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Tag code/trunk as code/tags/pcre-2.06.

1 README file for PCRE (Perl-compatible regular expressions)
2 ----------------------------------------------------------
3
4 *******************************************************************************
5 * IMPORTANT FOR THOSE UPGRADING FROM VERSIONS BEFORE 2.00 *
6 * *
7 * Please note that there has been a change in the API such that a larger *
8 * ovector is required at matching time, to provide some additional workspace. *
9 * The new man page has details. This change was necessary in order to support *
10 * some of the new functionality in Perl 5.005. *
11 * *
12 * IMPORTANT FOR THOSE UPGRADING FROM VERSION 2.00 *
13 * *
14 * Another (I hope this is the last!) change has been made to the API for the *
15 * pcre_compile() function. An additional argument has been added to make it *
16 * possible to pass over a pointer to character tables built in the current *
17 * locale by pcre_maketables(). To use the default tables, this new arguement *
18 * should be passed as NULL. *
19 * *
20 * IMPORTANT FOR THOSE UPGRADING FROM VERSION 2.05 *
21 * *
22 * Yet another (and again I hope this really is the last) change has been made *
23 * to the API for the pcre_exec() function. An additional argument has been *
24 * added to make it possible to start the match other than at the start of the *
25 * subject string. This is important if there are lookbehinds. The new man *
26 * page has the details, but you just want to convert existing programs, all *
27 * you need to do is to stick in a new fifth argument to pcre_exec(), with a *
28 * value of zero. For example, change *
29 * *
30 * pcre_exec(pattern, extra, subject, length, options, ovec, ovecsize) *
31 * to *
32 * pcre_exec(pattern, extra, subject, length, 0, options, ovec, ovecsize) *
33 *******************************************************************************
34
35
36 The distribution should contain the following files:
37
38 ChangeLog log of changes to the code
39 LICENCE conditions for the use of PCRE
40 Makefile for building PCRE
41 README this file
42 RunTest a shell script for running tests
43 Tech.Notes notes on the encoding
44 pcre.3 man page for the functions
45 pcreposix.3 man page for the POSIX wrapper API
46 dftables.c auxiliary program for building chartables.c
47 get.c )
48 maketables.c )
49 study.c ) source of
50 pcre.c ) the functions
51 pcreposix.c )
52 pcre.h header for the external API
53 pcreposix.h header for the external POSIX wrapper API
54 internal.h header for internal use
55 pcretest.c test program
56 pgrep.1 man page for pgrep
57 pgrep.c source of a grep utility that uses PCRE
58 perltest Perl test program
59 testinput1 test data, compatible with Perl 5.004 and 5.005
60 testinput2 test data for error messages and non-Perl things
61 testinput3 test data, compatible with Perl 5.005
62 testinput4 test data for locale-specific tests
63 testoutput1 test results corresponding to testinput1
64 testoutput2 test results corresponding to testinput2
65 testoutput3 test results corresponding to testinput3
66 testoutput4 test results corresponding to testinput4
67
68 To build PCRE, edit Makefile for your system (it is a fairly simple make file,
69 and there are some comments at the top) and then run it. It builds two
70 libraries called libpcre.a and libpcreposix.a, a test program called pcretest,
71 and the pgrep command.
72
73 To test PCRE, run the RunTest script in the pcre directory. This runs pcretest
74 on each of the testinput files in turn, and compares the output with the
75 contents of the corresponding testoutput file. A file called testtry is used to
76 hold the output from pcretest (which is documented below).
77
78 To run pcretest on just one of the test files, give its number as an argument
79 to RunTest, for example:
80
81 RunTest 3
82
83 The first and third test files can also be fed directly into the perltest
84 program to check that Perl gives the same results. The third file requires the
85 additional features of release 5.005, which is why it is kept separate from the
86 main test input, which needs only Perl 5.004. In the long run, when 5.005 is
87 widespread, these two test files may get amalgamated.
88
89 The second set of tests check pcre_info(), pcre_study(), pcre_copy_substring(),
90 pcre_get_substring(), pcre_get_substring_list(), error detection and run-time
91 flags that are specific to PCRE, as well as the POSIX wrapper API.
92
93 The fourth set of tests checks pcre_maketables(), the facility for building a
94 set of character tables for a specific locale and using them instead of the
95 default tables. The tests make use of the "fr" (French) locale. Before running
96 the test, the script checks for the presence of this locale by running the
97 "locale" command. If that command fails, or if it doesn't include "fr" in the
98 list of available locales, the fourth test cannot be run, and a comment is
99 output to say why. If running this test produces instances of the error
100
101 ** Failed to set locale "fr"
102
103 in the comparison output, it means that locale is not available on your system,
104 despite being listed by "locale". This does not mean that PCRE is broken.
105
106 To install PCRE, copy libpcre.a to any suitable library directory (e.g.
107 /usr/local/lib), pcre.h to any suitable include directory (e.g.
108 /usr/local/include), and pcre.3 to any suitable man directory (e.g.
109 /usr/local/man/man3).
110
111 To install the pgrep command, copy it to any suitable binary directory, (e.g.
112 /usr/local/bin) and pgrep.1 to any suitable man directory (e.g.
113 /usr/local/man/man1).
114
115 PCRE has its own native API, but a set of "wrapper" functions that are based on
116 the POSIX API are also supplied in the library libpcreposix.a. Note that this
117 just provides a POSIX calling interface to PCRE: the regular expressions
118 themselves still follow Perl syntax and semantics. The header file
119 for the POSIX-style functions is called pcreposix.h. The official POSIX name is
120 regex.h, but I didn't want to risk possible problems with existing files of
121 that name by distributing it that way. To use it with an existing program that
122 uses the POSIX API, it will have to be renamed or pointed at by a link.
123
124
125 Character tables
126 ----------------
127
128 PCRE uses four tables for manipulating and identifying characters. The final
129 argument of the pcre_compile() function is a pointer to a block of memory
130 containing the concatenated tables. A call to pcre_maketables() can be used to
131 generate a set of tables in the current locale. If the final argument for
132 pcre_compile() is passed as NULL, a set of default tables that is built into
133 the binary is used.
134
135 The source file called chartables.c contains the default set of tables. This is
136 not supplied in the distribution, but is built by the program dftables
137 (compiled from dftables.c), which uses the ANSI C character handling functions
138 such as isalnum(), isalpha(), isupper(), islower(), etc. to build the table
139 sources. This means that the default C locale which is set for your system will
140 control the contents of these default tables. You can change the default tables
141 by editing chartables.c and then re-building PCRE. If you do this, you should
142 probably also edit Makefile to ensure that the file doesn't ever get
143 re-generated.
144
145 The first two 256-byte tables provide lower casing and case flipping functions,
146 respectively. The next table consists of three 32-byte bit maps which identify
147 digits, "word" characters, and white space, respectively. These are used when
148 building 32-byte bit maps that represent character classes.
149
150 The final 256-byte table has bits indicating various character types, as
151 follows:
152
153 1 white space character
154 2 letter
155 4 decimal digit
156 8 hexadecimal digit
157 16 alphanumeric or '_'
158 128 regular expression metacharacter or binary zero
159
160 You should not alter the set of characters that contain the 128 bit, as that
161 will cause PCRE to malfunction.
162
163
164 The pcretest program
165 --------------------
166
167 This program is intended for testing PCRE, but it can also be used for
168 experimenting with regular expressions.
169
170 If it is given two filename arguments, it reads from the first and writes to
171 the second. If it is given only one filename argument, it reads from that file
172 and writes to stdout. Otherwise, it reads from stdin and writes to stdout, and
173 prompts for each line of input.
174
175 The program handles any number of sets of input on a single input file. Each
176 set starts with a regular expression, and continues with any number of data
177 lines to be matched against the pattern. An empty line signals the end of the
178 set. The regular expressions are given enclosed in any non-alphameric
179 delimiters other than backslash, for example
180
181 /(a|bc)x+yz/
182
183 White space before the initial delimiter is ignored. A regular expression may
184 be continued over several input lines, in which case the newline characters are
185 included within it. See the testinput files for many examples. It is possible
186 to include the delimiter within the pattern by escaping it, for example
187
188 /abc\/def/
189
190 If you do so, the escape and the delimiter form part of the pattern, but since
191 delimiters are always non-alphameric, this does not affect its interpretation.
192 If the terminating delimiter is immediately followed by a backslash, for
193 example,
194
195 /abc/\
196
197 then a backslash is added to the end of the pattern. This is done to provide a
198 way of testing the error condition that arises if a pattern finishes with a
199 backslash, because
200
201 /abc\/
202
203 is interpreted as the first line of a pattern that starts with "abc/", causing
204 pcretest to read the next line as a continuation of the regular expression.
205
206 The pattern may be followed by i, m, s, or x to set the PCRE_CASELESS,
207 PCRE_MULTILINE, PCRE_DOTALL, or PCRE_EXTENDED options, respectively. For
208 example:
209
210 /caseless/i
211
212 These modifier letters have the same effect as they do in Perl. There are
213 others which set PCRE options that do not correspond to anything in Perl: /A,
214 /E, and /X set PCRE_ANCHORED, PCRE_DOLLAR_ENDONLY, and PCRE_EXTRA respectively.
215
216 Searching for all possible matches within each subject string can be requested
217 by the /g or /G modifier. The /g modifier behaves similarly to the way it does
218 in Perl. After finding a match, PCRE is called again to search the remainder of
219 the subject string. The difference between /g and /G is that the former uses
220 the start_offset argument to pcre_exec() to start searching at a new point
221 within the entire string, whereas the latter passes over a shortened substring.
222 This makes a difference to the matching process if the pattern begins with a
223 lookbehind assertion (including \b or \B).
224
225 There are a number of other modifiers for controlling the way pcretest
226 operates.
227
228 The /+ modifier requests that as well as outputting the substring that matched
229 the entire pattern, pcretest should in addition output the remainder of the
230 subject string. This is useful for tests where the subject contains multiple
231 copies of the same substring.
232
233 The /L modifier must be followed directly by the name of a locale, for example,
234
235 /pattern/Lfr
236
237 For this reason, it must be the last modifier letter. The given locale is set,
238 pcre_maketables() is called to build a set of character tables for the locale,
239 and this is then passed to pcre_compile() when compiling the regular
240 expression. Without an /L modifier, NULL is passed as the tables pointer; that
241 is, /L applies only to the expression on which it appears.
242
243 The /I modifier requests that pcretest output information about the compiled
244 expression (whether it is anchored, has a fixed first character, and so on). It
245 does this by calling pcre_info() after compiling an expression, and outputting
246 the information it gets back. If the pattern is studied, the results of that
247 are also output.
248
249 The /D modifier is a PCRE debugging feature, which also assumes /I. It causes
250 the internal form of compiled regular expressions to be output after
251 compilation.
252
253 The /S modifier causes pcre_study() to be called after the expression has been
254 compiled, and the results used when the expression is matched.
255
256 The /M modifier causes information about the size of memory block used to hold
257 the compile pattern to be output.
258
259 Finally, the /P modifier causes pcretest to call PCRE via the POSIX wrapper API
260 rather than its native API. When this is done, all other modifiers except /i,
261 /m, and /+ are ignored. REG_ICASE is set if /i is present, and REG_NEWLINE is
262 set if /m is present. The wrapper functions force PCRE_DOLLAR_ENDONLY always,
263 and PCRE_DOTALL unless REG_NEWLINE is set.
264
265 Before each data line is passed to pcre_exec(), leading and trailing whitespace
266 is removed, and it is then scanned for \ escapes. The following are recognized:
267
268 \a alarm (= BEL)
269 \b backspace
270 \e escape
271 \f formfeed
272 \n newline
273 \r carriage return
274 \t tab
275 \v vertical tab
276 \nnn octal character (up to 3 octal digits)
277 \xhh hexadecimal character (up to 2 hex digits)
278
279 \A pass the PCRE_ANCHORED option to pcre_exec()
280 \B pass the PCRE_NOTBOL option to pcre_exec()
281 \Cdd call pcre_copy_substring() for substring dd after a successful match
282 (any decimal number less than 32)
283 \Gdd call pcre_get_substring() for substring dd after a successful match
284 (any decimal number less than 32)
285 \L call pcre_get_substringlist() after a successful match
286 \Odd set the size of the output vector passed to pcre_exec() to dd
287 (any number of decimal digits)
288 \Z pass the PCRE_NOTEOL option to pcre_exec()
289
290 A backslash followed by anything else just escapes the anything else. If the
291 very last character is a backslash, it is ignored. This gives a way of passing
292 an empty line as data, since a real empty line terminates the data input.
293
294 If /P was present on the regex, causing the POSIX wrapper API to be used, only
295 \B, and \Z have any effect, causing REG_NOTBOL and REG_NOTEOL to be passed to
296 regexec() respectively.
297
298 When a match succeeds, pcretest outputs the list of captured substrings that
299 pcre_exec() returns, starting with number 0 for the string that matched the
300 whole pattern. Here is an example of an interactive pcretest run.
301
302 $ pcretest
303 PCRE version 2.06 08-Jun-1999
304
305 re> /^abc(\d+)/
306 data> abc123
307 0: abc123
308 1: 123
309 data> xyz
310 No match
311
312 If the strings contain any non-printing characters, they are output as \0x
313 escapes. If the pattern has the /+ modifier, then the output for substring 0 is
314 followed by the the rest of the subject string, identified by "0+" like this:
315
316 re> /cat/+
317 data> cataract
318 0: cat
319 0+ aract
320
321 If the pattern has the /g or /G modifier, the results of successive matching
322 attempts are output in sequence, like this:
323
324 re> /\Bi(\w\w)/g
325 data> Mississippi
326 0: iss
327 1: ss
328 0: iss
329 1: ss
330 0: ipp
331 1: pp
332
333 "No match" is output only if the first match attempt fails.
334
335 If any of \C, \G, or \L are present in a data line that is successfully
336 matched, the substrings extracted by the convenience functions are output with
337 C, G, or L after the string number instead of a colon. This is in addition to
338 the normal full list. The string length (that is, the return from the
339 extraction function) is given in parentheses after each string for \C and \G.
340
341 Note that while patterns can be continued over several lines (a plain ">"
342 prompt is used for continuations), data lines may not. However newlines can be
343 included in data by means of the \n escape.
344
345 If the -p option is given to pcretest, it is equivalent to adding /P to each
346 regular expression: the POSIX wrapper API is used to call PCRE. None of the
347 following flags has any effect in this case.
348
349 If the option -d is given to pcretest, it is equivalent to adding /D to each
350 regular expression: the internal form is output after compilation.
351
352 If the option -i is given to pcretest, it is equivalent to adding /I to each
353 regular expression: information about the compiled pattern is given after
354 compilation.
355
356 If the option -m is given to pcretest, it outputs the size of each compiled
357 pattern after it has been compiled. It is equivalent to adding /M to each
358 regular expression. For compatibility with earlier versions of pcretest, -s is
359 a synonym for -m.
360
361 If the -t option is given, each compile, study, and match is run 20000 times
362 while being timed, and the resulting time per compile or match is output in
363 milliseconds. Do not set -t with -s, because you will then get the size output
364 20000 times and the timing will be distorted. If you want to change the number
365 of repetitions used for timing, edit the definition of LOOPREPEAT at the top of
366 pcretest.c
367
368
369
370 The perltest program
371 --------------------
372
373 The perltest program tests Perl's regular expressions; it has the same
374 specification as pcretest, and so can be given identical input, except that
375 input patterns can be followed only by Perl's lower case modifiers. The
376 contents of testinput1 and testinput3 meet this condition.
377
378 The data lines are processed as Perl strings, so if they contain $ or @
379 characters, these have to be escaped. For this reason, all such characters in
380 testinput1 and testinput3 are escaped so that they can be used for perltest as
381 well as for pcretest, and the special upper case modifiers such as /A that
382 pcretest recognizes are not used in these files. The output should be
383 identical, apart from the initial identifying banner.
384
385 The testinput2 and testinput4 files are not suitable for feeding to perltest,
386 since they do make use of the special upper case modifiers and escapes that
387 pcretest uses to test some features of PCRE. The first of these files also
388 contains malformed regular expressions, in order to check that PCRE diagnoses
389 them correctly.
390
391 Philip Hazel <ph10@cam.ac.uk>
392 June 1999

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