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PCRETEST(1) PCRETEST(1)
NAME
pcretest - a program for testing Perl-compatible regular expressions.
SYNOPSIS
pcretest [-C] [-d] [-dfa] [-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 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.
-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 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-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
/N PCRE_NO_AUTO_CAPTURE
/U PCRE_UNGREEDY
/X PCRE_EXTRA
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.
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
\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 (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()
\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()
\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()
\? pass the PCRE_NO_UTF8_CHECK option to
pcre_exec()
\>dd start the match at offset dd (any number of digits);
this sets the startoffset argument for 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 termi-
nates 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.
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> 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: 18 January 2006
Copyright (c) 1997-2006 University of Cambridge.
PCRETEST(1)
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