141 lines
6.4 KiB
HTML
141 lines
6.4 KiB
HTML
<html>
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<head>
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<title>pcreprecompile specification</title>
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</head>
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<body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB">
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<h1>pcreprecompile man page</h1>
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<p>
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Return to the <a href="index.html">PCRE index page</a>.
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</p>
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<p>
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This page is part of the PCRE HTML documentation. It was generated automatically
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from the original man page. If there is any nonsense in it, please consult the
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man page, in case the conversion went wrong.
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<br>
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<ul>
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<li><a name="TOC1" href="#SEC1">SAVING AND RE-USING PRECOMPILED PCRE PATTERNS</a>
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<li><a name="TOC2" href="#SEC2">SAVING A COMPILED PATTERN</a>
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<li><a name="TOC3" href="#SEC3">RE-USING A PRECOMPILED PATTERN</a>
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<li><a name="TOC4" href="#SEC4">COMPATIBILITY WITH DIFFERENT PCRE RELEASES</a>
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</ul>
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<br><a name="SEC1" href="#TOC1">SAVING AND RE-USING PRECOMPILED PCRE PATTERNS</a><br>
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<P>
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If you are running an application that uses a large number of regular
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expression patterns, it may be useful to store them in a precompiled form
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instead of having to compile them every time the application is run.
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If you are not using any private character tables (see the
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<a href="pcre_maketables.html"><b>pcre_maketables()</b></a>
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documentation), this is relatively straightforward. If you are using private
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tables, it is a little bit more complicated.
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</P>
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<P>
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If you save compiled patterns to a file, you can copy them to a different host
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and run them there. This works even if the new host has the opposite endianness
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to the one on which the patterns were compiled. There may be a small
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performance penalty, but it should be insignificant.
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</P>
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<br><a name="SEC2" href="#TOC1">SAVING A COMPILED PATTERN</a><br>
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<P>
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The value returned by <b>pcre_compile()</b> points to a single block of memory
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that holds the compiled pattern and associated data. You can find the length of
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this block in bytes by calling <b>pcre_fullinfo()</b> with an argument of
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PCRE_INFO_SIZE. You can then save the data in any appropriate manner. Here is
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sample code that compiles a pattern and writes it to a file. It assumes that
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the variable <i>fd</i> refers to a file that is open for output:
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<pre>
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int erroroffset, rc, size;
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char *error;
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pcre *re;
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re = pcre_compile("my pattern", 0, &error, &erroroffset, NULL);
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if (re == NULL) { ... handle errors ... }
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rc = pcre_fullinfo(re, NULL, PCRE_INFO_SIZE, &size);
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if (rc < 0) { ... handle errors ... }
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rc = fwrite(re, 1, size, fd);
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if (rc != size) { ... handle errors ... }
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</pre>
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In this example, the bytes that comprise the compiled pattern are copied
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exactly. Note that this is binary data that may contain any of the 256 possible
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byte values. On systems that make a distinction between binary and non-binary
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data, be sure that the file is opened for binary output.
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</P>
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<P>
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If you want to write more than one pattern to a file, you will have to devise a
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way of separating them. For binary data, preceding each pattern with its length
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is probably the most straightforward approach. Another possibility is to write
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out the data in hexadecimal instead of binary, one pattern to a line.
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</P>
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<P>
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Saving compiled patterns in a file is only one possible way of storing them for
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later use. They could equally well be saved in a database, or in the memory of
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some daemon process that passes them via sockets to the processes that want
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them.
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</P>
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<P>
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If the pattern has been studied, it is also possible to save the study data in
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a similar way to the compiled pattern itself. When studying generates
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additional information, <b>pcre_study()</b> returns a pointer to a
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<b>pcre_extra</b> data block. Its format is defined in the
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<a href="pcreapi.html#extradata">section on matching a pattern</a>
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in the
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<a href="pcreapi.html"><b>pcreapi</b></a>
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documentation. The <i>study_data</i> field points to the binary study data, and
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this is what you must save (not the <b>pcre_extra</b> block itself). The length
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of the study data can be obtained by calling <b>pcre_fullinfo()</b> with an
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argument of PCRE_INFO_STUDYSIZE. Remember to check that <b>pcre_study()</b> did
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return a non-NULL value before trying to save the study data.
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</P>
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<br><a name="SEC3" href="#TOC1">RE-USING A PRECOMPILED PATTERN</a><br>
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<P>
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Re-using a precompiled pattern is straightforward. Having reloaded it into main
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memory, you pass its pointer to <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b> in
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the usual way. This should work even on another host, and even if that host has
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the opposite endianness to the one where the pattern was compiled.
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</P>
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<P>
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However, if you passed a pointer to custom character tables when the pattern
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was compiled (the <i>tableptr</i> argument of <b>pcre_compile()</b>), you must
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now pass a similar pointer to <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b>,
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because the value saved with the compiled pattern will obviously be nonsense. A
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field in a <b>pcre_extra()</b> block is used to pass this data, as described in
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the
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<a href="pcreapi.html#extradata">section on matching a pattern</a>
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in the
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<a href="pcreapi.html"><b>pcreapi</b></a>
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documentation.
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</P>
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<P>
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If you did not provide custom character tables when the pattern was compiled,
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the pointer in the compiled pattern is NULL, which causes <b>pcre_exec()</b> to
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use PCRE's internal tables. Thus, you do not need to take any special action at
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run time in this case.
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</P>
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<P>
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If you saved study data with the compiled pattern, you need to create your own
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<b>pcre_extra</b> data block and set the <i>study_data</i> field to point to the
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reloaded study data. You must also set the PCRE_EXTRA_STUDY_DATA bit in the
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<i>flags</i> field to indicate that study data is present. Then pass the
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<b>pcre_extra</b> block to <b>pcre_exec()</b> or <b>pcre_dfa_exec()</b> in the
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usual way.
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</P>
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<br><a name="SEC4" href="#TOC1">COMPATIBILITY WITH DIFFERENT PCRE RELEASES</a><br>
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<P>
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The layout of the control block that is at the start of the data that makes up
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a compiled pattern was changed for release 5.0. If you have any saved patterns
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that were compiled with previous releases (not a facility that was previously
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advertised), you will have to recompile them for release 5.0. However, from now
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on, it should be possible to make changes in a compatible manner.
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</P>
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<P>
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Notwithstanding the above, if you have any saved patterns in UTF-8 mode that
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use \p or \P that were compiled with any release up to and including 6.4, you
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will have to recompile them for release 6.5 and above.
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</P>
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<P>
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Last updated: 01 February 2006
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<br>
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Copyright © 1997-2006 University of Cambridge.
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<p>
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Return to the <a href="index.html">PCRE index page</a>.
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</p>
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