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> 8Return to the <a href="index.html">PCRE2 index page</a>. 9</p> 10<p> 11This page is part of the PCRE2 HTML documentation. It was generated 12automatically from the original man page. If there is any nonsense in it, 13please 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">USING THE POSIX FUNCTIONS</a> 19<li><a name="TOC4" href="#SEC4">COMPILING A PATTERN</a> 20<li><a name="TOC5" href="#SEC5">MATCHING NEWLINE CHARACTERS</a> 21<li><a name="TOC6" href="#SEC6">MATCHING A PATTERN</a> 22<li><a name="TOC7" href="#SEC7">ERROR MESSAGES</a> 23<li><a name="TOC8" href="#SEC8">MEMORY USAGE</a> 24<li><a name="TOC9" href="#SEC9">AUTHOR</a> 25<li><a name="TOC10" href="#SEC10">REVISION</a> 26</ul> 27<br><a name="SEC1" href="#TOC1">SYNOPSIS</a><br> 28<P> 29<b>#include <pcre2posix.h></b> 30</P> 31<P> 32<b>int pcre2_regcomp(regex_t *<i>preg</i>, const char *<i>pattern</i>,</b> 33<b> int <i>cflags</i>);</b> 34<br> 35<br> 36<b>int pcre2_regexec(const regex_t *<i>preg</i>, const char *<i>string</i>,</b> 37<b> size_t <i>nmatch</i>, regmatch_t <i>pmatch</i>[], int <i>eflags</i>);</b> 38<br> 39<br> 40<b>size_t pcre2_regerror(int <i>errcode</i>, const regex_t *<i>preg</i>,</b> 41<b> char *<i>errbuf</i>, size_t <i>errbuf_size</i>);</b> 42<br> 43<br> 44<b>void pcre2_regfree(regex_t *<i>preg</i>);</b> 45</P> 46<br><a name="SEC2" href="#TOC1">DESCRIPTION</a><br> 47<P> 48This set of functions provides a POSIX-style API for the PCRE2 regular 49expression 8-bit library. There are no POSIX-style wrappers for PCRE2's 16-bit 50and 32-bit libraries. See the 51<a href="pcre2api.html"><b>pcre2api</b></a> 52documentation for a description of PCRE2's native API, which contains much 53additional functionality. 54</P> 55<P> 56The functions described here are wrapper functions that ultimately call the 57PCRE2 native API. Their prototypes are defined in the <b>pcre2posix.h</b> header 58file, and they all have unique names starting with <b>pcre2_</b>. However, the 59<b>pcre2posix.h</b> header also contains macro definitions that convert the 60standard POSIX names such <b>regcomp()</b> into <b>pcre2_regcomp()</b> etc. This 61means that a program can use the usual POSIX names without running the risk of 62accidentally linking with POSIX functions from a different library. 63</P> 64<P> 65On Unix-like systems the PCRE2 POSIX library is called <b>libpcre2-posix</b>, so 66can be accessed by adding <b>-lpcre2-posix</b> to the command for linking an 67application. Because the POSIX functions call the native ones, it is also 68necessary to add <b>-lpcre2-8</b>. 69</P> 70<P> 71Although they were not defined as protypes in <b>pcre2posix.h</b>, releases 7210.33 to 10.36 of the library contained functions with the POSIX names 73<b>regcomp()</b> etc. These simply passed their arguments to the PCRE2 74functions. These functions were provided for backwards compatibility with 75earlier versions of PCRE2, which had only POSIX names. However, this has proved 76troublesome in situations where a program links with several libraries, some of 77which use PCRE2's POSIX interface while others use the real POSIX functions. 78For this reason, the POSIX names have been removed since release 10.37. 79</P> 80<P> 81Calling the header file <b>pcre2posix.h</b> avoids any conflict with other POSIX 82libraries. It can, of course, be renamed or aliased as <b>regex.h</b>, which is 83the "correct" name, if there is no clash. It provides two structure types, 84<i>regex_t</i> for compiled internal forms, and <i>regmatch_t</i> for returning 85captured substrings. It also defines some constants whose names start with 86"REG_"; these are used for setting options and identifying error codes. 87</P> 88<br><a name="SEC3" href="#TOC1">USING THE POSIX FUNCTIONS</a><br> 89<P> 90Those POSIX option bits that can reasonably be mapped to PCRE2 native options 91have been implemented. In addition, the option REG_EXTENDED is defined with the 92value zero. This has no effect, but since programs that are written to the 93POSIX interface often use it, this makes it easier to slot in PCRE2 as a 94replacement library. Other POSIX options are not even defined. 95</P> 96<P> 97There are also some options that are not defined by POSIX. These have been 98added at the request of users who want to make use of certain PCRE2-specific 99features via the POSIX calling interface or to add BSD or GNU functionality. 100</P> 101<P> 102When PCRE2 is called via these functions, it is only the API that is POSIX-like 103in style. The syntax and semantics of the regular expressions themselves are 104still those of Perl, subject to the setting of various PCRE2 options, as 105described below. "POSIX-like in style" means that the API approximates to the 106POSIX definition; it is not fully POSIX-compatible, and in multi-unit encoding 107domains it is probably even less compatible. 108</P> 109<P> 110The descriptions below use the actual names of the functions, but, as described 111above, the standard POSIX names (without the <b>pcre2_</b> prefix) may also be 112used. 113</P> 114<br><a name="SEC4" href="#TOC1">COMPILING A PATTERN</a><br> 115<P> 116The function <b>pcre2_regcomp()</b> is called to compile a pattern into an 117internal form. By default, the pattern is a C string terminated by a binary 118zero (but see REG_PEND below). The <i>preg</i> argument is a pointer to a 119<b>regex_t</b> structure that is used as a base for storing information about 120the compiled regular expression. (It is also used for input when REG_PEND is 121set.) 122</P> 123<P> 124The argument <i>cflags</i> is either zero, or contains one or more of the bits 125defined by the following macros: 126<pre> 127 REG_DOTALL 128</pre> 129The PCRE2_DOTALL option is set when the regular expression is passed for 130compilation to the native function. Note that REG_DOTALL is not part of the 131POSIX standard. 132<pre> 133 REG_ICASE 134</pre> 135The PCRE2_CASELESS option is set when the regular expression is passed for 136compilation to the native function. 137<pre> 138 REG_NEWLINE 139</pre> 140The PCRE2_MULTILINE option is set when the regular expression is passed for 141compilation to the native function. Note that this does <i>not</i> mimic the 142defined POSIX behaviour for REG_NEWLINE (see the following section). 143<pre> 144 REG_NOSPEC 145</pre> 146The PCRE2_LITERAL option is set when the regular expression is passed for 147compilation to the native function. This disables all meta characters in the 148pattern, causing it to be treated as a literal string. The only other options 149that are allowed with REG_NOSPEC are REG_ICASE, REG_NOSUB, REG_PEND, and 150REG_UTF. Note that REG_NOSPEC is not part of the POSIX standard. 151<pre> 152 REG_NOSUB 153</pre> 154When a pattern that is compiled with this flag is passed to 155<b>pcre2_regexec()</b> for matching, the <i>nmatch</i> and <i>pmatch</i> arguments 156are ignored, and no captured strings are returned. Versions of the PCRE library 157prior to 10.22 used to set the PCRE2_NO_AUTO_CAPTURE compile option, but this 158no longer happens because it disables the use of backreferences. 159<pre> 160 REG_PEND 161</pre> 162If this option is set, the <b>reg_endp</b> field in the <i>preg</i> structure 163(which has the type const char *) must be set to point to the character beyond 164the end of the pattern before calling <b>pcre2_regcomp()</b>. The pattern itself 165may now contain binary zeros, which are treated as data characters. Without 166REG_PEND, a binary zero terminates the pattern and the <b>re_endp</b> field is 167ignored. This is a GNU extension to the POSIX standard and should be used with 168caution in software intended to be portable to other systems. 169<pre> 170 REG_UCP 171</pre> 172The PCRE2_UCP option is set when the regular expression is passed for 173compilation to the native function. This causes PCRE2 to use Unicode properties 174when matchine \d, \w, etc., instead of just recognizing ASCII values. Note 175that REG_UCP is not part of the POSIX standard. 176<pre> 177 REG_UNGREEDY 178</pre> 179The PCRE2_UNGREEDY option is set when the regular expression is passed for 180compilation to the native function. Note that REG_UNGREEDY is not part of the 181POSIX standard. 182<pre> 183 REG_UTF 184</pre> 185The PCRE2_UTF option is set when the regular expression is passed for 186compilation to the native function. This causes the pattern itself and all data 187strings used for matching it to be treated as UTF-8 strings. Note that REG_UTF 188is not part of the POSIX standard. 189</P> 190<P> 191In the absence of these flags, no options are passed to the native function. 192This means the the regex is compiled with PCRE2 default semantics. In 193particular, the way it handles newline characters in the subject string is the 194Perl way, not the POSIX way. Note that setting PCRE2_MULTILINE has only 195<i>some</i> of the effects specified for REG_NEWLINE. It does not affect the way 196newlines are matched by the dot metacharacter (they are not) or by a negative 197class such as [^a] (they are). 198</P> 199<P> 200The yield of <b>pcre2_regcomp()</b> is zero on success, and non-zero otherwise. 201The <i>preg</i> structure is filled in on success, and one other member of the 202structure (as well as <i>re_endp</i>) is public: <i>re_nsub</i> contains the 203number of capturing subpatterns in the regular expression. Various error codes 204are defined in the header file. 205</P> 206<P> 207NOTE: If the yield of <b>pcre2_regcomp()</b> is non-zero, you must not attempt 208to use the contents of the <i>preg</i> structure. If, for example, you pass it 209to <b>pcre2_regexec()</b>, the result is undefined and your program is likely to 210crash. 211</P> 212<br><a name="SEC5" href="#TOC1">MATCHING NEWLINE CHARACTERS</a><br> 213<P> 214This area is not simple, because POSIX and Perl take different views of things. 215It is not possible to get PCRE2 to obey POSIX semantics, but then PCRE2 was 216never intended to be a POSIX engine. The following table lists the different 217possibilities for matching newline characters in Perl and PCRE2: 218<pre> 219 Default Change with 220 221 . matches newline no PCRE2_DOTALL 222 newline matches [^a] yes not changeable 223 $ matches \n at end yes PCRE2_DOLLAR_ENDONLY 224 $ matches \n in middle no PCRE2_MULTILINE 225 ^ matches \n in middle no PCRE2_MULTILINE 226</pre> 227This is the equivalent table for a POSIX-compatible pattern matcher: 228<pre> 229 Default Change with 230 231 . matches newline yes REG_NEWLINE 232 newline matches [^a] yes REG_NEWLINE 233 $ matches \n at end no REG_NEWLINE 234 $ matches \n in middle no REG_NEWLINE 235 ^ matches \n in middle no REG_NEWLINE 236</pre> 237This behaviour is not what happens when PCRE2 is called via its POSIX 238API. By default, PCRE2's behaviour is the same as Perl's, except that there is 239no equivalent for PCRE2_DOLLAR_ENDONLY in Perl. In both PCRE2 and Perl, there 240is no way to stop newline from matching [^a]. 241</P> 242<P> 243Default POSIX newline handling can be obtained by setting PCRE2_DOTALL and 244PCRE2_DOLLAR_ENDONLY when calling <b>pcre2_compile()</b> directly, but there is 245no way to make PCRE2 behave exactly as for the REG_NEWLINE action. When using 246the POSIX API, passing REG_NEWLINE to PCRE2's <b>pcre2_regcomp()</b> function 247causes PCRE2_MULTILINE to be passed to <b>pcre2_compile()</b>, and REG_DOTALL 248passes PCRE2_DOTALL. There is no way to pass PCRE2_DOLLAR_ENDONLY. 249</P> 250<br><a name="SEC6" href="#TOC1">MATCHING A PATTERN</a><br> 251<P> 252The function <b>pcre2_regexec()</b> is called to match a compiled pattern 253<i>preg</i> against a given <i>string</i>, which is by default terminated by a 254zero byte (but see REG_STARTEND below), subject to the options in <i>eflags</i>. 255These can be: 256<pre> 257 REG_NOTBOL 258</pre> 259The PCRE2_NOTBOL option is set when calling the underlying PCRE2 matching 260function. 261<pre> 262 REG_NOTEMPTY 263</pre> 264The PCRE2_NOTEMPTY option is set when calling the underlying PCRE2 matching 265function. Note that REG_NOTEMPTY is not part of the POSIX standard. However, 266setting this option can give more POSIX-like behaviour in some situations. 267<pre> 268 REG_NOTEOL 269</pre> 270The PCRE2_NOTEOL option is set when calling the underlying PCRE2 matching 271function. 272<pre> 273 REG_STARTEND 274</pre> 275When this option is set, the subject string starts at <i>string</i> + 276<i>pmatch[0].rm_so</i> and ends at <i>string</i> + <i>pmatch[0].rm_eo</i>, which 277should point to the first character beyond the string. There may be binary 278zeros within the subject string, and indeed, using REG_STARTEND is the only 279way to pass a subject string that contains a binary zero. 280</P> 281<P> 282Whatever the value of <i>pmatch[0].rm_so</i>, the offsets of the matched string 283and any captured substrings are still given relative to the start of 284<i>string</i> itself. (Before PCRE2 release 10.30 these were given relative to 285<i>string</i> + <i>pmatch[0].rm_so</i>, but this differs from other 286implementations.) 287</P> 288<P> 289This is a BSD extension, compatible with but not specified by IEEE Standard 2901003.2 (POSIX.2), and should be used with caution in software intended to be 291portable to other systems. Note that a non-zero <i>rm_so</i> does not imply 292REG_NOTBOL; REG_STARTEND affects only the location and length of the string, 293not how it is matched. Setting REG_STARTEND and passing <i>pmatch</i> as NULL 294are mutually exclusive; the error REG_INVARG is returned. 295</P> 296<P> 297If the pattern was compiled with the REG_NOSUB flag, no data about any matched 298strings is returned. The <i>nmatch</i> and <i>pmatch</i> arguments of 299<b>pcre2_regexec()</b> are ignored (except possibly as input for REG_STARTEND). 300</P> 301<P> 302The value of <i>nmatch</i> may be zero, and the value <i>pmatch</i> may be NULL 303(unless REG_STARTEND is set); in both these cases no data about any matched 304strings is returned. 305</P> 306<P> 307Otherwise, the portion of the string that was matched, and also any captured 308substrings, are returned via the <i>pmatch</i> argument, which points to an 309array of <i>nmatch</i> structures of type <i>regmatch_t</i>, containing the 310members <i>rm_so</i> and <i>rm_eo</i>. These contain the byte offset to the first 311character of each substring and the offset to the first character after the end 312of each substring, respectively. The 0th element of the vector relates to the 313entire portion of <i>string</i> that was matched; subsequent elements relate to 314the capturing subpatterns of the regular expression. Unused entries in the 315array have both structure members set to -1. 316</P> 317<P> 318A successful match yields a zero return; various error codes are defined in the 319header file, of which REG_NOMATCH is the "expected" failure code. 320</P> 321<br><a name="SEC7" href="#TOC1">ERROR MESSAGES</a><br> 322<P> 323The <b>pcre2_regerror()</b> function maps a non-zero errorcode from either 324<b>pcre2_regcomp()</b> or <b>pcre2_regexec()</b> to a printable message. If 325<i>preg</i> is not NULL, the error should have arisen from the use of that 326structure. A message terminated by a binary zero is placed in <i>errbuf</i>. If 327the buffer is too short, only the first <i>errbuf_size</i> - 1 characters of the 328error message are used. The yield of the function is the size of buffer needed 329to hold the whole message, including the terminating zero. This value is 330greater than <i>errbuf_size</i> if the message was truncated. 331</P> 332<br><a name="SEC8" href="#TOC1">MEMORY USAGE</a><br> 333<P> 334Compiling a regular expression causes memory to be allocated and associated 335with the <i>preg</i> structure. The function <b>pcre2_regfree()</b> frees all 336such memory, after which <i>preg</i> may no longer be used as a compiled 337expression. 338</P> 339<br><a name="SEC9" href="#TOC1">AUTHOR</a><br> 340<P> 341Philip Hazel 342<br> 343University Computing Service 344<br> 345Cambridge, England. 346<br> 347</P> 348<br><a name="SEC10" href="#TOC1">REVISION</a><br> 349<P> 350Last updated: 26 April 2021 351<br> 352Copyright © 1997-2021 University of Cambridge. 353<br> 354<p> 355Return to the <a href="index.html">PCRE2 index page</a>. 356</p> 357