path: root/doc/doc-txt/pcretest.txt

This file contains the PCRE man page that described the pcretest program. Note
that not all of the features of PCRE are available in the limited version that
is built with Exim.
-------------------------------------------------------------------------------

PCRETEST(1)                                                        PCRETEST(1)


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


SYNOPSIS

       pcretest [options] [source] [destination]

       pcretest  was written as a test program for the PCRE regular expression
       library itself, 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  pcrepattern
       documentation. For details of the PCRE library function calls and their
       options, see the pcreapi documentation.


OPTIONS

       -C        Output the version number of the PCRE library, and all avail-
                 able   information  about  the  optional  features  that  are
                 included, and then exit.

       -d        Behave as if each regex has  the  /D  (debug)  modifier;  the
                 internal form is output after compilation.

       -dfa      Behave  as if each data line contains the \D escape sequence;
                 this    causes    the    alternative    matching    function,
                 pcre_dfa_exec(),   to   be   used  instead  of  the  standard
                 pcre_exec() function (more detail is given below).

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

       -m        Output  the  size  of each compiled pattern after it has been
                 compiled. This is equivalent to adding  /M  to  each  regular
                 expression.   For  compatibility  with  earlier  versions  of
                 pcretest, -s is a synonym for -m.

       -o osize  Set the number of elements in the output vector that is  used
                 when  calling  pcre_exec()  to be osize. The default value is
                 45, which is enough for 14 capturing subexpressions. The vec-
                 tor  size  can  be  changed  for individual matching calls by
                 including \O in the data line (see below).

       -p        Behave as if each regex has the /P modifier; the POSIX  wrap-
                 per  API  is used to call PCRE. None of the other options has
                 any effect when -p is set.

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

       -S size   On  Unix-like  systems,  set the size of the runtime stack to
                 size megabytes.

       -t        Run each compile, study, and match many times with  a  timer,
                 and  output resulting time per compile or match (in millisec-
                 onds). Do not set -m with -t, because you will then  get  the
                 size  output  a  zillion  times,  and the timing will be dis-
                 torted.


DESCRIPTION

       If pcretest is given two filename arguments, it reads  from  the  first
       and writes to the second. If it is given only one filename argument, it
       reads from that file and writes to stdout.  Otherwise,  it  reads  from
       stdin  and  writes to stdout, and prompts for each line of input, using
       "re>" to prompt for regular expressions, and "data>" to prompt for data
       lines.

       The program handles any number of sets of input on a single input file.
       Each set starts with a regular expression, and continues with any  num-
       ber of data lines to be matched against the pattern.

       Each  data 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,  depending  on  the newline setting) in a single line of input to
       encode the newline characters. There is no limit on the length of  data
       lines; the input buffer is automatically extended if it is too small.

       An  empty  line signals the end of the data lines, at which point a new
       regular expression is read. The regular expressions are given  enclosed
       in any non-alphanumeric delimiters other than backslash, for example:

         /(a|bc)x+yz/

       White  space before the initial delimiter is ignored. A regular expres-
       sion may be continued over several input lines, in which case the  new-
       line  characters  are included within it. It is possible to include the
       delimiter within the pattern by escaping it, for example

         /abc\/def/

       If you do so, the escape and the delimiter form part  of  the  pattern,
       but  since delimiters are always 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 pcretest to read the next line as a continuation of the regular
       expression.


PATTERN MODIFIERS

       A  pattern may be followed by any number of modifiers, which are mostly
       single characters. Following Perl usage, these are  referred  to  below
       as,  for  example,  "the /i modifier", even though the delimiter of the
       pattern need not always be a slash, and no slash is used  when  writing
       modifiers.  Whitespace  may  appear between the final pattern delimiter
       and the first modifier, and between the modifiers themselves.

       The /i, /m, /s, and /x modifiers set the PCRE_CASELESS, PCRE_MULTILINE,
       PCRE_DOTALL,  or  PCRE_EXTENDED  options,  respectively, when pcre_com-
       pile() is called. These four modifier letters have the same  effect  as
       they do in Perl. For example:

         /caseless/i

       The following table shows additional modifiers for setting PCRE options
       that do not correspond to anything in Perl:

         /A       PCRE_ANCHORED
         /C       PCRE_AUTO_CALLOUT
         /E       PCRE_DOLLAR_ENDONLY
         /f       PCRE_FIRSTLINE
         /J       PCRE_DUPNAMES
         /N       PCRE_NO_AUTO_CAPTURE
         /U       PCRE_UNGREEDY
         /X       PCRE_EXTRA
         /<cr>    PCRE_NEWLINE_CR
         /<lf>    PCRE_NEWLINE_LF
         /<crlf>  PCRE_NEWLINE_CRLF

       Those specifying line endings are literal strings as shown. Details  of
       the  meanings of these PCRE options are given in the pcreapi documenta-
       tion.

   Finding all matches in a string

       Searching for all possible matches within each subject  string  can  be
       requested  by  the  /g  or  /G modifier. After finding a match, PCRE is
       called again to search the remainder of the subject string. The differ-
       ence between /g and /G is that the former uses the startoffset argument
       to pcre_exec() to start searching at a  new  point  within  the  entire
       string  (which  is in effect what Perl does), whereas the latter passes
       over a shortened substring. This makes a  difference  to  the  matching
       process if the pattern begins with a lookbehind assertion (including \b
       or \B).

       If any call to pcre_exec() in a /g or  /G  sequence  matches  an  empty
       string,  the next call is done with the PCRE_NOTEMPTY and PCRE_ANCHORED
       flags set in order to search for another, non-empty, match at the  same
       point.   If  this  second  match fails, the start offset is advanced by
       one, and the normal match is retried. This imitates the way  Perl  han-
       dles such cases when using the /g modifier or the split() function.

   Other modifiers

       There are yet more modifiers for controlling the way pcretest operates.

       The /+ modifier requests that as well as outputting the substring  that
       matched  the  entire  pattern,  pcretest  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  /L modifier must be followed directly by the name of a locale, for
       example,

         /pattern/Lfr_FR

       For this reason, it must be the last modifier. The given locale is set,
       pcre_maketables()  is called to build a set of character tables for the
       locale, and this is then passed to pcre_compile()  when  compiling  the
       regular  expression.  Without  an  /L  modifier,  NULL is passed as the
       tables pointer; that is, /L applies only to the expression on which  it
       appears.

       The  /I  modifier  requests  that pcretest output information about the
       compiled pattern (whether it is anchored, has a fixed first  character,
       and  so  on). It does this by calling pcre_fullinfo() after compiling a
       pattern. If the pattern is studied, the results of that are  also  out-
       put.

       The /D modifier is a PCRE debugging feature, which also assumes /I.  It
       causes the internal form of compiled regular expressions to  be  output
       after compilation. If the pattern was studied, the information returned
       is also output.

       The /F modifier causes pcretest to flip the byte order of the fields in
       the  compiled  pattern  that  contain  2-byte  and 4-byte numbers. This
       facility is for testing the feature in PCRE that allows it  to  execute
       patterns that were compiled on a host with a different endianness. This
       feature is not available when the POSIX  interface  to  PCRE  is  being
       used,  that is, when the /P pattern modifier is specified. See also the
       section about saving and reloading compiled patterns below.

       The /S modifier causes pcre_study() to be called after  the  expression
       has been compiled, and the results used when the expression is matched.

       The /M modifier causes the size of memory block used to hold  the  com-
       piled pattern to be output.

       The  /P modifier causes pcretest to call PCRE via the POSIX wrapper API
       rather than its native API. When this  is  done,  all  other  modifiers
       except  /i,  /m, and /+ are ignored. REG_ICASE is set if /i is present,
       and REG_NEWLINE is set if /m is present. The  wrapper  functions  force
       PCRE_DOLLAR_ENDONLY  always, and PCRE_DOTALL unless REG_NEWLINE is set.

       The /8 modifier causes pcretest to call PCRE with the PCRE_UTF8  option
       set.  This  turns on support for UTF-8 character handling in PCRE, pro-
       vided that it was compiled with this  support  enabled.  This  modifier
       also causes any non-printing characters in output strings to be printed
       using the \x{hh...} notation if they are valid UTF-8 sequences.

       If the /? modifier  is  used  with  /8,  it  causes  pcretest  to  call
       pcre_compile()  with  the  PCRE_NO_UTF8_CHECK  option,  to suppress the
       checking of the string for UTF-8 validity.


DATA LINES

       Before each data line is passed to pcre_exec(),  leading  and  trailing
       whitespace  is  removed,  and it is then scanned for \ escapes. Some of
       these are pretty esoteric features, intended for checking out  some  of
       the  more  complicated features of PCRE. If you are just testing "ordi-
       nary" regular expressions, you probably don't need any  of  these.  The
       following escapes are recognized:

         \a         alarm (= BEL)
         \b         backspace
         \e         escape
         \f         formfeed
         \n         newline
         \qdd       set the PCRE_MATCH_LIMIT limit to dd
                      (any number of digits)
         \r         carriage return
         \t         tab
         \v         vertical tab
         \nnn       octal character (up to 3 octal digits)
         \xhh       hexadecimal character (up to 2 hex digits)
         \x{hh...}  hexadecimal character, any number of digits
                      in UTF-8 mode
         \A         pass the PCRE_ANCHORED option to pcre_exec()
                      or pcre_dfa_exec()
         \B         pass the PCRE_NOTBOL option to pcre_exec()
                      or pcre_dfa_exec()
         \Cdd       call pcre_copy_substring() for substring dd
                      after a successful match (number less than 32)
         \Cname     call pcre_copy_named_substring() for substring
                      "name" after a successful match (name termin-
                      ated by next non alphanumeric character)
         \C+        show the current captured substrings at callout
                      time
         \C-        do not supply a callout function
         \C!n       return 1 instead of 0 when callout number n is
                      reached
         \C!n!m     return 1 instead of 0 when callout number n is
                      reached for the nth time
         \C*n       pass the number n (may be negative) as callout
                      data; this is used as the callout return value
         \D         use the pcre_dfa_exec() match function
         \F         only shortest match for pcre_dfa_exec()
         \Gdd       call pcre_get_substring() for substring dd
                      after a successful match (number less than 32)
         \Gname     call pcre_get_named_substring() for substring
                      "name" after a successful match (name termin-
                      ated by next non-alphanumeric character)
         \L         call pcre_get_substringlist() after a
                      successful match
         \M         discover the minimum MATCH_LIMIT and
                      MATCH_LIMIT_RECURSION settings
         \N         pass the PCRE_NOTEMPTY option to pcre_exec()
                      or pcre_dfa_exec()
         \Odd       set the size of the output vector passed to
                      pcre_exec() to dd (any number of digits)
         \P         pass the PCRE_PARTIAL option to pcre_exec()
                      or pcre_dfa_exec()
         \Qdd       set the PCRE_MATCH_LIMIT_RECURSION limit to dd
                      (any number of digits)
         \R         pass the PCRE_DFA_RESTART option to pcre_dfa_exec()
         \S         output details of memory get/free calls during matching
         \Z         pass the PCRE_NOTEOL option to pcre_exec()
                      or pcre_dfa_exec()
         \?         pass the PCRE_NO_UTF8_CHECK option to
                      pcre_exec() or pcre_dfa_exec()
         \>dd       start the match at offset dd (any number of digits);
                      this sets the startoffset argument for pcre_exec()
                      or pcre_dfa_exec()
         \<cr>      pass the PCRE_NEWLINE_CR option to pcre_exec()
                      or pcre_dfa_exec()
         \<lf>      pass the PCRE_NEWLINE_LF option to pcre_exec()
                      or pcre_dfa_exec()
         \<crlf>    pass the PCRE_NEWLINE_CRLF option to pcre_exec()
                      or pcre_dfa_exec()

       The  escapes  that specify line endings are literal strings, exactly as
       shown.  A backslash followed by anything else just escapes the anything
       else.  If  the  very last character is a backslash, it is ignored. This
       gives a way of passing an empty line as data, since a real  empty  line
       terminates the data input.

       If  \M  is present, pcretest calls pcre_exec() several times, with dif-
       ferent values in the match_limit and  match_limit_recursion  fields  of
       the  pcre_extra  data structure, until it finds the minimum numbers for
       each parameter that allow pcre_exec() to complete. The match_limit num-
       ber  is  a  measure of the amount of backtracking that takes place, and
       checking it out 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. The match_limit_recursion number is a measure of how
       much stack (or, if PCRE is compiled with  NO_RECURSE,  how  much  heap)
       memory is needed to complete the match attempt.

       When  \O  is  used, the value specified may be higher or lower than the
       size set by the -O command line option (or defaulted to 45); \O applies
       only to the call of pcre_exec() for the line in which it appears.

       If  the /P modifier was present on the pattern, causing the POSIX wrap-
       per API to be used, the only option-setting  sequences  that  have  any
       effect  are \B and \Z, causing REG_NOTBOL and REG_NOTEOL, respectively,
       to be passed to regexec().

       The use of \x{hh...} to represent UTF-8 characters is not dependent  on
       the  use  of  the  /8 modifier on the pattern. It is recognized always.
       There may be any number of hexadecimal digits inside  the  braces.  The
       result  is from one to six bytes, encoded according to the UTF-8 rules.


THE ALTERNATIVE MATCHING FUNCTION

       By  default,  pcretest  uses  the  standard  PCRE  matching   function,
       pcre_exec() to match each data line. From release 6.0, PCRE supports an
       alternative matching function, pcre_dfa_test(),  which  operates  in  a
       different  way,  and has some restrictions. The differences between the
       two functions are described in the pcrematching documentation.

       If a data line contains the \D escape sequence, or if the command  line
       contains  the -dfa option, the alternative matching function is called.
       This function finds all possible matches at a given point. If, however,
       the  \F escape sequence is present in the data line, it stops after the
       first match is found. This is always the shortest possible match.


DEFAULT OUTPUT FROM PCRETEST

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

       When a match succeeds, pcretest outputs the list of captured substrings
       that pcre_exec() returns, starting with number 0 for  the  string  that
       matched the whole pattern. Otherwise, it outputs "No match" or "Partial
       match" when pcre_exec() returns PCRE_ERROR_NOMATCH  or  PCRE_ERROR_PAR-
       TIAL,  respectively, and otherwise the PCRE negative error number. Here
       is an example of an interactive pcretest run.

         $ pcretest
         PCRE version 5.00 07-Sep-2004

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

       If the strings contain any non-printing characters, they are output  as
       \0x  escapes,  or  as \x{...} escapes if the /8 modifier was present on
       the pattern. If the pattern has the /+ modifier, the  output  for  sub-
       string  0 is followed by the the rest of the subject string, identified
       by "0+" like this:

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

       If the pattern has the /g or /G modifier,  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.

       If  any  of the sequences \C, \G, or \L are present in a data line that
       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 paren-
       theses after each string for \C and \G.

       Note that while patterns can be continued over several lines  (a  plain
       ">" prompt is used for continuations), data lines may not. However new-
       lines can be included in data by means of the \n escape (or \r or  \r\n
       for those newline settings).


OUTPUT FROM THE ALTERNATIVE MATCHING FUNCTION

       When  the  alternative  matching function, pcre_dfa_exec(), is used (by
       means of the \D escape sequence or the -dfa command line  option),  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\D
          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).

       If /gP is present on  the  pattern,  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\D
          0: tangerine
          1: tang
          2: tan
          0: tang
          1: tan
          0: tan

       Since  the  matching  function  does not support substring capture, the
       escape sequences that are concerned with captured  substrings  are  not
       relevant.


RESTARTING AFTER A PARTIAL MATCH

       When the alternative matching function has given the PCRE_ERROR_PARTIAL
       return, indicating that the subject partially matched the pattern,  you
       can  restart  the match with additional subject data by means of the \R
       escape sequence. For example:

           re> /^?(jan|feb|mar|apr|may|jun|jul|aug|sep|oct|nov|dec)$/
         data> 23ja\P\D
         Partial match: 23ja
         data> n05\R\D
          0: n05

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


CALLOUTS

       If  the pattern contains any callout requests, pcretest's callout func-
       tion is called during matching. This works  with  both  matching  func-
       tions. By default, the called function displays the callout number, the
       start and current positions in the text at the callout  time,  and  the
       next pattern item to be tested. For example, the output

         --->pqrabcdef
           0    ^  ^     \d

       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 of the data, and when the next pattern item was
       \d. Just one circumflex is output if the start  and  current  positions
       are the same.

       Callouts numbered 255 are assumed to be automatic callouts, inserted as
       a result of the /C 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]\*/C
         data> E*
         --->E*
          +0 ^      \d?
          +3 ^      [A-E]
          +8 ^^     \*
         +10 ^ ^
          0: E*

       The callout function in pcretest returns zero (carry  on  matching)  by
       default,  but you can use a \C item in a data line (as described above)
       to change this.

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


SAVING AND RELOADING COMPILED PATTERNS

       The facilities described in this section are  not  available  when  the
       POSIX inteface to PCRE is being used, that is, when the /P pattern mod-
       ifier is specified.

       When the POSIX interface is not in use, you can cause pcretest to write
       a  compiled  pattern to a file, by following the modifiers with > and a
       file name.  For example:

         /pattern/im >/some/file

       See the pcreprecompile documentation for a discussion about saving  and
       re-using compiled patterns.

       The  data  that  is  written  is  binary. The first eight bytes are the
       length of the compiled pattern data  followed  by  the  length  of  the
       optional  study  data,  each  written as four bytes in big-endian order
       (most significant byte first). If there is no study  data  (either  the
       pattern was not studied, or studying did not return any data), the sec-
       ond length is zero. The lengths are followed by an exact  copy  of  the
       compiled pattern. If there is additional study data, this follows imme-
       diately after the compiled pattern. After writing  the  file,  pcretest
       expects to read a new pattern.

       A saved pattern can be reloaded into pcretest by specifing < and a file
       name instead of a pattern. The name of the file must not  contain  a  <
       character,  as  otherwise pcretest will interpret the line as a pattern
       delimited by < characters.  For example:

          re> </some/file
         Compiled regex loaded from /some/file
         No study data

       When the pattern has been loaded, pcretest proceeds to read data  lines
       in the usual way.

       You  can copy a file written by pcretest to a different host and reload
       it there, even if the new host has opposite endianness to  the  one  on
       which  the pattern was compiled. For example, you can compile on an i86
       machine and run on a SPARC machine.

       File names for saving and reloading can be absolute  or  relative,  but
       note  that the shell facility of expanding a file name that starts with
       a tilde (~) is not available.

       The ability to save and reload files in pcretest is intended for  test-
       ing  and experimentation. It is not intended for production use because
       only a single pattern can be written to a file. Furthermore,  there  is
       no  facility  for  supplying  custom  character  tables  for use with a
       reloaded pattern. If the original  pattern  was  compiled  with  custom
       tables,  an  attempt to match a subject string using a reloaded pattern
       is likely to cause pcretest to crash.  Finally, if you attempt to  load
       a file that is not in the correct format, the result is undefined.


AUTHOR

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

Last updated: 29 June 2006
Copyright (c) 1997-2006 University of Cambridge.