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Introduction to Library Functions PCREPOSIX(3)

NAME

PCRE - Perl-compatible regular expressions.

SYNOPSIS OF POSIX API

#include

int regcomp(regex_t *preg, const char *pattern,

int cflags);

int regexec(regex_t *preg, const char *string,

size_t nmatch, regmatch_t pmatch[], int eflags);

size_t regerror(int errcode, const regex_t *preg,

char *errbuf, size_t errbuf_size);

void regfree(regex_t *preg);

DESCRIPTION

This set of functions provides a POSIX-style API to the PCRE

regular expression package. See the pcreapi documentation for a description of PCRE's native API, which contains much additional functionality. The functions described here are just wrapper functions that ultimately call the PCRE native API. Their prototypes are

defined in the pcreposix.h header file, and on Unix systems

the library itself is called pcreposix.a, so can be accessed

by adding -lpcreposix to the command for linking an applica-

tion that uses them. Because the POSIX functions call the

native ones, it is also necessary to add -lpcre.

I have implemented only those option bits that can be rea-

sonably mapped to PCRE native options. In addition, the

option REG_EXTENDED is defined with the value zero. This has

no effect, but since programs that are written to the POSIX interface often use it, this makes it easier to slot in PCRE as a replacement library. Other POSIX options are not even defined. When PCRE is called via these functions, it is only the API

that is POSIX-like in style. The syntax and semantics of the

regular expressions themselves are still those of Perl, sub-

ject to the setting of various PCRE options, as described

below. "POSIX-like in style" means that the API approximates

to the POSIX definition; it is not fully POSIX-compatible,

and in multi-byte encoding domains it is probably even less

compatible.

The header for these functions is supplied as pcreposix.h to

avoid any potential clash with other POSIX libraries. It SunOS 5.10 Last change: 1 Introduction to Library Functions PCREPOSIX(3) can, of course, be renamed or aliased as regex.h, which is

the "correct" name. It provides two structure types, regex_t

for compiled internal forms, and regmatch_t for returning

captured substrings. It also defines some constants whose

names start with "REG_"; these are used for setting options

and identifying error codes. COMPILING A PATTERN The function regcomp() is called to compile a pattern into an internal form. The pattern is a C string terminated by a binary zero, and is passed in the argument pattern. The preg

argument is a pointer to a regex_t structure that is used as

a base for storing information about the compiled regular expression. The argument cflags is either zero, or contains one or more of the bits defined by the following macros:

REG_DOTALL

The PCRE_DOTALL option is set when the regular expression is

passed for compilation to the native function. Note that

REG_DOTALL is not part of the POSIX standard.

REG_ICASE

The PCRE_CASELESS option is set when the regular expression

is passed for compilation to the native function.

REG_NEWLINE

The PCRE_MULTILINE option is set when the regular expression

is passed for compilation to the native function. Note that this does not mimic the defined POSIX behaviour for

REG_NEWLINE (see the following section).

REG_NOSUB

The PCRE_NO_AUTO_CAPTURE option is set when the regular

expression is passed for compilation to the native function. In addition, when a pattern that is compiled with this flag is passed to regexec() for matching, the nmatch and pmatch arguments are ignored, and no captured strings are returned.

REG_UTF8

The PCRE_UTF8 option is set when the regular expression is

passed for compilation to the native function. This causes the pattern itself and all data strings used for matching it

to be treated as UTF-8 strings. Note that REG_UTF8 is not

part of the POSIX standard. SunOS 5.10 Last change: 2 Introduction to Library Functions PCREPOSIX(3) In the absence of these flags, no options are passed to the native function. This means the the regex is compiled with PCRE default semantics. In particular, the way it handles newline characters in the subject string is the Perl way,

not the POSIX way. Note that setting PCRE_MULTILINE has only

some of the effects specified for REG_NEWLINE. It does not

affect the way newlines are matched by . (they aren't) or by a negative class such as [^a] (they are).

The yield of regcomp() is zero on success, and non-zero oth-

erwise. The preg structure is filled in on success, and one

member of the structure is public: re_nsub contains the

number of capturing subpatterns in the regular expression. Various error codes are defined in the header file. MATCHING NEWLINE CHARACTERS

This area is not simple, because POSIX and Perl take dif-

ferent views of things. It is not possible to get PCRE to obey POSIX semantics, but then PCRE was never intended to be

a POSIX engine. The following table lists the different pos-

sibilities for matching newline characters in PCRE: Default Change with

. matches newline no PCRE_DOTALL

newline matches [^a] yes not changeable

$ matches \n at end yes PCRE_DOLLARENDONLY

$ matches \n in middle no PCRE_MULTILINE

^ matches \n in middle no PCRE_MULTILINE

This is the equivalent table for POSIX: Default Change with

. matches newline yes REG_NEWLINE

newline matches [^a] yes REG_NEWLINE

$ matches \n at end no REG_NEWLINE

$ matches \n in middle no REG_NEWLINE

^ matches \n in middle no REG_NEWLINE

PCRE's behaviour is the same as Perl's, except that there is

no equivalent for PCRE_DOLLAR_ENDONLY in Perl. In both PCRE

and Perl, there is no way to stop newline from matching [^a].

The default POSIX newline handling can be obtained by set-

ting PCRE_DOTALL and PCRE_DOLLAR_ENDONLY, but there is no

way to make PCRE behave exactly as for the REG_NEWLINE

action. SunOS 5.10 Last change: 3 Introduction to Library Functions PCREPOSIX(3) MATCHING A PATTERN The function regexec() is called to match a compiled pattern preg against a given string, which is by default terminated

by a zero byte (but see REG_STARTEND below), subject to the

options in eflags. These can be:

REG_NOTBOL

The PCRE_NOTBOL option is set when calling the underlying

PCRE matching function.

REG_NOTEOL

The PCRE_NOTEOL option is set when calling the underlying

PCRE matching function.

REG_STARTEND

The string is considered to start at string +

pmatch[0].rm_so and to have a terminating NUL located at

string + pmatch[0].rm_eo (there need not actually be a NUL

at that location), regardless of the value of nmatch. This is a BSD extension, compatible with but not specified by

IEEE Standard 1003.2 (POSIX.2), and should be used with cau-

tion in software intended to be portable to other systems.

Note that a non-zero rm_so does not imply REG_NOTBOL;

REG_STARTEND affects only the location of the string, not

how it is matched.

If the pattern was compiled with the REG_NOSUB flag, no data

about any matched strings is returned. The nmatch and pmatch arguments of regexec() are ignored. Otherwise,the portion of the string that was matched, and also any captured substrings, are returned via the pmatch argument, which points to an array of nmatch structures of

type regmatch_t, containing the members rm_so and rm_eo.

These contain the offset to the first character of each sub-

string and the offset to the first character after the end

of each substring, respectively. The 0th element of the vec-

tor relates to the entire portion of string that was

matched; subsequent elements relate to the capturing subpat-

terns of the regular expression. Unused entries in the array

have both structure members set to -1.

A successful match yields a zero return; various error codes

are defined in the header file, of which REG_NOMATCH is the

"expected" failure code.

ERROR MESSAGES

SunOS 5.10 Last change: 4 Introduction to Library Functions PCREPOSIX(3)

The regerror() function maps a non-zero errorcode from

either regcomp() or regexec() to a printable message. If preg is not NULL, the error should have arisen from the use of that structure. A message terminated by a binary zero is placed in errbuf. The length of the message, including the

zero, is limited to errbuf_size. The yield of the function

is the size of buffer needed to hold the whole message.

MEMORY USAGE

Compiling a regular expression causes memory to be allocated

and associated with the preg structure. The function reg-

free() frees all such memory, after which preg may no longer be used as a compiled expression. AUTHOR Philip Hazel University Computing Service Cambridge CB2 3QH, England. REVISION Last updated: 05 April 2008

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: 5