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 are not defined as protypes in <b>pcre2posix.h</b>, the library 72does contain functions with the POSIX names <b>regcomp()</b> etc. These simply 73pass their arguments to the PCRE2 functions. These functions are provided for 74backwards compatibility with earlier versions of PCRE2, so that existing 75programs do not have to be recompiled. 76</P> 77<P> 78Calling the header file <b>pcre2posix.h</b> avoids any conflict with other POSIX 79libraries. It can, of course, be renamed or aliased as <b>regex.h</b>, which is 80the "correct" name, if there is no clash. It provides two structure types, 81<i>regex_t</i> for compiled internal forms, and <i>regmatch_t</i> for returning 82captured substrings. It also defines some constants whose names start with 83"REG_"; these are used for setting options and identifying error codes. 84</P> 85<br><a name="SEC3" href="#TOC1">USING THE POSIX FUNCTIONS</a><br> 86<P> 87Those POSIX option bits that can reasonably be mapped to PCRE2 native options 88have been implemented. In addition, the option REG_EXTENDED is defined with the 89value zero. This has no effect, but since programs that are written to the 90POSIX interface often use it, this makes it easier to slot in PCRE2 as a 91replacement library. Other POSIX options are not even defined. 92</P> 93<P> 94There are also some options that are not defined by POSIX. These have been 95added at the request of users who want to make use of certain PCRE2-specific 96features via the POSIX calling interface or to add BSD or GNU functionality. 97</P> 98<P> 99When PCRE2 is called via these functions, it is only the API that is POSIX-like 100in style. The syntax and semantics of the regular expressions themselves are 101still those of Perl, subject to the setting of various PCRE2 options, as 102described below. "POSIX-like in style" means that the API approximates to the 103POSIX definition; it is not fully POSIX-compatible, and in multi-unit encoding 104domains it is probably even less compatible. 105</P> 106<P> 107The descriptions below use the actual names of the functions, but, as described 108above, the standard POSIX names (without the <b>pcre2_</b> prefix) may also be 109used. 110</P> 111<br><a name="SEC4" href="#TOC1">COMPILING A PATTERN</a><br> 112<P> 113The function <b>pcre2_regcomp()</b> is called to compile a pattern into an 114internal form. By default, the pattern is a C string terminated by a binary 115zero (but see REG_PEND below). The <i>preg</i> argument is a pointer to a 116<b>regex_t</b> structure that is used as a base for storing information about 117the compiled regular expression. (It is also used for input when REG_PEND is 118set.) 119</P> 120<P> 121The argument <i>cflags</i> is either zero, or contains one or more of the bits 122defined by the following macros: 123<pre> 124 REG_DOTALL 125</pre> 126The PCRE2_DOTALL option is set when the regular expression is passed for 127compilation to the native function. Note that REG_DOTALL is not part of the 128POSIX standard. 129<pre> 130 REG_ICASE 131</pre> 132The PCRE2_CASELESS option is set when the regular expression is passed for 133compilation to the native function. 134<pre> 135 REG_NEWLINE 136</pre> 137The PCRE2_MULTILINE option is set when the regular expression is passed for 138compilation to the native function. Note that this does <i>not</i> mimic the 139defined POSIX behaviour for REG_NEWLINE (see the following section). 140<pre> 141 REG_NOSPEC 142</pre> 143The PCRE2_LITERAL option is set when the regular expression is passed for 144compilation to the native function. This disables all meta characters in the 145pattern, causing it to be treated as a literal string. The only other options 146that are allowed with REG_NOSPEC are REG_ICASE, REG_NOSUB, REG_PEND, and 147REG_UTF. Note that REG_NOSPEC is not part of the POSIX standard. 148<pre> 149 REG_NOSUB 150</pre> 151When a pattern that is compiled with this flag is passed to 152<b>pcre2_regexec()</b> for matching, the <i>nmatch</i> and <i>pmatch</i> arguments 153are ignored, and no captured strings are returned. Versions of the PCRE library 154prior to 10.22 used to set the PCRE2_NO_AUTO_CAPTURE compile option, but this 155no longer happens because it disables the use of backreferences. 156<pre> 157 REG_PEND 158</pre> 159If this option is set, the <b>reg_endp</b> field in the <i>preg</i> structure 160(which has the type const char *) must be set to point to the character beyond 161the end of the pattern before calling <b>pcre2_regcomp()</b>. The pattern itself 162may now contain binary zeros, which are treated as data characters. Without 163REG_PEND, a binary zero terminates the pattern and the <b>re_endp</b> field is 164ignored. This is a GNU extension to the POSIX standard and should be used with 165caution in software intended to be portable to other systems. 166<pre> 167 REG_UCP 168</pre> 169The PCRE2_UCP option is set when the regular expression is passed for 170compilation to the native function. This causes PCRE2 to use Unicode properties 171when matchine \d, \w, etc., instead of just recognizing ASCII values. Note 172that REG_UCP is not part of the POSIX standard. 173<pre> 174 REG_UNGREEDY 175</pre> 176The PCRE2_UNGREEDY option is set when the regular expression is passed for 177compilation to the native function. Note that REG_UNGREEDY is not part of the 178POSIX standard. 179<pre> 180 REG_UTF 181</pre> 182The PCRE2_UTF option is set when the regular expression is passed for 183compilation to the native function. This causes the pattern itself and all data 184strings used for matching it to be treated as UTF-8 strings. Note that REG_UTF 185is not part of the POSIX standard. 186</P> 187<P> 188In the absence of these flags, no options are passed to the native function. 189This means the the regex is compiled with PCRE2 default semantics. In 190particular, the way it handles newline characters in the subject string is the 191Perl way, not the POSIX way. Note that setting PCRE2_MULTILINE has only 192<i>some</i> of the effects specified for REG_NEWLINE. It does not affect the way 193newlines are matched by the dot metacharacter (they are not) or by a negative 194class such as [^a] (they are). 195</P> 196<P> 197The yield of <b>pcre2_regcomp()</b> is zero on success, and non-zero otherwise. 198The <i>preg</i> structure is filled in on success, and one other member of the 199structure (as well as <i>re_endp</i>) is public: <i>re_nsub</i> contains the 200number of capturing subpatterns in the regular expression. Various error codes 201are defined in the header file. 202</P> 203<P> 204NOTE: If the yield of <b>pcre2_regcomp()</b> is non-zero, you must not attempt 205to use the contents of the <i>preg</i> structure. If, for example, you pass it 206to <b>pcre2_regexec()</b>, the result is undefined and your program is likely to 207crash. 208</P> 209<br><a name="SEC5" href="#TOC1">MATCHING NEWLINE CHARACTERS</a><br> 210<P> 211This area is not simple, because POSIX and Perl take different views of things. 212It is not possible to get PCRE2 to obey POSIX semantics, but then PCRE2 was 213never intended to be a POSIX engine. The following table lists the different 214possibilities for matching newline characters in Perl and PCRE2: 215<pre> 216 Default Change with 217 218 . matches newline no PCRE2_DOTALL 219 newline matches [^a] yes not changeable 220 $ matches \n at end yes PCRE2_DOLLAR_ENDONLY 221 $ matches \n in middle no PCRE2_MULTILINE 222 ^ matches \n in middle no PCRE2_MULTILINE 223</pre> 224This is the equivalent table for a POSIX-compatible pattern matcher: 225<pre> 226 Default Change with 227 228 . matches newline yes REG_NEWLINE 229 newline matches [^a] yes REG_NEWLINE 230 $ matches \n at end no REG_NEWLINE 231 $ matches \n in middle no REG_NEWLINE 232 ^ matches \n in middle no REG_NEWLINE 233</pre> 234This behaviour is not what happens when PCRE2 is called via its POSIX 235API. By default, PCRE2's behaviour is the same as Perl's, except that there is 236no equivalent for PCRE2_DOLLAR_ENDONLY in Perl. In both PCRE2 and Perl, there 237is no way to stop newline from matching [^a]. 238</P> 239<P> 240Default POSIX newline handling can be obtained by setting PCRE2_DOTALL and 241PCRE2_DOLLAR_ENDONLY when calling <b>pcre2_compile()</b> directly, but there is 242no way to make PCRE2 behave exactly as for the REG_NEWLINE action. When using 243the POSIX API, passing REG_NEWLINE to PCRE2's <b>pcre2_regcomp()</b> function 244causes PCRE2_MULTILINE to be passed to <b>pcre2_compile()</b>, and REG_DOTALL 245passes PCRE2_DOTALL. There is no way to pass PCRE2_DOLLAR_ENDONLY. 246</P> 247<br><a name="SEC6" href="#TOC1">MATCHING A PATTERN</a><br> 248<P> 249The function <b>pcre2_regexec()</b> is called to match a compiled pattern 250<i>preg</i> against a given <i>string</i>, which is by default terminated by a 251zero byte (but see REG_STARTEND below), subject to the options in <i>eflags</i>. 252These can be: 253<pre> 254 REG_NOTBOL 255</pre> 256The PCRE2_NOTBOL option is set when calling the underlying PCRE2 matching 257function. 258<pre> 259 REG_NOTEMPTY 260</pre> 261The PCRE2_NOTEMPTY option is set when calling the underlying PCRE2 matching 262function. Note that REG_NOTEMPTY is not part of the POSIX standard. However, 263setting this option can give more POSIX-like behaviour in some situations. 264<pre> 265 REG_NOTEOL 266</pre> 267The PCRE2_NOTEOL option is set when calling the underlying PCRE2 matching 268function. 269<pre> 270 REG_STARTEND 271</pre> 272When this option is set, the subject string starts at <i>string</i> + 273<i>pmatch[0].rm_so</i> and ends at <i>string</i> + <i>pmatch[0].rm_eo</i>, which 274should point to the first character beyond the string. There may be binary 275zeros within the subject string, and indeed, using REG_STARTEND is the only 276way to pass a subject string that contains a binary zero. 277</P> 278<P> 279Whatever the value of <i>pmatch[0].rm_so</i>, the offsets of the matched string 280and any captured substrings are still given relative to the start of 281<i>string</i> itself. (Before PCRE2 release 10.30 these were given relative to 282<i>string</i> + <i>pmatch[0].rm_so</i>, but this differs from other 283implementations.) 284</P> 285<P> 286This is a BSD extension, compatible with but not specified by IEEE Standard 2871003.2 (POSIX.2), and should be used with caution in software intended to be 288portable to other systems. Note that a non-zero <i>rm_so</i> does not imply 289REG_NOTBOL; REG_STARTEND affects only the location and length of the string, 290not how it is matched. Setting REG_STARTEND and passing <i>pmatch</i> as NULL 291are mutually exclusive; the error REG_INVARG is returned. 292</P> 293<P> 294If the pattern was compiled with the REG_NOSUB flag, no data about any matched 295strings is returned. The <i>nmatch</i> and <i>pmatch</i> arguments of 296<b>pcre2_regexec()</b> are ignored (except possibly as input for REG_STARTEND). 297</P> 298<P> 299The value of <i>nmatch</i> may be zero, and the value <i>pmatch</i> may be NULL 300(unless REG_STARTEND is set); in both these cases no data about any matched 301strings is returned. 302</P> 303<P> 304Otherwise, the portion of the string that was matched, and also any captured 305substrings, are returned via the <i>pmatch</i> argument, which points to an 306array of <i>nmatch</i> structures of type <i>regmatch_t</i>, containing the 307members <i>rm_so</i> and <i>rm_eo</i>. These contain the byte offset to the first 308character of each substring and the offset to the first character after the end 309of each substring, respectively. The 0th element of the vector relates to the 310entire portion of <i>string</i> that was matched; subsequent elements relate to 311the capturing subpatterns of the regular expression. Unused entries in the 312array have both structure members set to -1. 313</P> 314<P> 315A successful match yields a zero return; various error codes are defined in the 316header file, of which REG_NOMATCH is the "expected" failure code. 317</P> 318<br><a name="SEC7" href="#TOC1">ERROR MESSAGES</a><br> 319<P> 320The <b>pcre2_regerror()</b> function maps a non-zero errorcode from either 321<b>pcre2_regcomp()</b> or <b>pcre2_regexec()</b> to a printable message. If 322<i>preg</i> is not NULL, the error should have arisen from the use of that 323structure. A message terminated by a binary zero is placed in <i>errbuf</i>. If 324the buffer is too short, only the first <i>errbuf_size</i> - 1 characters of the 325error message are used. The yield of the function is the size of buffer needed 326to hold the whole message, including the terminating zero. This value is 327greater than <i>errbuf_size</i> if the message was truncated. 328</P> 329<br><a name="SEC8" href="#TOC1">MEMORY USAGE</a><br> 330<P> 331Compiling a regular expression causes memory to be allocated and associated 332with the <i>preg</i> structure. The function <b>pcre2_regfree()</b> frees all 333such memory, after which <i>preg</i> may no longer be used as a compiled 334expression. 335</P> 336<br><a name="SEC9" href="#TOC1">AUTHOR</a><br> 337<P> 338Philip Hazel 339<br> 340University Computing Service 341<br> 342Cambridge, England. 343<br> 344</P> 345<br><a name="SEC10" href="#TOC1">REVISION</a><br> 346<P> 347Last updated: 30 January 2019 348<br> 349Copyright © 1997-2019 University of Cambridge. 350<br> 351<p> 352Return to the <a href="index.html">PCRE2 index page</a>. 353</p> 354