+Return to the PCRE index page. +
+
+This page is part of the PCRE HTML documentation. It was generated automatically
+from the original man page. If there is any nonsense in it, please consult the
+man page, in case the conversion went wrong.
+
+
+This document describes the optional features of PCRE that can be selected when +the library is compiled. It assumes use of the configure script, where +the optional features are selected or deselected by providing options to +configure before running the make command. However, the same +options can be selected in both Unix-like and non-Unix-like environments using +the GUI facility of CMakeSetup if you are using CMake instead of +configure to build PCRE. +
++The complete list of options for configure (which includes the standard +ones such as the selection of the installation directory) can be obtained by +running +
+ ./configure --help ++The following sections include descriptions of options whose names begin with +--enable or --disable. These settings specify changes to the defaults for the +configure command. Because of the way that configure works, +--enable and --disable always come in pairs, so the complementary option always +exists as well, but as it specifies the default, it is not described. + +
+By default, the configure script will search for a C++ compiler and C++ +header files. If it finds them, it automatically builds the C++ wrapper library +for PCRE. You can disable this by adding +
+ --disable-cpp ++to the configure command. + +
+To build PCRE with support for UTF-8 character strings, add +
+ --enable-utf8 ++to the configure command. Of itself, this does not make PCRE treat +strings as UTF-8. As well as compiling PCRE with this option, you also have +have to set the PCRE_UTF8 option when you call the pcre_compile() +function. + +
+UTF-8 support allows PCRE to process character values greater than 255 in the +strings that it handles. On its own, however, it does not provide any +facilities for accessing the properties of such characters. If you want to be +able to use the pattern escapes \P, \p, and \X, which refer to Unicode +character properties, you must add +
+ --enable-unicode-properties ++to the configure command. This implies UTF-8 support, even if you have +not explicitly requested it. + +
+Including Unicode property support adds around 30K of tables to the PCRE +library. Only the general category properties such as Lu and Nd are +supported. Details are given in the +pcrepattern +documentation. +
++By default, PCRE interprets character 10 (linefeed, LF) as indicating the end +of a line. This is the normal newline character on Unix-like systems. You can +compile PCRE to use character 13 (carriage return, CR) instead, by adding +
+ --enable-newline-is-cr ++to the configure command. There is also a --enable-newline-is-lf option, +which explicitly specifies linefeed as the newline character. +
+ --enable-newline-is-crlf ++to the configure command. There is a fourth option, specified by +
+ --enable-newline-is-anycrlf ++which causes PCRE to recognize any of the three sequences CR, LF, or CRLF as +indicating a line ending. Finally, a fifth option, specified by +
+ --enable-newline-is-any ++causes PCRE to recognize any Unicode newline sequence. + +
+Whatever line ending convention is selected when PCRE is built can be +overridden when the library functions are called. At build time it is +conventional to use the standard for your operating system. +
++By default, the sequence \R in a pattern matches any Unicode newline sequence, +whatever has been selected as the line ending sequence. If you specify +
+ --enable-bsr-anycrlf ++the default is changed so that \R matches only CR, LF, or CRLF. Whatever is +selected when PCRE is built can be overridden when the library functions are +called. + +
+The PCRE building process uses libtool to build both shared and static +Unix libraries by default. You can suppress one of these by adding one of +
+ --disable-shared + --disable-static ++to the configure command, as required. + +
+When PCRE is called through the POSIX interface (see the +pcreposix +documentation), additional working storage is required for holding the pointers +to capturing substrings, because PCRE requires three integers per substring, +whereas the POSIX interface provides only two. If the number of expected +substrings is small, the wrapper function uses space on the stack, because this +is faster than using malloc() for each call. The default threshold above +which the stack is no longer used is 10; it can be changed by adding a setting +such as +
+ --with-posix-malloc-threshold=20 ++to the configure command. + +
+Within a compiled pattern, offset values are used to point from one part to +another (for example, from an opening parenthesis to an alternation +metacharacter). By default, two-byte values are used for these offsets, leading +to a maximum size for a compiled pattern of around 64K. This is sufficient to +handle all but the most gigantic patterns. Nevertheless, some people do want to +process enormous patterns, so it is possible to compile PCRE to use three-byte +or four-byte offsets by adding a setting such as +
+ --with-link-size=3 ++to the configure command. The value given must be 2, 3, or 4. Using +longer offsets slows down the operation of PCRE because it has to load +additional bytes when handling them. + +
+When matching with the pcre_exec() function, PCRE implements backtracking +by making recursive calls to an internal function called match(). In +environments where the size of the stack is limited, this can severely limit +PCRE's operation. (The Unix environment does not usually suffer from this +problem, but it may sometimes be necessary to increase the maximum stack size. +There is a discussion in the +pcrestack +documentation.) An alternative approach to recursion that uses memory from the +heap to remember data, instead of using recursive function calls, has been +implemented to work round the problem of limited stack size. If you want to +build a version of PCRE that works this way, add +
+ --disable-stack-for-recursion ++to the configure command. With this configuration, PCRE will use the +pcre_stack_malloc and pcre_stack_free variables to call memory +management functions. By default these point to malloc() and +free(), but you can replace the pointers so that your own functions are +used. + +
+Separate functions are provided rather than using pcre_malloc and +pcre_free because the usage is very predictable: the block sizes +requested are always the same, and the blocks are always freed in reverse +order. A calling program might be able to implement optimized functions that +perform better than malloc() and free(). PCRE runs noticeably more +slowly when built in this way. This option affects only the pcre_exec() +function; it is not relevant for the the pcre_dfa_exec() function. +
++Internally, PCRE has a function called match(), which it calls repeatedly +(sometimes recursively) when matching a pattern with the pcre_exec() +function. By controlling the maximum number of times this function may be +called during a single matching operation, a limit can be placed on the +resources used by a single call to pcre_exec(). The limit can be changed +at run time, as described in the +pcreapi +documentation. The default is 10 million, but this can be changed by adding a +setting such as +
+ --with-match-limit=500000 ++to the configure command. This setting has no effect on the +pcre_dfa_exec() matching function. + +
+In some environments it is desirable to limit the depth of recursive calls of +match() more strictly than the total number of calls, in order to +restrict the maximum amount of stack (or heap, if --disable-stack-for-recursion +is specified) that is used. A second limit controls this; it defaults to the +value that is set for --with-match-limit, which imposes no additional +constraints. However, you can set a lower limit by adding, for example, +
+ --with-match-limit-recursion=10000 ++to the configure command. This value can also be overridden at run time. + +
+PCRE uses fixed tables for processing characters whose code values are less +than 256. By default, PCRE is built with a set of tables that are distributed +in the file pcre_chartables.c.dist. These tables are for ASCII codes +only. If you add +
+ --enable-rebuild-chartables ++to the configure command, the distributed tables are no longer used. +Instead, a program called dftables is compiled and run. This outputs the +source for new set of tables, created in the default locale of your C runtime +system. (This method of replacing the tables does not work if you are cross +compiling, because dftables is run on the local host. If you need to +create alternative tables when cross compiling, you will have to do so "by +hand".) + +
+PCRE assumes by default that it will run in an environment where the character +code is ASCII (or Unicode, which is a superset of ASCII). This is the case for +most computer operating systems. PCRE can, however, be compiled to run in an +EBCDIC environment by adding +
+ --enable-ebcdic ++to the configure command. This setting implies +--enable-rebuild-chartables. You should only use it if you know that you are in +an EBCDIC environment (for example, an IBM mainframe operating system). + +
+By default, pcregrep reads all files as plain text. You can build it so +that it recognizes files whose names end in .gz or .bz2, and reads +them with libz or libbz2, respectively, by adding one or both of +
+ --enable-pcregrep-libz + --enable-pcregrep-libbz2 ++to the configure command. These options naturally require that the +relevant libraries are installed on your system. Configuration will fail if +they are not. + +
+If you add +
+ --enable-pcretest-libreadline ++to the configure command, pcretest is linked with the +libreadline library, and when its input is from a terminal, it reads it +using the readline() function. This provides line-editing and history +facilities. Note that libreadline is GPL-licenced, so if you distribute a +binary of pcretest linked in this way, there may be licensing issues. + +
+Setting this option causes the -lreadline option to be added to the +pcretest build. In many operating environments with a sytem-installed +libreadline this is sufficient. However, in some environments (e.g. +if an unmodified distribution version of readline is in use), some extra +configuration may be necessary. The INSTALL file for libreadline says +this: +
+ "Readline uses the termcap functions, but does not link with the + termcap or curses library itself, allowing applications which link + with readline the to choose an appropriate library." ++If your environment has not been set up so that an appropriate library is +automatically included, you may need to add something like +
+ LIBS="-ncurses" ++immediately before the configure command. + +
+pcreapi(3), pcre_config(3). +
+
+Philip Hazel
+
+University Computing Service
+
+Cambridge CB2 3QH, England.
+
+
+Last updated: 13 April 2008
+
+Copyright © 1997-2008 University of Cambridge.
+
+
+Return to the PCRE index page. +