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README file for PCRE (Perl-compatible regular expressions)
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----------------------------------------------------------
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*******************************************************************************
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* IMPORTANT FOR THOSE UPGRADING FROM VERSIONS BEFORE 2.00 *
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* *
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* Please note that there has been a change in the API such that a larger *
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* ovector is required at matching time, to provide some additional workspace. *
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* The new man page has details. This change was necessary in order to support *
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* some of the new functionality in Perl 5.005. *
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* *
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* IMPORTANT FOR THOSE UPGRADING FROM VERSION 2.00 *
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* *
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* Another (I hope this is the last!) change has been made to the API for the *
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* pcre_compile() function. An additional argument has been added to make it *
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* possible to pass over a pointer to character tables built in the current *
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* locale by pcre_maketables(). To use the default tables, this new arguement *
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* should be passed as NULL. *
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* *
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* IMPORTANT FOR THOSE UPGRADING FROM VERSION 2.05 *
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* *
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* Yet another (and again I hope this really is the last) change has been made *
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* to the API for the pcre_exec() function. An additional argument has been *
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* added to make it possible to start the match other than at the start of the *
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* subject string. This is important if there are lookbehinds. The new man *
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* page has the details, but you just want to convert existing programs, all *
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* you need to do is to stick in a new fifth argument to pcre_exec(), with a *
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* value of zero. For example, change *
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* *
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* pcre_exec(pattern, extra, subject, length, options, ovec, ovecsize) *
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* to *
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* pcre_exec(pattern, extra, subject, length, 0, options, ovec, ovecsize) *
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*******************************************************************************
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The distribution should contain the following files:
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ChangeLog log of changes to the code
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LICENCE conditions for the use of PCRE
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Makefile for building PCRE in Unix systems
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README this file
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RunTest a Unix shell script for running tests
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Tech.Notes notes on the encoding
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pcre.3 man page source for the functions
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pcre.3.txt plain text version
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pcre.3.html HTML version
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pcreposix.3 man page source for the POSIX wrapper API
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pcreposix.3.txt plain text version
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pcreposix.3.HTML HTML version
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dftables.c auxiliary program for building chartables.c
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get.c )
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maketables.c )
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study.c ) source of
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pcre.c ) the functions
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pcreposix.c )
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pcre.h header for the external API
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pcreposix.h header for the external POSIX wrapper API
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internal.h header for internal use
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pcretest.c test program
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pgrep.1 man page source for pgrep
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pgrep.1.txt plain text version
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pgrep.1.HTML HTML version
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pgrep.c source of a grep utility that uses PCRE
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perltest Perl test program
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testinput1 test data, compatible with Perl 5.004 and 5.005
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testinput2 test data for error messages and non-Perl things
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testinput3 test data, compatible with Perl 5.005
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testinput4 test data for locale-specific tests
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testoutput1 test results corresponding to testinput1
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testoutput2 test results corresponding to testinput2
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testoutput3 test results corresponding to testinput3
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testoutput4 test results corresponding to testinput4
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To build PCRE on a Unix system, first edit Makefile for your system. It is a
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fairly simple make file, and there are some comments near the top, after the
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text "On a Unix system". Then run "make". It builds two libraries called
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libpcre.a and libpcreposix.a, a test program called pcretest, and the pgrep
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command. You can use "make install" to copy these, and the public header file
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pcre.h, to appropriate live directories on your system. These installation
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directories are defined at the top of the Makefile, and you should edit them if
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necessary.
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For a non-Unix system, read the comments at the top of Makefile, which give
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some hints on what needs to be done. PCRE has been compiled on Windows systems
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and on Macintoshes, but I don't know the details as I don't use those systems.
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It should be straightforward to build PCRE on any system that has a Standard C
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compiler.
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To test PCRE, run the RunTest script in the pcre directory. This can also be
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run by "make runtest". It runs the pcretest test program (which is documented
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below) on each of the testinput files in turn, and compares the output with the
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contents of the corresponding testoutput file. A file called testtry is used to
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hold the output from pcretest. To run pcretest on just one of the test files,
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give its number as an argument to RunTest, for example:
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RunTest 3
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The first and third test files can also be fed directly into the perltest
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script to check that Perl gives the same results. The third file requires the
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additional features of release 5.005, which is why it is kept separate from the
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main test input, which needs only Perl 5.004. In the long run, when 5.005 is
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widespread, these two test files may get amalgamated.
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The second set of tests check pcre_info(), pcre_study(), pcre_copy_substring(),
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pcre_get_substring(), pcre_get_substring_list(), error detection and run-time
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flags that are specific to PCRE, as well as the POSIX wrapper API.
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The fourth set of tests checks pcre_maketables(), the facility for building a
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set of character tables for a specific locale and using them instead of the
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default tables. The tests make use of the "fr" (French) locale. Before running
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the test, the script checks for the presence of this locale by running the
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"locale" command. If that command fails, or if it doesn't include "fr" in the
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list of available locales, the fourth test cannot be run, and a comment is
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output to say why. If running this test produces instances of the error
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** Failed to set locale "fr"
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in the comparison output, it means that locale is not available on your system,
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despite being listed by "locale". This does not mean that PCRE is broken.
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PCRE has its own native API, but a set of "wrapper" functions that are based on
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the POSIX API are also supplied in the library libpcreposix.a. Note that this
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just provides a POSIX calling interface to PCRE: the regular expressions
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themselves still follow Perl syntax and semantics. The header file
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for the POSIX-style functions is called pcreposix.h. The official POSIX name is
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regex.h, but I didn't want to risk possible problems with existing files of
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that name by distributing it that way. To use it with an existing program that
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uses the POSIX API, it will have to be renamed or pointed at by a link.
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Character tables
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----------------
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PCRE uses four tables for manipulating and identifying characters. The final
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argument of the pcre_compile() function is a pointer to a block of memory
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containing the concatenated tables. A call to pcre_maketables() can be used to
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generate a set of tables in the current locale. If the final argument for
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pcre_compile() is passed as NULL, a set of default tables that is built into
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the binary is used.
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The source file called chartables.c contains the default set of tables. This is
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not supplied in the distribution, but is built by the program dftables
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(compiled from dftables.c), which uses the ANSI C character handling functions
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such as isalnum(), isalpha(), isupper(), islower(), etc. to build the table
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sources. This means that the default C locale which is set for your system will
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control the contents of these default tables. You can change the default tables
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by editing chartables.c and then re-building PCRE. If you do this, you should
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probably also edit Makefile to ensure that the file doesn't ever get
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re-generated.
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The first two 256-byte tables provide lower casing and case flipping functions,
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respectively. The next table consists of three 32-byte bit maps which identify
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digits, "word" characters, and white space, respectively. These are used when
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building 32-byte bit maps that represent character classes.
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The final 256-byte table has bits indicating various character types, as
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follows:
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1 white space character
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2 letter
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4 decimal digit
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8 hexadecimal digit
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16 alphanumeric or '_'
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128 regular expression metacharacter or binary zero
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You should not alter the set of characters that contain the 128 bit, as that
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will cause PCRE to malfunction.
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The pcretest program
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--------------------
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This program is intended for testing PCRE, but it can also be used for
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experimenting with regular expressions.
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If it is given two filename arguments, it reads from the first and writes to
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the second. If it is given only one filename argument, it reads from that file
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and writes to stdout. Otherwise, it reads from stdin and writes to stdout, and
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prompts for each line of input.
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The program handles any number of sets of input on a single input file. Each
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set starts with a regular expression, and continues with any number of data
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lines to be matched against the pattern. An empty line signals the end of the
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set. The regular expressions are given enclosed in any non-alphameric
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delimiters other than backslash, for example
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/(a|bc)x+yz/
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White space before the initial delimiter is ignored. A regular expression may
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be continued over several input lines, in which case the newline characters are
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included within it. See the testinput files for many examples. It is possible
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to include the delimiter within the pattern by escaping it, for example
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/abc\/def/
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If you do so, the escape and the delimiter form part of the pattern, but since
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delimiters are always non-alphameric, this does not affect its interpretation.
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If the terminating delimiter is immediately followed by a backslash, for
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example,
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/abc/\
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then a backslash is added to the end of the pattern. This is done to provide a
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way of testing the error condition that arises if a pattern finishes with a
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backslash, because
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/abc\/
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is interpreted as the first line of a pattern that starts with "abc/", causing
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pcretest to read the next line as a continuation of the regular expression.
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The pattern may be followed by i, m, s, or x to set the PCRE_CASELESS,
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PCRE_MULTILINE, PCRE_DOTALL, or PCRE_EXTENDED options, respectively. For
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example:
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/caseless/i
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These modifier letters have the same effect as they do in Perl. There are
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others which set PCRE options that do not correspond to anything in Perl: /A,
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/E, and /X set PCRE_ANCHORED, PCRE_DOLLAR_ENDONLY, and PCRE_EXTRA respectively.
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Searching for all possible matches within each subject string can be requested
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by the /g or /G modifier. The /g modifier behaves similarly to the way it does
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in Perl. After finding a match, PCRE is called again to search the remainder of
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the subject string. The difference between /g and /G is that the former uses
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the start_offset argument to pcre_exec() to start searching at a new point
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within the entire string, whereas the latter passes over a shortened substring.
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This makes a difference to the matching process if the pattern begins with a
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lookbehind assertion (including \b or \B).
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There are a number of other modifiers for controlling the way pcretest
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operates.
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The /+ modifier requests that as well as outputting the substring that matched
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the entire pattern, pcretest should in addition output the remainder of the
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subject string. This is useful for tests where the subject contains multiple
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copies of the same substring.
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The /L modifier must be followed directly by the name of a locale, for example,
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/pattern/Lfr
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For this reason, it must be the last modifier letter. The given locale is set,
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pcre_maketables() is called to build a set of character tables for the locale,
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and this is then passed to pcre_compile() when compiling the regular
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expression. Without an /L modifier, NULL is passed as the tables pointer; that
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is, /L applies only to the expression on which it appears.
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The /I modifier requests that pcretest output information about the compiled
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expression (whether it is anchored, has a fixed first character, and so on). It
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does this by calling pcre_info() after compiling an expression, and outputting
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the information it gets back. If the pattern is studied, the results of that
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are also output.
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The /D modifier is a PCRE debugging feature, which also assumes /I. It causes
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the internal form of compiled regular expressions to be output after
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compilation.
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The /S modifier causes pcre_study() to be called after the expression has been
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compiled, and the results used when the expression is matched.
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The /M modifier causes the size of memory block used to hold the compiled
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pattern to be output.
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Finally, the /P modifier causes pcretest to call PCRE via the POSIX wrapper API
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rather than its native API. When this is done, all other modifiers except /i,
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/m, and /+ are ignored. REG_ICASE is set if /i is present, and REG_NEWLINE is
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set if /m is present. The wrapper functions force PCRE_DOLLAR_ENDONLY always,
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and PCRE_DOTALL unless REG_NEWLINE is set.
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Before each data line is passed to pcre_exec(), leading and trailing whitespace
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is removed, and it is then scanned for \ escapes. The following are recognized:
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\a alarm (= BEL)
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\b backspace
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\e escape
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\f formfeed
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\n newline
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\r carriage return
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\t tab
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\v vertical tab
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\nnn octal character (up to 3 octal digits)
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\xhh hexadecimal character (up to 2 hex digits)
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\A pass the PCRE_ANCHORED option to pcre_exec()
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\B pass the PCRE_NOTBOL option to pcre_exec()
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\Cdd call pcre_copy_substring() for substring dd after a successful match
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(any decimal number less than 32)
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\Gdd call pcre_get_substring() for substring dd after a successful match
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(any decimal number less than 32)
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\L call pcre_get_substringlist() after a successful match
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\N pass the PCRE_NOTEMPTY option to pcre_exec()
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\Odd set the size of the output vector passed to pcre_exec() to dd
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(any number of decimal digits)
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\Z pass the PCRE_NOTEOL option to pcre_exec()
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A backslash followed by anything else just escapes the anything else. If the
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very last character is a backslash, it is ignored. This gives a way of passing
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an empty line as data, since a real empty line terminates the data input.
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If /P was present on the regex, causing the POSIX wrapper API to be used, only
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\B, and \Z have any effect, causing REG_NOTBOL and REG_NOTEOL to be passed to
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regexec() respectively.
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When a match succeeds, pcretest outputs the list of captured substrings that
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pcre_exec() returns, starting with number 0 for the string that matched the
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whole pattern. Here is an example of an interactive pcretest run.
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$ pcretest
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PCRE version 2.06 08-Jun-1999
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re> /^abc(\d+)/
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data> abc123
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0: abc123
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1: 123
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data> xyz
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No match
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If the strings contain any non-printing characters, they are output as \0x
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escapes. If the pattern has the /+ modifier, then the output for substring 0 is
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followed by the the rest of the subject string, identified by "0+" like this:
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re> /cat/+
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data> cataract
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0: cat
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0+ aract
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If the pattern has the /g or /G modifier, the results of successive matching
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attempts are output in sequence, like this:
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re> /\Bi(\w\w)/g
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data> Mississippi
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0: iss
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1: ss
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0: iss
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1: ss
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0: ipp
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1: pp
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"No match" is output only if the first match attempt fails.
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If any of \C, \G, or \L are present in a data line that is successfully
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matched, the substrings extracted by the convenience functions are output with
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C, G, or L after the string number instead of a colon. This is in addition to
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the normal full list. The string length (that is, the return from the
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extraction function) is given in parentheses after each string for \C and \G.
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Note that while patterns can be continued over several lines (a plain ">"
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prompt is used for continuations), data lines may not. However newlines can be
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included in data by means of the \n escape.
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If the -p option is given to pcretest, it is equivalent to adding /P to each
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regular expression: the POSIX wrapper API is used to call PCRE. None of the
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following flags has any effect in this case.
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If the option -d is given to pcretest, it is equivalent to adding /D to each
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regular expression: the internal form is output after compilation.
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If the option -i is given to pcretest, it is equivalent to adding /I to each
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regular expression: information about the compiled pattern is given after
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compilation.
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If the option -m is given to pcretest, it outputs the size of each compiled
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pattern after it has been compiled. It is equivalent to adding /M to each
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regular expression. For compatibility with earlier versions of pcretest, -s is
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a synonym for -m.
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If the -t option is given, each compile, study, and match is run 20000 times
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while being timed, and the resulting time per compile or match is output in
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milliseconds. Do not set -t with -s, because you will then get the size output
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20000 times and the timing will be distorted. If you want to change the number
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of repetitions used for timing, edit the definition of LOOPREPEAT at the top of
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pcretest.c
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The perltest program
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--------------------
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The perltest program tests Perl's regular expressions; it has the same
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specification as pcretest, and so can be given identical input, except that
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input patterns can be followed only by Perl's lower case modifiers. The
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contents of testinput1 and testinput3 meet this condition.
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The data lines are processed as Perl double-quoted strings, so if they contain
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" \ $ or @ characters, these have to be escaped. For this reason, all such
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characters in testinput1 and testinput3 are escaped so that they can be used
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for perltest as well as for pcretest, and the special upper case modifiers such
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as /A that pcretest recognizes are not used in these files. The output should
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be identical, apart from the initial identifying banner.
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The testinput2 and testinput4 files are not suitable for feeding to perltest,
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since they do make use of the special upper case modifiers and escapes that
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pcretest uses to test some features of PCRE. The first of these files also
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contains malformed regular expressions, in order to check that PCRE diagnoses
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them correctly.
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Philip Hazel <ph10@cam.ac.uk>
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July 1999
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