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1 README file for PCRE (Perl-compatible regular expressions)
2 ----------------------------------------------------------
4 *******************************************************************************
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 * *
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 *******************************************************************************
21 The distribution should contain the following files:
23 ChangeLog log of changes to the code
24 LICENCE conditions for the use of PCRE
25 Makefile for building PCRE
26 README this file
27 RunTest a shell script for running tests
28 Tech.Notes notes on the encoding
29 pcre.3 man page for the functions
30 pcreposix.3 man page for the POSIX wrapper API
31 dftables.c auxiliary program for building chartables.c
32 get.c )
33 maketables.c )
34 study.c ) source of
35 pcre.c ) the functions
36 pcreposix.c )
37 pcre.h header for the external API
38 pcreposix.h header for the external POSIX wrapper API
39 internal.h header for internal use
40 pcretest.c test program
41 pgrep.1 man page for pgrep
42 pgrep.c source of a grep utility that uses PCRE
43 perltest Perl test program
44 testinput test data, compatible with Perl 5.004 and 5.005
45 testinput2 test data for error messages and non-Perl things
46 testinput3 test data, compatible with Perl 5.005
47 testinput4 test data for locale-specific tests
48 testoutput test results corresponding to testinput
49 testoutput2 test results corresponding to testinput2
50 testoutput3 test results corresponding to testinput3
51 testoutput4 test results corresponding to testinput4
53 To build PCRE, edit Makefile for your system (it is a fairly simple make file,
54 and there are some comments at the top) and then run it. It builds two
55 libraries called libpcre.a and libpcreposix.a, a test program called pcretest,
56 and the pgrep command.
58 To test PCRE, run the RunTest script in the pcre directory. This runs pcretest
59 on each of the testinput files in turn, and compares the output with the
60 contents of the corresponding testoutput file. A file called testtry is used to
61 hold the output from pcretest (which is documented below).
63 To run pcretest on just one of the test files, give its number as an argument
64 to RunTest, for example:
66 RunTest 3
68 The first and third test files can also be fed directly into the perltest
69 program to check that Perl gives the same results. The third file requires the
70 additional features of release 5.005, which is why it is kept separate from the
71 main test input, which needs only Perl 5.004. In the long run, when 5.005 is
72 widespread, these two test files may get amalgamated.
74 The second set of tests check pcre_info(), pcre_study(), pcre_copy_substring(),
75 pcre_get_substring(), pcre_get_substring_list(), error detection and run-time
76 flags that are specific to PCRE, as well as the POSIX wrapper API.
78 The fourth set of tests checks pcre_maketables(), the facility for building a
79 set of character tables for a specific locale and using them instead of the
80 default tables. The tests make use of the "fr" (French) locale. Before running
81 the test, the script checks for the presence of this locale by running the
82 "locale" command. If that command fails, or if it doesn't include "fr" in the
83 list of available locales, the fourth test cannot be run, and a comment is
84 output to say why. If running this test produces instances of the error
86 ** Failed to set locale "fr"
88 in the comparison output, it means that locale is not available on your system,
89 despite being listed by "locale". This does not mean that PCRE is broken.
91 To install PCRE, copy libpcre.a to any suitable library directory (e.g.
92 /usr/local/lib), pcre.h to any suitable include directory (e.g.
93 /usr/local/include), and pcre.3 to any suitable man directory (e.g.
94 /usr/local/man/man3).
96 To install the pgrep command, copy it to any suitable binary directory, (e.g.
97 /usr/local/bin) and pgrep.1 to any suitable man directory (e.g.
98 /usr/local/man/man1).
100 PCRE has its own native API, but a set of "wrapper" functions that are based on
101 the POSIX API are also supplied in the library libpcreposix.a. Note that this
102 just provides a POSIX calling interface to PCRE: the regular expressions
103 themselves still follow Perl syntax and semantics. The header file
104 for the POSIX-style functions is called pcreposix.h. The official POSIX name is
105 regex.h, but I didn't want to risk possible problems with existing files of
106 that name by distributing it that way. To use it with an existing program that
107 uses the POSIX API, it will have to be renamed or pointed at by a link.
110 Character tables
111 ----------------
113 PCRE uses four tables for manipulating and identifying characters. The final
114 argument of the pcre_compile() function is a pointer to a block of memory
115 containing the concatenated tables. A call to pcre_maketables() is used to
116 generate a set of tables in the current locale. However, if the final argument
117 is passed as NULL, a set of default tables that is built into the binary is
118 used.
120 The source file called chartables.c contains the default set of tables. This is
121 not supplied in the distribution, but is built by the program dftables
122 (compiled from dftables.c), which uses the ANSI C character handling functions
123 such as isalnum(), isalpha(), isupper(), islower(), etc. to build the table
124 sources. This means that the default C locale set your system will control the
125 contents of the tables. You can change the default tables by editing
126 chartables.c and then re-building PCRE. If you do this, you should probably
127 also edit Makefile to ensure that the file doesn't ever get re-generated.
129 The first two 256-byte tables provide lower casing and case flipping functions,
130 respectively. The next table consists of three 32-byte bit maps which identify
131 digits, "word" characters, and white space, respectively. These are used when
132 building 32-byte bit maps that represent character classes.
134 The final 256-byte table has bits indicating various character types, as
135 follows:
137 1 white space character
138 2 letter
139 4 decimal digit
140 8 hexadecimal digit
141 16 alphanumeric or '_'
142 128 regular expression metacharacter or binary zero
144 You should not alter the set of characters that contain the 128 bit, as that
145 will cause PCRE to malfunction.
148 The pcretest program
149 --------------------
151 This program is intended for testing PCRE, but it can also be used for
152 experimenting with regular expressions.
154 If it is given two filename arguments, it reads from the first and writes to
155 the second. If it is given only one filename argument, it reads from that file
156 and writes to stdout. Otherwise, it reads from stdin and writes to stdout, and
157 prompts for each line of input.
159 The program handles any number of sets of input on a single input file. Each
160 set starts with a regular expression, and continues with any number of data
161 lines to be matched against the pattern. An empty line signals the end of the
162 set. The regular expressions are given enclosed in any non-alphameric
163 delimiters other than backslash, for example
165 /(a|bc)x+yz/
167 White space before the initial delimiter is ignored. A regular expression may
168 be continued over several input lines, in which case the newline characters are
169 included within it. See the testinput files for many examples. It is possible
170 to include the delimiter within the pattern by escaping it, for example
172 /abc\/def/
174 If you do so, the escape and the delimiter form part of the pattern, but since
175 delimiters are always non-alphameric, this does not affect its interpretation.
176 If the terminating delimiter is immediately followed by a backslash, for
177 example,
179 /abc/\
181 then a backslash is added to the end of the pattern. This provides a way of
182 testing the error condition that arises if a pattern finishes with a backslash,
183 because
185 /abc\/
187 is interpreted as the first line of a pattern that starts with "abc/", causing
188 pcretest to read the next line as a continuation of the regular expression.
190 The pattern may be followed by i, m, s, or x to set the PCRE_CASELESS,
191 PCRE_MULTILINE, PCRE_DOTALL, or PCRE_EXTENDED options, respectively. These
192 options have the same effect as they do in Perl.
194 There are also some upper case options that do not match Perl options: /A, /E,
195 and /X set PCRE_ANCHORED, PCRE_DOLLAR_ENDONLY, and PCRE_EXTRA respectively.
197 The /L option must be followed directly by the name of a locale, for example,
199 /pattern/Lfr
201 For this reason, it must be the last option letter. The given locale is set,
202 pcre_maketables() is called to build a set of character tables for the locale,
203 and this is then passed to pcre_compile() when compiling the regular
204 expression. Without an /L option, NULL is passed as the tables pointer; that
205 is, /L applies only to the expression on which it appears.
207 The /I option requests that pcretest output information about the compiled
208 expression (whether it is anchored, has a fixed first character, and so on). It
209 does this by calling pcre_info() after compiling an expression, and outputting
210 the information it gets back. If the pattern is studied, the results of that
211 are also output.
213 The /D option is a PCRE debugging feature, which also assumes /I. It causes the
214 internal form of compiled regular expressions to be output after compilation.
216 The /S option causes pcre_study() to be called after the expression has been
217 compiled, and the results used when the expression is matched.
219 Finally, the /P option causes pcretest to call PCRE via the POSIX wrapper API
220 rather than its native API. When this is done, all other options except /i and
221 /m are ignored. REG_ICASE is set if /i is present, and REG_NEWLINE is set if /m
222 is present. The wrapper functions force PCRE_DOLLAR_ENDONLY always, and
223 PCRE_DOTALL unless REG_NEWLINE is set.
225 Before each data line is passed to pcre_exec(), leading and trailing whitespace
226 is removed, and it is then scanned for \ escapes. The following are recognized:
228 \a alarm (= BEL)
229 \b backspace
230 \e escape
231 \f formfeed
232 \n newline
233 \r carriage return
234 \t tab
235 \v vertical tab
236 \nnn octal character (up to 3 octal digits)
237 \xhh hexadecimal character (up to 2 hex digits)
239 \A pass the PCRE_ANCHORED option to pcre_exec()
240 \B pass the PCRE_NOTBOL option to pcre_exec()
241 \Cdd call pcre_copy_substring() for substring dd after a successful match
242 (any decimal number less than 32)
243 \Gdd call pcre_get_substring() for substring dd after a successful match
244 (any decimal number less than 32)
245 \L call pcre_get_substringlist() after a successful match
246 \Odd set the size of the output vector passed to pcre_exec() to dd
247 (any number of decimal digits)
248 \Z pass the PCRE_NOTEOL option to pcre_exec()
250 A backslash followed by anything else just escapes the anything else. If the
251 very last character is a backslash, it is ignored. This gives a way of passing
252 an empty line as data, since a real empty line terminates the data input.
254 If /P was present on the regex, causing the POSIX wrapper API to be used, only
255 \B, and \Z have any effect, causing REG_NOTBOL and REG_NOTEOL to be passed to
256 regexec() respectively.
258 When a match succeeds, pcretest outputs the list of captured substrings that
259 pcre_exec() returns, starting with number 0 for the string that matched the
260 whole pattern. Here is an example of an interactive pcretest run.
262 $ pcretest
263 Testing Perl-Compatible Regular Expressions
264 PCRE version 0.90 08-Sep-1997
266 re> /^abc(\d+)/
267 data> abc123
268 0: abc123
269 1: 123
270 data> xyz
271 No match
273 If any of \C, \G, or \L are present in a data line that is successfully
274 matched, the substrings extracted by the convenience functions are output with
275 C, G, or L after the string number instead of a colon. This is in addition to
276 the normal full list. The string length (that is, the return from the
277 extraction function) is given in parentheses after each string for \C and \G.
279 Note that while patterns can be continued over several lines (a plain ">"
280 prompt is used for continuations), data lines may not. However newlines can be
281 included in data by means of the \n escape.
283 If the -p option is given to pcretest, it is equivalent to adding /P to each
284 regular expression: the POSIX wrapper API is used to call PCRE. None of the
285 following flags has any effect in this case.
287 If the option -d is given to pcretest, it is equivalent to adding /D to each
288 regular expression: the internal form is output after compilation.
290 If the option -i is given to pcretest, it is equivalent to adding /I to each
291 regular expression: information about the compiled pattern is given after
292 compilation.
294 If the option -s is given to pcretest, it outputs the size of each compiled
295 pattern after it has been compiled.
297 If the -t option is given, each compile, study, and match is run 20000 times
298 while being timed, and the resulting time per compile or match is output in
299 milliseconds. Do not set -t with -s, because you will then get the size output
300 20000 times and the timing will be distorted. If you want to change the number
301 of repetitions used for timing, edit the definition of LOOPREPEAT at the top of
302 pcretest.c
306 The perltest program
307 --------------------
309 The perltest program tests Perl's regular expressions; it has the same
310 specification as pcretest, and so can be given identical input, except that
311 input patterns can be followed only by Perl's lower case options. The contents
312 of testinput and testinput3 meet this condition.
314 The data lines are processed as Perl strings, so if they contain $ or @
315 characters, these have to be escaped. For this reason, all such characters in
316 the testinput file are escaped so that it can be used for perltest as well as
317 for pcretest, and the special upper case options such as /A that pcretest
318 recognizes are not used in this file. The output should be identical, apart
319 from the initial identifying banner.
321 The testinput2 and testinput4 files are not suitable for feeding to Perltest,
322 since they do make use of the special upper case options and escapes that
323 pcretest uses to test some features of PCRE. The first of these files also
324 contains malformed regular expressions, in order to check that PCRE diagnoses
325 them correctly.
327 Philip Hazel <ph10@cam.ac.uk>
328 February 1999

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