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 some.file diff some.file 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 some.file diff some.file testoutput2 The make target "runtest" runs both these tests, using the file "testtry" to store the intermediate output, deleting it at the end if all goes well. 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 October 1997