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

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Load pcre-3.0 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 flag set so that it cannot match an
67 empty string again at the same point. If however, this second match fails, the
68 start offset is advanced by one, and the match is retried. This imitates the
69 way Perl handles such cases when using the /g modifier or the split() function.
71 There are a number of other modifiers for controlling the way pcretest
72 operates.
74 The /+ modifier requests that as well as outputting the substring that matched
75 the entire pattern, pcretest should in addition output the remainder of the
76 subject string. This is useful for tests where the subject contains multiple
77 copies of the same substring.
79 The /L modifier must be followed directly by the name of a locale, for example,
81 /pattern/Lfr
83 For this reason, it must be the last modifier letter. The given locale is set,
84 pcre_maketables() is called to build a set of character tables for the locale,
85 and this is then passed to pcre_compile() when compiling the regular
86 expression. Without an /L modifier, NULL is passed as the tables pointer; that
87 is, /L applies only to the expression on which it appears.
89 The /I modifier requests that pcretest output information about the compiled
90 expression (whether it is anchored, has a fixed first character, and so on). It
91 does this by calling pcre_fullinfo() after compiling an expression, and
92 outputting the information it gets back. If the pattern is studied, the results
93 of that are also output.
95 The /D modifier is a PCRE debugging feature, which also assumes /I. It causes
96 the internal form of compiled regular expressions to be output after
97 compilation.
99 The /S modifier causes pcre_study() to be called after the expression has been
100 compiled, and the results used when the expression is matched.
102 The /M modifier causes the size of memory block used to hold the compiled
103 pattern to be output.
105 Finally, the /P modifier causes pcretest to call PCRE via the POSIX wrapper API
106 rather than its native API. When this is done, all other modifiers except /i,
107 /m, and /+ are ignored. REG_ICASE is set if /i is present, and REG_NEWLINE is
108 set if /m is present. The wrapper functions force PCRE_DOLLAR_ENDONLY always,
109 and PCRE_DOTALL unless REG_NEWLINE is set.
111 Before each data line is passed to pcre_exec(), leading and trailing whitespace
112 is removed, and it is then scanned for \ escapes. The following are recognized:
114 \a alarm (= BEL)
115 \b backspace
116 \e escape
117 \f formfeed
118 \n newline
119 \r carriage return
120 \t tab
121 \v vertical tab
122 \nnn octal character (up to 3 octal digits)
123 \xhh hexadecimal character (up to 2 hex digits)
125 \A pass the PCRE_ANCHORED option to pcre_exec()
126 \B pass the PCRE_NOTBOL option to pcre_exec()
127 \Cdd call pcre_copy_substring() for substring dd after a successful match
128 (any decimal number less than 32)
129 \Gdd call pcre_get_substring() for substring dd after a successful match
130 (any decimal number less than 32)
131 \L call pcre_get_substringlist() after a successful match
132 \N pass the PCRE_NOTEMPTY option to pcre_exec()
133 \Odd set the size of the output vector passed to pcre_exec() to dd
134 (any number of decimal digits)
135 \Z pass the PCRE_NOTEOL option to pcre_exec()
137 A backslash followed by anything else just escapes the anything else. If the
138 very last character is a backslash, it is ignored. This gives a way of passing
139 an empty line as data, since a real empty line terminates the data input.
141 If /P was present on the regex, causing the POSIX wrapper API to be used, only
142 \B, and \Z have any effect, causing REG_NOTBOL and REG_NOTEOL to be passed to
143 regexec() respectively.
145 When a match succeeds, pcretest outputs the list of captured substrings that
146 pcre_exec() returns, starting with number 0 for the string that matched the
147 whole pattern. Here is an example of an interactive pcretest run.
149 $ pcretest
150 PCRE version 2.06 08-Jun-1999
152 re> /^abc(\d+)/
153 data> abc123
154 0: abc123
155 1: 123
156 data> xyz
157 No match
159 If the strings contain any non-printing characters, they are output as \0x
160 escapes. If the pattern has the /+ modifier, then the output for substring 0 is
161 followed by the the rest of the subject string, identified by "0+" like this:
163 re> /cat/+
164 data> cataract
165 0: cat
166 0+ aract
168 If the pattern has the /g or /G modifier, the results of successive matching
169 attempts are output in sequence, like this:
171 re> /\Bi(\w\w)/g
172 data> Mississippi
173 0: iss
174 1: ss
175 0: iss
176 1: ss
177 0: ipp
178 1: pp
180 "No match" is output only if the first match attempt fails.
182 If any of \C, \G, or \L are present in a data line that is successfully
183 matched, the substrings extracted by the convenience functions are output with
184 C, G, or L after the string number instead of a colon. This is in addition to
185 the normal full list. The string length (that is, the return from the
186 extraction function) is given in parentheses after each string for \C and \G.
188 Note that while patterns can be continued over several lines (a plain ">"
189 prompt is used for continuations), data lines may not. However newlines can be
190 included in data by means of the \n escape.
192 If the -p option is given to pcretest, it is equivalent to adding /P to each
193 regular expression: the POSIX wrapper API is used to call PCRE. None of the
194 following flags has any effect in this case.
196 If the option -d is given to pcretest, it is equivalent to adding /D to each
197 regular expression: the internal form is output after compilation.
199 If the option -i is given to pcretest, it is equivalent to adding /I to each
200 regular expression: information about the compiled pattern is given after
201 compilation.
203 If the option -m is given to pcretest, it outputs the size of each compiled
204 pattern after it has been compiled. It is equivalent to adding /M to each
205 regular expression. For compatibility with earlier versions of pcretest, -s is
206 a synonym for -m.
208 If the -t option is given, each compile, study, and match is run 20000 times
209 while being timed, and the resulting time per compile or match is output in
210 milliseconds. Do not set -t with -s, because you will then get the size output
211 20000 times and the timing will be distorted. If you want to change the number
212 of repetitions used for timing, edit the definition of LOOPREPEAT at the top of
213 pcretest.c
215 Philip Hazel <ph10@cam.ac.uk>
216 January 2000

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