Contents of /code/trunk/README

README file for PCRE (Perl-compatible regular expressions)
----------------------------------------------------------

The distribution should contain the following files:

  ChangeLog         log of changes to the code
  Makefile          for building PCRE
  Performance       notes on performance
  README            this file
  Tech.Notes        notes on the encoding
  pcre.3            man page for the functions
  pcreposix.3       man page for the POSIX wrapper API
  maketables.c      auxiliary program for building chartables.c
  study.c           ) source of
  pcre.c            )   the functions
  pcreposix.c       )
  pcre.h            header for the external API
  pcreposix.h       header for the external POSIX wrapper API
  internal.h        header for internal use
  pcretest.c        test program
  pgrep.1           man page for pgrep
  pgrep.c           source of a grep utility that uses PCRE
  perltest          Perl test program
  testinput         test data, compatible with Perl
  testinput2        test data for error messages and non-Perl things
  testoutput        test results corresponding to testinput
  testoutput2       test results corresponding to testinput2

To build PCRE, edit Makefile for your system (it is a fairly simple make file)
and then run it. It builds a two libraries called libpcre.a and libpcreposix.a,
a test program called pcretest, and the pgrep command.

To test PCRE, run pcretest on the file testinput, and compare the output with
the contents of testoutput. There should be no differences. For example:

  pcretest testinput /tmp/anything
  diff /tmp/anything testoutput

Do the same with testinput2, comparing the output with testoutput2, but this
time using the -i flag for pcretest, i.e.

  pcretest -i testinput2 /tmp/anything
  diff /tmp/anything testoutput2

There are two sets of tests because the first set can also be fed directly into
the perltest program to check that Perl gives the same results. The second set
of tests check pcre_info(), pcre_study(), error detection and run-time flags
that are specific to PCRE, as well as the POSIX wrapper API.

To install PCRE, copy libpcre.a to any suitable library directory (e.g.
/usr/local/lib), pcre.h to any suitable include directory (e.g.
/usr/local/include), and pcre.3 to any suitable man directory (e.g.
/usr/local/man/man3).

To install the pgrep command, copy it to any suitable binary directory, (e.g.
/usr/local/bin) and pgrep.1 to any suitable man directory (e.g.
/usr/local/man/man1).

PCRE has its own native API, but a set of "wrapper" functions that are based on
the POSIX API are also supplied in the library libpcreposix.a. Note that this
just provides a POSIX calling interface to PCRE: the regular expressions
themselves still follow Perl syntax and semantics. The header file
for the POSIX-style functions is called pcreposix.h. The official POSIX name is
regex.h, but I didn't want to risk possible problems with existing files of
that name by distributing it that way. To use it with an existing program that
uses the POSIX API it will have to be renamed or pointed at by a link.


Character tables
----------------

PCRE uses four tables for manipulating and identifying characters. These are
compiled from a source file called chartables.c. This is not supplied in
the distribution, but is built by the program maketables (compiled from
maketables.c), which uses the ANSI C character handling functions such as
isalnum(), isalpha(), isupper(), islower(), etc. to build the table sources.
This means that the default C locale set in your system may affect the contents
of the tables. You can change the tables by editing chartables.c and then
re-building PCRE. If you do this, you should probably also edit Makefile to
ensure that the file doesn't ever get re-generated.

The first two tables pcre_lcc[] and pcre_fcc[] provide lower casing and a
case flipping functions, respectively. The pcre_cbits[] table consists of four
32-byte bit maps which identify digits, letters, "word" characters, and white
space, respectively. These are used when building 32-byte bit maps that
represent character classes.

The pcre_ctypes[] table has bits indicating various character types, as
follows:

    1   white space character
    2   letter
    4   decimal digit
    8   hexadecimal digit
   16   alphanumeric or '_'
  128   regular expression metacharacter or binary zero

You should not alter the set of characters that contain the 128 bit, as that
will cause PCRE to malfunction.


The pcretest program
--------------------

This program is intended for testing PCRE, but it can also be used for
experimenting with regular expressions.

If it is given two filename arguments, it reads from the first and writes to
the second. If it is given only one filename argument, it reads from that file
and writes to stdout. Otherwise, it reads from stdin and writes to stdout, and
prompts for each line of input.

The program handles any number of sets of input on a single input file. Each
set starts with a regular expression, and continues with any number of data
lines to be matched against the pattern. An empty line signals the end of the
set. The regular expressions are given enclosed in any non-alphameric
delimiters, for example

  /(a|bc)x+yz/

and may be followed by i, m, s, or x to set the PCRE_CASELESS, PCRE_MULTILINE,
PCRE_DOTALL, or PCRE_EXTENDED options, respectively. These options have the
same effect as they do in Perl.

There are also some upper case options that do not match Perl options: /A, /E,
and /X set PCRE_ANCHORED, PCRE_DOLLAR_ENDONLY, and PCRE_EXTRA respectively.
The /D option is a PCRE debugging feature. It causes the internal form of
compiled regular expressions to be output after compilation. The /S option
causes pcre_study() to be called after the expression has been compiled, and
the results used when the expression is matched. If /I is present as well as
/S, then pcre_study() is called with the PCRE_CASELESS option.

Finally, the /P option causes pcretest to call PCRE via the POSIX wrapper API
rather than its native API. When this is done, all other options except /i and
/m are ignored. REG_ICASE is set if /i is present, and REG_NEWLINE is set if /m
is present. The wrapper functions force PCRE_DOLLAR_ENDONLY always, and
PCRE_DOTALL unless REG_NEWLINE is set.

A regular expression can extend over several lines of input; the newlines are
included in it. See the testinput file for many examples.

Before each data line is passed to pcre_exec(), leading and trailing whitespace
is removed, and it is then scanned for \ escapes. The following are recognized:

  \a     alarm (= BEL)
  \b     backspace
  \e     escape
  \f     formfeed
  \n     newline
  \r     carriage return
  \t     tab
  \v     vertical tab
  \nnn   octal character (up to 3 octal digits)
  \xhh   hexadecimal character (up to 2 hex digits)

  \A     pass the PCRE_ANCHORED option to pcre_exec()
  \B     pass the PCRE_NOTBOL option to pcre_exec()
  \E     pass the PCRE_DOLLAR_ENDONLY option to pcre_exec()
  \I     pass the PCRE_CASELESS option to pcre_exec()
  \M     pass the PCRE_MULTILINE option to pcre_exec()
  \S     pass the PCRE_DOTALL option to pcre_exec()
  \Odd   set the size of the output vector passed to pcre_exec() to dd
           (any number of decimal digits)
  \Z     pass the PCRE_NOTEOL option to pcre_exec()

A backslash followed by anything else just escapes the anything else. If the
very last character is a backslash, it is ignored. This gives a way of passing
an empty line as data, since a real empty line terminates the data input.

If /P was present on the regex, causing the POSIX wrapper API to be used, only
\B, and \Z have any effect, causing REG_NOTBOL and REG_NOTEOL to be passed to
regexec() respectively.

When a match succeeds, pcretest outputs the list of identified substrings that
pcre_exec() returns, starting with number 0 for the string that matched the
whole pattern. Here is an example of an interactive pcretest run.

  $ pcretest
  Testing Perl-Compatible Regular Expressions
  PCRE version 0.90 08-Sep-1997

      re> /^abc(\d+)/
    data> abc123
   0: abc123
   1: 123
    data> xyz
  No match

Note that while patterns can be continued over several lines (a plain ">"
prompt is used for continuations), data lines may not. However newlines can be
included in data by means of the \n escape.

If the -p option is given to pcretest, it is equivalent to adding /P to each
regular expression: the POSIX wrapper API is used to call PCRE. None of the
following flags has any effect in this case.

If the option -d is given to pcretest, it is equivalent to adding /D to each
regular expression: the internal form is output after compilation.

If the option -i (for "information") is given to pcretest, it calls pcre_info()
after compiling an expression, and outputs the information it gets back. If the
pattern is studied, the results of that are also output.

If the option -s is given to pcretest, it outputs the size of each compiled
pattern after it has been compiled.

If the -t option is given, each compile, study, and match is run 2000 times
while being timed, and the resulting time per compile or match is output in
milliseconds. Do not set -t with -s, because you will then get the size output
2000 times and the timing will be distorted.


The perltest program
--------------------

The perltest program tests Perl's regular expressions; it has the same
specification as pcretest, and so can be given identical input, except that
input patterns can be followed only by Perl's lower case options.

The data lines are processed as Perl strings, so if they contain $ or @
characters, these have to be escaped. For this reason, all such characters in
the testinput file are escaped so that it can be used for perltest as well as
for pcretest, and the special upper case options such as /A that pcretest
recognizes are not used in this file. The output should be identical, apart
from the initial identifying banner.

The testinput2 file is not suitable for feeding to Perltest, since it does
make use of the special upper case options and escapes that pcretest uses to
test additional features of PCRE.

Philip Hazel <ph10@cam.ac.uk>
October 1997
1	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