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1 nigel 3 README file for PCRE (Perl-compatible regular expressions)
2     ----------------------------------------------------------
4 nigel 23 *******************************************************************************
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 nigel 25 * *
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 nigel 35 * *
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 nigel 23 *******************************************************************************
35 nigel 35
36 nigel 3 The distribution should contain the following files:
38     ChangeLog log of changes to the code
39 nigel 29 LICENCE conditions for the use of PCRE
40 nigel 37 Makefile for building PCRE in Unix systems
41 nigel 3 README this file
42 nigel 37 RunTest a Unix shell script for running tests
43 nigel 3 Tech.Notes notes on the encoding
44 nigel 37 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 nigel 27 dftables.c auxiliary program for building chartables.c
51 nigel 29 get.c )
52 nigel 25 maketables.c )
53 nigel 3 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 nigel 37 pgrep.1 man page source for pgrep
61     pgrep.1.txt plain text version
62     pgrep.1.HTML HTML version
63 nigel 3 pgrep.c source of a grep utility that uses PCRE
64     perltest Perl test program
65 nigel 33 testinput1 test data, compatible with Perl 5.004 and 5.005
66 nigel 3 testinput2 test data for error messages and non-Perl things
67 nigel 23 testinput3 test data, compatible with Perl 5.005
68 nigel 25 testinput4 test data for locale-specific tests
69 nigel 35 testoutput1 test results corresponding to testinput1
70 nigel 3 testoutput2 test results corresponding to testinput2
71 nigel 25 testoutput3 test results corresponding to testinput3
72     testoutput4 test results corresponding to testinput4
73 nigel 3
74 nigel 37 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 nigel 3
83 nigel 37 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.
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 nigel 23 contents of the corresponding testoutput file. A file called testtry is used to
93 nigel 37 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 nigel 3
96 nigel 23 RunTest 3
97 nigel 3
98 nigel 23 The first and third test files can also be fed directly into the perltest
99 nigel 37 script to check that Perl gives the same results. The third file requires the
100 nigel 23 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 nigel 3
104 nigel 29 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 nigel 7
108 nigel 25 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
116     ** Failed to set locale "fr"
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.
121 nigel 3 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 nigel 23 uses the POSIX API, it will have to be renamed or pointed at by a link.
129 nigel 3
131     Character tables
132     ----------------
134 nigel 25 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 nigel 35 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 nigel 3
141 nigel 25 The source file called chartables.c contains the default set of tables. This is
142 nigel 27 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 nigel 25 such as isalnum(), isalpha(), isupper(), islower(), etc. to build the table
145 nigel 35 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 nigel 3
151 nigel 25 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.
156     The final 256-byte table has bits indicating various character types, as
157 nigel 3 follows:
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
166     You should not alter the set of characters that contain the 128 bit, as that
167     will cause PCRE to malfunction.
170     The pcretest program
171     --------------------
173     This program is intended for testing PCRE, but it can also be used for
174     experimenting with regular expressions.
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.
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 nigel 29 delimiters other than backslash, for example
186 nigel 3
187     /(a|bc)x+yz/
189 nigel 29 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 nigel 3
194 nigel 29 /abc\/def/
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,
201     /abc/\
203 nigel 35 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 nigel 29
207     /abc\/
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.
212     The pattern may be followed by i, m, s, or x to set the PCRE_CASELESS,
213 nigel 35 PCRE_MULTILINE, PCRE_DOTALL, or PCRE_EXTENDED options, respectively. For
214     example:
215 nigel 29
216 nigel 35 /caseless/i
217 nigel 3
218 nigel 35 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 nigel 25
222 nigel 35 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).
231     There are a number of other modifiers for controlling the way pcretest
232     operates.
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.
239     The /L modifier must be followed directly by the name of a locale, for example,
241 nigel 25 /pattern/Lfr
243 nigel 35 For this reason, it must be the last modifier letter. The given locale is set,
244 nigel 25 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 nigel 35 expression. Without an /L modifier, NULL is passed as the tables pointer; that
247 nigel 25 is, /L applies only to the expression on which it appears.
249 nigel 35 The /I modifier requests that pcretest output information about the compiled
250 nigel 25 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.
255 nigel 35 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 nigel 25
259 nigel 35 The /S modifier causes pcre_study() to be called after the expression has been
260 nigel 25 compiled, and the results used when the expression is matched.
262 nigel 37 The /M modifier causes the size of memory block used to hold the compiled
263     pattern to be output.
264 nigel 31
265 nigel 35 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 nigel 3
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:
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)
285     \A pass the PCRE_ANCHORED option to pcre_exec()
286     \B pass the PCRE_NOTBOL option to pcre_exec()
287 nigel 29 \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 nigel 37 \N pass the PCRE_NOTEMPTY option to pcre_exec()
293 nigel 3 \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()
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.
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.
305 nigel 29 When a match succeeds, pcretest outputs the list of captured substrings that
306 nigel 3 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.
309     $ pcretest
310 nigel 35 PCRE version 2.06 08-Jun-1999
311 nigel 3
312 nigel 23 re> /^abc(\d+)/
313     data> abc123
314 nigel 35 0: abc123
315     1: 123
316 nigel 23 data> xyz
317 nigel 3 No match
319 nigel 35 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:
323     re> /cat/+
324     data> cataract
325     0: cat
326     0+ aract
328     If the pattern has the /g or /G modifier, the results of successive matching
329     attempts are output in sequence, like this:
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
340     "No match" is output only if the first match attempt fails.
342 nigel 29 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.
348 nigel 3 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.
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.
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.
359 nigel 25 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 nigel 3
363 nigel 31 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 nigel 3
368 nigel 29 If the -t option is given, each compile, study, and match is run 20000 times
369 nigel 3 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 nigel 29 20000 times and the timing will be distorted. If you want to change the number
372 nigel 23 of repetitions used for timing, edit the definition of LOOPREPEAT at the top of
373     pcretest.c
374 nigel 3
377     The perltest program
378     --------------------
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 nigel 35 input patterns can be followed only by Perl's lower case modifiers. The
383     contents of testinput1 and testinput3 meet this condition.
384 nigel 3
385 nigel 37 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 nigel 3
392 nigel 35 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 nigel 25 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 nigel 3
398     Philip Hazel <ph10@cam.ac.uk>
399 nigel 37 July 1999

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