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Contents of /code/trunk/doc/pcretest.txt

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Load pcre-3.2 into code/trunk.
1 The pcretest program
2 --------------------
4 This program is intended for testing PCRE, but it can also be used for
5 experimenting with regular expressions.
7 If it is given two filename arguments, it reads from the first and writes to
8 the second. If it is given only one filename argument, it reads from that file
9 and writes to stdout. Otherwise, it reads from stdin and writes to stdout, and
10 prompts for each line of input, using "re>" to prompt for regular expressions,
11 and "data>" to prompt for data lines.
13 The program handles any number of sets of input on a single input file. Each
14 set starts with a regular expression, and continues with any number of data
15 lines to be matched against the pattern. An empty line signals the end of the
16 data lines, at which point a new regular expression is read. The regular
17 expressions are given enclosed in any non-alphameric delimiters other than
18 backslash, for example
20 /(a|bc)x+yz/
22 White space before the initial delimiter is ignored. A regular expression may
23 be continued over several input lines, in which case the newline characters are
24 included within it. See the test input files in the testdata directory for many
25 examples. It is possible to include the delimiter within the pattern by
26 escaping it, for example
28 /abc\/def/
30 If you do so, the escape and the delimiter form part of the pattern, but since
31 delimiters are always non-alphameric, this does not affect its interpretation.
32 If the terminating delimiter is immediately followed by a backslash, for
33 example,
35 /abc/\
37 then a backslash is added to the end of the pattern. This is done to provide a
38 way of testing the error condition that arises if a pattern finishes with a
39 backslash, because
41 /abc\/
43 is interpreted as the first line of a pattern that starts with "abc/", causing
44 pcretest to read the next line as a continuation of the regular expression.
46 The pattern may be followed by i, m, s, or x to set the PCRE_CASELESS,
47 PCRE_MULTILINE, PCRE_DOTALL, or PCRE_EXTENDED options, respectively. For
48 example:
50 /caseless/i
52 These modifier letters have the same effect as they do in Perl. There are
53 others which set PCRE options that do not correspond to anything in Perl: /A,
54 /E, and /X set PCRE_ANCHORED, PCRE_DOLLAR_ENDONLY, and PCRE_EXTRA respectively.
56 Searching for all possible matches within each subject string can be requested
57 by the /g or /G modifier. After finding a match, PCRE is called again to search
58 the remainder of the subject string. The difference between /g and /G is that
59 the former uses the startoffset argument to pcre_exec() to start searching at
60 a new point within the entire string (which is in effect what Perl does),
61 whereas the latter passes over a shortened substring. This makes a difference
62 to the matching process if the pattern begins with a lookbehind assertion
63 (including \b or \B).
65 If any call to pcre_exec() in a /g or /G sequence matches an empty string, the
66 next call is done with the PCRE_NOTEMPTY and PCRE_ANCHORED flags set in order
67 to search for another, non-empty, match at the same point. If this second match
68 fails, the start offset is advanced by one, and the normal match is retried.
69 This imitates the way Perl handles such cases when using the /g modifier or the
70 split() function.
72 There are a number of other modifiers for controlling the way pcretest
73 operates.
75 The /+ modifier requests that as well as outputting the substring that matched
76 the entire pattern, pcretest should in addition output the remainder of the
77 subject string. This is useful for tests where the subject contains multiple
78 copies of the same substring.
80 The /L modifier must be followed directly by the name of a locale, for example,
82 /pattern/Lfr
84 For this reason, it must be the last modifier letter. The given locale is set,
85 pcre_maketables() is called to build a set of character tables for the locale,
86 and this is then passed to pcre_compile() when compiling the regular
87 expression. Without an /L modifier, NULL is passed as the tables pointer; that
88 is, /L applies only to the expression on which it appears.
90 The /I modifier requests that pcretest output information about the compiled
91 expression (whether it is anchored, has a fixed first character, and so on). It
92 does this by calling pcre_fullinfo() after compiling an expression, and
93 outputting the information it gets back. If the pattern is studied, the results
94 of that are also output.
96 The /D modifier is a PCRE debugging feature, which also assumes /I. It causes
97 the internal form of compiled regular expressions to be output after
98 compilation.
100 The /S modifier causes pcre_study() to be called after the expression has been
101 compiled, and the results used when the expression is matched.
103 The /M modifier causes the size of memory block used to hold the compiled
104 pattern to be output.
106 Finally, the /P modifier causes pcretest to call PCRE via the POSIX wrapper API
107 rather than its native API. When this is done, all other modifiers except /i,
108 /m, and /+ are ignored. REG_ICASE is set if /i is present, and REG_NEWLINE is
109 set if /m is present. The wrapper functions force PCRE_DOLLAR_ENDONLY always,
110 and PCRE_DOTALL unless REG_NEWLINE is set.
112 Before each data line is passed to pcre_exec(), leading and trailing whitespace
113 is removed, and it is then scanned for \ escapes. The following are recognized:
115 \a alarm (= BEL)
116 \b backspace
117 \e escape
118 \f formfeed
119 \n newline
120 \r carriage return
121 \t tab
122 \v vertical tab
123 \nnn octal character (up to 3 octal digits)
124 \xhh hexadecimal character (up to 2 hex digits)
126 \A pass the PCRE_ANCHORED option to pcre_exec()
127 \B pass the PCRE_NOTBOL option to pcre_exec()
128 \Cdd call pcre_copy_substring() for substring dd after a successful match
129 (any decimal number less than 32)
130 \Gdd call pcre_get_substring() for substring dd after a successful match
131 (any decimal number less than 32)
132 \L call pcre_get_substringlist() after a successful match
133 \N pass the PCRE_NOTEMPTY option to pcre_exec()
134 \Odd set the size of the output vector passed to pcre_exec() to dd
135 (any number of decimal digits)
136 \Z pass the PCRE_NOTEOL option to pcre_exec()
138 A backslash followed by anything else just escapes the anything else. If the
139 very last character is a backslash, it is ignored. This gives a way of passing
140 an empty line as data, since a real empty line terminates the data input.
142 If /P was present on the regex, causing the POSIX wrapper API to be used, only
143 \B, and \Z have any effect, causing REG_NOTBOL and REG_NOTEOL to be passed to
144 regexec() respectively.
146 When a match succeeds, pcretest outputs the list of captured substrings that
147 pcre_exec() returns, starting with number 0 for the string that matched the
148 whole pattern. Here is an example of an interactive pcretest run.
150 $ pcretest
151 PCRE version 2.06 08-Jun-1999
153 re> /^abc(\d+)/
154 data> abc123
155 0: abc123
156 1: 123
157 data> xyz
158 No match
160 If the strings contain any non-printing characters, they are output as \0x
161 escapes. If the pattern has the /+ modifier, then the output for substring 0 is
162 followed by the the rest of the subject string, identified by "0+" like this:
164 re> /cat/+
165 data> cataract
166 0: cat
167 0+ aract
169 If the pattern has the /g or /G modifier, the results of successive matching
170 attempts are output in sequence, like this:
172 re> /\Bi(\w\w)/g
173 data> Mississippi
174 0: iss
175 1: ss
176 0: iss
177 1: ss
178 0: ipp
179 1: pp
181 "No match" is output only if the first match attempt fails.
183 If any of \C, \G, or \L are present in a data line that is successfully
184 matched, the substrings extracted by the convenience functions are output with
185 C, G, or L after the string number instead of a colon. This is in addition to
186 the normal full list. The string length (that is, the return from the
187 extraction function) is given in parentheses after each string for \C and \G.
189 Note that while patterns can be continued over several lines (a plain ">"
190 prompt is used for continuations), data lines may not. However newlines can be
191 included in data by means of the \n escape.
193 If the -p option is given to pcretest, it is equivalent to adding /P to each
194 regular expression: the POSIX wrapper API is used to call PCRE. None of the
195 following flags has any effect in this case.
197 If the option -d is given to pcretest, it is equivalent to adding /D to each
198 regular expression: the internal form is output after compilation.
200 If the option -i is given to pcretest, it is equivalent to adding /I to each
201 regular expression: information about the compiled pattern is given after
202 compilation.
204 If the option -m is given to pcretest, it outputs the size of each compiled
205 pattern after it has been compiled. It is equivalent to adding /M to each
206 regular expression. For compatibility with earlier versions of pcretest, -s is
207 a synonym for -m.
209 If the -t option is given, each compile, study, and match is run 20000 times
210 while being timed, and the resulting time per compile or match is output in
211 milliseconds. Do not set -t with -s, because you will then get the size output
212 20000 times and the timing will be distorted. If you want to change the number
213 of repetitions used for timing, edit the definition of LOOPREPEAT at the top of
214 pcretest.c
216 Philip Hazel <ph10@cam.ac.uk>
217 January 2000

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