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Introduction to Library Functions PCREPRECOMPILE(3)

NAME

PCRE - Perl-compatible regular expressions

SAVING AND RE-USING PRECOMPILED PCRE PATTERNS

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() documen-

tation), this is relatively straightforward. If you are using private tables, it is a little bit more complicated. If you save compiled patterns to a file, you can copy them to a different host and run them there. This works even if the new host has the opposite endianness to the one on which the patterns were compiled. There may be a small performance penalty, but it should be insignificant. However, compiling regular expressions with one version of PCRE for use with a different version is not guaranteed to work and may cause crashes. SAVING A COMPILED PATTERN

The value returned by pcre_compile() points to a single

block of memory that holds the compiled pattern and associ-

ated data. You can find the length of this block in bytes by

calling pcre_fullinfo() with an argument of PCRE_INFO_SIZE.

You can then save the data in any appropriate manner. Here is sample code that compiles a pattern and writes it to a file. It assumes that the variable fd refers to a file that is open for output: 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 pat-

tern 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 SunOS 5.10 Last change: 1 Introduction to Library Functions PCREPRECOMPILE(3) 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 study data in a similar way to the compiled pattern itself. When studying generates additional information,

pcre_study() returns a pointer to a pcre_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_extra block itself). The length of the study data

can be obtained by calling pcre_fullinfo() with an argument

of PCRE_INFO_STUDYSIZE. Remember to check that pcre_study()

did return a non-NULL value before trying to save the study

data.

RE-USING A PRECOMPILED PATTERN

Re-using a precompiled pattern is straightforward. Having

reloaded it into main memory, you pass its pointer to

pcre_exec() or pcre_dfa_exec() in the usual way. This should

work even on another host, and even if that host has the

opposite endianness to the one where the pattern was com-

piled. However, if you passed a pointer to custom character tables when the pattern was compiled (the tableptr argument of

pcre_compile()), you must now pass a similar pointer to

pcre_exec() or pcre_dfa_exec(), because the value saved with

the compiled pattern will obviously be nonsense. A field in

a pcre_extra() block is used to pass this data, as described

in the section on matching a pattern in the pcreapi documen-

tation.

If you did not provide custom character tables when the pat-

tern was compiled, the pointer in the compiled pattern is

NULL, which causes pcre_exec() 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_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

SunOS 5.10 Last change: 2 Introduction to Library Functions PCREPRECOMPILE(3) field to indicate that study data is present. Then pass the

pcre_extra block to pcre_exec() or pcre_dfa_exec() in the

usual way. COMPATIBILITY WITH DIFFERENT PCRE RELEASES In general, it is safest to recompile all saved patterns when you update to a new PCRE release, though not all updates actually require this. Recompiling is definitely needed for release 7.2. AUTHOR Philip Hazel University Computing Service Cambridge CB2 3QH, England. REVISION Last updated: 13 June 2007

ATTRIBUTES

See attributes(5) for descriptions of the following attri-

butes:

_______________________________________

| ATTRIBUTE TYPE | ATTRIBUTE VALUE|

|____________________|__________________|_

| Availability | library/pcre |

|____________________|__________________|_

| Interface Stability| Uncommitted |

|____________________|_________________|

NOTES Source for PCRE is available on http://opensolaris.org. SunOS 5.10 Last change: 3