
       pile_recursion_guard(), a function that is  provided  to  enable  stack
       availability  to  be checked during compilation (see the pcre2api docu-
       mentation for details). If the number  specified  by  the  modifier  is
       greater than zero, pcre2_set_compile_recursion_guard() is called to set
       up  callback  from pcre2_compile() to a local function. The argument it
       receives is the current nesting parenthesis depth; if this  is  greater
       than the value given by the modifier, non-zero is returned, causing the
       compilation to be aborted.

   Using alternative character tables

       The  value  specified for the tables modifier must be one of the digits
       0, 1, 2, or 3. It causes a specific set of built-in character tables to
       be passed to pcre2_compile(). This is used in the PCRE2 tests to  check
       behaviour  with different character tables. The digit specifies the ta-
       bles as follows:

         0   do not pass any special character tables
         1   the default ASCII tables, as distributed in
               pcre2_chartables.c.dist
         2   a set of tables defining ISO 8859 characters
         3   a set of tables loaded by the #loadtables command

       In tables 2, some characters whose codes are greater than 128 are iden-
       tified as letters, digits, spaces, etc. Tables 3 can be used only after
       a #loadtables command has loaded them from a binary file.  Setting  al-
       ternate character tables and a locale are mutually exclusive.

   Setting certain match controls

       The following modifiers are really subject modifiers, and are described
       under  "Subject  Modifiers"  below.  However, they may be included in a
       pattern's modifier list, in which case they are applied to  every  sub-
       ject  line  that is processed with that pattern. These modifiers do not
       affect the compilation process.

             aftertext                   show text after match
             allaftertext                show text after captures
             allcaptures                 show all captures
             allvector                   show the entire ovector
             allusedtext                 show all consulted text
             altglobal                   alternative global matching
         /g  global                      global matching
             heapframes_size             show match data heapframes size
             jitstack=<n>                set size of JIT stack
             mark                        show mark values
             replace=<string>            specify a replacement string
             startchar                   show starting character when relevant
             substitute_callout          use substitution callouts
             substitute_extended         use PCRE2_SUBSTITUTE_EXTENDED
             substitute_literal          use PCRE2_SUBSTITUTE_LITERAL
             substitute_matched          use PCRE2_SUBSTITUTE_MATCHED
             substitute_overflow_length  use PCRE2_SUBSTITUTE_OVERFLOW_LENGTH
             substitute_replacement_only use PCRE2_SUBSTITUTE_REPLACEMENT_ONLY
             substitute_skip=<n>         skip substitution <n>
             substitute_stop=<n>         skip substitution <n> and following
             substitute_unknown_unset    use PCRE2_SUBSTITUTE_UNKNOWN_UNSET
             substitute_unset_empty      use PCRE2_SUBSTITUTE_UNSET_EMPTY

       These modifiers may not appear in a #pattern command. If you want  them
       as defaults, set them in a #subject command.

   Specifying literal subject lines

       If  the  subject_literal modifier is present on a pattern, all the sub-
       ject lines that it matches are taken as literal strings, with no inter-
       pretation of backslashes. It is not possible to set  subject  modifiers
       on  such  lines, but any that are set as defaults by a #subject command
       are recognized.

   Saving a compiled pattern

       When a pattern with the push modifier is successfully compiled,  it  is
       pushed  onto  a  stack  of compiled patterns, and pcre2test expects the
       next line to contain a new pattern (or a command) instead of a  subject
       line. This facility is used when saving compiled patterns to a file, as
       described  in  the section entitled "Saving and restoring compiled pat-
       terns" below.  If pushcopy is used instead of push, a copy of the  com-
       piled  pattern  is  stacked,  leaving the original as current, ready to
       match the following input lines. This provides a  way  of  testing  the
       pcre2_code_copy()  function.   The push and pushcopy  modifiers are in-
       compatible with compilation modifiers such as global that act at  match
       time. Any that are specified are ignored (for the stacked copy), with a
       warning  message,  except for replace, which causes an error. Note that
       jitverify, which is allowed, does not carry through to  any  subsequent
       matching that uses a stacked pattern.

   Testing foreign pattern conversion

       The  experimental  foreign pattern conversion functions in PCRE2 can be
       tested by setting the convert modifier. Its argument is  a  colon-sepa-
       rated  list  of  options,  which  set  the  equivalent  option  for the
       pcre2_pattern_convert() function:

         glob                    PCRE2_CONVERT_GLOB
         glob_no_starstar        PCRE2_CONVERT_GLOB_NO_STARSTAR
         glob_no_wild_separator  PCRE2_CONVERT_GLOB_NO_WILD_SEPARATOR
         posix_basic             PCRE2_CONVERT_POSIX_BASIC
         posix_extended          PCRE2_CONVERT_POSIX_EXTENDED
         unset                   Unset all options

       The "unset" value is useful for turning off a default that has been set
       by a #pattern command. When one of these options is set, the input pat-
       tern is passed to pcre2_pattern_convert(). If the  conversion  is  suc-
       cessful,  the  result  is  reflected  in  the output and then passed to
       pcre2_compile(). The normal utf and no_utf_check options, if set, cause
       the PCRE2_CONVERT_UTF  and  PCRE2_CONVERT_NO_UTF_CHECK  options  to  be
       passed to pcre2_pattern_convert().

       By default, the conversion function is allowed to allocate a buffer for
       its  output.  However, if the convert_length modifier is set to a value
       greater than zero, pcre2test passes a buffer of the given length.  This
       makes it possible to test the length check.

       The  convert_glob_escape  and  convert_glob_separator  modifiers can be
       used to specify the escape and separator characters for  glob  process-
       ing, overriding the defaults, which are operating-system dependent.


SUBJECT MODIFIERS

       The modifiers that can appear in subject lines and the #subject command
       are of two types.

   Setting match options

       The    following   modifiers   set   options   for   pcre2_match()   or
       pcre2_dfa_match(). See pcreapi for a description of their effects.

             anchored                   set PCRE2_ANCHORED
             endanchored                set PCRE2_ENDANCHORED
             dfa_restart                set PCRE2_DFA_RESTART
             dfa_shortest               set PCRE2_DFA_SHORTEST
             disable_recurseloop_check  set PCRE2_DISABLE_RECURSELOOP_CHECK
             no_jit                     set PCRE2_NO_JIT
             no_utf_check               set PCRE2_NO_UTF_CHECK
             notbol                     set PCRE2_NOTBOL
             notempty                   set PCRE2_NOTEMPTY
             notempty_atstart           set PCRE2_NOTEMPTY_ATSTART
             noteol                     set PCRE2_NOTEOL
             partial_hard (or ph)       set PCRE2_PARTIAL_HARD
             partial_soft (or ps)       set PCRE2_PARTIAL_SOFT

       The partial matching modifiers are provided with abbreviations  because
       they appear frequently in tests.

       If  the posix or posix_nosub modifier was present on the pattern, caus-
       ing the POSIX wrapper API to be used, the only option-setting modifiers
       that have any effect are notbol, notempty, and noteol, causing REG_NOT-
       BOL, REG_NOTEMPTY,  and  REG_NOTEOL,  respectively,  to  be  passed  to
       regexec(). The other modifiers are ignored, with a warning message.

       There  is one additional modifier that can be used with the POSIX wrap-
       per. It is ignored (with a warning) if used for non-POSIX matching.

             posix_startend=<n>[:<m>]

       This causes the subject string to be  passed  to  regexec()  using  the
       REG_STARTEND  option,  which  uses offsets to specify which part of the
       string is searched. If only one number is  given,  the  end  offset  is
       passed  as  the end of the subject string. For more detail of REG_STAR-
       TEND, see the pcre2posix documentation. If the subject string  contains
       binary  zeros  (coded  as escapes such as \x{00} because pcre2test does
       not support actual binary zeros in its input), you must use posix_star-
       tend to specify its length.

   Setting match controls

       The following modifiers affect the matching process  or  request  addi-
       tional  information.  Some  of  them may also be specified on a pattern
       line (see above), in which case they apply to every subject  line  that
       is  matched against that pattern, but can be overridden by modifiers on
       the subject.

             aftertext                  show text after match
             allaftertext               show text after captures
             allcaptures                show all captures
             allvector                  show the entire ovector
             allusedtext                show all consulted text (non-JIT only)
             altglobal                  alternative global matching
             callout_capture            show captures at callout time
             callout_data=<n>           set a value to pass via callouts
             callout_error=<n>[:<m>]    control callout error
             callout_extra              show extra callout information
             callout_fail=<n>[:<m>]     control callout failure
             callout_no_where           do not show position of a callout
             callout_none               do not supply a callout function
             copy=<number or name>      copy captured substring
             depth_limit=<n>            set a depth limit
             dfa                        use pcre2_dfa_match()
             find_limits                find heap, match and depth limits
             find_limits_noheap         find match and depth limits
             get=<number or name>       extract captured substring
             getall                     extract all captured substrings
         /g  global                     global matching
             heapframes_size            show match data heapframes size
             heap_limit=<n>             set a limit on heap memory (Kbytes)
             jitstack=<n>               set size of JIT stack
             mark                       show mark values
             match_limit=<n>            set a match limit
             memory                     show heap memory usage
             null_context               match with a NULL context
             null_replacement           substitute with NULL replacement
             null_subject               match with NULL subject
             offset=<n>                 set starting offset
             offset_limit=<n>           set offset limit
             ovector=<n>                set size of output vector
             recursion_limit=<n>        obsolete synonym for depth_limit
             replace=<string>           specify a replacement string
             startchar                  show startchar when relevant
             startoffset=<n>            same as offset=<n>
             substitute_callout         use substitution callouts
             substitute_extedded        use PCRE2_SUBSTITUTE_EXTENDED
             substitute_literal         use PCRE2_SUBSTITUTE_LITERAL
             substitute_matched         use PCRE2_SUBSTITUTE_MATCHED
             substitute_overflow_length use PCRE2_SUBSTITUTE_OVERFLOW_LENGTH
             substitute_replacement_only use PCRE2_SUBSTITUTE_REPLACEMENT_ONLY
             substitute_skip=<n>        skip substitution number n
             substitute_stop=<n>        skip substitution number n and greater
             substitute_unknown_unset   use PCRE2_SUBSTITUTE_UNKNOWN_UNSET
             substitute_unset_empty     use PCRE2_SUBSTITUTE_UNSET_EMPTY
             zero_terminate             pass the subject as zero-terminated

       The effects of these modifiers are described in the following sections.
       When matching via the POSIX wrapper API, the  aftertext,  allaftertext,
       and  ovector subject modifiers work as described below. All other modi-
       fiers are either ignored, with a warning message, or cause an error.

   Showing more text

       The aftertext modifier requests that as well as outputting the part  of
       the subject string that matched the entire pattern, pcre2test should in
       addition output the remainder of the subject string. This is useful for
       tests where the subject contains multiple copies of the same substring.
       The  allaftertext  modifier  requests the same action for captured sub-
       strings as well as the main matched substring. In each case the remain-
       der is output on the following line with a plus character following the
       capture number.

       The allusedtext modifier requests that all the text that was  consulted
       during  a  successful pattern match by the interpreter should be shown,
       for both full and partial matches. This feature is  not  supported  for
       JIT  matching,  and if requested with JIT it is ignored (with a warning
       message). Setting this modifier affects the output if there is a  look-
       behind  at  the start of a match, or, for a complete match, a lookahead
       at the end, or if \K is used in the pattern. Characters that precede or
       follow the start and end of the actual match are indicated in the  out-
       put by '<' or '>' characters underneath them.  Here is an example:

           re> /(?<=pqr)abc(?=xyz)/
         data> 123pqrabcxyz456\=allusedtext
          0: pqrabcxyz
             <<<   >>>
         data> 123pqrabcxy\=ph,allusedtext
         Partial match: pqrabcxy
                        <<<

       The  first, complete match shows that the matched string is "abc", with
       the preceding and following strings "pqr" and "xyz"  having  been  con-
       sulted  during  the match (when processing the assertions). The partial
       match can indicate only the preceding string.

       The startchar modifier requests that the  starting  character  for  the
       match  be  indicated,  if  it  is different to the start of the matched
       string. The only time when this occurs is when \K has been processed as
       part of the match. In this situation, the output for the matched string
       is displayed from the starting character  instead  of  from  the  match
       point, with circumflex characters under the earlier characters. For ex-
       ample:

           re> /abc\Kxyz/
         data> abcxyz\=startchar
          0: abcxyz
             ^^^

       Unlike  allusedtext, the startchar modifier can be used with JIT.  How-
       ever, these two modifiers are mutually exclusive.

   Showing the value of all capture groups

       The allcaptures modifier requests that the values of all potential cap-
       tured parentheses be output after a match. By default, only those up to
       the highest one actually used in the match are output (corresponding to
       the return code from pcre2_match()). Groups that did not take  part  in
       the  match  are  output as "<unset>". This modifier is not relevant for
       DFA matching (which does no capturing) and does not apply when  replace
       is specified; it is ignored, with a warning message, if present.

   Showing the entire ovector, for all outcomes

       The allvector modifier requests that the entire ovector be shown, what-
       ever the outcome of the match. Compare allcaptures, which shows only up
       to  the maximum number of capture groups for the pattern, and then only
       for a successful complete non-DFA match. This modifier, which acts  af-
       ter  any  match  result, and also for DFA matching, provides a means of
       checking that there are no unexpected modifications to ovector  fields.
       Before  each match attempt, the ovector is filled with a special value,
       and if this is found in  both  elements  of  a  capturing  pair,  "<un-
       changed>"  is  output.  After  a  successful match, this applies to all
       groups after the maximum capture group for the pattern. In other  cases
       it  applies to the entire ovector. After a partial match, the first two
       elements are the only ones that should be set. After a DFA  match,  the
       amount  of  ovector  that is used depends on the number of matches that
       were found.

   Testing pattern callouts

       A callout function is supplied when pcre2test calls the library  match-
       ing  functions,  unless callout_none is specified. Its behaviour can be
       controlled by various modifiers listed above  whose  names  begin  with
       callout_.  Details  are given in the section entitled "Callouts" below.
       Testing callouts from pcre2_substitute()  is  described  separately  in
       "Testing the substitution function" below.

   Finding all matches in a string

       Searching for all possible matches within a subject can be requested by
       the  global  or altglobal modifier. After finding a match, the matching
       function is called again to search the remainder of  the  subject.  The
       difference  between  global  and  altglobal is that the former uses the
       start_offset argument to pcre2_match() or  pcre2_dfa_match()  to  start
       searching  at  a new point within the entire string (which is what Perl
       does), whereas the latter passes over a shortened subject. This makes a
       difference to the matching process if the pattern begins with a lookbe-
       hind assertion (including \b or \B).

       If an empty string  is  matched,  the  next  match  is  done  with  the
       PCRE2_NOTEMPTY_ATSTART and PCRE2_ANCHORED flags set, in order to search
       for another, non-empty, match at the same point in the subject. If this
       match  fails, the start offset is advanced, and the normal match is re-
       tried. This imitates the way Perl handles such cases when using the  /g
       modifier  or  the  split()  function. Normally, the start offset is ad-
       vanced by one character, but if the newline convention recognizes  CRLF
       as  a  newline,  and the current character is CR followed by LF, an ad-
       vance of two characters occurs.

   Testing substring extraction functions

       The copy  and  get  modifiers  can  be  used  to  test  the  pcre2_sub-
       string_copy_xxx() and pcre2_substring_get_xxx() functions.  They can be
       given more than once, and each can specify a capture group name or num-
       ber, for example:

          abcd\=copy=1,copy=3,get=G1

       If  the  #subject command is used to set default copy and/or get lists,
       these can be unset by specifying a negative number to cancel  all  num-
       bered groups and an empty name to cancel all named groups.

       The  getall  modifier  tests pcre2_substring_list_get(), which extracts
       all captured substrings.

       If the subject line is successfully matched, the  substrings  extracted
       by  the  convenience  functions  are  output  with C, G, or L after the
       string number instead of a colon. This is in  addition  to  the  normal
       full  list.  The string length (that is, the return from the extraction
       function) is given in parentheses after each substring, followed by the
       name when the extraction was by name.

   Testing the substitution function

       If the replace modifier is  set,  the  pcre2_substitute()  function  is
       called  instead  of one of the matching functions (or after one call of
       pcre2_match() in the case of PCRE2_SUBSTITUTE_MATCHED). Note  that  re-
       placement  strings cannot contain commas, because a comma signifies the
       end of a modifier. This is not thought to be an issue in  a  test  pro-
       gram.

       Specifying  a  completely  empty replacement string disables this modi-
       fier.  However, it is possible to specify an empty replacement by  pro-
       viding  a buffer length, as described below, for an otherwise empty re-
       placement.

       Unlike subject strings, pcre2test does not process replacement  strings
       for  escape  sequences. In UTF mode, a replacement string is checked to
       see if it is a valid UTF-8 string. If so, it is correctly converted  to
       a  UTF  string of the appropriate code unit width. If it is not a valid
       UTF-8 string, the individual code units are copied directly. This  pro-
       vides a means of passing an invalid UTF-8 string for testing purposes.

       The  following modifiers set options (in additional to the normal match
       options) for pcre2_substitute():

         global                      PCRE2_SUBSTITUTE_GLOBAL
         substitute_extended         PCRE2_SUBSTITUTE_EXTENDED
         substitute_literal          PCRE2_SUBSTITUTE_LITERAL
         substitute_matched          PCRE2_SUBSTITUTE_MATCHED
         substitute_overflow_length  PCRE2_SUBSTITUTE_OVERFLOW_LENGTH
         substitute_replacement_only PCRE2_SUBSTITUTE_REPLACEMENT_ONLY
         substitute_unknown_unset    PCRE2_SUBSTITUTE_UNKNOWN_UNSET
         substitute_unset_empty      PCRE2_SUBSTITUTE_UNSET_EMPTY

       See the pcre2api documentation for details of these options.

       After a successful substitution, the modified string  is  output,  pre-
       ceded  by the number of replacements. This may be zero if there were no
       matches. Here is a simple example of a substitution test:

         /abc/replace=xxx
             =abc=abc=
          1: =xxx=abc=
             =abc=abc=\=global
          2: =xxx=xxx=

       Subject and replacement strings should be kept relatively short  (fewer
       than  256 characters) for substitution tests, as fixed-size buffers are
       used. To make it easy to test for buffer overflow, if  the  replacement
       string  starts  with a number in square brackets, that number is passed
       to pcre2_substitute() as the size of the output buffer,  with  the  re-
       placement  string  starting  at  the next character. Here is an example
       that tests the edge case:

         /abc/
             123abc123\=replace=[10]XYZ
          1: 123XYZ123
             123abc123\=replace=[9]XYZ
         Failed: error -47: no more memory

       The  default  action  of  pcre2_substitute()  is  to  return  PCRE2_ER-
       ROR_NOMEMORY  when  the  output  buffer  is  too small. However, if the
       PCRE2_SUBSTITUTE_OVERFLOW_LENGTH option is set (by  using  the  substi-
       tute_overflow_length  modifier),  pcre2_substitute()  continues  to  go
       through the motions of matching and substituting  (but  not  doing  any
       callouts),  in  order  to  compute the size of buffer that is required.
       When this happens, pcre2test shows the required  buffer  length  (which
       includes space for the trailing zero) as part of the error message. For
       example:

         /abc/substitute_overflow_length
             123abc123\=replace=[9]XYZ
         Failed: error -47: no more memory: 10 code units are needed

       A replacement string is ignored with POSIX and DFA matching. Specifying
       partial  matching  provokes  an  error return ("bad option value") from
       pcre2_substitute().

   Testing substitute callouts

       If the substitute_callout modifier is set, a substitution callout func-
       tion is set up. The null_context modifier must not be set, because  the
       address  of the callout function is passed in a match context. When the
       callout function is called (after each substitution),  details  of  the
       input and output strings are output. For example:

         /abc/g,replace=<$0>,substitute_callout
             abcdefabcpqr
          1(1) Old 0 3 "abc" New 0 5 "<abc>"
          2(1) Old 6 9 "abc" New 8 13 "<abc>"
          2: <abc>def<abc>pqr

       The  first  number  on  each  callout line is the count of matches. The
       parenthesized number is the number of pairs that are set in the ovector
       (that is, one more than the number of capturing groups that were  set).
       Then are listed the offsets of the old substring, its contents, and the
       same for the replacement.

       By  default,  the substitution callout function returns zero, which ac-
       cepts the replacement and causes matching to continue if /g  was  used.
       Two  further modifiers can be used to test other return values. If sub-
       stitute_skip is set to a value greater than zero the  callout  function
       returns  +1 for the match of that number, and similarly substitute_stop
       returns -1. These cause the replacement to be rejected, and  -1  causes
       no  further  matching to take place. If either of them are set, substi-
       tute_callout is assumed. For example:

         /abc/g,replace=<$0>,substitute_skip=1
             abcdefabcpqr
          1(1) Old 0 3 "abc" New 0 5 "<abc> SKIPPED"
          2(1) Old 6 9 "abc" New 6 11 "<abc>"
          2: abcdef<abc>pqr
             abcdefabcpqr\=substitute_stop=1
          1(1) Old 0 3 "abc" New 0 5 "<abc> STOPPED"
          1: abcdefabcpqr

       If both are set for the same number, stop takes precedence. Only a sin-
       gle skip or stop is supported, which is sufficient for testing that the
       feature works.

   Setting the JIT stack size

       The jitstack modifier provides a way of setting the maximum stack  size
       that  is  used  by the just-in-time optimization code. It is ignored if
       JIT optimization is not being used. The value is a number of  kibibytes
       (units  of  1024  bytes). Setting zero reverts to the default of 32KiB.
       Providing a stack that is larger than the default is necessary only for
       very complicated patterns. If jitstack is set  non-zero  on  a  subject
       line it overrides any value that was set on the pattern.

   Setting heap, match, and depth limits

       The  heap_limit,  match_limit, and depth_limit modifiers set the appro-
       priate limits in the match context. These values are ignored  when  the
       find_limits or find_limits_noheap modifier is specified.

   Finding minimum limits

       If  the  find_limits  modifier  is present on a subject line, pcre2test
       calls the relevant matching function several times,  setting  different
       values    in    the    match    context   via   pcre2_set_heap_limit(),
       pcre2_set_match_limit(), or pcre2_set_depth_limit() until it finds  the
       smallest  value  for  each  parameter that allows the match to complete
       without a "limit exceeded" error. The match itself may succeed or fail.
       An alternative modifier, find_limits_noheap, omits the heap limit. This
       is used in the standard tests, because the minimum  heap  limit  varies
       between  systems.  If  JIT is being used, only the match limit is rele-
       vant, and the other two are automatically omitted.

       When using this modifier, the pattern should not contain any limit set-
       tings such as (*LIMIT_MATCH=...)  within  it.  If  such  a  setting  is
       present and is lower than the minimum matching value, the minimum value
       cannot  be  found because pcre2_set_match_limit() etc. are only able to
       reduce the value of an in-pattern limit; they cannot increase it.

       For non-DFA matching, the minimum depth_limit number is  a  measure  of
       how much nested backtracking happens (that is, how deeply the pattern's
       tree  is  searched).  In the case of DFA matching, depth_limit controls
       the depth of recursive calls of the internal function that is used  for
       handling pattern recursion, lookaround assertions, and atomic groups.

       For non-DFA matching, the match_limit number is a measure of the amount
       of backtracking that takes place, and learning the minimum value can be
       instructive.  For  most  simple matches, the number is quite small, but
       for patterns with very large numbers of matching possibilities, it  can
       become  large very quickly with increasing length of subject string. In
       the case of DFA matching, match_limit  controls  the  total  number  of
       calls, both recursive and non-recursive, to the internal matching func-
       tion, thus controlling the overall amount of computing resource that is
       used.

       For  both  kinds  of  matching,  the  heap_limit  number,  which  is in
       kibibytes (units of 1024 bytes), limits the amount of heap memory  used
       for matching.

   Showing MARK names


       The mark modifier causes the names from backtracking control verbs that
       are  returned from calls to pcre2_match() to be displayed. If a mark is
       returned for a match, non-match, or partial match, pcre2test shows  it.
       For  a  match, it is on a line by itself, tagged with "MK:". Otherwise,
       it is added to the non-match message.

   Showing memory usage

       The memory modifier causes pcre2test to log the sizes of all heap  mem-
       ory   allocation  and  freeing  calls  that  occur  during  a  call  to
       pcre2_match() or pcre2_dfa_match(). In the latter case, heap memory  is
       used  only  when  a match requires more internal workspace that the de-
       fault allocation on the stack, so in many cases there will be  no  out-
       put.  No  heap  memory  is allocated during matching with JIT. For this
       modifier to work, the null_context modifier must not be set on both the
       pattern and the subject, though it can be set on one or the other.

   Showing the heap frame overall vector size

       The  heapframes_size   modifier   is   relevant   for   matches   using
       pcre2_match() without JIT. After a match has run (whether successful or
       not)  the  size,  in bytes, of the allocated heap frames vector that is
       left attached to the match data block is shown. If the matching  action
       involved  several  calls to pcre2_match() (for example, global matching
       or for timing) only the final value is shown.

       This modifier is ignored, with a warning, for POSIX  or  DFA  matching.
       JIT matching does not use the heap frames vector, so the size is always
       zero,  unless there was a previous non-JIT match. Note that specifing a
       size of zero for the output vector (see below) causes pcre2test to free
       its match data block (and associated heap frames vector) and allocate a
       new one.

   Setting a starting offset

       The offset modifier sets an offset  in  the  subject  string  at  which
       matching starts. Its value is a number of code units, not characters.

   Setting an offset limit

       The  offset_limit  modifier  sets  a limit for unanchored matches. If a
       match cannot be found starting at or before this offset in the subject,
       a "no match" return is given. The data value is a number of code units,
       not characters. When this modifier is used, the use_offset_limit  modi-
       fier must have been set for the pattern; if not, an error is generated.

   Setting the size of the output vector

       The  ovector  modifier applies only to the subject line in which it ap-
       pears, though of course it can also be used to set a default in a #sub-
       ject command. It specifies the number of  pairs  of  offsets  that  are
       available for storing matching information. The default is 15.

       A  value of zero is useful when testing the POSIX API because it causes
       regexec() to be called with a NULL capture vector. When not testing the
       POSIX API, a value of  zero  is  used  to  cause  pcre2_match_data_cre-
       ate_from_pattern()  to  be called, in order to create a new match block
       of exactly the right size for the pattern. (It is not possible to  cre-
       ate  a match block with a zero-length ovector; there is always at least
       one pair of offsets.) The old match data block is freed.

   Passing the subject as zero-terminated

       By default, the subject string is passed to a native API matching func-
       tion with its correct length. In order to test the facility for passing
       a zero-terminated string, the zero_terminate modifier is  provided.  It
       causes  the length to be passed as PCRE2_ZERO_TERMINATED. When matching
       via the POSIX interface, this modifier is ignored, with a warning.

       When testing pcre2_substitute(), this modifier also has the  effect  of
       passing the replacement string as zero-terminated.

   Passing a NULL context, subject, or replacement

       Normally,   pcre2test   passes   a   context  block  to  pcre2_match(),
       pcre2_dfa_match(), pcre2_jit_match()  or  pcre2_substitute().   If  the
       null_context  modifier  is  set,  however,  NULL is passed. This is for
       testing that the matching and substitution functions  behave  correctly
       in  this  case  (they use default values). This modifier cannot be used
       with the find_limits, find_limits_noheap, or  substitute_callout  modi-
       fiers.

       Similarly,  for  testing purposes, if the null_subject or null_replace-
       ment modifier is set, the subject or replacement  string  pointers  are
       passed as NULL, respectively, to the relevant functions.


THE ALTERNATIVE MATCHING FUNCTION

       By  default,  pcre2test  uses  the  standard  PCRE2  matching function,
       pcre2_match() to match each subject line. PCRE2 also supports an alter-
       native matching function, pcre2_dfa_match(), which operates in  a  dif-
       ferent  way, and has some restrictions. The differences between the two
       functions are described in the pcre2matching documentation.

       If the dfa modifier is set, the alternative matching function is  used.
       This  function  finds all possible matches at a given point in the sub-
       ject. If, however, the dfa_shortest modifier is set,  processing  stops
       after  the  first  match is found. This is always the shortest possible
       match.


DEFAULT OUTPUT FROM pcre2test

       This section describes the output when the  normal  matching  function,
       pcre2_match(), is being used.

       When  a  match  succeeds,  pcre2test  outputs the list of captured sub-
       strings, starting with number 0 for the string that matched  the  whole
       pattern.  Otherwise, it outputs "No match" when the return is PCRE2_ER-
       ROR_NOMATCH,  or  "Partial  match:"  followed by the partially matching
       substring when the return is PCRE2_ERROR_PARTIAL. (Note  that  this  is
       the  entire  substring  that was inspected during the partial match; it
       may include characters before the actual match start  if  a  lookbehind
       assertion, \K, \b, or \B was involved.)

       For any other return, pcre2test outputs the PCRE2 negative error number
       and  a  short  descriptive  phrase. If the error is a failed UTF string
       check, the code unit offset of the start of the  failing  character  is
       also output. Here is an example of an interactive pcre2test run.

         $ pcre2test
         PCRE2 version 10.22 2016-07-29

           re> /^abc(\d+)/
         data> abc123
          0: abc123
          1: 123
         data> xyz
         No match

       Unset capturing substrings that are not followed by one that is set are
       not shown by pcre2test unless the allcaptures modifier is specified. In
       the following example, there are two capturing substrings, but when the
       first  data  line is matched, the second, unset substring is not shown.
       An "internal" unset substring is shown as "<unset>", as for the  second
       data line.

           re> /(a)|(b)/
         data> a
          0: a
          1: a
         data> b
          0: b
          1: <unset>
          2: b

       If  the strings contain any non-printing characters, they are output as
       \xhh escapes if the value is less than 256 and UTF  mode  is  not  set.
       Otherwise they are output as \x{hh...} escapes. See below for the defi-
       nition  of  non-printing  characters. If the aftertext modifier is set,
       the output for substring 0 is followed  by  the  rest  of  the  subject
       string, identified by "0+" like this:

           re> /cat/aftertext
         data> cataract
          0: cat
          0+ aract

       If global matching is requested, the results of successive matching at-
       tempts are output in sequence, like this:

           re> /\Bi(\w\w)/g
         data> Mississippi
          0: iss
          1: ss
          0: iss
          1: ss
          0: ipp
          1: pp

       "No  match" is output only if the first match attempt fails. Here is an
       example of a failure message (the offset 4 that  is  specified  by  the
       offset modifier is past the end of the subject string):

           re> /xyz/
         data> xyz\=offset=4
         Error -24 (bad offset value)

       Note that whereas patterns can be continued over several lines (a plain
       ">"  prompt  is used for continuations), subject lines may not. However
       newlines can be included in a subject by means of the \n escape (or \r,
       \r\n, etc., depending on the newline sequence setting).


OUTPUT FROM THE ALTERNATIVE MATCHING FUNCTION

       When the alternative matching function, pcre2_dfa_match(), is used, the
       output consists of a list of all the matches that start  at  the  first
       point in the subject where there is at least one match. For example:

           re> /(tang|tangerine|tan)/
         data> yellow tangerine\=dfa
          0: tangerine
          1: tang
          2: tan

       Using  the normal matching function on this data finds only "tang". The
       longest matching string is always given first (and numbered zero).  Af-
       ter  a PCRE2_ERROR_PARTIAL return, the output is "Partial match:", fol-
       lowed by the partially matching substring. Note that this is the entire
       substring that was inspected during the partial match; it  may  include
       characters before the actual match start if a lookbehind assertion, \b,
       or \B was involved. (\K is not supported for DFA matching.)

       If global matching is requested, the search for further matches resumes
       at the end of the longest match. For example:

           re> /(tang|tangerine|tan)/g
         data> yellow tangerine and tangy sultana\=dfa
          0: tangerine
          1: tang
          2: tan
          0: tang
          1: tan
          0: tan

       The  alternative  matching function does not support substring capture,
       so the modifiers that are concerned with captured  substrings  are  not
       relevant.


RESTARTING AFTER A PARTIAL MATCH

       When  the  alternative matching function has given the PCRE2_ERROR_PAR-
       TIAL return, indicating that the subject partially matched the pattern,
       you can restart the match with additional subject data by means of  the
       dfa_restart modifier. For example:

           re> /^\d?\d(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)\d\d$/
         data> 23ja\=ps,dfa
         Partial match: 23ja
         data> n05\=dfa,dfa_restart
          0: n05

       For  further  information  about partial matching, see the pcre2partial
       documentation.


CALLOUTS

       If the pattern contains any callout requests, pcre2test's callout func-
       tion is called during matching unless callout_none is  specified.  This
       works with both matching functions, and with JIT, though there are some
       differences  in behaviour. The output for callouts with numerical argu-
       ments and those with string arguments is slightly different.

   Callouts with numerical arguments

       By default, the callout function displays the callout number, the start
       and current positions in the subject text at the callout time, and  the
       next pattern item to be tested. For example:

         --->pqrabcdef
           0    ^  ^     \d

       This  output  indicates  that callout number 0 occurred for a match at-
       tempt starting at the fourth character of the subject string, when  the
       pointer  was  at  the seventh character, and when the next pattern item
       was \d. Just one circumflex is output if the start  and  current  posi-
       tions are the same, or if the current position precedes the start posi-
       tion, which can happen if the callout is in a lookbehind assertion.

       Callouts numbered 255 are assumed to be automatic callouts, inserted as
       a result of the auto_callout pattern modifier. In this case, instead of
       showing  the  callout  number, the offset in the pattern, preceded by a
       plus, is output. For example:

           re> /\d?[A-E]\*/auto_callout
         data> E*
         --->E*
          +0 ^      \d?
          +3 ^      [A-E]
          +8 ^^     \*
         +10 ^ ^
          0: E*

       If a pattern contains (*MARK) items, an additional line is output when-
       ever a change of latest mark is passed to the callout function. For ex-
       ample:

           re> /a(*MARK:X)bc/auto_callout
         data> abc
         --->abc
          +0 ^       a
          +1 ^^      (*MARK:X)
         +10 ^^      b
         Latest Mark: X
         +11 ^ ^     c
         +12 ^  ^
          0: abc

       The mark changes between matching "a" and "b", but stays the  same  for
       the  rest  of  the match, so nothing more is output. If, as a result of
       backtracking, the mark reverts to being unset, the  text  "<unset>"  is
       output.

   Callouts with string arguments

       The output for a callout with a string argument is similar, except that
       instead  of outputting a callout number before the position indicators,
       the callout string and its offset in the pattern string are output  be-
       fore  the  reflection  of the subject string, and the subject string is
       reflected for each callout. For example:

           re> /^ab(?C'first')cd(?C"second")ef/
         data> abcdefg
         Callout (7): 'first'
         --->abcdefg
             ^ ^         c
         Callout (20): "second"
         --->abcdefg
             ^   ^       e
          0: abcdef


   Callout modifiers

       The callout function in pcre2test returns zero (carry on  matching)  by
       default,  but  you can use a callout_fail modifier in a subject line to
       change this and other parameters of the callout (see below).

       If the callout_capture modifier is set, the current captured groups are
       output when a callout occurs. This is useful only for non-DFA matching,
       as pcre2_dfa_match() does not support capturing,  so  no  captures  are
       ever shown.

       The normal callout output, showing the callout number or pattern offset
       (as  described above) is suppressed if the callout_no_where modifier is
       set.

       When using the interpretive  matching  function  pcre2_match()  without
       JIT,  setting  the callout_extra modifier causes additional output from
       pcre2test's callout function to be generated. For the first callout  in
       a  match  attempt at a new starting position in the subject, "New match
       attempt" is output. If there has been a backtrack since the last  call-
       out (or start of matching if this is the first callout), "Backtrack" is
       output,  followed  by  "No other matching paths" if the backtrack ended
       the previous match attempt. For example:

          re> /(a+)b/auto_callout,no_start_optimize,no_auto_possess
         data> aac\=callout_extra
         New match attempt
         --->aac
          +0 ^       (
          +1 ^       a+
          +3 ^ ^     )
          +4 ^ ^     b
         Backtrack
         --->aac
          +3 ^^      )
          +4 ^^      b
         Backtrack
         No other matching paths
         New match attempt
         --->aac
          +0  ^      (
          +1  ^      a+
          +3  ^^     )
          +4  ^^     b
         Backtrack
         No other matching paths
         New match attempt
         --->aac
          +0   ^     (
          +1   ^     a+
         Backtrack
         No other matching paths
         New match attempt
         --->aac
          +0    ^    (
          +1    ^    a+
         No match

       Notice that various optimizations must be turned off if  you  want  all
       possible  matching  paths  to  be  scanned. If no_start_optimize is not
       used, there is an immediate "no match", without any  callouts,  because
       the  starting  optimization  fails to find "b" in the subject, which it
       knows must be present for any match. If no_auto_possess  is  not  used,
       the  "a+"  item is turned into "a++", which reduces the number of back-
       tracks.

       The callout_extra modifier has no effect if used with the DFA  matching
       function, or with JIT.

   Return values from callouts

       The  default  return  from  the  callout function is zero, which allows
       matching to continue. The callout_fail modifier can be given one or two
       numbers. If there is only one number, 1 is returned instead of 0 (caus-
       ing matching to backtrack) when a callout of that number is reached. If
       two numbers (<n>:<m>) are given, 1 is  returned  when  callout  <n>  is
       reached  and  there  have been at least <m> callouts. The callout_error
       modifier is similar, except that PCRE2_ERROR_CALLOUT is returned, caus-
       ing the entire matching process to be aborted. If both these  modifiers
       are  set  for  the same callout number, callout_error takes precedence.
       Note that callouts with string arguments are always  given  the  number
       zero.

       The  callout_data  modifier can be given an unsigned or a negative num-
       ber.  This is set as the "user data" that is  passed  to  the  matching
       function,  and  passed  back  when the callout function is invoked. Any
       value other than zero is used as  a  return  from  pcre2test's  callout
       function.

       Inserting callouts can be helpful when using pcre2test to check compli-
       cated  regular expressions. For further information about callouts, see
       the pcre2callout documentation.


NON-PRINTING CHARACTERS

       When pcre2test is outputting text in the compiled version of a pattern,
       bytes other than 32-126 are always treated as  non-printing  characters
       and are therefore shown as hex escapes.

       When  pcre2test  is outputting text that is a matched part of a subject
       string, it behaves in the same way, unless a different locale has  been
       set  for the pattern (using the locale modifier). In this case, the is-
       print() function is used to distinguish printing and non-printing char-
       acters.


SAVING AND RESTORING COMPILED PATTERNS

       It is possible to save compiled patterns on disc or elsewhere, and  re-
       load  them  later, subject to a number of restrictions. JIT data cannot
       be saved. The host on which the patterns are reloaded must  be  running
       the same version of PCRE2, with the same code unit width, and must also
       have  the  same  endianness,  pointer width and PCRE2_SIZE type. Before
       compiled patterns can be saved they must be serialized, that  is,  con-
       verted  to a stream of bytes. A single byte stream may contain any num-
       ber of compiled patterns, but they must all use the same character  ta-
       bles.  A  single copy of the tables is included in the byte stream (its
       size is 1088 bytes).

       The functions whose names begin with pcre2_serialize_ are used for  se-
       rializing  and de-serializing. They are described in the pcre2serialize
       documentation. In this section we describe the  features  of  pcre2test
       that can be used to test these functions.

       Note  that  "serialization" in PCRE2 does not convert compiled patterns
       to an abstract format like Java or .NET. It  just  makes  a  reloadable
       byte code stream.  Hence the restrictions on reloading mentioned above.

       In  pcre2test,  when  a pattern with push modifier is successfully com-
       piled, it is pushed onto a stack of compiled  patterns,  and  pcre2test
       expects  the next line to contain a new pattern (or command) instead of
       a subject line. By contrast, the pushcopy modifier causes a copy of the
       compiled pattern to be stacked, leaving the original available for  im-
       mediate  matching.  By using push and/or pushcopy, a number of patterns
       can be compiled and retained. These  modifiers  are  incompatible  with
       posix, and control modifiers that act at match time are ignored (with a
       message)  for the stacked patterns. The jitverify modifier applies only
       at compile time.

       The command

         #save <filename>

       causes all the stacked patterns to be serialized and the result written
       to the named file. Afterwards, all the stacked patterns are freed.  The
       command

         #load <filename>

       reads  the  data in the file, and then arranges for it to be de-serial-
       ized, with the resulting compiled patterns added to the pattern  stack.
       The  pattern  on the top of the stack can be retrieved by the #pop com-
       mand, which must be followed by  lines  of  subjects  that  are  to  be
       matched  with  the pattern, terminated as usual by an empty line or end
       of file. This command may be followed by  a  modifier  list  containing
       only  control  modifiers that act after a pattern has been compiled. In
       particular, hex, posix, posix_nosub, push, and  pushcopy  are  not  al-
       lowed,  nor  are  any option-setting modifiers.  The JIT modifiers are,
       however permitted. Here is an example that saves and reloads  two  pat-
       terns.

         /abc/push
         /xyz/push
         #save tempfile
         #load tempfile
         #pop info
         xyz

         #pop jit,bincode
         abc

       If  jitverify  is  used with #pop, it does not automatically imply jit,
       which is different behaviour from when it is used on a pattern.

       The #popcopy command is analogous to the pushcopy modifier in  that  it
       makes current a copy of the topmost stack pattern, leaving the original
       still on the stack.


SEE ALSO

       pcre2(3),  pcre2api(3),  pcre2callout(3),  pcre2jit,  pcre2matching(3),
       pcre2partial(d), pcre2pattern(3), pcre2serialize(3).


AUTHOR

       Philip Hazel
       Retired from University Computing Service
       Cambridge, England.


REVISION

       Last updated: 24 April 2024
       Copyright (c) 1997-2024 University of Cambridge.


PCRE 10.44                       24 April 2024                    PCRE2TEST(1)