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1 nigel 3 README file for PCRE (Perl-compatible regular expressions)
2     ----------------------------------------------------------
3    
4     The distribution should contain the following files:
5    
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
28    
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.
32    
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:
35    
36     pcretest testinput /tmp/anything
37     diff /tmp/anything testoutput
38    
39     Do the same with testinput2, comparing the output with testoutput2, but this
40     time using the -i flag for pcretest, i.e.
41    
42     pcretest -i testinput2 /tmp/anything
43     diff /tmp/anything testoutput2
44    
45     There are two sets of tests because the first set can also be fed directly into
46     the perltest program to check that Perl gives the same results. The second set
47     of tests check pcre_info(), pcre_study(), error detection and run-time flags
48     that are specific to PCRE, as well as the POSIX wrapper API.
49    
50     To install PCRE, copy libpcre.a to any suitable library directory (e.g.
51     /usr/local/lib), pcre.h to any suitable include directory (e.g.
52     /usr/local/include), and pcre.3 to any suitable man directory (e.g.
53     /usr/local/man/man3).
54    
55     To install the pgrep command, copy it to any suitable binary directory, (e.g.
56     /usr/local/bin) and pgrep.1 to any suitable man directory (e.g.
57     /usr/local/man/man1).
58    
59     PCRE has its own native API, but a set of "wrapper" functions that are based on
60     the POSIX API are also supplied in the library libpcreposix.a. Note that this
61     just provides a POSIX calling interface to PCRE: the regular expressions
62     themselves still follow Perl syntax and semantics. The header file
63     for the POSIX-style functions is called pcreposix.h. The official POSIX name is
64     regex.h, but I didn't want to risk possible problems with existing files of
65     that name by distributing it that way. To use it with an existing program that
66     uses the POSIX API it will have to be renamed or pointed at by a link.
67    
68    
69     Character tables
70     ----------------
71    
72     PCRE uses four tables for manipulating and identifying characters. These are
73     compiled from a source file called chartables.c. This is not supplied in
74     the distribution, but is built by the program maketables (compiled from
75     maketables.c), which uses the ANSI C character handling functions such as
76     isalnum(), isalpha(), isupper(), islower(), etc. to build the table sources.
77     This means that the default C locale set in your system may affect the contents
78     of the tables. You can change the tables by editing chartables.c and then
79     re-building PCRE. If you do this, you should probably also edit Makefile to
80     ensure that the file doesn't ever get re-generated.
81    
82     The first two tables pcre_lcc[] and pcre_fcc[] provide lower casing and a
83     case flipping functions, respectively. The pcre_cbits[] table consists of four
84     32-byte bit maps which identify digits, letters, "word" characters, and white
85     space, respectively. These are used when building 32-byte bit maps that
86     represent character classes.
87    
88     The pcre_ctypes[] table has bits indicating various character types, as
89     follows:
90    
91     1 white space character
92     2 letter
93     4 decimal digit
94     8 hexadecimal digit
95     16 alphanumeric or '_'
96     128 regular expression metacharacter or binary zero
97    
98     You should not alter the set of characters that contain the 128 bit, as that
99     will cause PCRE to malfunction.
100    
101    
102     The pcretest program
103     --------------------
104    
105     This program is intended for testing PCRE, but it can also be used for
106     experimenting with regular expressions.
107    
108     If it is given two filename arguments, it reads from the first and writes to
109     the second. If it is given only one filename argument, it reads from that file
110     and writes to stdout. Otherwise, it reads from stdin and writes to stdout, and
111     prompts for each line of input.
112    
113     The program handles any number of sets of input on a single input file. Each
114     set starts with a regular expression, and continues with any number of data
115     lines to be matched against the pattern. An empty line signals the end of the
116     set. The regular expressions are given enclosed in any non-alphameric
117     delimiters, for example
118    
119     /(a|bc)x+yz/
120    
121     and may be followed by i, m, s, or x to set the PCRE_CASELESS, PCRE_MULTILINE,
122     PCRE_DOTALL, or PCRE_EXTENDED options, respectively. These options have the
123     same effect as they do in Perl.
124    
125     There are also some upper case options that do not match Perl options: /A, /E,
126     and /X set PCRE_ANCHORED, PCRE_DOLLAR_ENDONLY, and PCRE_EXTRA respectively.
127     The /D option is a PCRE debugging feature. It causes the internal form of
128     compiled regular expressions to be output after compilation. The /S option
129     causes pcre_study() to be called after the expression has been compiled, and
130     the results used when the expression is matched. If /I is present as well as
131     /S, then pcre_study() is called with the PCRE_CASELESS option.
132    
133     Finally, the /P option causes pcretest to call PCRE via the POSIX wrapper API
134     rather than its native API. When this is done, all other options except /i and
135     /m are ignored. REG_ICASE is set if /i is present, and REG_NEWLINE is set if /m
136     is present. The wrapper functions force PCRE_DOLLAR_ENDONLY always, and
137     PCRE_DOTALL unless REG_NEWLINE is set.
138    
139     A regular expression can extend over several lines of input; the newlines are
140     included in it. See the testinput file for many examples.
141    
142     Before each data line is passed to pcre_exec(), leading and trailing whitespace
143     is removed, and it is then scanned for \ escapes. The following are recognized:
144    
145     \a alarm (= BEL)
146     \b backspace
147     \e escape
148     \f formfeed
149     \n newline
150     \r carriage return
151     \t tab
152     \v vertical tab
153     \nnn octal character (up to 3 octal digits)
154     \xhh hexadecimal character (up to 2 hex digits)
155    
156     \A pass the PCRE_ANCHORED option to pcre_exec()
157     \B pass the PCRE_NOTBOL option to pcre_exec()
158     \E pass the PCRE_DOLLAR_ENDONLY option to pcre_exec()
159     \I pass the PCRE_CASELESS option to pcre_exec()
160     \M pass the PCRE_MULTILINE option to pcre_exec()
161     \S pass the PCRE_DOTALL option to pcre_exec()
162     \Odd set the size of the output vector passed to pcre_exec() to dd
163     (any number of decimal digits)
164     \Z pass the PCRE_NOTEOL option to pcre_exec()
165    
166     A backslash followed by anything else just escapes the anything else. If the
167     very last character is a backslash, it is ignored. This gives a way of passing
168     an empty line as data, since a real empty line terminates the data input.
169    
170     If /P was present on the regex, causing the POSIX wrapper API to be used, only
171     \B, and \Z have any effect, causing REG_NOTBOL and REG_NOTEOL to be passed to
172     regexec() respectively.
173    
174     When a match succeeds, pcretest outputs the list of identified substrings that
175     pcre_exec() returns, starting with number 0 for the string that matched the
176     whole pattern. Here is an example of an interactive pcretest run.
177    
178     $ pcretest
179     Testing Perl-Compatible Regular Expressions
180     PCRE version 0.90 08-Sep-1997
181    
182     re> /^abc(\d+)/
183     data> abc123
184     0: abc123
185     1: 123
186     data> xyz
187     No match
188    
189     Note that while patterns can be continued over several lines (a plain ">"
190     prompt is used for continuations), data lines may not. However newlines can be
191     included in data by means of the \n escape.
192    
193     If the -p option is given to pcretest, it is equivalent to adding /P to each
194     regular expression: the POSIX wrapper API is used to call PCRE. None of the
195     following flags has any effect in this case.
196    
197     If the option -d is given to pcretest, it is equivalent to adding /D to each
198     regular expression: the internal form is output after compilation.
199    
200     If the option -i (for "information") is given to pcretest, it calls pcre_info()
201     after compiling an expression, and outputs the information it gets back. If the
202     pattern is studied, the results of that are also output.
203    
204     If the option -s is given to pcretest, it outputs the size of each compiled
205     pattern after it has been compiled.
206    
207     If the -t option is given, each compile, study, and match is run 2000 times
208     while being timed, and the resulting time per compile or match is output in
209     milliseconds. Do not set -t with -s, because you will then get the size output
210     2000 times and the timing will be distorted.
211    
212    
213    
214     The perltest program
215     --------------------
216    
217     The perltest program tests Perl's regular expressions; it has the same
218     specification as pcretest, and so can be given identical input, except that
219     input patterns can be followed only by Perl's lower case options.
220    
221     The data lines are processed as Perl strings, so if they contain $ or @
222     characters, these have to be escaped. For this reason, all such characters in
223     the testinput file are escaped so that it can be used for perltest as well as
224     for pcretest, and the special upper case options such as /A that pcretest
225     recognizes are not used in this file. The output should be identical, apart
226     from the initial identifying banner.
227    
228     The testinput2 file is not suitable for feeding to Perltest, since it does
229     make use of the special upper case options and escapes that pcretest uses to
230     test additional features of PCRE.
231    
232     Philip Hazel <ph10@cam.ac.uk>
233     October 1997

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