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Note that not all of the features of PCRE are relevant in the context of Exim. In particular, the version of PCRE that is compiled with Exim does not include UTF-8 support, there is no mechanism for changing the options with which the PCRE functions are called, and features such as callout are not accessible.


pcretest [-d] [-i] [-m] [-o osize] [-p] [-t] [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 PCRE and its options, see the pcreapi documentation.


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

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

-i Behave as if each regex had 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 to be osize. The default value is 45, which is enough for 14 capturing subexpressions. The vector size can be changed for individual matching calls by including \O in the data line (see below).

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

-t Run each compile, study, and match many times with a timer, and output resulting time per compile or match (in milliseconds). Do not set -t with -m, because you will then get the size output 20000 times and the timing will be distorted.


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 number of data lines to be matched against the pattern.

Each line is matched separately and independently. If you want to do multiple-line matches, you have to use the \n escape sequence in a single line of input to encode the newline characters. The maximum length of data line is 30,000 characters.

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-alphameric delimiters other than backslash, for example


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


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


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


is interpreted as the first line of a pattern that starts with "abc/", causing pcretest to read the next line as a continuation of the regular expression.


The pattern may be followed by i, m, s, or x to set the PCRE_CASELESS, PCRE_MULTILINE, PCRE_DOTALL, or PCRE_EXTENDED options, respectively. For example:


These modifier letters have the same effect as they do in Perl. There are others that set PCRE options that do not correspond to anything in Perl: /A, /E, /N, /U, and /X set PCRE_ANCHORED, PCRE_DOLLAR_ENDONLY, PCRE_NO_AUTO_CAPTURE, PCRE_UNGREEDY, and PCRE_EXTRA respectively.

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 difference 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 handles such cases when using the /g modifier or the split() function.

There are a number of other 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,


For this reason, it must be the last modifier letter. 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 expression (whether it is anchored, has a fixed first character, and so on). It does this by calling pcre_fullinfo() after compiling an expression, and outputting the information it gets back. If the pattern is studied, the results of that are also output.

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 /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 compiled 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, provided 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.


If the pattern contains any callout requests, pcretest's callout function will be called. By default, it displays the callout number, and the start and current positions in the text at the callout time. For example, the output

    0    ^  ^

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. The callout function returns zero (carry on matching) by default.

Inserting callouts may be helpful when using pcretest to check complicated regular expressions. For further information about callouts, see the pcrecallout documentation.

For testing the PCRE library, additional control of callout behaviour is available via escape sequences in the data, as described in the following section. In particular, it is possible to pass in a number as callout data (the default is zero). If the callout function receives a non-zero number, it returns that value instead of zero.


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 "ordinary" 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
  \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()
  \B         pass the PCRE_NOTBOL option to pcre_exec()
  \Cdd       call pcre_copy_substring() for substring dd
               after a successful match (any decimal 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
  \C-        do not supply a callout function
  \C!n       return 1 instead of 0 when callout number n is
  \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
  \Gdd       call pcre_get_substring() for substring dd
               after a successful match (any decimal 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 setting
  \N         pass the PCRE_NOTEMPTY option to pcre_exec()
  \Odd       set the size of the output vector passed to
               pcre_exec() to dd (any number of decimal
  \S         output details of memory get/free calls during matching
  \Z         pass the PCRE_NOTEOL option to pcre_exec()
  \?         pass the PCRE_NO_UTF8_CHECK option to

If \M is present, pcretest calls pcre_exec() several times, with different values in the match_limit field of the pcre_extra data structure, until it finds the minimum number that is needed for pcre_exec() to complete. This number is a measure of the amount of recursion and 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.

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

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 /P was present on the regex, causing the POSIX wrapper API to be used, only \B, and \Z have any effect, causing REG_NOTBOL and REG_NOTEOL to be passed to regexec() respectively.

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.


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. Here is an example of an interactive pcretest run.

  $ pcretest
  PCRE version 4.00 08-Jan-2003

    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, then the output for substring 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 parentheses 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 newlines can be included in data by means of the \n escape.


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

Last updated: 09 December 2003
Copyright © 1997-2003 University of Cambridge.