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

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