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1 nigel 3 README file for PCRE (Perl-compatible regular expressions)
2     ----------------------------------------------------------
4     The distribution should contain the following files:
6     ChangeLog log of changes to the code
7     Makefile for building PCRE
8     Performance notes on performance
9     README this file
10     Tech.Notes notes on the encoding
11     pcre.3 man page for the functions
12     pcreposix.3 man page for the POSIX wrapper API
13     maketables.c auxiliary program for building chartables.c
14     study.c ) source of
15     pcre.c ) the functions
16     pcreposix.c )
17     pcre.h header for the external API
18     pcreposix.h header for the external POSIX wrapper API
19     internal.h header for internal use
20     pcretest.c test program
21     pgrep.1 man page for pgrep
22     pgrep.c source of a grep utility that uses PCRE
23     perltest Perl test program
24     testinput test data, compatible with Perl
25     testinput2 test data for error messages and non-Perl things
26     testoutput test results corresponding to testinput
27     testoutput2 test results corresponding to testinput2
29     To build PCRE, edit Makefile for your system (it is a fairly simple make file)
30     and then run it. It builds a two libraries called libpcre.a and libpcreposix.a,
31     a test program called pcretest, and the pgrep command.
33     To test PCRE, run pcretest on the file testinput, and compare the output with
34     the contents of testoutput. There should be no differences. For example:
36 nigel 7 pcretest testinput some.file
37     diff some.file testoutput
38 nigel 3
39     Do the same with testinput2, comparing the output with testoutput2, but this
40     time using the -i flag for pcretest, i.e.
42 nigel 7 pcretest -i testinput2 some.file
43     diff some.file testoutput2
44 nigel 3
45 nigel 7 The make target "runtest" runs both these tests, using the file "testtry" to
46     store the intermediate output, deleting it at the end if all goes well.
48 nigel 3 There are two sets of tests because the first set can also be fed directly into
49     the perltest program to check that Perl gives the same results. The second set
50     of tests check pcre_info(), pcre_study(), error detection and run-time flags
51     that are specific to PCRE, as well as the POSIX wrapper API.
53     To install PCRE, copy libpcre.a to any suitable library directory (e.g.
54     /usr/local/lib), pcre.h to any suitable include directory (e.g.
55     /usr/local/include), and pcre.3 to any suitable man directory (e.g.
56     /usr/local/man/man3).
58     To install the pgrep command, copy it to any suitable binary directory, (e.g.
59     /usr/local/bin) and pgrep.1 to any suitable man directory (e.g.
60     /usr/local/man/man1).
62     PCRE has its own native API, but a set of "wrapper" functions that are based on
63     the POSIX API are also supplied in the library libpcreposix.a. Note that this
64     just provides a POSIX calling interface to PCRE: the regular expressions
65     themselves still follow Perl syntax and semantics. The header file
66     for the POSIX-style functions is called pcreposix.h. The official POSIX name is
67     regex.h, but I didn't want to risk possible problems with existing files of
68     that name by distributing it that way. To use it with an existing program that
69     uses the POSIX API it will have to be renamed or pointed at by a link.
72     Character tables
73     ----------------
75     PCRE uses four tables for manipulating and identifying characters. These are
76     compiled from a source file called chartables.c. This is not supplied in
77     the distribution, but is built by the program maketables (compiled from
78     maketables.c), which uses the ANSI C character handling functions such as
79     isalnum(), isalpha(), isupper(), islower(), etc. to build the table sources.
80     This means that the default C locale set in your system may affect the contents
81     of the tables. You can change the tables by editing chartables.c and then
82     re-building PCRE. If you do this, you should probably also edit Makefile to
83     ensure that the file doesn't ever get re-generated.
85     The first two tables pcre_lcc[] and pcre_fcc[] provide lower casing and a
86     case flipping functions, respectively. The pcre_cbits[] table consists of four
87     32-byte bit maps which identify digits, letters, "word" characters, and white
88     space, respectively. These are used when building 32-byte bit maps that
89     represent character classes.
91     The pcre_ctypes[] table has bits indicating various character types, as
92     follows:
94     1 white space character
95     2 letter
96     4 decimal digit
97     8 hexadecimal digit
98     16 alphanumeric or '_'
99     128 regular expression metacharacter or binary zero
101     You should not alter the set of characters that contain the 128 bit, as that
102     will cause PCRE to malfunction.
105     The pcretest program
106     --------------------
108     This program is intended for testing PCRE, but it can also be used for
109     experimenting with regular expressions.
111     If it is given two filename arguments, it reads from the first and writes to
112     the second. If it is given only one filename argument, it reads from that file
113     and writes to stdout. Otherwise, it reads from stdin and writes to stdout, and
114     prompts for each line of input.
116     The program handles any number of sets of input on a single input file. Each
117     set starts with a regular expression, and continues with any number of data
118     lines to be matched against the pattern. An empty line signals the end of the
119     set. The regular expressions are given enclosed in any non-alphameric
120     delimiters, for example
122     /(a|bc)x+yz/
124     and may be followed by i, m, s, or x to set the PCRE_CASELESS, PCRE_MULTILINE,
125     PCRE_DOTALL, or PCRE_EXTENDED options, respectively. These options have the
126     same effect as they do in Perl.
128     There are also some upper case options that do not match Perl options: /A, /E,
129     and /X set PCRE_ANCHORED, PCRE_DOLLAR_ENDONLY, and PCRE_EXTRA respectively.
130     The /D option is a PCRE debugging feature. It causes the internal form of
131     compiled regular expressions to be output after compilation. The /S option
132     causes pcre_study() to be called after the expression has been compiled, and
133     the results used when the expression is matched. If /I is present as well as
134     /S, then pcre_study() is called with the PCRE_CASELESS option.
136     Finally, the /P option causes pcretest to call PCRE via the POSIX wrapper API
137     rather than its native API. When this is done, all other options except /i and
138     /m are ignored. REG_ICASE is set if /i is present, and REG_NEWLINE is set if /m
139     is present. The wrapper functions force PCRE_DOLLAR_ENDONLY always, and
140     PCRE_DOTALL unless REG_NEWLINE is set.
142     A regular expression can extend over several lines of input; the newlines are
143     included in it. See the testinput file for many examples.
145     Before each data line is passed to pcre_exec(), leading and trailing whitespace
146     is removed, and it is then scanned for \ escapes. The following are recognized:
148     \a alarm (= BEL)
149     \b backspace
150     \e escape
151     \f formfeed
152     \n newline
153     \r carriage return
154     \t tab
155     \v vertical tab
156     \nnn octal character (up to 3 octal digits)
157     \xhh hexadecimal character (up to 2 hex digits)
159     \A pass the PCRE_ANCHORED option to pcre_exec()
160     \B pass the PCRE_NOTBOL option to pcre_exec()
161     \E pass the PCRE_DOLLAR_ENDONLY option to pcre_exec()
162     \I pass the PCRE_CASELESS option to pcre_exec()
163     \M pass the PCRE_MULTILINE option to pcre_exec()
164     \S pass the PCRE_DOTALL option to pcre_exec()
165     \Odd set the size of the output vector passed to pcre_exec() to dd
166     (any number of decimal digits)
167     \Z pass the PCRE_NOTEOL option to pcre_exec()
169     A backslash followed by anything else just escapes the anything else. If the
170     very last character is a backslash, it is ignored. This gives a way of passing
171     an empty line as data, since a real empty line terminates the data input.
173     If /P was present on the regex, causing the POSIX wrapper API to be used, only
174     \B, and \Z have any effect, causing REG_NOTBOL and REG_NOTEOL to be passed to
175     regexec() respectively.
177     When a match succeeds, pcretest outputs the list of identified substrings that
178     pcre_exec() returns, starting with number 0 for the string that matched the
179     whole pattern. Here is an example of an interactive pcretest run.
181     $ pcretest
182     Testing Perl-Compatible Regular Expressions
183     PCRE version 0.90 08-Sep-1997
185     re> /^abc(\d+)/
186     data> abc123
187     0: abc123
188     1: 123
189     data> xyz
190     No match
192     Note that while patterns can be continued over several lines (a plain ">"
193     prompt is used for continuations), data lines may not. However newlines can be
194     included in data by means of the \n escape.
196     If the -p option is given to pcretest, it is equivalent to adding /P to each
197     regular expression: the POSIX wrapper API is used to call PCRE. None of the
198     following flags has any effect in this case.
200     If the option -d is given to pcretest, it is equivalent to adding /D to each
201     regular expression: the internal form is output after compilation.
203     If the option -i (for "information") is given to pcretest, it calls pcre_info()
204     after compiling an expression, and outputs the information it gets back. If the
205     pattern is studied, the results of that are also output.
207     If the option -s is given to pcretest, it outputs the size of each compiled
208     pattern after it has been compiled.
210     If the -t option is given, each compile, study, and match is run 2000 times
211     while being timed, and the resulting time per compile or match is output in
212     milliseconds. Do not set -t with -s, because you will then get the size output
213     2000 times and the timing will be distorted.
217     The perltest program
218     --------------------
220     The perltest program tests Perl's regular expressions; it has the same
221     specification as pcretest, and so can be given identical input, except that
222     input patterns can be followed only by Perl's lower case options.
224     The data lines are processed as Perl strings, so if they contain $ or @
225     characters, these have to be escaped. For this reason, all such characters in
226     the testinput file are escaped so that it can be used for perltest as well as
227     for pcretest, and the special upper case options such as /A that pcretest
228     recognizes are not used in this file. The output should be identical, apart
229     from the initial identifying banner.
231     The testinput2 file is not suitable for feeding to Perltest, since it does
232     make use of the special upper case options and escapes that pcretest uses to
233     test additional features of PCRE.
235     Philip Hazel <ph10@cam.ac.uk>
236     October 1997

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