Provided by: pcre2-utils_10.32-5_amd64 bug


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


       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
       documentation. For details of the PCRE2 library function calls and their options, 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  function
       options, control how the subject is processed, and what output is produced.

       As  the  original fairly simple PCRE library evolved, it acquired many different features,
       and as a result, the original pcretest program ended up with a lot of options in a  messy,
       arcane  syntax  for  testing  all  the features. The move to the new PCRE2 API provided an
       opportunity to re-implement the test program as pcre2test, with a cleaner modifier syntax.
       Nevertheless,  there  are  still  many  obscure  modifiers, some of which are specifically
       designed 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.


       Different versions of the PCRE2 library can be built to support character 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 installed. 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 library functions. Results are converted back to 8-bit
       code units for output.

       In the rest of this document, the names of library functions and structures are  given  in
       generic  form,  for example, pcre_compile(). The actual names used in the libraries have a
       suffix _8, _16, or _32, as appropriate.


       Input to pcre2test is processed line by line, either by calling the  C  library's  fgets()
       function,  or  via the libreadline 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 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 characters  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 options" 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 appropriate.

       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  character
       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.


       -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

       -16       If  the 16-bit library has been built, this option causes it to be used. If only
                 the 16-bit library has 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 only
                 the 32-bit library has been built, this is the default. If  the  32-bit  library
                 has not been built, this option causes an error.

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

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

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

       -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 options 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  internal  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.

                 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 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 -LM 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 output 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

       -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 output.

       -version  Output the PCRE2 version number and then exit.


       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 pattern. 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 script that is distributed  with  PCRE2  as  a  means  of  checking  that  the
       behaviour  of  PCRE2  and  Perl  is  the same. For a specification of, see the
       comments near its beginning.

       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 expected if there is still input to be read.


       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:


       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

       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 information, 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.

         #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 contain tests of various newline conventions, but the  majority  of  the  tests
       expect  a single linefeed to be recognized as a newline by default. Without special action
       the tests would fail when PCRE2 is compiled 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, ANYCRLF, 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. Otherwise, except  when
       testing  the  POSIX API, a newline modifier that specifies the first newline convention in
       the list (LF in the above example) 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  default  newline
       convention, though it is possible to set the newline convention 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 subsequent patterns.
       Modifiers on a pattern can change these settings.


       The appearance of this line causes all subsequent modifier  settings  to  be  checked  for
       compatibility  with  the script, which is used to confirm that Perl gives the
       same results as PCRE2. Also, apart from comment lines,  #pattern  commands,  and  #subject
       commands  that  set or unset "mark", no command lines are permitted, because they and many
       of the modifiers are specific to pcre2test, and should not be used in test files that  are
       also  processed  by  The  #perltest  command  helps  detect  tests  that are
       accidentally put in the wrong file.

         #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 patterns" below.

         #subject <modifier-list>

       This command sets a default modifier list that applies to all  subsequent  subject  lines.
       Modifiers on a subject line can change these settings.


       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
       "anchored",  and some of them must be followed by an equals sign and a value, for example,
       "offset=12". Values cannot contain comma characters, 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 letters, 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:


       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.


       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 delimiter within the pattern by escaping it with a backslash, for


       If you do this, the escape and the delimiter form part  of  the  pattern,  but  since  the
       delimiters  are  all  non-alphanumeric,  this  does  not affect its interpretation. If the
       terminating delimiter is immediately followed by a backslash, for example,


       then 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


       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 regular expression.

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


       Before each subject line is passed to  pcre2_match()  or  pcre2_dfa_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
       encoding 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  hexadecimal  digits  inside  the  braces;
       invalid values provoke error messages.

       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


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


       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:


       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 escapes 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  backslashes.   No  replication  is
       possible, and any subject modifiers must be set as defaults by a #subject command.


       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. For the main options, there are
       some single-letter abbreviations that are the same  as  Perl  options.  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  difference  to  the  way  pcre2_compile()  behaves.  See  pcre2api  for a
       description of the effects of these options.

             allow_empty_class         set PCRE2_ALLOW_EMPTY_CLASS
             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
             auto_callout              set PCRE2_AUTO_CALLOUT
             bad_escape_is_literal     set PCRE2_EXTRA_BAD_ESCAPE_IS_LITERAL
         /i  caseless                  set PCRE2_CASELESS
             dollar_endonly            set PCRE2_DOLLAR_ENDONLY
         /s  dotall                    set PCRE2_DOTALL
             dupnames                  set PCRE2_DUPNAMES
             endanchored               set PCRE2_ENDANCHORED
         /x  extended                  set PCRE2_EXTENDED
         /xx extended_more             set PCRE2_EXTENDED_MORE
             firstline                 set PCRE2_FIRSTLINE
             literal                   set PCRE2_LITERAL
             match_line                set PCRE2_EXTRA_MATCH_LINE
             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  information  about  the
       pattern.  There are single-letter abbreviations for some that are heavily used in the test

             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_length=<n>    set the maximum pattern length
             memory                    show memory used
             newline=<type>            set newline type
             null_context              compile with a NULL context
             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]            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 Unicode.

       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

       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 different internal link  sizes  and  different  code
       unit  widths.  By  using  bincode,  the  same  regression  tests  can be used in different

       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
         Capturing subpattern 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
         Capturing subpattern 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 framesize  modifier  shows  the  size,  in  bytes,  of  the  storage  frames  used  by
       pcre2_match()  for  handling  backtracking.  The  size  depends on the number of capturing
       parentheses in the pattern.

       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 information that is requested. For each
       callout, either its number or string is given, followed by the item that follows it in the

   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).

   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 interpreted as pairs of hexadecimal digits.
       This feature is provided as a way of creating patterns that contain binary zeros and other
       non-printing 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 hexadecimal:

         /ab "literal" 32/hex

       Either single or double quotes may be used. There is no way  of  including  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-terminated strings but
       can be passed by length instead of being zero-terminated. 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 zeros.

       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 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 creating 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


       are expanded before the pattern is passed to pcre2_compile(). For example, \[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 recognized 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 optionally 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 complete 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 automatically be used when an
       appropriate type of match is run, except when incompatible 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  sanity  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 compilation 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:


       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_compile() 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  character  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 pattern 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 error.  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).

   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 documentation.  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:


       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 below. 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  default,  but  if  the
       use_length or hex modifiers are set, the REG_PEND extension is used to pass it by length.

   Testing the stack guard feature

       The  stackguard modifier is used to test the use of pcre2_set_compile_recursion_guard(), a
       function that is provided to enable stack availability to be  checked  during  compilation
       (see  the  pcre2api documentation 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, or 2. 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 tables as follows:

         0   do not pass any special character tables
         1   the default ASCII tables, as distributed in
         2   a set of tables defining ISO 8859 characters

       In table 2, some characters whose codes are greater than 128 are  identified  as  letters,
       digits,  spaces,  etc.  Setting  alternate  character  tables  and  a  locale are mutually

   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 subject 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
             allusedtext                show all consulted text
             altglobal                  alternative global matching
         /g  global                     global matching
             jitstack=<n>               set size of JIT stack
             mark                       show mark values
             replace=<string>           specify a replacement string
             startchar                  show starting character when relevant
             substitute_extended        use PCRE2_SUBSTITUTE_EXTENDED
             substitute_overflow_length use PCRE2_SUBSTITUTE_OVERFLOW_LENGTH
             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  subject  lines  that  it
       matches  are  taken  as  literal strings, with no interpretation 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  patterns"
       below.   If  pushcopy  is used instead of push, a copy of the compiled 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
       incompatible 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-separated 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   pattern   is   passed   to
       pcre2_pattern_convert().  If  the conversion is successful, 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

       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 processing, overriding the defaults, which are
       operating-system dependent.


       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
             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, causing the POSIX wrapper
       API  to  be  used,  the  only  option-setting  modifiers  that have any effect are notbol,
       notempty, and noteol, causing REG_NOTBOL, 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 wrapper. It is ignored
       (with a warning) if used for non-POSIX matching.


       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_STARTEND,  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_startend to specify its length.

   Setting match controls

       The  following  modifiers  affect  the matching process or request additional 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.

             aftertext                  show text after match
             allaftertext               show text after captures
             allcaptures                show all captures
             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 match and depth limits
             get=<number or name>       extract captured substring
             getall                     extract all captured substrings
         /g  global                     global matching
             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
             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_extedded        use PCRE2_SUBSTITUTE_EXTENDED
             substitute_overflow_length use PCRE2_SUBSTITUTE_OVERFLOW_LENGTH
             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 modifiers 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 substrings
       as well as the main matched substring. In  each  case  the  remainder  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. 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 lookbehind  at  the  start  of  a  match,  or  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 output by '<' or '>' characters
       underneath them. Here is an example:

           re> /(?<=pqr)abc(?=xyz)/
         data> 123pqrabcxyz456\=allusedtext
          0: pqrabcxyz
             <<<   >>>

       This  shows  that  the  matched  string is "abc", with the preceding and following strings
       "pqr" and "xyz" having been consulted during the match (when processing the assertions).

       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 example:

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

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

   Showing the value of all capture groups

       The allcaptures modifier requests that the values of all potential captured 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); it is ignored, with a warning message, if present.

   Testing callouts

       A callout function is supplied when pcre2test calls the library matching 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.

   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 lookbehind 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 retried. This imitates the way Perl handles such cases when using the /g modifier
       or the split() function. Normally, the start offset is advanced by one character,  but  if
       the  newline  convention  recognizes  CRLF  as  a newline, and the current character is CR
       followed by LF, an advance of two characters occurs.

   Testing substring extraction functions

       The copy and get  modifiers  can  be  used  to  test  the  pcre2_substring_copy_xxx()  and
       pcre2_substring_get_xxx()  functions.   They  can  be  given  more than once, and each can
       specify a group name or number, for example:


       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 numbered groups and an empty name to cancel
       all named groups.

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

       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. Note that replacement strings cannot contain commas, because  a
       comma  signifies  the  end  of  a  modifier.  This is not thought to be an issue in a test

       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 provides 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

         global                      PCRE2_SUBSTITUTE_GLOBAL
         substitute_extended         PCRE2_SUBSTITUTE_EXTENDED
         substitute_overflow_length  PCRE2_SUBSTITUTE_OVERFLOW_LENGTH
         substitute_unknown_unset    PCRE2_SUBSTITUTE_UNKNOWN_UNSET
         substitute_unset_empty      PCRE2_SUBSTITUTE_UNSET_EMPTY

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

          1: =xxx=abc=
          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 replacement string starting at the next character. Here is an example that tests
       the edge case:

          1: 123XYZ123
         Failed: error -47: no more memory

       The default action of pcre2_substitute() is to return PCRE2_ERROR_NOMEMORY when the output
       buffer  is  too  small. However, if the PCRE2_SUBSTITUTE_OVERFLOW_LENGTH option is set (by
       using the substitute_overflow_length modifier), pcre2_substitute() continues to go through
       the  motions  of matching and substituting, 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:

         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().

   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 appropriate limits in the
       match context. These values are ignored when the find_limits 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  minimum values for each parameter that allows the match to complete without error. If
       JIT is being used, only the match limit is relevant.

       When using this modifier, the pattern should  not  contain  any  limit  settings  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 function, 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. A value of zero disables the
       use of any heap memory; many simple pattern matches can be done without using the heap, so
       zero is not an unreasonable setting.

   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  memory  allocation  and
       freeing  calls that occur during a call to pcre2_match() or pcre2_dfa_match(). These occur
       only when a match requires a bigger vector than the default for  remembering  backtracking
       points  (pcre2_match()) or for internal workspace (pcre2_dfa_match()). In many cases there
       will be no heap memory used  and  therefore  no  additional  output.  No  heap  memory  is
       allocated  during  matching  with  JIT,  so in that case the memory modifier never has any
       effect. 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.

   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  modifier  must  have  been  set  for  the  pattern;  if not, an error is

   Setting the size of the output vector

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

       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_create_from_pattern() to be called, in order to create a match
       block of exactly the right size for the pattern. (It is not possible  to  create  a  match
       block with a zero-length ovector; there is always at least one pair of offsets.)

   Passing the subject as zero-terminated

       By  default,  the  subject  string  is  passed  to a native API matching function 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

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


       By default, pcre2test uses the standard PCRE2 matching function,  pcre2_match()  to  match
       each   subject   line.   PCRE2   also   supports   an   alternative   matching   function,
       pcre2_dfa_match(), which operates in a different  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 subject. If, however, the  dfa_shortest
       modifier  is  set,  processing  stops  after  the first match is found. This is always the
       shortest possible match.


       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 substrings, starting with
       number 0 for the string that matched the whole pattern.  Otherwise, it outputs "No  match"
       when  the  return  is  PCRE2_ERROR_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  definition  of  non-printing  characters. If the aftertext
       modifier is set, the output for substring 0 is followed by the 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 attempts 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).


       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). After a PCRE2_ERROR_PARTIAL return, the
       output is "Partial match:", followed 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.


       When   the  alternative  matching  function  has  given  the  PCRE2_ERROR_PARTIAL  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\=P,dfa
         Partial match: 23ja
         data> n05\=dfa,dfa_restart
          0: n05

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


       If  the  pattern  contains  any  callout  requests, pcre2test's callout function 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 arguments 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:

           0    ^  ^     \d

       This output indicates that callout number 0 occurred for a match attempt 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
       positions  are the same, or if the current position precedes the start position, 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*
          +0 ^      \d?
          +3 ^      [A-E]
          +8 ^^     \*
         +10 ^ ^
          0: E*

       If a pattern contains (*MARK) items, an additional line is output  whenever  a  change  of
       latest mark is passed to the callout function. For example:

           re> /a(*MARK:X)bc/auto_callout
         data> 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 before 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'
             ^ ^         c
         Callout (20): "second"
             ^   ^       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
       callout  (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
          +0 ^       (
          +1 ^       a+
          +3 ^ ^     )
          +4 ^ ^     b
          +3 ^^      )
          +4 ^^      b
         No other matching paths
         New match attempt
          +0  ^      (
          +1  ^      a+
          +3  ^^     )
          +4  ^^     b
         No other matching paths
         New match attempt
          +0   ^     (
          +1   ^     a+
         No other matching paths
         New match attempt
          +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 backtracks.

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

   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 (causing 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,  causing  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 number.  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  complicated  regular
       expressions. For further information about callouts, see the pcre2callout documentation.


       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

       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 isprint() function is used to distinguish printing and non-
       printing characters.


       It is possible to save compiled patterns on disc or  elsewhere,  and  reload  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, converted to a stream  of
       bytes. A single byte stream may contain any number of compiled patterns, but they must all
       use the same character tables. 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 serializing 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 compiled, 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 immediate
       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-serialized, with the
       resulting compiled patterns added to the pattern stack. The pattern  on  the  top  of  the
       stack  can  be  retrieved by the #pop command, 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  allowed, nor are any option-setting modifiers.  The JIT modifiers
       are, however permitted. Here is an example that saves and reloads two patterns.

         #save tempfile
         #load tempfile
         #pop info

         #pop jit,bincode

       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 analagous to the pushcopy modifier in that it makes current a copy
       of the topmost stack pattern, leaving the original still on the stack.


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


       Philip Hazel
       University Computing Service
       Cambridge, England.


       Last updated: 21 July 2018
       Copyright (c) 1997-2018 University of Cambridge.