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

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Load pcre-2.08a 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.
12 The program handles any number of sets of input on a single input file. Each
13 set starts with a regular expression, and continues with any number of data
14 lines to be matched against the pattern. An empty line signals the end of the
15 set. The regular expressions are given enclosed in any non-alphameric
16 delimiters other than backslash, for example
18 /(a|bc)x+yz/
20 White space before the initial delimiter is ignored. A regular expression may
21 be continued over several input lines, in which case the newline characters are
22 included within it. See the testinput files for many examples. It is possible
23 to include the delimiter within the pattern by escaping it, for example
25 /abc\/def/
27 If you do so, the escape and the delimiter form part of the pattern, but since
28 delimiters are always non-alphameric, this does not affect its interpretation.
29 If the terminating delimiter is immediately followed by a backslash, for
30 example,
32 /abc/\
34 then a backslash is added to the end of the pattern. This is done to provide a
35 way of testing the error condition that arises if a pattern finishes with a
36 backslash, because
38 /abc\/
40 is interpreted as the first line of a pattern that starts with "abc/", causing
41 pcretest to read the next line as a continuation of the regular expression.
43 The pattern may be followed by i, m, s, or x to set the PCRE_CASELESS,
44 PCRE_MULTILINE, PCRE_DOTALL, or PCRE_EXTENDED options, respectively. For
45 example:
47 /caseless/i
49 These modifier letters have the same effect as they do in Perl. There are
50 others which set PCRE options that do not correspond to anything in Perl: /A,
51 /E, and /X set PCRE_ANCHORED, PCRE_DOLLAR_ENDONLY, and PCRE_EXTRA respectively.
53 Searching for all possible matches within each subject string can be requested
54 by the /g or /G modifier. After finding a match, PCRE is called again to search
55 the remainder of the subject string. The difference between /g and /G is that
56 the former uses the startoffset argument to pcre_exec() to start searching at
57 a new point within the entire string (which is in effect what Perl does),
58 whereas the latter passes over a shortened substring. This makes a difference
59 to the matching process if the pattern begins with a lookbehind assertion
60 (including \b or \B).
62 If any call to pcre_exec() in a /g or /G sequence matches an empty string, the
63 next call is done with the PCRE_NOTEMPTY flag set so that it cannot match an
64 empty string again at the same point. If however, this second match fails, the
65 start offset is advanced by one, and the match is retried. This imitates the
66 way Perl handles such cases when using the /g modifier or the split() function.
68 There are a number of other modifiers for controlling the way pcretest
69 operates.
71 The /+ modifier requests that as well as outputting the substring that matched
72 the entire pattern, pcretest should in addition output the remainder of the
73 subject string. This is useful for tests where the subject contains multiple
74 copies of the same substring.
76 The /L modifier must be followed directly by the name of a locale, for example,
78 /pattern/Lfr
80 For this reason, it must be the last modifier letter. The given locale is set,
81 pcre_maketables() is called to build a set of character tables for the locale,
82 and this is then passed to pcre_compile() when compiling the regular
83 expression. Without an /L modifier, NULL is passed as the tables pointer; that
84 is, /L applies only to the expression on which it appears.
86 The /I modifier requests that pcretest output information about the compiled
87 expression (whether it is anchored, has a fixed first character, and so on). It
88 does this by calling pcre_info() after compiling an expression, and outputting
89 the information it gets back. If the pattern is studied, the results of that
90 are also output.
92 The /D modifier is a PCRE debugging feature, which also assumes /I. It causes
93 the internal form of compiled regular expressions to be output after
94 compilation.
96 The /S modifier causes pcre_study() to be called after the expression has been
97 compiled, and the results used when the expression is matched.
99 The /M modifier causes the size of memory block used to hold the compiled
100 pattern to be output.
102 Finally, the /P modifier causes pcretest to call PCRE via the POSIX wrapper API
103 rather than its native API. When this is done, all other modifiers except /i,
104 /m, and /+ are ignored. REG_ICASE is set if /i is present, and REG_NEWLINE is
105 set if /m is present. The wrapper functions force PCRE_DOLLAR_ENDONLY always,
106 and PCRE_DOTALL unless REG_NEWLINE is set.
108 Before each data line is passed to pcre_exec(), leading and trailing whitespace
109 is removed, and it is then scanned for \ escapes. The following are recognized:
111 \a alarm (= BEL)
112 \b backspace
113 \e escape
114 \f formfeed
115 \n newline
116 \r carriage return
117 \t tab
118 \v vertical tab
119 \nnn octal character (up to 3 octal digits)
120 \xhh hexadecimal character (up to 2 hex digits)
122 \A pass the PCRE_ANCHORED option to pcre_exec()
123 \B pass the PCRE_NOTBOL option to pcre_exec()
124 \Cdd call pcre_copy_substring() for substring dd after a successful match
125 (any decimal number less than 32)
126 \Gdd call pcre_get_substring() for substring dd after a successful match
127 (any decimal number less than 32)
128 \L call pcre_get_substringlist() after a successful match
129 \N pass the PCRE_NOTEMPTY option to pcre_exec()
130 \Odd set the size of the output vector passed to pcre_exec() to dd
131 (any number of decimal digits)
132 \Z pass the PCRE_NOTEOL option to pcre_exec()
134 A backslash followed by anything else just escapes the anything else. If the
135 very last character is a backslash, it is ignored. This gives a way of passing
136 an empty line as data, since a real empty line terminates the data input.
138 If /P was present on the regex, causing the POSIX wrapper API to be used, only
139 \B, and \Z have any effect, causing REG_NOTBOL and REG_NOTEOL to be passed to
140 regexec() respectively.
142 When a match succeeds, pcretest outputs the list of captured substrings that
143 pcre_exec() returns, starting with number 0 for the string that matched the
144 whole pattern. Here is an example of an interactive pcretest run.
146 $ pcretest
147 PCRE version 2.06 08-Jun-1999
149 re> /^abc(\d+)/
150 data> abc123
151 0: abc123
152 1: 123
153 data> xyz
154 No match
156 If the strings contain any non-printing characters, they are output as \0x
157 escapes. If the pattern has the /+ modifier, then the output for substring 0 is
158 followed by the the rest of the subject string, identified by "0+" like this:
160 re> /cat/+
161 data> cataract
162 0: cat
163 0+ aract
165 If the pattern has the /g or /G modifier, the results of successive matching
166 attempts are output in sequence, like this:
168 re> /\Bi(\w\w)/g
169 data> Mississippi
170 0: iss
171 1: ss
172 0: iss
173 1: ss
174 0: ipp
175 1: pp
177 "No match" is output only if the first match attempt fails.
179 If any of \C, \G, or \L are present in a data line that is successfully
180 matched, the substrings extracted by the convenience functions are output with
181 C, G, or L after the string number instead of a colon. This is in addition to
182 the normal full list. The string length (that is, the return from the
183 extraction function) is given in parentheses after each string for \C and \G.
185 Note that while patterns can be continued over several lines (a plain ">"
186 prompt is used for continuations), data lines may not. However newlines can be
187 included in data by means of the \n escape.
189 If the -p option is given to pcretest, it is equivalent to adding /P to each
190 regular expression: the POSIX wrapper API is used to call PCRE. None of the
191 following flags has any effect in this case.
193 If the option -d is given to pcretest, it is equivalent to adding /D to each
194 regular expression: the internal form is output after compilation.
196 If the option -i is given to pcretest, it is equivalent to adding /I to each
197 regular expression: information about the compiled pattern is given after
198 compilation.
200 If the option -m is given to pcretest, it outputs the size of each compiled
201 pattern after it has been compiled. It is equivalent to adding /M to each
202 regular expression. For compatibility with earlier versions of pcretest, -s is
203 a synonym for -m.
205 If the -t option is given, each compile, study, and match is run 20000 times
206 while being timed, and the resulting time per compile or match is output in
207 milliseconds. Do not set -t with -s, because you will then get the size output
208 20000 times and the timing will be distorted. If you want to change the number
209 of repetitions used for timing, edit the definition of LOOPREPEAT at the top of
210 pcretest.c
212 Philip Hazel <ph10@cam.ac.uk>
213 January 2000

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