1 <html> 2 <head> 3 <title>pcre2posix specification</title> 4 </head> 5 <body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB"> 6 <h1>pcre2posix man page</h1> 7 <p> 8 Return to the <a href="index.html">PCRE2 index page</a>. 9 </p> 10 <p> 11 This page is part of the PCRE2 HTML documentation. It was generated 12 automatically from the original man page. If there is any nonsense in it, 13 please consult the man page, in case the conversion went wrong. 14 <br> 15 <ul> 16 <li><a name="TOC1" href="#SEC1">SYNOPSIS</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</a><br> 27 <P> 28 <b>#include <pcre2posix.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 <br> 34 <br> 35 <b>int regexec(const 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 <br> 38 <br> 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 <br> 42 <br> 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 for the PCRE2 regular 48 expression 8-bit library. See the 49 <a href="pcre2api.html"><b>pcre2api</b></a> 50 documentation for a description of PCRE2's native API, which contains much 51 additional functionality. There are no POSIX-style wrappers for PCRE2's 16-bit 52 and 32-bit libraries. 53 </P> 54 <P> 55 The functions described here are just wrapper functions that ultimately call 56 the PCRE2 native API. Their prototypes are defined in the <b>pcre2posix.h</b> 57 header file, and on Unix systems the library itself is called 58 <b>libpcre2-posix.a</b>, so can be accessed by adding <b>-lpcre2-posix</b> to the 59 command for linking an application that uses them. Because the POSIX functions 60 call the native ones, it is also necessary to add <b>-lpcre2-8</b>. 61 </P> 62 <P> 63 Those POSIX option bits that can reasonably be mapped to PCRE2 native options 64 have been implemented. In addition, the option REG_EXTENDED is defined with the 65 value zero. This has no effect, but since programs that are written to the 66 POSIX interface often use it, this makes it easier to slot in PCRE2 as a 67 replacement library. Other POSIX options are not even defined. 68 </P> 69 <P> 70 There are also some options that are not defined by POSIX. These have been 71 added at the request of users who want to make use of certain PCRE2-specific 72 features via the POSIX calling interface. 73 </P> 74 <P> 75 When PCRE2 is called via these functions, it is only the API that is POSIX-like 76 in style. The syntax and semantics of the regular expressions themselves are 77 still those of Perl, subject to the setting of various PCRE2 options, as 78 described below. "POSIX-like in style" means that the API approximates to the 79 POSIX definition; it is not fully POSIX-compatible, and in multi-unit encoding 80 domains it is probably even less compatible. 81 </P> 82 <P> 83 The header for these functions is supplied as <b>pcre2posix.h</b> to avoid any 84 potential clash with other POSIX libraries. It can, of course, be renamed or 85 aliased as <b>regex.h</b>, which is the "correct" name. It provides two 86 structure types, <i>regex_t</i> for compiled internal forms, and 87 <i>regmatch_t</i> for returning captured substrings. It also defines some 88 constants whose names start with "REG_"; these are used for setting options and 89 identifying error codes. 90 </P> 91 <br><a name="SEC3" href="#TOC1">COMPILING A PATTERN</a><br> 92 <P> 93 The function <b>regcomp()</b> is called to compile a pattern into an 94 internal form. The pattern is a C string terminated by a binary zero, and 95 is passed in the argument <i>pattern</i>. The <i>preg</i> argument is a pointer 96 to a <b>regex_t</b> structure that is used as a base for storing information 97 about the compiled regular expression. 98 </P> 99 <P> 100 The argument <i>cflags</i> is either zero, or contains one or more of the bits 101 defined by the following macros: 102 <pre> 103 REG_DOTALL 104 </pre> 105 The PCRE2_DOTALL option is set when the regular expression is passed for 106 compilation to the native function. Note that REG_DOTALL is not part of the 107 POSIX standard. 108 <pre> 109 REG_ICASE 110 </pre> 111 The PCRE2_CASELESS option is set when the regular expression is passed for 112 compilation to the native function. 113 <pre> 114 REG_NEWLINE 115 </pre> 116 The PCRE2_MULTILINE option is set when the regular expression is passed for 117 compilation to the native function. Note that this does <i>not</i> mimic the 118 defined POSIX behaviour for REG_NEWLINE (see the following section). 119 <pre> 120 REG_NOSUB 121 </pre> 122 When a pattern that is compiled with this flag is passed to <b>regexec()</b> for 123 matching, the <i>nmatch</i> and <i>pmatch</i> arguments are ignored, and no 124 captured strings are returned. Versions of the PCRE library prior to 10.22 used 125 to set the PCRE2_NO_AUTO_CAPTURE compile option, but this no longer happens 126 because it disables the use of back references. 127 <pre> 128 REG_UCP 129 </pre> 130 The PCRE2_UCP option is set when the regular expression is passed for 131 compilation to the native function. This causes PCRE2 to use Unicode properties 132 when matchine \d, \w, etc., instead of just recognizing ASCII values. Note 133 that REG_UCP is not part of the POSIX standard. 134 <pre> 135 REG_UNGREEDY 136 </pre> 137 The PCRE2_UNGREEDY option is set when the regular expression is passed for 138 compilation to the native function. Note that REG_UNGREEDY is not part of the 139 POSIX standard. 140 <pre> 141 REG_UTF 142 </pre> 143 The PCRE2_UTF option is set when the regular expression is passed for 144 compilation to the native function. This causes the pattern itself and all data 145 strings used for matching it to be treated as UTF-8 strings. Note that REG_UTF 146 is not part of the POSIX standard. 147 </P> 148 <P> 149 In the absence of these flags, no options are passed to the native function. 150 This means the the regex is compiled with PCRE2 default semantics. In 151 particular, the way it handles newline characters in the subject string is the 152 Perl way, not the POSIX way. Note that setting PCRE2_MULTILINE has only 153 <i>some</i> of the effects specified for REG_NEWLINE. It does not affect the way 154 newlines are matched by the dot metacharacter (they are not) or by a negative 155 class such as [^a] (they are). 156 </P> 157 <P> 158 The yield of <b>regcomp()</b> is zero on success, and non-zero otherwise. The 159 <i>preg</i> structure is filled in on success, and one member of the structure 160 is public: <i>re_nsub</i> contains the number of capturing subpatterns in 161 the regular expression. Various error codes are defined in the header file. 162 </P> 163 <P> 164 NOTE: If the yield of <b>regcomp()</b> is non-zero, you must not attempt to 165 use the contents of the <i>preg</i> structure. If, for example, you pass it to 166 <b>regexec()</b>, the result is undefined and your program is likely to crash. 167 </P> 168 <br><a name="SEC4" href="#TOC1">MATCHING NEWLINE CHARACTERS</a><br> 169 <P> 170 This area is not simple, because POSIX and Perl take different views of things. 171 It is not possible to get PCRE2 to obey POSIX semantics, but then PCRE2 was 172 never intended to be a POSIX engine. The following table lists the different 173 possibilities for matching newline characters in Perl and PCRE2: 174 <pre> 175 Default Change with 176 177 . matches newline no PCRE2_DOTALL 178 newline matches [^a] yes not changeable 179 $ matches \n at end yes PCRE2_DOLLAR_ENDONLY 180 $ matches \n in middle no PCRE2_MULTILINE 181 ^ matches \n in middle no PCRE2_MULTILINE 182 </pre> 183 This is the equivalent table for a POSIX-compatible pattern matcher: 184 <pre> 185 Default Change with 186 187 . matches newline yes REG_NEWLINE 188 newline matches [^a] yes REG_NEWLINE 189 $ matches \n at end no REG_NEWLINE 190 $ matches \n in middle no REG_NEWLINE 191 ^ matches \n in middle no REG_NEWLINE 192 </pre> 193 This behaviour is not what happens when PCRE2 is called via its POSIX 194 API. By default, PCRE2's behaviour is the same as Perl's, except that there is 195 no equivalent for PCRE2_DOLLAR_ENDONLY in Perl. In both PCRE2 and Perl, there 196 is no way to stop newline from matching [^a]. 197 </P> 198 <P> 199 Default POSIX newline handling can be obtained by setting PCRE2_DOTALL and 200 PCRE2_DOLLAR_ENDONLY when calling <b>pcre2_compile()</b> directly, but there is 201 no way to make PCRE2 behave exactly as for the REG_NEWLINE action. When using 202 the POSIX API, passing REG_NEWLINE to PCRE2's <b>regcomp()</b> function 203 causes PCRE2_MULTILINE to be passed to <b>pcre2_compile()</b>, and REG_DOTALL 204 passes PCRE2_DOTALL. There is no way to pass PCRE2_DOLLAR_ENDONLY. 205 </P> 206 <br><a name="SEC5" href="#TOC1">MATCHING A PATTERN</a><br> 207 <P> 208 The function <b>regexec()</b> is called to match a compiled pattern <i>preg</i> 209 against a given <i>string</i>, which is by default terminated by a zero byte 210 (but see REG_STARTEND below), subject to the options in <i>eflags</i>. These can 211 be: 212 <pre> 213 REG_NOTBOL 214 </pre> 215 The PCRE2_NOTBOL option is set when calling the underlying PCRE2 matching 216 function. 217 <pre> 218 REG_NOTEMPTY 219 </pre> 220 The PCRE2_NOTEMPTY option is set when calling the underlying PCRE2 matching 221 function. Note that REG_NOTEMPTY is not part of the POSIX standard. However, 222 setting this option can give more POSIX-like behaviour in some situations. 223 <pre> 224 REG_NOTEOL 225 </pre> 226 The PCRE2_NOTEOL option is set when calling the underlying PCRE2 matching 227 function. 228 <pre> 229 REG_STARTEND 230 </pre> 231 The string is considered to start at <i>string</i> + <i>pmatch[0].rm_so</i> and 232 to have a terminating NUL located at <i>string</i> + <i>pmatch[0].rm_eo</i> 233 (there need not actually be a NUL at that location), regardless of the value of 234 <i>nmatch</i>. This is a BSD extension, compatible with but not specified by 235 IEEE Standard 1003.2 (POSIX.2), and should be used with caution in software 236 intended to be portable to other systems. Note that a non-zero <i>rm_so</i> does 237 not imply REG_NOTBOL; REG_STARTEND affects only the location of the string, not 238 how it is matched. Setting REG_STARTEND and passing <i>pmatch</i> as NULL are 239 mutually exclusive; the error REG_INVARG is returned. 240 </P> 241 <P> 242 If the pattern was compiled with the REG_NOSUB flag, no data about any matched 243 strings is returned. The <i>nmatch</i> and <i>pmatch</i> arguments of 244 <b>regexec()</b> are ignored (except possibly as input for REG_STARTEND). 245 </P> 246 <P> 247 The value of <i>nmatch</i> may be zero, and the value <i>pmatch</i> may be NULL 248 (unless REG_STARTEND is set); in both these cases no data about any matched 249 strings is returned. 250 </P> 251 <P> 252 Otherwise, the portion of the string that was matched, and also any captured 253 substrings, are returned via the <i>pmatch</i> argument, which points to an 254 array of <i>nmatch</i> structures of type <i>regmatch_t</i>, containing the 255 members <i>rm_so</i> and <i>rm_eo</i>. These contain the byte offset to the first 256 character of each substring and the offset to the first character after the end 257 of each substring, respectively. The 0th element of the vector relates to the 258 entire portion of <i>string</i> that was matched; subsequent elements relate to 259 the capturing subpatterns of the regular expression. Unused entries in the 260 array have both structure members set to -1. 261 </P> 262 <P> 263 A successful match yields a zero return; various error codes are defined in the 264 header file, of which REG_NOMATCH is the "expected" failure code. 265 </P> 266 <br><a name="SEC6" href="#TOC1">ERROR MESSAGES</a><br> 267 <P> 268 The <b>regerror()</b> function maps a non-zero errorcode from either 269 <b>regcomp()</b> or <b>regexec()</b> to a printable message. If <i>preg</i> is not 270 NULL, the error should have arisen from the use of that structure. A message 271 terminated by a binary zero is placed in <i>errbuf</i>. If the buffer is too 272 short, only the first <i>errbuf_size</i> - 1 characters of the error message are 273 used. The yield of the function is the size of buffer needed to hold the whole 274 message, including the terminating zero. This value is greater than 275 <i>errbuf_size</i> if the message was truncated. 276 </P> 277 <br><a name="SEC7" href="#TOC1">MEMORY USAGE</a><br> 278 <P> 279 Compiling a regular expression causes memory to be allocated and associated 280 with the <i>preg</i> structure. The function <b>regfree()</b> frees all such 281 memory, after which <i>preg</i> may no longer be used as a compiled expression. 282 </P> 283 <br><a name="SEC8" href="#TOC1">AUTHOR</a><br> 284 <P> 285 Philip Hazel 286 <br> 287 University Computing Service 288 <br> 289 Cambridge, England. 290 <br> 291 </P> 292 <br><a name="SEC9" href="#TOC1">REVISION</a><br> 293 <P> 294 Last updated: 31 January 2016 295 <br> 296 Copyright © 1997-2016 University of Cambridge. 297 <br> 298 <p> 299 Return to the <a href="index.html">PCRE2 index page</a>. 300 </p> 301
