PCREPRECOMPILE(3)         Library Functions Manual         PCREPRECOMPILE(3)

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       PCRE - Perl-compatible regular expressions


       If you are running an application that uses a large number of regular
       expression patterns, it may be useful to store them in a precompiled
       form instead of having to compile them every time the application is
       run.  If you are not using any private character tables (see the
       pcre_maketables() documentation), this is relatively straightforward.
       If you are using private tables, it is a little bit more complicated.
       However, if you are using the just-in-time optimization feature, it
       is not possible to save and reload the JIT data.

       If you save compiled patterns to a file, you can copy them to a
       different host and run them there. If the two hosts have different
       endianness (byte order), you should run the
       pcre[16|32]_pattern_to_host_byte_order() function on the new host
       before trying to match the pattern. The matching functions return
       PCRE_ERROR_BADENDIANNESS if they detect a pattern with the wrong

       Compiling regular expressions with one version of PCRE for use with a
       different version is not guaranteed to work and may cause crashes,
       and saving and restoring a compiled pattern loses any JIT
       optimization data.


       The value returned by pcre[16|32]_compile() points to a single block
       of memory that holds the compiled pattern and associated data. You
       can find the length of this block in bytes by calling
       pcre[16|32]_fullinfo() with an argument of PCRE_INFO_SIZE. You can
       then save the data in any appropriate manner. Here is sample code for
       the 8-bit library that compiles a pattern and writes it to a file. It
       assumes that the variable fd refers to a file that is open for

         int erroroffset, rc, size;
         char *error;
         pcre *re;

         re = pcre_compile("my pattern", 0, &error, &erroroffset, NULL);
         if (re == NULL) { ... handle errors ... }
         rc = pcre_fullinfo(re, NULL, PCRE_INFO_SIZE, &size);
         if (rc < 0) { ... handle errors ... }
         rc = fwrite(re, 1, size, fd);
         if (rc != size) { ... handle errors ... }

       In this example, the bytes that comprise the compiled pattern are
       copied exactly. Note that this is binary data that may contain any of
       the 256 possible byte values. On systems that make a distinction
       between binary and non-binary data, be sure that the file is opened
       for binary output.

       If you want to write more than one pattern to a file, you will have
       to devise a way of separating them. For binary data, preceding each
       pattern with its length is probably the most straightforward
       approach. Another possibility is to write out the data in hexadecimal
       instead of binary, one pattern to a line.

       Saving compiled patterns in a file is only one possible way of
       storing them for later use. They could equally well be saved in a
       database, or in the memory of some daemon process that passes them
       via sockets to the processes that want them.

       If the pattern has been studied, it is also possible to save the
       normal study data in a similar way to the compiled pattern itself.
       However, if the PCRE_STUDY_JIT_COMPILE was used, the just-in-time
       data that is created cannot be saved because it is too dependent on
       the current environment. When studying generates additional
       information, pcre[16|32]_study() returns a pointer to a
       pcre[16|32]_extra data block. Its format is defined in the section on
       matching a pattern in the pcreapi documentation. The study_data field
       points to the binary study data, and this is what you must save (not
       the pcre[16|32]_extra block itself). The length of the study data can
       be obtained by calling pcre[16|32]_fullinfo() with an argument of
       PCRE_INFO_STUDYSIZE. Remember to check that pcre[16|32]_study() did
       return a non-NULL value before trying to save the study data.


       Re-using a precompiled pattern is straightforward. Having reloaded it
       into main memory, called pcre[16|32]_pattern_to_host_byte_order() if
       necessary, you pass its pointer to pcre[16|32]_exec() or
       pcre[16|32]_dfa_exec() in the usual way.

       However, if you passed a pointer to custom character tables when the
       pattern was compiled (the tableptr argument of
       pcre[16|32]_compile()), you must now pass a similar pointer to
       pcre[16|32]_exec() or pcre[16|32]_dfa_exec(), because the value saved
       with the compiled pattern will obviously be nonsense. A field in a
       pcre[16|32]_extra() block is used to pass this data, as described in
       the section on matching a pattern in the pcreapi documentation.

       Warning: The tables that pcre_exec() and pcre_dfa_exec() use must be
       the same as those that were used when the pattern was compiled. If
       this is not the case, the behaviour is undefined.

       If you did not provide custom character tables when the pattern was
       compiled, the pointer in the compiled pattern is NULL, which causes
       the matching functions to use PCRE's internal tables. Thus, you do
       not need to take any special action at run time in this case.

       If you saved study data with the compiled pattern, you need to create
       your own pcre[16|32]_extra data block and set the study_data field to
       point to the reloaded study data. You must also set the
       PCRE_EXTRA_STUDY_DATA bit in the flags field to indicate that study
       data is present. Then pass the pcre[16|32]_extra block to the
       matching function in the usual way. If the pattern was studied for
       just-in-time optimization, that data cannot be saved, and so is lost
       by a save/restore cycle.


       In general, it is safest to recompile all saved patterns when you
       update to a new PCRE release, though not all updates actually require

AUTHOR         top

       Philip Hazel
       University Computing Service
       Cambridge CB2 3QH, England.

REVISION         top

       Last updated: 12 November 2013
       Copyright (c) 1997-2013 University of Cambridge.

COLOPHON         top

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PCRE 8.34                     12 November 2013             PCREPRECOMPILE(3)

Pages that refer to this page: pcretest(1)pcreapi(3)