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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 in Unix systems
41 README this file
42 RunTest a Unix shell script for running tests
43 Tech.Notes notes on the encoding
44 pcre.3 man page source for the functions
45 pcre.3.txt plain text version
46 pcre.3.html HTML version
47 pcreposix.3 man page source for the POSIX wrapper API
48 pcreposix.3.txt plain text version
49 pcreposix.3.HTML HTML version
50 dftables.c auxiliary program for building chartables.c
51 get.c )
52 maketables.c )
53 study.c ) source of
54 pcre.c ) the functions
55 pcreposix.c )
56 pcre.h header for the external API
57 pcreposix.h header for the external POSIX wrapper API
58 internal.h header for internal use
59 pcretest.c test program
60 pgrep.1 man page source for pgrep
61 pgrep.1.txt plain text version
62 pgrep.1.HTML HTML version
63 pgrep.c source of a grep utility that uses PCRE
64 perltest Perl test program
65 testinput1 test data, compatible with Perl 5.004 and 5.005
66 testinput2 test data for error messages and non-Perl things
67 testinput3 test data, compatible with Perl 5.005
68 testinput4 test data for locale-specific tests
69 testoutput1 test results corresponding to testinput1
70 testoutput2 test results corresponding to testinput2
71 testoutput3 test results corresponding to testinput3
72 testoutput4 test results corresponding to testinput4
73 dll.mk for Win32 DLL
74 pcre.def ditto
75
76 To build PCRE on a Unix system, first edit Makefile for your system. It is a
77 fairly simple make file, and there are some comments near the top, after the
78 text "On a Unix system". Then run "make". It builds two libraries called
79 libpcre.a and libpcreposix.a, a test program called pcretest, and the pgrep
80 command. You can use "make install" to copy these, and the public header file
81 pcre.h, to appropriate live directories on your system. These installation
82 directories are defined at the top of the Makefile, and you should edit them if
83 necessary.
84
85 For a non-Unix system, read the comments at the top of Makefile, which give
86 some hints on what needs to be done. PCRE has been compiled on Windows systems
87 and on Macintoshes, but I don't know the details as I don't use those systems.
88 It should be straightforward to build PCRE on any system that has a Standard C
89 compiler.
90
91 Some help in building a Win32 DLL of PCRE in GnuWin32 environments was
92 contributed by Paul.Sokolovsky@technologist.com. These environments are
93 Mingw32 (http://www.xraylith.wisc.edu/~khan/software/gnu-win32/) and
94 CygWin (http://sourceware.cygnus.com/cygwin/). Paul comments:
95
96 For CygWin, set CFLAGS=-mno-cygwin, and do 'make dll'. You'll get
97 pcre.dll (containing pcreposix also), libpcre.dll.a, and dynamically
98 linked pgrep and pcretest. If you have /bin/sh, run RunTest (three
99 main test go ok, locale not supported).
100
101 To test PCRE, run the RunTest script in the pcre directory. This can also be
102 run by "make runtest". It runs the pcretest test program (which is documented
103 below) on each of the testinput files in turn, and compares the output with the
104 contents of the corresponding testoutput file. A file called testtry is used to
105 hold the output from pcretest. To run pcretest on just one of the test files,
106 give its number as an argument to RunTest, for example:
107
108 RunTest 3
109
110 The first and third test files can also be fed directly into the perltest
111 script to check that Perl gives the same results. The third file requires the
112 additional features of release 5.005, which is why it is kept separate from the
113 main test input, which needs only Perl 5.004. In the long run, when 5.005 is
114 widespread, these two test files may get amalgamated.
115
116 The second set of tests check pcre_info(), pcre_study(), pcre_copy_substring(),
117 pcre_get_substring(), pcre_get_substring_list(), error detection and run-time
118 flags that are specific to PCRE, as well as the POSIX wrapper API.
119
120 The fourth set of tests checks pcre_maketables(), the facility for building a
121 set of character tables for a specific locale and using them instead of the
122 default tables. The tests make use of the "fr" (French) locale. Before running
123 the test, the script checks for the presence of this locale by running the
124 "locale" command. If that command fails, or if it doesn't include "fr" in the
125 list of available locales, the fourth test cannot be run, and a comment is
126 output to say why. If running this test produces instances of the error
127
128 ** Failed to set locale "fr"
129
130 in the comparison output, it means that locale is not available on your system,
131 despite being listed by "locale". This does not mean that PCRE is broken.
132
133 PCRE has its own native API, but a set of "wrapper" functions that are based on
134 the POSIX API are also supplied in the library libpcreposix.a. Note that this
135 just provides a POSIX calling interface to PCRE: the regular expressions
136 themselves still follow Perl syntax and semantics. The header file
137 for the POSIX-style functions is called pcreposix.h. The official POSIX name is
138 regex.h, but I didn't want to risk possible problems with existing files of
139 that name by distributing it that way. To use it with an existing program that
140 uses the POSIX API, it will have to be renamed or pointed at by a link.
141
142
143 Character tables
144 ----------------
145
146 PCRE uses four tables for manipulating and identifying characters. The final
147 argument of the pcre_compile() function is a pointer to a block of memory
148 containing the concatenated tables. A call to pcre_maketables() can be used to
149 generate a set of tables in the current locale. If the final argument for
150 pcre_compile() is passed as NULL, a set of default tables that is built into
151 the binary is used.
152
153 The source file called chartables.c contains the default set of tables. This is
154 not supplied in the distribution, but is built by the program dftables
155 (compiled from dftables.c), which uses the ANSI C character handling functions
156 such as isalnum(), isalpha(), isupper(), islower(), etc. to build the table
157 sources. This means that the default C locale which is set for your system will
158 control the contents of these default tables. You can change the default tables
159 by editing chartables.c and then re-building PCRE. If you do this, you should
160 probably also edit Makefile to ensure that the file doesn't ever get
161 re-generated.
162
163 The first two 256-byte tables provide lower casing and case flipping functions,
164 respectively. The next table consists of three 32-byte bit maps which identify
165 digits, "word" characters, and white space, respectively. These are used when
166 building 32-byte bit maps that represent character classes.
167
168 The final 256-byte table has bits indicating various character types, as
169 follows:
170
171 1 white space character
172 2 letter
173 4 decimal digit
174 8 hexadecimal digit
175 16 alphanumeric or '_'
176 128 regular expression metacharacter or binary zero
177
178 You should not alter the set of characters that contain the 128 bit, as that
179 will cause PCRE to malfunction.
180
181
182 The pcretest program
183 --------------------
184
185 This program is intended for testing PCRE, but it can also be used for
186 experimenting with regular expressions.
187
188 If it is given two filename arguments, it reads from the first and writes to
189 the second. If it is given only one filename argument, it reads from that file
190 and writes to stdout. Otherwise, it reads from stdin and writes to stdout, and
191 prompts for each line of input.
192
193 The program handles any number of sets of input on a single input file. Each
194 set starts with a regular expression, and continues with any number of data
195 lines to be matched against the pattern. An empty line signals the end of the
196 set. The regular expressions are given enclosed in any non-alphameric
197 delimiters other than backslash, for example
198
199 /(a|bc)x+yz/
200
201 White space before the initial delimiter is ignored. A regular expression may
202 be continued over several input lines, in which case the newline characters are
203 included within it. See the testinput files for many examples. It is possible
204 to include the delimiter within the pattern by escaping it, for example
205
206 /abc\/def/
207
208 If you do so, the escape and the delimiter form part of the pattern, but since
209 delimiters are always non-alphameric, this does not affect its interpretation.
210 If the terminating delimiter is immediately followed by a backslash, for
211 example,
212
213 /abc/\
214
215 then a backslash is added to the end of the pattern. This is done to provide a
216 way of testing the error condition that arises if a pattern finishes with a
217 backslash, because
218
219 /abc\/
220
221 is interpreted as the first line of a pattern that starts with "abc/", causing
222 pcretest to read the next line as a continuation of the regular expression.
223
224 The pattern may be followed by i, m, s, or x to set the PCRE_CASELESS,
225 PCRE_MULTILINE, PCRE_DOTALL, or PCRE_EXTENDED options, respectively. For
226 example:
227
228 /caseless/i
229
230 These modifier letters have the same effect as they do in Perl. There are
231 others which set PCRE options that do not correspond to anything in Perl: /A,
232 /E, and /X set PCRE_ANCHORED, PCRE_DOLLAR_ENDONLY, and PCRE_EXTRA respectively.
233
234 Searching for all possible matches within each subject string can be requested
235 by the /g or /G modifier. After finding a match, PCRE is called again to search
236 the remainder of the subject string. The difference between /g and /G is that
237 the former uses the startoffset argument to pcre_exec() to start searching at
238 a new point within the entire string (which is in effect what Perl does),
239 whereas the latter passes over a shortened substring. This makes a difference
240 to the matching process if the pattern begins with a lookbehind assertion
241 (including \b or \B).
242
243 If any call to pcre_exec() in a /g or /G sequence matches an empty string, the
244 next call is done with the PCRE_NOTEMPTY flag set so that it cannot match an
245 empty string again. This imitates the way Perl handles such cases when using
246 the /g modifier or the split() function.
247
248 There are a number of other modifiers for controlling the way pcretest
249 operates.
250
251 The /+ modifier requests that as well as outputting the substring that matched
252 the entire pattern, pcretest should in addition output the remainder of the
253 subject string. This is useful for tests where the subject contains multiple
254 copies of the same substring.
255
256 The /L modifier must be followed directly by the name of a locale, for example,
257
258 /pattern/Lfr
259
260 For this reason, it must be the last modifier letter. The given locale is set,
261 pcre_maketables() is called to build a set of character tables for the locale,
262 and this is then passed to pcre_compile() when compiling the regular
263 expression. Without an /L modifier, NULL is passed as the tables pointer; that
264 is, /L applies only to the expression on which it appears.
265
266 The /I modifier requests that pcretest output information about the compiled
267 expression (whether it is anchored, has a fixed first character, and so on). It
268 does this by calling pcre_info() after compiling an expression, and outputting
269 the information it gets back. If the pattern is studied, the results of that
270 are also output.
271
272 The /D modifier is a PCRE debugging feature, which also assumes /I. It causes
273 the internal form of compiled regular expressions to be output after
274 compilation.
275
276 The /S modifier causes pcre_study() to be called after the expression has been
277 compiled, and the results used when the expression is matched.
278
279 The /M modifier causes the size of memory block used to hold the compiled
280 pattern to be output.
281
282 Finally, the /P modifier causes pcretest to call PCRE via the POSIX wrapper API
283 rather than its native API. When this is done, all other modifiers except /i,
284 /m, and /+ are ignored. REG_ICASE is set if /i is present, and REG_NEWLINE is
285 set if /m is present. The wrapper functions force PCRE_DOLLAR_ENDONLY always,
286 and PCRE_DOTALL unless REG_NEWLINE is set.
287
288 Before each data line is passed to pcre_exec(), leading and trailing whitespace
289 is removed, and it is then scanned for \ escapes. The following are recognized:
290
291 \a alarm (= BEL)
292 \b backspace
293 \e escape
294 \f formfeed
295 \n newline
296 \r carriage return
297 \t tab
298 \v vertical tab
299 \nnn octal character (up to 3 octal digits)
300 \xhh hexadecimal character (up to 2 hex digits)
301
302 \A pass the PCRE_ANCHORED option to pcre_exec()
303 \B pass the PCRE_NOTBOL option to pcre_exec()
304 \Cdd call pcre_copy_substring() for substring dd after a successful match
305 (any decimal number less than 32)
306 \Gdd call pcre_get_substring() for substring dd after a successful match
307 (any decimal number less than 32)
308 \L call pcre_get_substringlist() after a successful match
309 \N pass the PCRE_NOTEMPTY option to pcre_exec()
310 \Odd set the size of the output vector passed to pcre_exec() to dd
311 (any number of decimal digits)
312 \Z pass the PCRE_NOTEOL option to pcre_exec()
313
314 A backslash followed by anything else just escapes the anything else. If the
315 very last character is a backslash, it is ignored. This gives a way of passing
316 an empty line as data, since a real empty line terminates the data input.
317
318 If /P was present on the regex, causing the POSIX wrapper API to be used, only
319 \B, and \Z have any effect, causing REG_NOTBOL and REG_NOTEOL to be passed to
320 regexec() respectively.
321
322 When a match succeeds, pcretest outputs the list of captured substrings that
323 pcre_exec() returns, starting with number 0 for the string that matched the
324 whole pattern. Here is an example of an interactive pcretest run.
325
326 $ pcretest
327 PCRE version 2.06 08-Jun-1999
328
329 re> /^abc(\d+)/
330 data> abc123
331 0: abc123
332 1: 123
333 data> xyz
334 No match
335
336 If the strings contain any non-printing characters, they are output as \0x
337 escapes. If the pattern has the /+ modifier, then the output for substring 0 is
338 followed by the the rest of the subject string, identified by "0+" like this:
339
340 re> /cat/+
341 data> cataract
342 0: cat
343 0+ aract
344
345 If the pattern has the /g or /G modifier, the results of successive matching
346 attempts are output in sequence, like this:
347
348 re> /\Bi(\w\w)/g
349 data> Mississippi
350 0: iss
351 1: ss
352 0: iss
353 1: ss
354 0: ipp
355 1: pp
356
357 "No match" is output only if the first match attempt fails.
358
359 If any of \C, \G, or \L are present in a data line that is successfully
360 matched, the substrings extracted by the convenience functions are output with
361 C, G, or L after the string number instead of a colon. This is in addition to
362 the normal full list. The string length (that is, the return from the
363 extraction function) is given in parentheses after each string for \C and \G.
364
365 Note that while patterns can be continued over several lines (a plain ">"
366 prompt is used for continuations), data lines may not. However newlines can be
367 included in data by means of the \n escape.
368
369 If the -p option is given to pcretest, it is equivalent to adding /P to each
370 regular expression: the POSIX wrapper API is used to call PCRE. None of the
371 following flags has any effect in this case.
372
373 If the option -d is given to pcretest, it is equivalent to adding /D to each
374 regular expression: the internal form is output after compilation.
375
376 If the option -i is given to pcretest, it is equivalent to adding /I to each
377 regular expression: information about the compiled pattern is given after
378 compilation.
379
380 If the option -m is given to pcretest, it outputs the size of each compiled
381 pattern after it has been compiled. It is equivalent to adding /M to each
382 regular expression. For compatibility with earlier versions of pcretest, -s is
383 a synonym for -m.
384
385 If the -t option is given, each compile, study, and match is run 20000 times
386 while being timed, and the resulting time per compile or match is output in
387 milliseconds. Do not set -t with -s, because you will then get the size output
388 20000 times and the timing will be distorted. If you want to change the number
389 of repetitions used for timing, edit the definition of LOOPREPEAT at the top of
390 pcretest.c
391
392
393
394 The perltest program
395 --------------------
396
397 The perltest program tests Perl's regular expressions; it has the same
398 specification as pcretest, and so can be given identical input, except that
399 input patterns can be followed only by Perl's lower case modifiers. The
400 contents of testinput1 and testinput3 meet this condition.
401
402 The data lines are processed as Perl double-quoted strings, so if they contain
403 " \ $ or @ characters, these have to be escaped. For this reason, all such
404 characters in testinput1 and testinput3 are escaped so that they can be used
405 for perltest as well as for pcretest, and the special upper case modifiers such
406 as /A that pcretest recognizes are not used in these files. The output should
407 be identical, apart from the initial identifying banner.
408
409 The testinput2 and testinput4 files are not suitable for feeding to perltest,
410 since they do make use of the special upper case modifiers and escapes that
411 pcretest uses to test some features of PCRE. The first of these files also
412 contains malformed regular expressions, in order to check that PCRE diagnoses
413 them correctly.
414
415 Philip Hazel <ph10@cam.ac.uk>
416 July 1999

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