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

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1 nigel 41 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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