Tristan Matthews | 0461646 | 2013-11-14 16:09:34 -0500 | [diff] [blame] | 1 | <html> |
| 2 | <head> |
| 3 | <title>pcreposix specification</title> |
| 4 | </head> |
| 5 | <body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB"> |
| 6 | <h1>pcreposix man page</h1> |
| 7 | <p> |
| 8 | Return to the <a href="index.html">PCRE index page</a>. |
| 9 | </p> |
| 10 | <p> |
| 11 | This page is part of the PCRE HTML documentation. It was generated automatically |
| 12 | from the original man page. If there is any nonsense in it, please consult the |
| 13 | man page, in case the conversion went wrong. |
| 14 | <br> |
| 15 | <ul> |
| 16 | <li><a name="TOC1" href="#SEC1">SYNOPSIS OF POSIX API</a> |
| 17 | <li><a name="TOC2" href="#SEC2">DESCRIPTION</a> |
| 18 | <li><a name="TOC3" href="#SEC3">COMPILING A PATTERN</a> |
| 19 | <li><a name="TOC4" href="#SEC4">MATCHING NEWLINE CHARACTERS</a> |
| 20 | <li><a name="TOC5" href="#SEC5">MATCHING A PATTERN</a> |
| 21 | <li><a name="TOC6" href="#SEC6">ERROR MESSAGES</a> |
| 22 | <li><a name="TOC7" href="#SEC7">MEMORY USAGE</a> |
| 23 | <li><a name="TOC8" href="#SEC8">AUTHOR</a> |
| 24 | <li><a name="TOC9" href="#SEC9">REVISION</a> |
| 25 | </ul> |
| 26 | <br><a name="SEC1" href="#TOC1">SYNOPSIS OF POSIX API</a><br> |
| 27 | <P> |
| 28 | <b>#include <pcreposix.h></b> |
| 29 | </P> |
| 30 | <P> |
| 31 | <b>int regcomp(regex_t *<i>preg</i>, const char *<i>pattern</i>,</b> |
| 32 | <b>int <i>cflags</i>);</b> |
| 33 | </P> |
| 34 | <P> |
| 35 | <b>int regexec(regex_t *<i>preg</i>, const char *<i>string</i>,</b> |
| 36 | <b>size_t <i>nmatch</i>, regmatch_t <i>pmatch</i>[], int <i>eflags</i>);</b> |
| 37 | </P> |
| 38 | <P> |
| 39 | <b>size_t regerror(int <i>errcode</i>, const regex_t *<i>preg</i>,</b> |
| 40 | <b>char *<i>errbuf</i>, size_t <i>errbuf_size</i>);</b> |
| 41 | </P> |
| 42 | <P> |
| 43 | <b>void regfree(regex_t *<i>preg</i>);</b> |
| 44 | </P> |
| 45 | <br><a name="SEC2" href="#TOC1">DESCRIPTION</a><br> |
| 46 | <P> |
| 47 | This set of functions provides a POSIX-style API to the PCRE regular expression |
| 48 | package. See the |
| 49 | <a href="pcreapi.html"><b>pcreapi</b></a> |
| 50 | documentation for a description of PCRE's native API, which contains much |
| 51 | additional functionality. |
| 52 | </P> |
| 53 | <P> |
| 54 | The functions described here are just wrapper functions that ultimately call |
| 55 | the PCRE native API. Their prototypes are defined in the <b>pcreposix.h</b> |
| 56 | header file, and on Unix systems the library itself is called |
| 57 | <b>pcreposix.a</b>, so can be accessed by adding <b>-lpcreposix</b> to the |
| 58 | command for linking an application that uses them. Because the POSIX functions |
| 59 | call the native ones, it is also necessary to add <b>-lpcre</b>. |
| 60 | </P> |
| 61 | <P> |
| 62 | I have implemented only those POSIX option bits that can be reasonably mapped |
| 63 | to PCRE native options. In addition, the option REG_EXTENDED is defined with |
| 64 | the value zero. This has no effect, but since programs that are written to the |
| 65 | POSIX interface often use it, this makes it easier to slot in PCRE as a |
| 66 | replacement library. Other POSIX options are not even defined. |
| 67 | </P> |
| 68 | <P> |
| 69 | There are also some other options that are not defined by POSIX. These have |
| 70 | been added at the request of users who want to make use of certain |
| 71 | PCRE-specific features via the POSIX calling interface. |
| 72 | </P> |
| 73 | <P> |
| 74 | When PCRE is called via these functions, it is only the API that is POSIX-like |
| 75 | in style. The syntax and semantics of the regular expressions themselves are |
| 76 | still those of Perl, subject to the setting of various PCRE options, as |
| 77 | described below. "POSIX-like in style" means that the API approximates to the |
| 78 | POSIX definition; it is not fully POSIX-compatible, and in multi-byte encoding |
| 79 | domains it is probably even less compatible. |
| 80 | </P> |
| 81 | <P> |
| 82 | The header for these functions is supplied as <b>pcreposix.h</b> to avoid any |
| 83 | potential clash with other POSIX libraries. It can, of course, be renamed or |
| 84 | aliased as <b>regex.h</b>, which is the "correct" name. It provides two |
| 85 | structure types, <i>regex_t</i> for compiled internal forms, and |
| 86 | <i>regmatch_t</i> for returning captured substrings. It also defines some |
| 87 | constants whose names start with "REG_"; these are used for setting options and |
| 88 | identifying error codes. |
| 89 | </P> |
| 90 | <br><a name="SEC3" href="#TOC1">COMPILING A PATTERN</a><br> |
| 91 | <P> |
| 92 | The function <b>regcomp()</b> is called to compile a pattern into an |
| 93 | internal form. The pattern is a C string terminated by a binary zero, and |
| 94 | is passed in the argument <i>pattern</i>. The <i>preg</i> argument is a pointer |
| 95 | to a <b>regex_t</b> structure that is used as a base for storing information |
| 96 | about the compiled regular expression. |
| 97 | </P> |
| 98 | <P> |
| 99 | The argument <i>cflags</i> is either zero, or contains one or more of the bits |
| 100 | defined by the following macros: |
| 101 | <pre> |
| 102 | REG_DOTALL |
| 103 | </pre> |
| 104 | The PCRE_DOTALL option is set when the regular expression is passed for |
| 105 | compilation to the native function. Note that REG_DOTALL is not part of the |
| 106 | POSIX standard. |
| 107 | <pre> |
| 108 | REG_ICASE |
| 109 | </pre> |
| 110 | The PCRE_CASELESS option is set when the regular expression is passed for |
| 111 | compilation to the native function. |
| 112 | <pre> |
| 113 | REG_NEWLINE |
| 114 | </pre> |
| 115 | The PCRE_MULTILINE option is set when the regular expression is passed for |
| 116 | compilation to the native function. Note that this does <i>not</i> mimic the |
| 117 | defined POSIX behaviour for REG_NEWLINE (see the following section). |
| 118 | <pre> |
| 119 | REG_NOSUB |
| 120 | </pre> |
| 121 | The PCRE_NO_AUTO_CAPTURE option is set when the regular expression is passed |
| 122 | for compilation to the native function. In addition, when a pattern that is |
| 123 | compiled with this flag is passed to <b>regexec()</b> for matching, the |
| 124 | <i>nmatch</i> and <i>pmatch</i> arguments are ignored, and no captured strings |
| 125 | are returned. |
| 126 | <pre> |
| 127 | REG_UCP |
| 128 | </pre> |
| 129 | The PCRE_UCP option is set when the regular expression is passed for |
| 130 | compilation to the native function. This causes PCRE to use Unicode properties |
| 131 | when matchine \d, \w, etc., instead of just recognizing ASCII values. Note |
| 132 | that REG_UTF8 is not part of the POSIX standard. |
| 133 | <pre> |
| 134 | REG_UNGREEDY |
| 135 | </pre> |
| 136 | The PCRE_UNGREEDY option is set when the regular expression is passed for |
| 137 | compilation to the native function. Note that REG_UNGREEDY is not part of the |
| 138 | POSIX standard. |
| 139 | <pre> |
| 140 | REG_UTF8 |
| 141 | </pre> |
| 142 | The PCRE_UTF8 option is set when the regular expression is passed for |
| 143 | compilation to the native function. This causes the pattern itself and all data |
| 144 | strings used for matching it to be treated as UTF-8 strings. Note that REG_UTF8 |
| 145 | is not part of the POSIX standard. |
| 146 | </P> |
| 147 | <P> |
| 148 | In the absence of these flags, no options are passed to the native function. |
| 149 | This means the the regex is compiled with PCRE default semantics. In |
| 150 | particular, the way it handles newline characters in the subject string is the |
| 151 | Perl way, not the POSIX way. Note that setting PCRE_MULTILINE has only |
| 152 | <i>some</i> of the effects specified for REG_NEWLINE. It does not affect the way |
| 153 | newlines are matched by . (they are not) or by a negative class such as [^a] |
| 154 | (they are). |
| 155 | </P> |
| 156 | <P> |
| 157 | The yield of <b>regcomp()</b> is zero on success, and non-zero otherwise. The |
| 158 | <i>preg</i> structure is filled in on success, and one member of the structure |
| 159 | is public: <i>re_nsub</i> contains the number of capturing subpatterns in |
| 160 | the regular expression. Various error codes are defined in the header file. |
| 161 | </P> |
| 162 | <P> |
| 163 | NOTE: If the yield of <b>regcomp()</b> is non-zero, you must not attempt to |
| 164 | use the contents of the <i>preg</i> structure. If, for example, you pass it to |
| 165 | <b>regexec()</b>, the result is undefined and your program is likely to crash. |
| 166 | </P> |
| 167 | <br><a name="SEC4" href="#TOC1">MATCHING NEWLINE CHARACTERS</a><br> |
| 168 | <P> |
| 169 | This area is not simple, because POSIX and Perl take different views of things. |
| 170 | It is not possible to get PCRE to obey POSIX semantics, but then PCRE was never |
| 171 | intended to be a POSIX engine. The following table lists the different |
| 172 | possibilities for matching newline characters in PCRE: |
| 173 | <pre> |
| 174 | Default Change with |
| 175 | |
| 176 | . matches newline no PCRE_DOTALL |
| 177 | newline matches [^a] yes not changeable |
| 178 | $ matches \n at end yes PCRE_DOLLARENDONLY |
| 179 | $ matches \n in middle no PCRE_MULTILINE |
| 180 | ^ matches \n in middle no PCRE_MULTILINE |
| 181 | </pre> |
| 182 | This is the equivalent table for POSIX: |
| 183 | <pre> |
| 184 | Default Change with |
| 185 | |
| 186 | . matches newline yes REG_NEWLINE |
| 187 | newline matches [^a] yes REG_NEWLINE |
| 188 | $ matches \n at end no REG_NEWLINE |
| 189 | $ matches \n in middle no REG_NEWLINE |
| 190 | ^ matches \n in middle no REG_NEWLINE |
| 191 | </pre> |
| 192 | PCRE's behaviour is the same as Perl's, except that there is no equivalent for |
| 193 | PCRE_DOLLAR_ENDONLY in Perl. In both PCRE and Perl, there is no way to stop |
| 194 | newline from matching [^a]. |
| 195 | </P> |
| 196 | <P> |
| 197 | The default POSIX newline handling can be obtained by setting PCRE_DOTALL and |
| 198 | PCRE_DOLLAR_ENDONLY, but there is no way to make PCRE behave exactly as for the |
| 199 | REG_NEWLINE action. |
| 200 | </P> |
| 201 | <br><a name="SEC5" href="#TOC1">MATCHING A PATTERN</a><br> |
| 202 | <P> |
| 203 | The function <b>regexec()</b> is called to match a compiled pattern <i>preg</i> |
| 204 | against a given <i>string</i>, which is by default terminated by a zero byte |
| 205 | (but see REG_STARTEND below), subject to the options in <i>eflags</i>. These can |
| 206 | be: |
| 207 | <pre> |
| 208 | REG_NOTBOL |
| 209 | </pre> |
| 210 | The PCRE_NOTBOL option is set when calling the underlying PCRE matching |
| 211 | function. |
| 212 | <pre> |
| 213 | REG_NOTEMPTY |
| 214 | </pre> |
| 215 | The PCRE_NOTEMPTY option is set when calling the underlying PCRE matching |
| 216 | function. Note that REG_NOTEMPTY is not part of the POSIX standard. However, |
| 217 | setting this option can give more POSIX-like behaviour in some situations. |
| 218 | <pre> |
| 219 | REG_NOTEOL |
| 220 | </pre> |
| 221 | The PCRE_NOTEOL option is set when calling the underlying PCRE matching |
| 222 | function. |
| 223 | <pre> |
| 224 | REG_STARTEND |
| 225 | </pre> |
| 226 | The string is considered to start at <i>string</i> + <i>pmatch[0].rm_so</i> and |
| 227 | to have a terminating NUL located at <i>string</i> + <i>pmatch[0].rm_eo</i> |
| 228 | (there need not actually be a NUL at that location), regardless of the value of |
| 229 | <i>nmatch</i>. This is a BSD extension, compatible with but not specified by |
| 230 | IEEE Standard 1003.2 (POSIX.2), and should be used with caution in software |
| 231 | intended to be portable to other systems. Note that a non-zero <i>rm_so</i> does |
| 232 | not imply REG_NOTBOL; REG_STARTEND affects only the location of the string, not |
| 233 | how it is matched. |
| 234 | </P> |
| 235 | <P> |
| 236 | If the pattern was compiled with the REG_NOSUB flag, no data about any matched |
| 237 | strings is returned. The <i>nmatch</i> and <i>pmatch</i> arguments of |
| 238 | <b>regexec()</b> are ignored. |
| 239 | </P> |
| 240 | <P> |
| 241 | If the value of <i>nmatch</i> is zero, or if the value <i>pmatch</i> is NULL, |
| 242 | no data about any matched strings is returned. |
| 243 | </P> |
| 244 | <P> |
| 245 | Otherwise,the portion of the string that was matched, and also any captured |
| 246 | substrings, are returned via the <i>pmatch</i> argument, which points to an |
| 247 | array of <i>nmatch</i> structures of type <i>regmatch_t</i>, containing the |
| 248 | members <i>rm_so</i> and <i>rm_eo</i>. These contain the offset to the first |
| 249 | character of each substring and the offset to the first character after the end |
| 250 | of each substring, respectively. The 0th element of the vector relates to the |
| 251 | entire portion of <i>string</i> that was matched; subsequent elements relate to |
| 252 | the capturing subpatterns of the regular expression. Unused entries in the |
| 253 | array have both structure members set to -1. |
| 254 | </P> |
| 255 | <P> |
| 256 | A successful match yields a zero return; various error codes are defined in the |
| 257 | header file, of which REG_NOMATCH is the "expected" failure code. |
| 258 | </P> |
| 259 | <br><a name="SEC6" href="#TOC1">ERROR MESSAGES</a><br> |
| 260 | <P> |
| 261 | The <b>regerror()</b> function maps a non-zero errorcode from either |
| 262 | <b>regcomp()</b> or <b>regexec()</b> to a printable message. If <i>preg</i> is not |
| 263 | NULL, the error should have arisen from the use of that structure. A message |
| 264 | terminated by a binary zero is placed in <i>errbuf</i>. The length of the |
| 265 | message, including the zero, is limited to <i>errbuf_size</i>. The yield of the |
| 266 | function is the size of buffer needed to hold the whole message. |
| 267 | </P> |
| 268 | <br><a name="SEC7" href="#TOC1">MEMORY USAGE</a><br> |
| 269 | <P> |
| 270 | Compiling a regular expression causes memory to be allocated and associated |
| 271 | with the <i>preg</i> structure. The function <b>regfree()</b> frees all such |
| 272 | memory, after which <i>preg</i> may no longer be used as a compiled expression. |
| 273 | </P> |
| 274 | <br><a name="SEC8" href="#TOC1">AUTHOR</a><br> |
| 275 | <P> |
| 276 | Philip Hazel |
| 277 | <br> |
| 278 | University Computing Service |
| 279 | <br> |
| 280 | Cambridge CB2 3QH, England. |
| 281 | <br> |
| 282 | </P> |
| 283 | <br><a name="SEC9" href="#TOC1">REVISION</a><br> |
| 284 | <P> |
| 285 | Last updated: 16 May 2010 |
| 286 | <br> |
| 287 | Copyright © 1997-2010 University of Cambridge. |
| 288 | <br> |
| 289 | <p> |
| 290 | Return to the <a href="index.html">PCRE index page</a>. |
| 291 | </p> |