DESCRIPTION

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(3) documentation. For details of the PCRE library function calls and their options, see the pcreapi(3) documentation.

OPTIONS

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.

When pcretest is built, a configuration option can specify that it should be linked with the libreadline 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 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 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, 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 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 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

/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 followed 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_compile() 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:

Those specifying line ending sequences are literal strings as shown, but the letters can be in either case. This example sets multiline matching with CRLF as the line ending sequence:

/^abc/m<crlf>

Details of the meanings of these PCRE options are given in the pcreapi(3) documentation.

/pattern/Lfr_FR

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 "ordinary" regular expressions, you probably don't need any of these. The following escapes are recognized:

The escapes that specify line ending sequences are literal strings, exactly as shown. No more than one newline setting should be present in any data line.

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 different 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 number 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 wrapper 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 original UTF-8 rules of RFC 2279. This allows for values in the range 0 to 0x7FFFFFFF. Note that not all of those are valid Unicode code points, or indeed valid UTF-8 characters according to the later rules in RFC 3629.

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(3) 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_PARTIAL, respectively, and otherwise the PCRE negative error number. Here is an example of an interactive pcretest run.

 $ pcretest
 PCRE version 7.0 30-Nov-2006

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

Note that unset capturing substrings that are not followed by one that is set are not returned by pcre_exec(), and are not shown by pcretest. 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 \0x escapes, or as \x{...} escapes if the /8 modifier was present on the pattern. See below for the definition of non-printing characters. If the pattern has the /+ modifier, 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 whereas 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 (or \r, \r\n, etc., depending on the newline sequence setting).

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

For further information about partial matching, see the pcrepartial(3) documentation.

CALLOUTS

If the pattern contains any callout requests, pcretest's callout function is called during matching. This works with both matching functions. 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 complicated regular expressions. For further information about callouts, see the pcrecallout(3) documentation.

NON-PRINTING CHARACTERS

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

When pcretest 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 /L modifier). In this case, the isprint() function to distinguish printing and non-printing characters.

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 modifier 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(3) 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 second length is zero. The lengths are followed by an exact copy of the compiled pattern. If there is additional study data, this follows immediately 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 testing 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.

SEE ALSO

pcre(3), pcreapi(3), pcrecallout(3), pcrematching(3), pcrepartial(d), pcrepattern(3), pcreprecompile(3).

AUTHOR

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

REVISION

Last updated: 18 December 2007
Copyright (c) 1997-2007 University of Cambridge.