--- /dev/null
+.TH PCRE2POSIX 3 "15 June 2017" "PCRE2 10.30"
+.SH NAME
+PCRE2 - Perl-compatible regular expressions (revised API)
+.SH "SYNOPSIS"
+.rs
+.sp
+.B #include <pcre2posix.h>
+.PP
+.nf
+.B int regcomp(regex_t *\fIpreg\fP, const char *\fIpattern\fP,
+.B " int \fIcflags\fP);"
+.sp
+.B int regexec(const regex_t *\fIpreg\fP, const char *\fIstring\fP,
+.B " size_t \fInmatch\fP, regmatch_t \fIpmatch\fP[], int \fIeflags\fP);"
+.sp
+.B "size_t regerror(int \fIerrcode\fP, const regex_t *\fIpreg\fP,"
+.B " char *\fIerrbuf\fP, size_t \fIerrbuf_size\fP);"
+.sp
+.B void regfree(regex_t *\fIpreg\fP);
+.fi
+.
+.SH DESCRIPTION
+.rs
+.sp
+This set of functions provides a POSIX-style API for the PCRE2 regular
+expression 8-bit library. See the
+.\" HREF
+\fBpcre2api\fP
+.\"
+documentation for a description of PCRE2's native API, which contains much
+additional functionality. There are no POSIX-style wrappers for PCRE2's 16-bit
+and 32-bit libraries.
+.P
+The functions described here are just wrapper functions that ultimately call
+the PCRE2 native API. Their prototypes are defined in the \fBpcre2posix.h\fP
+header file, and on Unix systems the library itself is called
+\fBlibpcre2-posix.a\fP, so can be accessed by adding \fB-lpcre2-posix\fP to the
+command for linking an application that uses them. Because the POSIX functions
+call the native ones, it is also necessary to add \fB-lpcre2-8\fP.
+.P
+Those POSIX option bits that can reasonably be mapped to PCRE2 native options
+have been implemented. In addition, the option REG_EXTENDED is defined with the
+value zero. This has no effect, but since programs that are written to the
+POSIX interface often use it, this makes it easier to slot in PCRE2 as a
+replacement library. Other POSIX options are not even defined.
+.P
+There are also some options that are not defined by POSIX. These have been
+added at the request of users who want to make use of certain PCRE2-specific
+features via the POSIX calling interface or to add BSD or GNU functionality.
+.P
+When PCRE2 is called via these functions, it is only the API that is POSIX-like
+in style. The syntax and semantics of the regular expressions themselves are
+still those of Perl, subject to the setting of various PCRE2 options, as
+described below. "POSIX-like in style" means that the API approximates to the
+POSIX definition; it is not fully POSIX-compatible, and in multi-unit encoding
+domains it is probably even less compatible.
+.P
+The header for these functions is supplied as \fBpcre2posix.h\fP to avoid any
+potential clash with other POSIX libraries. It can, of course, be renamed or
+aliased as \fBregex.h\fP, which is the "correct" name. It provides two
+structure types, \fIregex_t\fP for compiled internal forms, and
+\fIregmatch_t\fP for returning captured substrings. It also defines some
+constants whose names start with "REG_"; these are used for setting options and
+identifying error codes.
+.
+.
+.SH "COMPILING A PATTERN"
+.rs
+.sp
+The function \fBregcomp()\fP is called to compile a pattern into an
+internal form. By default, the pattern is a C string terminated by a binary
+zero (but see REG_PEND below). The \fIpreg\fP argument is a pointer to a
+\fBregex_t\fP structure that is used as a base for storing information about
+the compiled regular expression. (It is also used for input when REG_PEND is
+set.)
+.P
+The argument \fIcflags\fP is either zero, or contains one or more of the bits
+defined by the following macros:
+.sp
+ REG_DOTALL
+.sp
+The PCRE2_DOTALL option is set when the regular expression is passed for
+compilation to the native function. Note that REG_DOTALL is not part of the
+POSIX standard.
+.sp
+ REG_ICASE
+.sp
+The PCRE2_CASELESS option is set when the regular expression is passed for
+compilation to the native function.
+.sp
+ REG_NEWLINE
+.sp
+The PCRE2_MULTILINE option is set when the regular expression is passed for
+compilation to the native function. Note that this does \fInot\fP mimic the
+defined POSIX behaviour for REG_NEWLINE (see the following section).
+.sp
+ REG_NOSPEC
+.sp
+The PCRE2_LITERAL option is set when the regular expression is passed for
+compilation to the native function. This disables all meta characters in the
+pattern, causing it to be treated as a literal string. The only other options
+that are allowed with REG_NOSPEC are REG_ICASE, REG_NOSUB, REG_PEND, and
+REG_UTF. Note that REG_NOSPEC is not part of the POSIX standard.
+.sp
+ REG_NOSUB
+.sp
+When a pattern that is compiled with this flag is passed to \fBregexec()\fP for
+matching, the \fInmatch\fP and \fIpmatch\fP arguments are ignored, and no
+captured strings are returned. Versions of the PCRE library prior to 10.22 used
+to set the PCRE2_NO_AUTO_CAPTURE compile option, but this no longer happens
+because it disables the use of backreferences.
+.sp
+ REG_PEND
+.sp
+If this option is set, the \fBreg_endp\fP field in the \fIpreg\fP structure
+(which has the type const char *) must be set to point to the character beyond
+the end of the pattern before calling \fBregcomp()\fP. The pattern itself may
+now contain binary zeros, which are treated as data characters. Without
+REG_PEND, a binary zero terminates the pattern and the \fBre_endp\fP field is
+ignored. This is a GNU extension to the POSIX standard and should be used with
+caution in software intended to be portable to other systems.
+.sp
+ REG_UCP
+.sp
+The PCRE2_UCP option is set when the regular expression is passed for
+compilation to the native function. This causes PCRE2 to use Unicode properties
+when matchine \ed, \ew, etc., instead of just recognizing ASCII values. Note
+that REG_UCP is not part of the POSIX standard.
+.sp
+ REG_UNGREEDY
+.sp
+The PCRE2_UNGREEDY option is set when the regular expression is passed for
+compilation to the native function. Note that REG_UNGREEDY is not part of the
+POSIX standard.
+.sp
+ REG_UTF
+.sp
+The PCRE2_UTF option is set when the regular expression is passed for
+compilation to the native function. This causes the pattern itself and all data
+strings used for matching it to be treated as UTF-8 strings. Note that REG_UTF
+is not part of the POSIX standard.
+.P
+In the absence of these flags, no options are passed to the native function.
+This means the the regex is compiled with PCRE2 default semantics. In
+particular, the way it handles newline characters in the subject string is the
+Perl way, not the POSIX way. Note that setting PCRE2_MULTILINE has only
+\fIsome\fP of the effects specified for REG_NEWLINE. It does not affect the way
+newlines are matched by the dot metacharacter (they are not) or by a negative
+class such as [^a] (they are).
+.P
+The yield of \fBregcomp()\fP is zero on success, and non-zero otherwise. The
+\fIpreg\fP structure is filled in on success, and one other member of the
+structure (as well as \fIre_endp\fP) is public: \fIre_nsub\fP contains the
+number of capturing subpatterns in the regular expression. Various error codes
+are defined in the header file.
+.P
+NOTE: If the yield of \fBregcomp()\fP is non-zero, you must not attempt to
+use the contents of the \fIpreg\fP structure. If, for example, you pass it to
+\fBregexec()\fP, the result is undefined and your program is likely to crash.
+.
+.
+.SH "MATCHING NEWLINE CHARACTERS"
+.rs
+.sp
+This area is not simple, because POSIX and Perl take different views of things.
+It is not possible to get PCRE2 to obey POSIX semantics, but then PCRE2 was
+never intended to be a POSIX engine. The following table lists the different
+possibilities for matching newline characters in Perl and PCRE2:
+.sp
+ Default Change with
+.sp
+ . matches newline no PCRE2_DOTALL
+ newline matches [^a] yes not changeable
+ $ matches \en at end yes PCRE2_DOLLAR_ENDONLY
+ $ matches \en in middle no PCRE2_MULTILINE
+ ^ matches \en in middle no PCRE2_MULTILINE
+.sp
+This is the equivalent table for a POSIX-compatible pattern matcher:
+.sp
+ Default Change with
+.sp
+ . matches newline yes REG_NEWLINE
+ newline matches [^a] yes REG_NEWLINE
+ $ matches \en at end no REG_NEWLINE
+ $ matches \en in middle no REG_NEWLINE
+ ^ matches \en in middle no REG_NEWLINE
+.sp
+This behaviour is not what happens when PCRE2 is called via its POSIX
+API. By default, PCRE2's behaviour is the same as Perl's, except that there is
+no equivalent for PCRE2_DOLLAR_ENDONLY in Perl. In both PCRE2 and Perl, there
+is no way to stop newline from matching [^a].
+.P
+Default POSIX newline handling can be obtained by setting PCRE2_DOTALL and
+PCRE2_DOLLAR_ENDONLY when calling \fBpcre2_compile()\fP directly, but there is
+no way to make PCRE2 behave exactly as for the REG_NEWLINE action. When using
+the POSIX API, passing REG_NEWLINE to PCRE2's \fBregcomp()\fP function
+causes PCRE2_MULTILINE to be passed to \fBpcre2_compile()\fP, and REG_DOTALL
+passes PCRE2_DOTALL. There is no way to pass PCRE2_DOLLAR_ENDONLY.
+.
+.
+.SH "MATCHING A PATTERN"
+.rs
+.sp
+The function \fBregexec()\fP is called to match a compiled pattern \fIpreg\fP
+against a given \fIstring\fP, which is by default terminated by a zero byte
+(but see REG_STARTEND below), subject to the options in \fIeflags\fP. These can
+be:
+.sp
+ REG_NOTBOL
+.sp
+The PCRE2_NOTBOL option is set when calling the underlying PCRE2 matching
+function.
+.sp
+ REG_NOTEMPTY
+.sp
+The PCRE2_NOTEMPTY option is set when calling the underlying PCRE2 matching
+function. Note that REG_NOTEMPTY is not part of the POSIX standard. However,
+setting this option can give more POSIX-like behaviour in some situations.
+.sp
+ REG_NOTEOL
+.sp
+The PCRE2_NOTEOL option is set when calling the underlying PCRE2 matching
+function.
+.sp
+ REG_STARTEND
+.sp
+When this option is set, the subject string starts at \fIstring\fP +
+\fIpmatch[0].rm_so\fP and ends at \fIstring\fP + \fIpmatch[0].rm_eo\fP, which
+should point to the first character beyond the string. There may be binary
+zeros within the subject string, and indeed, using REG_STARTEND is the only
+way to pass a subject string that contains a binary zero.
+.P
+Whatever the value of \fIpmatch[0].rm_so\fP, the offsets of the matched string
+and any captured substrings are still given relative to the start of
+\fIstring\fP itself. (Before PCRE2 release 10.30 these were given relative to
+\fIstring\fP + \fIpmatch[0].rm_so\fP, but this differs from other
+implementations.)
+.P
+This is a BSD extension, compatible with but not specified by IEEE Standard
+1003.2 (POSIX.2), and should be used with caution in software intended to be
+portable to other systems. Note that a non-zero \fIrm_so\fP does not imply
+REG_NOTBOL; REG_STARTEND affects only the location and length of the string,
+not how it is matched. Setting REG_STARTEND and passing \fIpmatch\fP as NULL
+are mutually exclusive; the error REG_INVARG is returned.
+.P
+If the pattern was compiled with the REG_NOSUB flag, no data about any matched
+strings is returned. The \fInmatch\fP and \fIpmatch\fP arguments of
+\fBregexec()\fP are ignored (except possibly as input for REG_STARTEND).
+.P
+The value of \fInmatch\fP may be zero, and the value \fIpmatch\fP may be NULL
+(unless REG_STARTEND is set); in both these cases no data about any matched
+strings is returned.
+.P
+Otherwise, the portion of the string that was matched, and also any captured
+substrings, are returned via the \fIpmatch\fP argument, which points to an
+array of \fInmatch\fP structures of type \fIregmatch_t\fP, containing the
+members \fIrm_so\fP and \fIrm_eo\fP. These contain the byte offset to the first
+character of each substring and the offset to the first character after the end
+of each substring, respectively. The 0th element of the vector relates to the
+entire portion of \fIstring\fP that was matched; subsequent elements relate to
+the capturing subpatterns of the regular expression. Unused entries in the
+array have both structure members set to -1.
+.P
+A successful match yields a zero return; various error codes are defined in the
+header file, of which REG_NOMATCH is the "expected" failure code.
+.
+.
+.SH "ERROR MESSAGES"
+.rs
+.sp
+The \fBregerror()\fP function maps a non-zero errorcode from either
+\fBregcomp()\fP or \fBregexec()\fP to a printable message. If \fIpreg\fP is not
+NULL, the error should have arisen from the use of that structure. A message
+terminated by a binary zero is placed in \fIerrbuf\fP. If the buffer is too
+short, only the first \fIerrbuf_size\fP - 1 characters of the error message are
+used. The yield of the function is the size of buffer needed to hold the whole
+message, including the terminating zero. This value is greater than
+\fIerrbuf_size\fP if the message was truncated.
+.
+.
+.SH MEMORY USAGE
+.rs
+.sp
+Compiling a regular expression causes memory to be allocated and associated
+with the \fIpreg\fP structure. The function \fBregfree()\fP frees all such
+memory, after which \fIpreg\fP may no longer be used as a compiled expression.
+.
+.
+.SH AUTHOR
+.rs
+.sp
+.nf
+Philip Hazel
+University Computing Service
+Cambridge, England.
+.fi
+.
+.
+.SH REVISION
+.rs
+.sp
+.nf
+Last updated: 15 June 2017
+Copyright (c) 1997-2017 University of Cambridge.
+.fi
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