Annotation of embedaddon/pcre/doc/pcreposix.3, revision 1.1
1.1 ! misho 1: .TH PCREPOSIX 3
! 2: .SH NAME
! 3: PCRE - Perl-compatible regular expressions.
! 4: .SH "SYNOPSIS OF POSIX API"
! 5: .rs
! 6: .sp
! 7: .B #include <pcreposix.h>
! 8: .PP
! 9: .SM
! 10: .B int regcomp(regex_t *\fIpreg\fP, const char *\fIpattern\fP,
! 11: .ti +5n
! 12: .B int \fIcflags\fP);
! 13: .PP
! 14: .B int regexec(regex_t *\fIpreg\fP, const char *\fIstring\fP,
! 15: .ti +5n
! 16: .B size_t \fInmatch\fP, regmatch_t \fIpmatch\fP[], int \fIeflags\fP);
! 17: .PP
! 18: .B size_t regerror(int \fIerrcode\fP, const regex_t *\fIpreg\fP,
! 19: .ti +5n
! 20: .B char *\fIerrbuf\fP, size_t \fIerrbuf_size\fP);
! 21: .PP
! 22: .B void regfree(regex_t *\fIpreg\fP);
! 23: .
! 24: .SH DESCRIPTION
! 25: .rs
! 26: .sp
! 27: This set of functions provides a POSIX-style API to the PCRE regular expression
! 28: package. See the
! 29: .\" HREF
! 30: \fBpcreapi\fP
! 31: .\"
! 32: documentation for a description of PCRE's native API, which contains much
! 33: additional functionality.
! 34: .P
! 35: The functions described here are just wrapper functions that ultimately call
! 36: the PCRE native API. Their prototypes are defined in the \fBpcreposix.h\fP
! 37: header file, and on Unix systems the library itself is called
! 38: \fBpcreposix.a\fP, so can be accessed by adding \fB-lpcreposix\fP to the
! 39: command for linking an application that uses them. Because the POSIX functions
! 40: call the native ones, it is also necessary to add \fB-lpcre\fP.
! 41: .P
! 42: I have implemented only those POSIX option bits that can be reasonably mapped
! 43: to PCRE native options. In addition, the option REG_EXTENDED is defined with
! 44: the value zero. This has no effect, but since programs that are written to the
! 45: POSIX interface often use it, this makes it easier to slot in PCRE as a
! 46: replacement library. Other POSIX options are not even defined.
! 47: .P
! 48: There are also some other options that are not defined by POSIX. These have
! 49: been added at the request of users who want to make use of certain
! 50: PCRE-specific features via the POSIX calling interface.
! 51: .P
! 52: When PCRE is called via these functions, it is only the API that is POSIX-like
! 53: in style. The syntax and semantics of the regular expressions themselves are
! 54: still those of Perl, subject to the setting of various PCRE options, as
! 55: described below. "POSIX-like in style" means that the API approximates to the
! 56: POSIX definition; it is not fully POSIX-compatible, and in multi-byte encoding
! 57: domains it is probably even less compatible.
! 58: .P
! 59: The header for these functions is supplied as \fBpcreposix.h\fP to avoid any
! 60: potential clash with other POSIX libraries. It can, of course, be renamed or
! 61: aliased as \fBregex.h\fP, which is the "correct" name. It provides two
! 62: structure types, \fIregex_t\fP for compiled internal forms, and
! 63: \fIregmatch_t\fP for returning captured substrings. It also defines some
! 64: constants whose names start with "REG_"; these are used for setting options and
! 65: identifying error codes.
! 66: .
! 67: .
! 68: .SH "COMPILING A PATTERN"
! 69: .rs
! 70: .sp
! 71: The function \fBregcomp()\fP is called to compile a pattern into an
! 72: internal form. The pattern is a C string terminated by a binary zero, and
! 73: is passed in the argument \fIpattern\fP. The \fIpreg\fP argument is a pointer
! 74: to a \fBregex_t\fP structure that is used as a base for storing information
! 75: about the compiled regular expression.
! 76: .P
! 77: The argument \fIcflags\fP is either zero, or contains one or more of the bits
! 78: defined by the following macros:
! 79: .sp
! 80: REG_DOTALL
! 81: .sp
! 82: The PCRE_DOTALL option is set when the regular expression is passed for
! 83: compilation to the native function. Note that REG_DOTALL is not part of the
! 84: POSIX standard.
! 85: .sp
! 86: REG_ICASE
! 87: .sp
! 88: The PCRE_CASELESS option is set when the regular expression is passed for
! 89: compilation to the native function.
! 90: .sp
! 91: REG_NEWLINE
! 92: .sp
! 93: The PCRE_MULTILINE option is set when the regular expression is passed for
! 94: compilation to the native function. Note that this does \fInot\fP mimic the
! 95: defined POSIX behaviour for REG_NEWLINE (see the following section).
! 96: .sp
! 97: REG_NOSUB
! 98: .sp
! 99: The PCRE_NO_AUTO_CAPTURE option is set when the regular expression is passed
! 100: for compilation to the native function. In addition, when a pattern that is
! 101: compiled with this flag is passed to \fBregexec()\fP for matching, the
! 102: \fInmatch\fP and \fIpmatch\fP arguments are ignored, and no captured strings
! 103: are returned.
! 104: .sp
! 105: REG_UCP
! 106: .sp
! 107: The PCRE_UCP option is set when the regular expression is passed for
! 108: compilation to the native function. This causes PCRE to use Unicode properties
! 109: when matchine \ed, \ew, etc., instead of just recognizing ASCII values. Note
! 110: that REG_UTF8 is not part of the POSIX standard.
! 111: .sp
! 112: REG_UNGREEDY
! 113: .sp
! 114: The PCRE_UNGREEDY option is set when the regular expression is passed for
! 115: compilation to the native function. Note that REG_UNGREEDY is not part of the
! 116: POSIX standard.
! 117: .sp
! 118: REG_UTF8
! 119: .sp
! 120: The PCRE_UTF8 option is set when the regular expression is passed for
! 121: compilation to the native function. This causes the pattern itself and all data
! 122: strings used for matching it to be treated as UTF-8 strings. Note that REG_UTF8
! 123: is not part of the POSIX standard.
! 124: .P
! 125: In the absence of these flags, no options are passed to the native function.
! 126: This means the the regex is compiled with PCRE default semantics. In
! 127: particular, the way it handles newline characters in the subject string is the
! 128: Perl way, not the POSIX way. Note that setting PCRE_MULTILINE has only
! 129: \fIsome\fP of the effects specified for REG_NEWLINE. It does not affect the way
! 130: newlines are matched by . (they are not) or by a negative class such as [^a]
! 131: (they are).
! 132: .P
! 133: The yield of \fBregcomp()\fP is zero on success, and non-zero otherwise. The
! 134: \fIpreg\fP structure is filled in on success, and one member of the structure
! 135: is public: \fIre_nsub\fP contains the number of capturing subpatterns in
! 136: the regular expression. Various error codes are defined in the header file.
! 137: .P
! 138: NOTE: If the yield of \fBregcomp()\fP is non-zero, you must not attempt to
! 139: use the contents of the \fIpreg\fP structure. If, for example, you pass it to
! 140: \fBregexec()\fP, the result is undefined and your program is likely to crash.
! 141: .
! 142: .
! 143: .SH "MATCHING NEWLINE CHARACTERS"
! 144: .rs
! 145: .sp
! 146: This area is not simple, because POSIX and Perl take different views of things.
! 147: It is not possible to get PCRE to obey POSIX semantics, but then PCRE was never
! 148: intended to be a POSIX engine. The following table lists the different
! 149: possibilities for matching newline characters in PCRE:
! 150: .sp
! 151: Default Change with
! 152: .sp
! 153: . matches newline no PCRE_DOTALL
! 154: newline matches [^a] yes not changeable
! 155: $ matches \en at end yes PCRE_DOLLARENDONLY
! 156: $ matches \en in middle no PCRE_MULTILINE
! 157: ^ matches \en in middle no PCRE_MULTILINE
! 158: .sp
! 159: This is the equivalent table for POSIX:
! 160: .sp
! 161: Default Change with
! 162: .sp
! 163: . matches newline yes REG_NEWLINE
! 164: newline matches [^a] yes REG_NEWLINE
! 165: $ matches \en at end no REG_NEWLINE
! 166: $ matches \en in middle no REG_NEWLINE
! 167: ^ matches \en in middle no REG_NEWLINE
! 168: .sp
! 169: PCRE's behaviour is the same as Perl's, except that there is no equivalent for
! 170: PCRE_DOLLAR_ENDONLY in Perl. In both PCRE and Perl, there is no way to stop
! 171: newline from matching [^a].
! 172: .P
! 173: The default POSIX newline handling can be obtained by setting PCRE_DOTALL and
! 174: PCRE_DOLLAR_ENDONLY, but there is no way to make PCRE behave exactly as for the
! 175: REG_NEWLINE action.
! 176: .
! 177: .
! 178: .SH "MATCHING A PATTERN"
! 179: .rs
! 180: .sp
! 181: The function \fBregexec()\fP is called to match a compiled pattern \fIpreg\fP
! 182: against a given \fIstring\fP, which is by default terminated by a zero byte
! 183: (but see REG_STARTEND below), subject to the options in \fIeflags\fP. These can
! 184: be:
! 185: .sp
! 186: REG_NOTBOL
! 187: .sp
! 188: The PCRE_NOTBOL option is set when calling the underlying PCRE matching
! 189: function.
! 190: .sp
! 191: REG_NOTEMPTY
! 192: .sp
! 193: The PCRE_NOTEMPTY option is set when calling the underlying PCRE matching
! 194: function. Note that REG_NOTEMPTY is not part of the POSIX standard. However,
! 195: setting this option can give more POSIX-like behaviour in some situations.
! 196: .sp
! 197: REG_NOTEOL
! 198: .sp
! 199: The PCRE_NOTEOL option is set when calling the underlying PCRE matching
! 200: function.
! 201: .sp
! 202: REG_STARTEND
! 203: .sp
! 204: The string is considered to start at \fIstring\fP + \fIpmatch[0].rm_so\fP and
! 205: to have a terminating NUL located at \fIstring\fP + \fIpmatch[0].rm_eo\fP
! 206: (there need not actually be a NUL at that location), regardless of the value of
! 207: \fInmatch\fP. This is a BSD extension, compatible with but not specified by
! 208: IEEE Standard 1003.2 (POSIX.2), and should be used with caution in software
! 209: intended to be portable to other systems. Note that a non-zero \fIrm_so\fP does
! 210: not imply REG_NOTBOL; REG_STARTEND affects only the location of the string, not
! 211: how it is matched.
! 212: .P
! 213: If the pattern was compiled with the REG_NOSUB flag, no data about any matched
! 214: strings is returned. The \fInmatch\fP and \fIpmatch\fP arguments of
! 215: \fBregexec()\fP are ignored.
! 216: .P
! 217: If the value of \fInmatch\fP is zero, or if the value \fIpmatch\fP is NULL,
! 218: no data about any matched strings is returned.
! 219: .P
! 220: Otherwise,the portion of the string that was matched, and also any captured
! 221: substrings, are returned via the \fIpmatch\fP argument, which points to an
! 222: array of \fInmatch\fP structures of type \fIregmatch_t\fP, containing the
! 223: members \fIrm_so\fP and \fIrm_eo\fP. These contain the offset to the first
! 224: character of each substring and the offset to the first character after the end
! 225: of each substring, respectively. The 0th element of the vector relates to the
! 226: entire portion of \fIstring\fP that was matched; subsequent elements relate to
! 227: the capturing subpatterns of the regular expression. Unused entries in the
! 228: array have both structure members set to -1.
! 229: .P
! 230: A successful match yields a zero return; various error codes are defined in the
! 231: header file, of which REG_NOMATCH is the "expected" failure code.
! 232: .
! 233: .
! 234: .SH "ERROR MESSAGES"
! 235: .rs
! 236: .sp
! 237: The \fBregerror()\fP function maps a non-zero errorcode from either
! 238: \fBregcomp()\fP or \fBregexec()\fP to a printable message. If \fIpreg\fP is not
! 239: NULL, the error should have arisen from the use of that structure. A message
! 240: terminated by a binary zero is placed in \fIerrbuf\fP. The length of the
! 241: message, including the zero, is limited to \fIerrbuf_size\fP. The yield of the
! 242: function is the size of buffer needed to hold the whole message.
! 243: .
! 244: .
! 245: .SH MEMORY USAGE
! 246: .rs
! 247: .sp
! 248: Compiling a regular expression causes memory to be allocated and associated
! 249: with the \fIpreg\fP structure. The function \fBregfree()\fP frees all such
! 250: memory, after which \fIpreg\fP may no longer be used as a compiled expression.
! 251: .
! 252: .
! 253: .SH AUTHOR
! 254: .rs
! 255: .sp
! 256: .nf
! 257: Philip Hazel
! 258: University Computing Service
! 259: Cambridge CB2 3QH, England.
! 260: .fi
! 261: .
! 262: .
! 263: .SH REVISION
! 264: .rs
! 265: .sp
! 266: .nf
! 267: Last updated: 16 May 2010
! 268: Copyright (c) 1997-2010 University of Cambridge.
! 269: .fi
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