pcretest.txt

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The pcretest program
--------------------

This program is intended for testing PCRE, but it can also be used for
experimenting with regular expressions.

If it 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. 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

  /(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. See the test input files in the testdata directory for many
examples. 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-alphameric, 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.

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:

  /caseless/i

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

  /pattern/Lfr

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.

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.

Finally, 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.

Before each data line is passed to pcre_exec(), leading and trailing whitespace
is removed, and it is then scanned for \ escapes. The following 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)

  \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)
  \Gdd   call pcre_get_substring() for substring dd after a successful match
           (any decimal number less than 32)
  \L     call pcre_get_substringlist() after a successful match
  \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 digits)
  \Z     pass the PCRE_NOTEOL option to pcre_exec()

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.

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 2.06 08-Jun-1999

    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. 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 \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.

If the -p option is given to pcretest, it is equivalent to adding /P to each
regular expression: the POSIX wrapper API is used to call PCRE. None of the
following flags has any effect in this case.

If the option -d is given to pcretest, it is equivalent to adding /D to each
regular expression: the internal form is output after compilation.

If the option -i is given to pcretest, it is equivalent to adding /I to each
regular expression: information about the compiled pattern is given after
compilation.

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

If the -t option is given, each compile, study, and match is run 20000 times
while being timed, and the resulting time per compile or match is output in
milliseconds. Do not set -t with -s, because you will then get the size output
20000 times and the timing will be distorted. If you want to change the number
of repetitions used for timing, edit the definition of LOOPREPEAT at the top of
pcretest.c

Philip Hazel <[e-mail]>
January 2000