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1 nigel 3 README file for PCRE (Perl-compatible regular expressions)
2     ----------------------------------------------------------
3    
4 nigel 23 *******************************************************************************
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 nigel 25 * *
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 nigel 35 * *
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 nigel 23 *******************************************************************************
34    
35 nigel 35
36 nigel 3 The distribution should contain the following files:
37    
38     ChangeLog log of changes to the code
39 nigel 29 LICENCE conditions for the use of PCRE
40 nigel 3 Makefile for building PCRE
41     README this file
42 nigel 23 RunTest a shell script for running tests
43 nigel 3 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 nigel 27 dftables.c auxiliary program for building chartables.c
47 nigel 29 get.c )
48 nigel 25 maketables.c )
49 nigel 3 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 nigel 33 testinput1 test data, compatible with Perl 5.004 and 5.005
60 nigel 3 testinput2 test data for error messages and non-Perl things
61 nigel 23 testinput3 test data, compatible with Perl 5.005
62 nigel 25 testinput4 test data for locale-specific tests
63 nigel 35 testoutput1 test results corresponding to testinput1
64 nigel 3 testoutput2 test results corresponding to testinput2
65 nigel 25 testoutput3 test results corresponding to testinput3
66     testoutput4 test results corresponding to testinput4
67 nigel 3
68 nigel 23 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 nigel 3
73 nigel 23 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 nigel 3
78 nigel 23 To run pcretest on just one of the test files, give its number as an argument
79     to RunTest, for example:
80 nigel 3
81 nigel 23 RunTest 3
82 nigel 3
83 nigel 23 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 nigel 3
89 nigel 29 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 nigel 7
93 nigel 25 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 nigel 3 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 nigel 23 uses the POSIX API, it will have to be renamed or pointed at by a link.
123 nigel 3
124    
125     Character tables
126     ----------------
127    
128 nigel 25 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 nigel 35 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 nigel 3
135 nigel 25 The source file called chartables.c contains the default set of tables. This is
136 nigel 27 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 nigel 25 such as isalnum(), isalpha(), isupper(), islower(), etc. to build the table
139 nigel 35 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 nigel 3
145 nigel 25 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 nigel 3 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 nigel 29 delimiters other than backslash, for example
180 nigel 3
181     /(a|bc)x+yz/
182    
183 nigel 29 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 nigel 3
188 nigel 29 /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 nigel 35 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 nigel 29
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 nigel 35 PCRE_MULTILINE, PCRE_DOTALL, or PCRE_EXTENDED options, respectively. For
208     example:
209 nigel 29
210 nigel 35 /caseless/i
211 nigel 3
212 nigel 35 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 nigel 25
216 nigel 35 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 nigel 25 /pattern/Lfr
236    
237 nigel 35 For this reason, it must be the last modifier letter. The given locale is set,
238 nigel 25 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 nigel 35 expression. Without an /L modifier, NULL is passed as the tables pointer; that
241 nigel 25 is, /L applies only to the expression on which it appears.
242    
243 nigel 35 The /I modifier requests that pcretest output information about the compiled
244 nigel 25 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 nigel 35 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 nigel 25
253 nigel 35 The /S modifier causes pcre_study() to be called after the expression has been
254 nigel 25 compiled, and the results used when the expression is matched.
255    
256 nigel 35 The /M modifier causes information about the size of memory block used to hold
257 nigel 31 the compile pattern to be output.
258    
259 nigel 35 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 nigel 3
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 nigel 29 \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 nigel 3 \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 nigel 29 When a match succeeds, pcretest outputs the list of captured substrings that
299 nigel 3 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 nigel 35 PCRE version 2.06 08-Jun-1999
304 nigel 3
305 nigel 23 re> /^abc(\d+)/
306     data> abc123
307 nigel 35 0: abc123
308     1: 123
309 nigel 23 data> xyz
310 nigel 3 No match
311    
312 nigel 35 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 nigel 29 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 nigel 3 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 nigel 25 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 nigel 3
356 nigel 31 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 nigel 3
361 nigel 29 If the -t option is given, each compile, study, and match is run 20000 times
362 nigel 3 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 nigel 29 20000 times and the timing will be distorted. If you want to change the number
365 nigel 23 of repetitions used for timing, edit the definition of LOOPREPEAT at the top of
366     pcretest.c
367 nigel 3
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 nigel 35 input patterns can be followed only by Perl's lower case modifiers. The
376     contents of testinput1 and testinput3 meet this condition.
377 nigel 3
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 nigel 35 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 nigel 3
385 nigel 35 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 nigel 25 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 nigel 3
391     Philip Hazel <ph10@cam.ac.uk>
392 nigel 35 June 1999

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