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✏️ Editing: pcre2test.txt

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
       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  func-
       tion  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.

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
       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 struc-
       tures  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 ENCODING

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 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 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 com-
                 piled.

-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 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
                 options are ignored. If both -C and -LM are  present,  which-
                 ever 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.

-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 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 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.

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.

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.

#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
       default. 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
       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  subse-
       quent patterns. Modifiers on a pattern can change these settings.

#perltest

The  appearance of this line causes all subsequent modifier settings to
       be checked for compatibility with the perltest.sh 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 perltest.sh. 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 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
       "anchored",  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 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, this does not affect
       its interpretation. If the terminating delimiter  is  immediately  fol-
       lowed by a backslash, for example,

/abc/\

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

/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()   or
       pcre2_dfa_match(), leading and trailing white space is removed, and the
       line is scanned for backslash escapes, unless the subject_literal modi-
       fier 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  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
       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 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.  For  the  main options, there are some single-letter
       abbreviations that are the same as Perl options. There is special  han-
       dling  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 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_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 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
         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 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).

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
       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  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
       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  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
       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  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
       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 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
       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_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, 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 be-
       haviour 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
               pcre2_chartables.c.dist
         2   a set of tables defining ISO 8859 characters

In  table 2, some characters whose codes are greater than 128 are iden-
       tified as letters, digits, spaces,  etc.  Setting  alternate  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
             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  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
       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  subse-
       quent 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
             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.

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 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.
       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 indi-
       cated 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.  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); it is ignored, with a warning
       message, if present.

Testing 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.

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
       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_sub-
       string_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:

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. 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 program.

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_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, 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
       replacement 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_ERROR_NOMEMORY when the output buffer is too small.  However,  if
       the  PCRE2_SUBSTITUTE_OVERFLOW_LENGTH  option is set (by using the sub-
       stitute_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:

/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().

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 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 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. 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 mem-
       ory  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  addi-
       tional output. No heap memory is allocated during matching with JIT, so
       in that case the memory modifier never has any effect. For  this  modi-
       fier  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  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
       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 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 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 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

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.

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_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 defi-
       nition  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).

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).
       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 asser-
       tion, \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\=P,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
       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*
         --->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
       example:

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

SAVING AND RESTORING COMPILED PATTERNS

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, 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
       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  pcre2serial-
       ize  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
       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-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
       allowed,  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 analagous to the pushcopy modifier in  that  it
       makes current a copy of the topmost stack pattern, leaving the original
       still on the stack.

MR SKB