\input texinfo @c %**start of header @setfilename regex.info @settitle Regex @c %**end of header @c \\{fill-paragraph} works better (for me, anyway) if the text in the @c source file isn't indented. @paragraphindent 2 @c Define a new index for our magic constants. @defcodeindex cn @c Put everything in one index (arbitrarily chosen to be the concept index). @syncodeindex cn cp @syncodeindex ky cp @syncodeindex pg cp @syncodeindex tp cp @syncodeindex vr cp @c Here is what we use in the Info `dir' file: @c * Regex: (regex). Regular expression library. @ifinfo This file documents the GNU regular expression library. Copyright (C) 1992, 1993 Free Software Foundation, Inc. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. @ignore Permission is granted to process this file through TeX and print the results, provided the printed document carries a copying permission notice identical to this one except for the removal of this paragraph (this paragraph not being relevant to the printed manual). @end ignore Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided also that the section entitled ``GNU General Public License'' is included exactly as in the original, and provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that the section entitled ``GNU General Public License'' may be included in a translation approved by the Free Software Foundation instead of in the original English. @end ifinfo @titlepage @title Regex @subtitle edition 0.12a @subtitle 19 September 1992 @author Kathryn A. Hargreaves @author Karl Berry @page @vskip 0pt plus 1filll Copyright @copyright{} 1992 Free Software Foundation. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided also that the section entitled ``GNU General Public License'' is included exactly as in the original, and provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that the section entitled ``GNU General Public License'' may be included in a translation approved by the Free Software Foundation instead of in the original English. @end titlepage @ifinfo @node Top, Overview, (dir), (dir) @top Regular Expression Library This manual documents how to program with the GNU regular expression library. This is edition 0.12a of the manual, 19 September 1992. The first part of this master menu lists the major nodes in this Info document, including the index. The rest of the menu lists all the lower level nodes in the document. @menu * Overview:: * Regular Expression Syntax:: * Common Operators:: * GNU Operators:: * GNU Emacs Operators:: * What Gets Matched?:: * Programming with Regex:: * Copying:: Copying and sharing Regex. * Index:: General index. --- The Detailed Node Listing --- Regular Expression Syntax * Syntax Bits:: * Predefined Syntaxes:: * Collating Elements vs. Characters:: * The Backslash Character:: Common Operators * Match-self Operator:: Ordinary characters. * Match-any-character Operator:: . * Concatenation Operator:: Juxtaposition. * Repetition Operators:: * + ? @{@} * Alternation Operator:: | * List Operators:: [...] [^...] * Grouping Operators:: (...) * Back-reference Operator:: \digit * Anchoring Operators:: ^ $ Repetition Operators * Match-zero-or-more Operator:: * * Match-one-or-more Operator:: + * Match-zero-or-one Operator:: ? * Interval Operators:: @{@} List Operators (@code{[} @dots{} @code{]} and @code{[^} @dots{} @code{]}) * Character Class Operators:: [:class:] * Range Operator:: start-end Anchoring Operators * Match-beginning-of-line Operator:: ^ * Match-end-of-line Operator:: $ GNU Operators * Word Operators:: * Buffer Operators:: Word Operators * Non-Emacs Syntax Tables:: * Match-word-boundary Operator:: \b * Match-within-word Operator:: \B * Match-beginning-of-word Operator:: \< * Match-end-of-word Operator:: \> * Match-word-constituent Operator:: \w * Match-non-word-constituent Operator:: \W Buffer Operators * Match-beginning-of-buffer Operator:: \` * Match-end-of-buffer Operator:: \' GNU Emacs Operators * Syntactic Class Operators:: Syntactic Class Operators * Emacs Syntax Tables:: * Match-syntactic-class Operator:: \sCLASS * Match-not-syntactic-class Operator:: \SCLASS Programming with Regex * GNU Regex Functions:: * POSIX Regex Functions:: * BSD Regex Functions:: GNU Regex Functions * GNU Pattern Buffers:: The re_pattern_buffer type. * GNU Regular Expression Compiling:: re_compile_pattern () * GNU Matching:: re_match () * GNU Searching:: re_search () * Matching/Searching with Split Data:: re_match_2 (), re_search_2 () * Searching with Fastmaps:: re_compile_fastmap () * GNU Translate Tables:: The `translate' field. * Using Registers:: The re_registers type and related fns. * Freeing GNU Pattern Buffers:: regfree () POSIX Regex Functions * POSIX Pattern Buffers:: The regex_t type. * POSIX Regular Expression Compiling:: regcomp () * POSIX Matching:: regexec () * Reporting Errors:: regerror () * Using Byte Offsets:: The regmatch_t type. * Freeing POSIX Pattern Buffers:: regfree () BSD Regex Functions * BSD Regular Expression Compiling:: re_comp () * BSD Searching:: re_exec () @end menu @end ifinfo @node Overview, Regular Expression Syntax, Top, Top @chapter Overview A @dfn{regular expression} (or @dfn{regexp}, or @dfn{pattern}) is a text string that describes some (mathematical) set of strings. A regexp @var{r} @dfn{matches} a string @var{s} if @var{s} is in the set of strings described by @var{r}. Using the Regex library, you can: @itemize @bullet @item see if a string matches a specified pattern as a whole, and @item search within a string for a substring matching a specified pattern. @end itemize Some regular expressions match only one string, i.e., the set they describe has only one member. For example, the regular expression @samp{foo} matches the string @samp{foo} and no others. Other regular expressions match more than one string, i.e., the set they describe has more than one member. For example, the regular expression @samp{f*} matches the set of strings made up of any number (including zero) of @samp{f}s. As you can see, some characters in regular expressions match themselves (such as @samp{f}) and some don't (such as @samp{*}); the ones that don't match themselves instead let you specify patterns that describe many different strings. To either match or search for a regular expression with the Regex library functions, you must first compile it with a Regex pattern compiling function. A @dfn{compiled pattern} is a regular expression converted to the internal format used by the library functions. Once you've compiled a pattern, you can use it for matching or searching any number of times. The Regex library consists of two source files: @file{regex.h} and @file{regex.c}. @pindex regex.h @pindex regex.c Regex provides three groups of functions with which you can operate on regular expressions. One group---the @sc{gnu} group---is more powerful but not completely compatible with the other two, namely the @sc{posix} and Berkeley @sc{unix} groups; its interface was designed specifically for @sc{gnu}. The other groups have the same interfaces as do the regular expression functions in @sc{posix} and Berkeley @sc{unix}. We wrote this chapter with programmers in mind, not users of programs---such as Emacs---that use Regex. We describe the Regex library in its entirety, not how to write regular expressions that a particular program understands. @node Regular Expression Syntax, Common Operators, Overview, Top @chapter Regular Expression Syntax @cindex regular expressions, syntax of @cindex syntax of regular expressions @dfn{Characters} are things you can type. @dfn{Operators} are things in a regular expression that match one or more characters. You compose regular expressions from operators, which in turn you specify using one or more characters. Most characters represent what we call the match-self operator, i.e., they match themselves; we call these characters @dfn{ordinary}. Other characters represent either all or parts of fancier operators; e.g., @samp{.} represents what we call the match-any-character operator (which, no surprise, matches (almost) any character); we call these characters @dfn{special}. Two different things determine what characters represent what operators: @enumerate @item the regular expression syntax your program has told the Regex library to recognize, and @item the context of the character in the regular expression. @end enumerate In the following sections, we describe these things in more detail. @menu * Syntax Bits:: * Predefined Syntaxes:: * Collating Elements vs. Characters:: * The Backslash Character:: @end menu @node Syntax Bits, Predefined Syntaxes, , Regular Expression Syntax @section Syntax Bits @cindex syntax bits In any particular syntax for regular expressions, some characters are always special, others are sometimes special, and others are never special. The particular syntax that Regex recognizes for a given regular expression depends on the value in the @code{syntax} field of the pattern buffer of that regular expression. You get a pattern buffer by compiling a regular expression. @xref{GNU Pattern Buffers}, and @ref{POSIX Pattern Buffers}, for more information on pattern buffers. @xref{GNU Regular Expression Compiling}, @ref{POSIX Regular Expression Compiling}, and @ref{BSD Regular Expression Compiling}, for more information on compiling. Regex considers the value of the @code{syntax} field to be a collection of bits; we refer to these bits as @dfn{syntax bits}. In most cases, they affect what characters represent what operators. We describe the meanings of the operators to which we refer in @ref{Common Operators}, @ref{GNU Operators}, and @ref{GNU Emacs Operators}. For reference, here is the complete list of syntax bits, in alphabetical order: @table @code @cnindex RE_BACKSLASH_ESCAPE_IN_LIST @item RE_BACKSLASH_ESCAPE_IN_LISTS If this bit is set, then @samp{\} inside a list (@pxref{List Operators} quotes (makes ordinary, if it's special) the following character; if this bit isn't set, then @samp{\} is an ordinary character inside lists. (@xref{The Backslash Character}, for what `\' does outside of lists.) @cnindex RE_BK_PLUS_QM @item RE_BK_PLUS_QM If this bit is set, then @samp{\+} represents the match-one-or-more operator and @samp{\?} represents the match-zero-or-more operator; if this bit isn't set, then @samp{+} represents the match-one-or-more operator and @samp{?} represents the match-zero-or-one operator. This bit is irrelevant if @code{RE_LIMITED_OPS} is set. @cnindex RE_CHAR_CLASSES @item RE_CHAR_CLASSES If this bit is set, then you can use character classes in lists; if this bit isn't set, then you can't. @cnindex RE_CONTEXT_INDEP_ANCHORS @item RE_CONTEXT_INDEP_ANCHORS If this bit is set, then @samp{^} and @samp{$} are special anywhere outside a list; if this bit isn't set, then these characters are special only in certain contexts. @xref{Match-beginning-of-line Operator}, and @ref{Match-end-of-line Operator}. @cnindex RE_CONTEXT_INDEP_OPS @item RE_CONTEXT_INDEP_OPS If this bit is set, then certain characters are special anywhere outside a list; if this bit isn't set, then those characters are special only in some contexts and are ordinary elsewhere. Specifically, if this bit isn't set then @samp{*}, and (if the syntax bit @code{RE_LIMITED_OPS} isn't set) @samp{+} and @samp{?} (or @samp{\+} and @samp{\?}, depending on the syntax bit @code{RE_BK_PLUS_QM}) represent repetition operators only if they're not first in a regular expression or just after an open-group or alternation operator. The same holds for @samp{@{} (or @samp{\@{}, depending on the syntax bit @code{RE_NO_BK_BRACES}) if it is the beginning of a valid interval and the syntax bit @code{RE_INTERVALS} is set. @cnindex RE_CONTEXT_INVALID_OPS @item RE_CONTEXT_INVALID_OPS If this bit is set, then repetition and alternation operators can't be in certain positions within a regular expression. Specifically, the regular expression is invalid if it has: @itemize @bullet @item a repetition operator first in the regular expression or just after a match-beginning-of-line, open-group, or alternation operator; or @item an alternation operator first or last in the regular expression, just before a match-end-of-line operator, or just after an alternation or open-group operator. @end itemize If this bit isn't set, then you can put the characters representing the repetition and alternation characters anywhere in a regular expression. Whether or not they will in fact be operators in certain positions depends on other syntax bits. @cnindex RE_DOT_NEWLINE @item RE_DOT_NEWLINE If this bit is set, then the match-any-character operator matches a newline; if this bit isn't set, then it doesn't. @cnindex RE_DOT_NOT_NULL @item RE_DOT_NOT_NULL If this bit is set, then the match-any-character operator doesn't match a null character; if this bit isn't set, then it does. @cnindex RE_INTERVALS @item RE_INTERVALS If this bit is set, then Regex recognizes interval operators; if this bit isn't set, then it doesn't. @cnindex RE_LIMITED_OPS @item RE_LIMITED_OPS If this bit is set, then Regex doesn't recognize the match-one-or-more, match-zero-or-one or alternation operators; if this bit isn't set, then it does. @cnindex RE_NEWLINE_ALT @item RE_NEWLINE_ALT If this bit is set, then newline represents the alternation operator; if this bit isn't set, then newline is ordinary. @cnindex RE_NO_BK_BRACES @item RE_NO_BK_BRACES If this bit is set, then @samp{@{} represents the open-interval operator and @samp{@}} represents the close-interval operator; if this bit isn't set, then @samp{\@{} represents the open-interval operator and @samp{\@}} represents the close-interval operator. This bit is relevant only if @code{RE_INTERVALS} is set. @cnindex RE_NO_BK_PARENS @item RE_NO_BK_PARENS If this bit is set, then @samp{(} represents the open-group operator and @samp{)} represents the close-group operator; if this bit isn't set, then @samp{\(} represents the open-group operator and @samp{\)} represents the close-group operator. @cnindex RE_NO_BK_REFS @item RE_NO_BK_REFS If this bit is set, then Regex doesn't recognize @samp{\}@var{digit} as the back reference operator; if this bit isn't set, then it does. @cnindex RE_NO_BK_VBAR @item RE_NO_BK_VBAR If this bit is set, then @samp{|} represents the alternation operator; if this bit isn't set, then @samp{\|} represents the alternation operator. This bit is irrelevant if @code{RE_LIMITED_OPS} is set. @cnindex RE_NO_EMPTY_RANGES @item RE_NO_EMPTY_RANGES If this bit is set, then a regular expression with a range whose ending point collates lower than its starting point is invalid; if this bit isn't set, then Regex considers such a range to be empty. @cnindex RE_UNMATCHED_RIGHT_PAREN_ORD @item RE_UNMATCHED_RIGHT_PAREN_ORD If this bit is set and the regular expression has no matching open-group operator, then Regex considers what would otherwise be a close-group operator (based on how @code{RE_NO_BK_PARENS} is set) to match @samp{)}. @end table @node Predefined Syntaxes, Collating Elements vs. Characters, Syntax Bits, Regular Expression Syntax @section Predefined Syntaxes If you're programming with Regex, you can set a pattern buffer's (@pxref{GNU Pattern Buffers}, and @ref{POSIX Pattern Buffers}) @code{syntax} field either to an arbitrary combination of syntax bits (@pxref{Syntax Bits}) or else to the configurations defined by Regex. These configurations define the syntaxes used by certain programs---@sc{gnu} Emacs, @cindex Emacs @sc{posix} Awk, @cindex POSIX Awk traditional Awk, @cindex Awk Grep, @cindex Grep @cindex Egrep Egrep---in addition to syntaxes for @sc{posix} basic and extended regular expressions. The predefined syntaxes--taken directly from @file{regex.h}---are: @example #define RE_SYNTAX_EMACS 0 #define RE_SYNTAX_AWK \ (RE_BACKSLASH_ESCAPE_IN_LISTS | RE_DOT_NOT_NULL \ | RE_NO_BK_PARENS | RE_NO_BK_REFS \ | RE_NO_BK_VBAR | RE_NO_EMPTY_RANGES \ | RE_UNMATCHED_RIGHT_PAREN_ORD) #define RE_SYNTAX_POSIX_AWK \ (RE_SYNTAX_POSIX_EXTENDED | RE_BACKSLASH_ESCAPE_IN_LISTS) #define RE_SYNTAX_GREP \ (RE_BK_PLUS_QM | RE_CHAR_CLASSES \ | RE_HAT_LISTS_NOT_NEWLINE | RE_INTERVALS \ | RE_NEWLINE_ALT) #define RE_SYNTAX_EGREP \ (RE_CHAR_CLASSES | RE_CONTEXT_INDEP_ANCHORS \ | RE_CONTEXT_INDEP_OPS | RE_HAT_LISTS_NOT_NEWLINE \ | RE_NEWLINE_ALT | RE_NO_BK_PARENS \ | RE_NO_BK_VBAR) #define RE_SYNTAX_POSIX_EGREP \ (RE_SYNTAX_EGREP | RE_INTERVALS | RE_NO_BK_BRACES) /* P1003.2/D11.2, section 4.20.7.1, lines 5078ff. */ #define RE_SYNTAX_ED RE_SYNTAX_POSIX_BASIC #define RE_SYNTAX_SED RE_SYNTAX_POSIX_BASIC /* Syntax bits common to both basic and extended POSIX regex syntax. */ #define _RE_SYNTAX_POSIX_COMMON \ (RE_CHAR_CLASSES | RE_DOT_NEWLINE | RE_DOT_NOT_NULL \ | RE_INTERVALS | RE_NO_EMPTY_RANGES) #define RE_SYNTAX_POSIX_BASIC \ (_RE_SYNTAX_POSIX_COMMON | RE_BK_PLUS_QM) /* Differs from ..._POSIX_BASIC only in that RE_BK_PLUS_QM becomes RE_LIMITED_OPS, i.e., \? \+ \| are not recognized. Actually, this isn't minimal, since other operators, such as \`, aren't disabled. */ #define RE_SYNTAX_POSIX_MINIMAL_BASIC \ (_RE_SYNTAX_POSIX_COMMON | RE_LIMITED_OPS) #define RE_SYNTAX_POSIX_EXTENDED \ (_RE_SYNTAX_POSIX_COMMON | RE_CONTEXT_INDEP_ANCHORS \ | RE_CONTEXT_INDEP_OPS | RE_NO_BK_BRACES \ | RE_NO_BK_PARENS | RE_NO_BK_VBAR \ | RE_UNMATCHED_RIGHT_PAREN_ORD) /* Differs from ..._POSIX_EXTENDED in that RE_CONTEXT_INVALID_OPS replaces RE_CONTEXT_INDEP_OPS and RE_NO_BK_REFS is added. */ #define RE_SYNTAX_POSIX_MINIMAL_EXTENDED \ (_RE_SYNTAX_POSIX_COMMON | RE_CONTEXT_INDEP_ANCHORS \ | RE_CONTEXT_INVALID_OPS | RE_NO_BK_BRACES \ | RE_NO_BK_PARENS | RE_NO_BK_REFS \ | RE_NO_BK_VBAR | RE_UNMATCHED_RIGHT_PAREN_ORD) @end example @node Collating Elements vs. Characters, The Backslash Character, Predefined Syntaxes, Regular Expression Syntax @section Collating Elements vs.@: Characters @sc{posix} generalizes the notion of a character to that of a collating element. It defines a @dfn{collating element} to be ``a sequence of one or more bytes defined in the current collating sequence as a unit of collation.'' This generalizes the notion of a character in two ways. First, a single character can map into two or more collating elements. For example, the German @tex `\ss' @end tex @ifinfo ``es-zet'' @end ifinfo collates as the collating element @samp{s} followed by another collating element @samp{s}. Second, two or more characters can map into one collating element. For example, the Spanish @samp{ll} collates after @samp{l} and before @samp{m}. Since @sc{posix}'s ``collating element'' preserves the essential idea of a ``character,'' we use the latter, more familiar, term in this document. @node The Backslash Character, , Collating Elements vs. Characters, Regular Expression Syntax @section The Backslash Character @cindex \ The @samp{\} character has one of four different meanings, depending on the context in which you use it and what syntax bits are set (@pxref{Syntax Bits}). It can: 1) stand for itself, 2) quote the next character, 3) introduce an operator, or 4) do nothing. @enumerate @item It stands for itself inside a list (@pxref{List Operators}) if the syntax bit @code{RE_BACKSLASH_ESCAPE_IN_LISTS} is not set. For example, @samp{[\]} would match @samp{\}. @item It quotes (makes ordinary, if it's special) the next character when you use it either: @itemize @bullet @item outside a list,@footnote{Sometimes you don't have to explicitly quote special characters to make them ordinary. For instance, most characters lose any special meaning inside a list (@pxref{List Operators}). In addition, if the syntax bits @code{RE_CONTEXT_INVALID_OPS} and @code{RE_CONTEXT_INDEP_OPS} aren't set, then (for historical reasons) the matcher considers special characters ordinary if they are in contexts where the operations they represent make no sense; for example, then the match-zero-or-more operator (represented by @samp{*}) matches itself in the regular expression @samp{*foo} because there is no preceding expression on which it can operate. It is poor practice, however, to depend on this behavior; if you want a special character to be ordinary outside a list, it's better to always quote it, regardless.} or @item inside a list and the syntax bit @code{RE_BACKSLASH_ESCAPE_IN_LISTS} is set. @end itemize @item It introduces an operator when followed by certain ordinary characters---sometimes only when certain syntax bits are set. See the cases @code{RE_BK_PLUS_QM}, @code{RE_NO_BK_BRACES}, @code{RE_NO_BK_VAR}, @code{RE_NO_BK_PARENS}, @code{RE_NO_BK_REF} in @ref{Syntax Bits}. Also: @itemize @bullet @item @samp{\b} represents the match-word-boundary operator (@pxref{Match-word-boundary Operator}). @item @samp{\B} represents the match-within-word operator (@pxref{Match-within-word Operator}). @item @samp{\<} represents the match-beginning-of-word operator @* (@pxref{Match-beginning-of-word Operator}). @item @samp{\>} represents the match-end-of-word operator (@pxref{Match-end-of-word Operator}). @item @samp{\w} represents the match-word-constituent operator (@pxref{Match-word-constituent Operator}). @item @samp{\W} represents the match-non-word-constituent operator (@pxref{Match-non-word-constituent Operator}). @item @samp{\`} represents the match-beginning-of-buffer operator and @samp{\'} represents the match-end-of-buffer operator (@pxref{Buffer Operators}). @item If Regex was compiled with the C preprocessor symbol @code{emacs} defined, then @samp{\s@var{class}} represents the match-syntactic-class operator and @samp{\S@var{class}} represents the match-not-syntactic-class operator (@pxref{Syntactic Class Operators}). @end itemize @item In all other cases, Regex ignores @samp{\}. For example, @samp{\n} matches @samp{n}. @end enumerate @node Common Operators, GNU Operators, Regular Expression Syntax, Top @chapter Common Operators You compose regular expressions from operators. In the following sections, we describe the regular expression operators specified by @sc{posix}; @sc{gnu} also uses these. Most operators have more than one representation as characters. @xref{Regular Expression Syntax}, for what characters represent what operators under what circumstances. For most operators that can be represented in two ways, one representation is a single character and the other is that character preceded by @samp{\}. For example, either @samp{(} or @samp{\(} represents the open-group operator. Which one does depends on the setting of a syntax bit, in this case @code{RE_NO_BK_PARENS}. Why is this so? Historical reasons dictate some of the varying representations, while @sc{posix} dictates others. Finally, almost all characters lose any special meaning inside a list (@pxref{List Operators}). @menu * Match-self Operator:: Ordinary characters. * Match-any-character Operator:: . * Concatenation Operator:: Juxtaposition. * Repetition Operators:: * + ? @{@} * Alternation Operator:: | * List Operators:: [...] [^...] * Grouping Operators:: (...) * Back-reference Operator:: \digit * Anchoring Operators:: ^ $ @end menu @node Match-self Operator, Match-any-character Operator, , Common Operators @section The Match-self Operator (@var{ordinary character}) This operator matches the character itself. All ordinary characters (@pxref{Regular Expression Syntax}) represent this operator. For example, @samp{f} is always an ordinary character, so the regular expression @samp{f} matches only the string @samp{f}. In particular, it does @emph{not} match the string @samp{ff}. @node Match-any-character Operator, Concatenation Operator, Match-self Operator, Common Operators @section The Match-any-character Operator (@code{.}) @cindex @samp{.} This operator matches any single printing or nonprinting character except it won't match a: @table @asis @item newline if the syntax bit @code{RE_DOT_NEWLINE} isn't set. @item null if the syntax bit @code{RE_DOT_NOT_NULL} is set. @end table The @samp{.} (period) character represents this operator. For example, @samp{a.b} matches any three-character string beginning with @samp{a} and ending with @samp{b}. @node Concatenation Operator, Repetition Operators, Match-any-character Operator, Common Operators @section The Concatenation Operator This operator concatenates two regular expressions @var{a} and @var{b}. No character represents this operator; you simply put @var{b} after @var{a}. The result is a regular expression that will match a string if @var{a} matches its first part and @var{b} matches the rest. For example, @samp{xy} (two match-self operators) matches @samp{xy}. @node Repetition Operators, Alternation Operator, Concatenation Operator, Common Operators @section Repetition Operators Repetition operators repeat the preceding regular expression a specified number of times. @menu * Match-zero-or-more Operator:: * * Match-one-or-more Operator:: + * Match-zero-or-one Operator:: ? * Interval Operators:: @{@} @end menu @node Match-zero-or-more Operator, Match-one-or-more Operator, , Repetition Operators @subsection The Match-zero-or-more Operator (@code{*}) @cindex @samp{*} This operator repeats the smallest possible preceding regular expression as many times as necessary (including zero) to match the pattern. @samp{*} represents this operator. For example, @samp{o*} matches any string made up of zero or more @samp{o}s. Since this operator operates on the smallest preceding regular expression, @samp{fo*} has a repeating @samp{o}, not a repeating @samp{fo}. So, @samp{fo*} matches @samp{f}, @samp{fo}, @samp{foo}, and so on. Since the match-zero-or-more operator is a suffix operator, it may be useless as such when no regular expression precedes it. This is the case when it: @itemize @bullet @item is first in a regular expression, or @item follows a match-beginning-of-line, open-group, or alternation operator. @end itemize @noindent Three different things can happen in these cases: @enumerate @item If the syntax bit @code{RE_CONTEXT_INVALID_OPS} is set, then the regular expression is invalid. @item If @code{RE_CONTEXT_INVALID_OPS} isn't set, but @code{RE_CONTEXT_INDEP_OPS} is, then @samp{*} represents the match-zero-or-more operator (which then operates on the empty string). @item Otherwise, @samp{*} is ordinary. @end enumerate @cindex backtracking The matcher processes a match-zero-or-more operator by first matching as many repetitions of the smallest preceding regular expression as it can. Then it continues to match the rest of the pattern. If it can't match the rest of the pattern, it backtracks (as many times as necessary), each time discarding one of the matches until it can either match the entire pattern or be certain that it cannot get a match. For example, when matching @samp{ca*ar} against @samp{caaar}, the matcher first matches all three @samp{a}s of the string with the @samp{a*} of the regular expression. However, it cannot then match the final @samp{ar} of the regular expression against the final @samp{r} of the string. So it backtracks, discarding the match of the last @samp{a} in the string. It can then match the remaining @samp{ar}. @node Match-one-or-more Operator, Match-zero-or-one Operator, Match-zero-or-more Operator, Repetition Operators @subsection The Match-one-or-more Operator (@code{+} or @code{\+}) @cindex @samp{+} If the syntax bit @code{RE_LIMITED_OPS} is set, then Regex doesn't recognize this operator. Otherwise, if the syntax bit @code{RE_BK_PLUS_QM} isn't set, then @samp{+} represents this operator; if it is, then @samp{\+} does. This operator is similar to the match-zero-or-more operator except that it repeats the preceding regular expression at least once; @pxref{Match-zero-or-more Operator}, for what it operates on, how some syntax bits affect it, and how Regex backtracks to match it. For example, supposing that @samp{+} represents the match-one-or-more operator; then @samp{ca+r} matches, e.g., @samp{car} and @samp{caaaar}, but not @samp{cr}. @node Match-zero-or-one Operator, Interval Operators, Match-one-or-more Operator, Repetition Operators @subsection The Match-zero-or-one Operator (@code{?} or @code{\?}) @cindex @samp{?} If the syntax bit @code{RE_LIMITED_OPS} is set, then Regex doesn't recognize this operator. Otherwise, if the syntax bit @code{RE_BK_PLUS_QM} isn't set, then @samp{?} represents this operator; if it is, then @samp{\?} does. This operator is similar to the match-zero-or-more operator except that it repeats the preceding regular expression once or not at all; @pxref{Match-zero-or-more Operator}, to see what it operates on, how some syntax bits affect it, and how Regex backtracks to match it. For example, supposing that @samp{?} represents the match-zero-or-one operator; then @samp{ca?r} matches both @samp{car} and @samp{cr}, but nothing else. @node Interval Operators, , Match-zero-or-one Operator, Repetition Operators @subsection Interval Operators (@code{@{} @dots{} @code{@}} or @code{\@{} @dots{} @code{\@}}) @cindex interval expression @cindex @samp{@{} @cindex @samp{@}} @cindex @samp{\@{} @cindex @samp{\@}} If the syntax bit @code{RE_INTERVALS} is set, then Regex recognizes @dfn{interval expressions}. They repeat the smallest possible preceding regular expression a specified number of times. If the syntax bit @code{RE_NO_BK_BRACES} is set, @samp{@{} represents the @dfn{open-interval operator} and @samp{@}} represents the @dfn{close-interval operator} ; otherwise, @samp{\@{} and @samp{\@}} do. Specifically, supposing that @samp{@{} and @samp{@}} represent the open-interval and close-interval operators; then: @table @code @item @{@var{count}@} matches exactly @var{count} occurrences of the preceding regular expression. @item @{@var{min,}@} matches @var{min} or more occurrences of the preceding regular expression. @item @{@var{min, max}@} matches at least @var{min} but no more than @var{max} occurrences of the preceding regular expression. @end table The interval expression (but not necessarily the regular expression that contains it) is invalid if: @itemize @bullet @item @var{min} is greater than @var{max}, or @item any of @var{count}, @var{min}, or @var{max} are outside the range zero to @code{RE_DUP_MAX} (which symbol @file{regex.h} defines). @end itemize If the interval expression is invalid and the syntax bit @code{RE_NO_BK_BRACES} is set, then Regex considers all the characters in the would-be interval to be ordinary. If that bit isn't set, then the regular expression is invalid. If the interval expression is valid but there is no preceding regular expression on which to operate, then if the syntax bit @code{RE_CONTEXT_INVALID_OPS} is set, the regular expression is invalid. If that bit isn't set, then Regex considers all the characters---other than backslashes, which it ignores---in the would-be interval to be ordinary. @node Alternation Operator, List Operators, Repetition Operators, Common Operators @section The Alternation Operator (@code{|} or @code{\|}) @kindex | @kindex \| @cindex alternation operator @cindex or operator If the syntax bit @code{RE_LIMITED_OPS} is set, then Regex doesn't recognize this operator. Otherwise, if the syntax bit @code{RE_NO_BK_VBAR} is set, then @samp{|} represents this operator; otherwise, @samp{\|} does. Alternatives match one of a choice of regular expressions: if you put the character(s) representing the alternation operator between any two regular expressions @var{a} and @var{b}, the result matches the union of the strings that @var{a} and @var{b} match. For example, supposing that @samp{|} is the alternation operator, then @samp{foo|bar|quux} would match any of @samp{foo}, @samp{bar} or @samp{quux}. @ignore @c Nobody needs to disallow empty alternatives any more. If the syntax bit @code{RE_NO_EMPTY_ALTS} is set, then if either of the regular expressions @var{a} or @var{b} is empty, the regular expression is invalid. More precisely, if this syntax bit is set, then the alternation operator can't: @itemize @bullet @item be first or last in a regular expression; @item follow either another alternation operator or an open-group operator (@pxref{Grouping Operators}); or @item precede a close-group operator. @end itemize @noindent For example, supposing @samp{(} and @samp{)} represent the open and close-group operators, then @samp{|foo}, @samp{foo|}, @samp{foo||bar}, @samp{foo(|bar)}, and @samp{(foo|)bar} would all be invalid. @end ignore The alternation operator operates on the @emph{largest} possible surrounding regular expressions. (Put another way, it has the lowest precedence of any regular expression operator.) Thus, the only way you can delimit its arguments is to use grouping. For example, if @samp{(} and @samp{)} are the open and close-group operators, then @samp{fo(o|b)ar} would match either @samp{fooar} or @samp{fobar}. (@samp{foo|bar} would match @samp{foo} or @samp{bar}.) @cindex backtracking The matcher usually tries all combinations of alternatives so as to match the longest possible string. For example, when matching @samp{(fooq|foo)*(qbarquux|bar)} against @samp{fooqbarquux}, it cannot take, say, the first (``depth-first'') combination it could match, since then it would be content to match just @samp{fooqbar}. @comment xx something about leftmost-longest @node List Operators, Grouping Operators, Alternation Operator, Common Operators @section List Operators (@code{[} @dots{} @code{]} and @code{[^} @dots{} @code{]}) @cindex matching list @cindex @samp{[} @cindex @samp{]} @cindex @samp{^} @cindex @samp{-} @cindex @samp{\} @cindex @samp{[^} @cindex nonmatching list @cindex matching newline @cindex bracket expression @dfn{Lists}, also called @dfn{bracket expressions}, are a set of one or more items. An @dfn{item} is a character, @ignore (These get added when they get implemented.) a collating symbol, an equivalence class expression, @end ignore a character class expression, or a range expression. The syntax bits affect which kinds of items you can put in a list. We explain the last two items in subsections below. Empty lists are invalid. A @dfn{matching list} matches a single character represented by one of the list items. You form a matching list by enclosing one or more items within an @dfn{open-matching-list operator} (represented by @samp{[}) and a @dfn{close-list operator} (represented by @samp{]}). For example, @samp{[ab]} matches either @samp{a} or @samp{b}. @samp{[ad]*} matches the empty string and any string composed of just @samp{a}s and @samp{d}s in any order. Regex considers invalid a regular expression with a @samp{[} but no matching @samp{]}. @dfn{Nonmatching lists} are similar to matching lists except that they match a single character @emph{not} represented by one of the list items. You use an @dfn{open-nonmatching-list operator} (represented by @samp{[^}@footnote{Regex therefore doesn't consider the @samp{^} to be the first character in the list. If you put a @samp{^} character first in (what you think is) a matching list, you'll turn it into a nonmatching list.}) instead of an open-matching-list operator to start a nonmatching list. For example, @samp{[^ab]} matches any character except @samp{a} or @samp{b}. If the @code{posix_newline} field in the pattern buffer (@pxref{GNU Pattern Buffers} is set, then nonmatching lists do not match a newline. Most characters lose any special meaning inside a list. The special characters inside a list follow. @table @samp @item ] ends the list if it's not the first list item. So, if you want to make the @samp{]} character a list item, you must put it first. @item \ quotes the next character if the syntax bit @code{RE_BACKSLASH_ESCAPE_IN_LISTS} is set. @ignore Put these in if they get implemented. @item [. represents the open-collating-symbol operator (@pxref{Collating Symbol Operators}). @item .] represents the close-collating-symbol operator. @item [= represents the open-equivalence-class operator (@pxref{Equivalence Class Operators}). @item =] represents the close-equivalence-class operator. @end ignore @item [: represents the open-character-class operator (@pxref{Character Class Operators}) if the syntax bit @code{RE_CHAR_CLASSES} is set and what follows is a valid character class expression. @item :] represents the close-character-class operator if the syntax bit @code{RE_CHAR_CLASSES} is set and what precedes it is an open-character-class operator followed by a valid character class name. @item - represents the range operator (@pxref{Range Operator}) if it's not first or last in a list or the ending point of a range. @end table @noindent All other characters are ordinary. For example, @samp{[.*]} matches @samp{.} and @samp{*}. @menu * Character Class Operators:: [:class:] * Range Operator:: start-end @end menu @ignore (If collating symbols and equivalence class expressions get implemented, then add this.) node Collating Symbol Operators subsubsection Collating Symbol Operators (@code{[.} @dots{} @code{.]}) If the syntax bit @code{XX} is set, then you can represent collating symbols inside lists. You form a @dfn{collating symbol} by putting a collating element between an @dfn{open-collating-symbol operator} and an @dfn{close-collating-symbol operator}. @samp{[.} represents the open-collating-symbol operator and @samp{.]} represents the close-collating-symbol operator. For example, if @samp{ll} is a collating element, then @samp{[[.ll.]]} would match @samp{ll}. node Equivalence Class Operators subsubsection Equivalence Class Operators (@code{[=} @dots{} @code{=]}) @cindex equivalence class expression in regex @cindex @samp{[=} in regex @cindex @samp{=]} in regex If the syntax bit @code{XX} is set, then Regex recognizes equivalence class expressions inside lists. A @dfn{equivalence class expression} is a set of collating elements which all belong to the same equivalence class. You form an equivalence class expression by putting a collating element between an @dfn{open-equivalence-class operator} and a @dfn{close-equivalence-class operator}. @samp{[=} represents the open-equivalence-class operator and @samp{=]} represents the close-equivalence-class operator. For example, if @samp{a} and @samp{A} were an equivalence class, then both @samp{[[=a=]]} and @samp{[[=A=]]} would match both @samp{a} and @samp{A}. If the collating element in an equivalence class expression isn't part of an equivalence class, then the matcher considers the equivalence class expression to be a collating symbol. @end ignore @node Character Class Operators, Range Operator, , List Operators @subsection Character Class Operators (@code{[:} @dots{} @code{:]}) @cindex character classes @cindex @samp{[:} in regex @cindex @samp{:]} in regex If the syntax bit @code{RE_CHARACTER_CLASSES} is set, then Regex recognizes character class expressions inside lists. A @dfn{character class expression} matches one character from a given class. You form a character class expression by putting a character class name between an @dfn{open-character-class operator} (represented by @samp{[:}) and a @dfn{close-character-class operator} (represented by @samp{:]}). The character class names and their meanings are: @table @code @item alnum letters and digits @item alpha letters @item blank system-dependent; for @sc{gnu}, a space or tab @item cntrl control characters (in the @sc{ascii} encoding, code 0177 and codes less than 040) @item digit digits @item graph same as @code{print} except omits space @item lower lowercase letters @item print printable characters (in the @sc{ascii} encoding, space tilde---codes 040 through 0176) @item punct neither control nor alphanumeric characters @item space space, carriage return, newline, vertical tab, and form feed @item upper uppercase letters @item xdigit hexadecimal digits: @code{0}--@code{9}, @code{a}--@code{f}, @code{A}--@code{F} @end table @noindent These correspond to the definitions in the C library's @file{} facility. For example, @samp{[:alpha:]} corresponds to the standard facility @code{isalpha}. Regex recognizes character class expressions only inside of lists; so @samp{[[:alpha:]]} matches any letter, but @samp{[:alpha:]} outside of a bracket expression and not followed by a repetition operator matches just itself. @node Range Operator, , Character Class Operators, List Operators @subsection The Range Operator (@code{-}) Regex recognizes @dfn{range expressions} inside a list. They represent those characters that fall between two elements in the current collating sequence. You form a range expression by putting a @dfn{range operator} between two @ignore (If these get implemented, then substitute this for ``characters.'') of any of the following: characters, collating elements, collating symbols, and equivalence class expressions. The starting point of the range and the ending point of the range don't have to be the same kind of item, e.g., the starting point could be a collating element and the ending point could be an equivalence class expression. If a range's ending point is an equivalence class, then all the collating elements in that class will be in the range. @end ignore characters.@footnote{You can't use a character class for the starting or ending point of a range, since a character class is not a single character.} @samp{-} represents the range operator. For example, @samp{a-f} within a list represents all the characters from @samp{a} through @samp{f} inclusively. If the syntax bit @code{RE_NO_EMPTY_RANGES} is set, then if the range's ending point collates less than its starting point, the range (and the regular expression containing it) is invalid. For example, the regular expression @samp{[z-a]} would be invalid. If this bit isn't set, then Regex considers such a range to be empty. Since @samp{-} represents the range operator, if you want to make a @samp{-} character itself a list item, you must do one of the following: @itemize @bullet @item Put the @samp{-} either first or last in the list. @item Include a range whose starting point collates strictly lower than @samp{-} and whose ending point collates equal or higher. Unless a range is the first item in a list, a @samp{-} can't be its starting point, but @emph{can} be its ending point. That is because Regex considers @samp{-} to be the range operator unless it is preceded by another @samp{-}. For example, in the @sc{ascii} encoding, @samp{)}, @samp{*}, @samp{+}, @samp{,}, @samp{-}, @samp{.}, and @samp{/} are contiguous characters in the collating sequence. You might think that @samp{[)-+--/]} has two ranges: @samp{)-+} and @samp{--/}. Rather, it has the ranges @samp{)-+} and @samp{+--}, plus the character @samp{/}, so it matches, e.g., @samp{,}, not @samp{.}. @item Put a range whose starting point is @samp{-} first in the list. @end itemize For example, @samp{[-a-z]} matches a lowercase letter or a hyphen (in English, in @sc{ascii}). @node Grouping Operators, Back-reference Operator, List Operators, Common Operators @section Grouping Operators (@code{(} @dots{} @code{)} or @code{\(} @dots{} @code{\)}) @kindex ( @kindex ) @kindex \( @kindex \) @cindex grouping @cindex subexpressions @cindex parenthesizing A @dfn{group}, also known as a @dfn{subexpression}, consists of an @dfn{open-group operator}, any number of other operators, and a @dfn{close-group operator}. Regex treats this sequence as a unit, just as mathematics and programming languages treat a parenthesized expression as a unit. Therefore, using @dfn{groups}, you can: @itemize @bullet @item delimit the argument(s) to an alternation operator (@pxref{Alternation Operator}) or a repetition operator (@pxref{Repetition Operators}). @item keep track of the indices of the substring that matched a given group. @xref{Using Registers}, for a precise explanation. This lets you: @itemize @bullet @item use the back-reference operator (@pxref{Back-reference Operator}). @item use registers (@pxref{Using Registers}). @end itemize @end itemize If the syntax bit @code{RE_NO_BK_PARENS} is set, then @samp{(} represents the open-group operator and @samp{)} represents the close-group operator; otherwise, @samp{\(} and @samp{\)} do. If the syntax bit @code{RE_UNMATCHED_RIGHT_PAREN_ORD} is set and a close-group operator has no matching open-group operator, then Regex considers it to match @samp{)}. @node Back-reference Operator, Anchoring Operators, Grouping Operators, Common Operators @section The Back-reference Operator (@dfn{\}@var{digit}) @cindex back references If the syntax bit @code{RE_NO_BK_REF} isn't set, then Regex recognizes back references. A back reference matches a specified preceding group. The back reference operator is represented by @samp{\@var{digit}} anywhere after the end of a regular expression's @w{@var{digit}-th} group (@pxref{Grouping Operators}). @var{digit} must be between @samp{1} and @samp{9}. The matcher assigns numbers 1 through 9 to the first nine groups it encounters. By using one of @samp{\1} through @samp{\9} after the corresponding group's close-group operator, you can match a substring identical to the one that the group does. Back references match according to the following (in all examples below, @samp{(} represents the open-group, @samp{)} the close-group, @samp{@{} the open-interval and @samp{@}} the close-interval operator): @itemize @bullet @item If the group matches a substring, the back reference matches an identical substring. For example, @samp{(a)\1} matches @samp{aa} and @samp{(bana)na\1bo\1} matches @samp{bananabanabobana}. Likewise, @samp{(.*)\1} matches any (newline-free if the syntax bit @code{RE_DOT_NEWLINE} isn't set) string that is composed of two identical halves; the @samp{(.*)} matches the first half and the @samp{\1} matches the second half. @item If the group matches more than once (as it might if followed by, e.g., a repetition operator), then the back reference matches the substring the group @emph{last} matched. For example, @samp{((a*)b)*\1\2} matches @samp{aabababa}; first @w{group 1} (the outer one) matches @samp{aab} and @w{group 2} (the inner one) matches @samp{aa}. Then @w{group 1} matches @samp{ab} and @w{group 2} matches @samp{a}. So, @samp{\1} matches @samp{ab} and @samp{\2} matches @samp{a}. @item If the group doesn't participate in a match, i.e., it is part of an alternative not taken or a repetition operator allows zero repetitions of it, then the back reference makes the whole match fail. For example, @samp{(one()|two())-and-(three\2|four\3)} matches @samp{one-and-three} and @samp{two-and-four}, but not @samp{one-and-four} or @samp{two-and-three}. For example, if the pattern matches @samp{one-and-}, then its @w{group 2} matches the empty string and its @w{group 3} doesn't participate in the match. So, if it then matches @samp{four}, then when it tries to back reference @w{group 3}---which it will attempt to do because @samp{\3} follows the @samp{four}---the match will fail because @w{group 3} didn't participate in the match. @end itemize You can use a back reference as an argument to a repetition operator. For example, @samp{(a(b))\2*} matches @samp{a} followed by two or more @samp{b}s. Similarly, @samp{(a(b))\2@{3@}} matches @samp{abbbb}. If there is no preceding @w{@var{digit}-th} subexpression, the regular expression is invalid. @node Anchoring Operators, , Back-reference Operator, Common Operators @section Anchoring Operators @cindex anchoring @cindex regexp anchoring These operators can constrain a pattern to match only at the beginning or end of the entire string or at the beginning or end of a line. @menu * Match-beginning-of-line Operator:: ^ * Match-end-of-line Operator:: $ @end menu @node Match-beginning-of-line Operator, Match-end-of-line Operator, , Anchoring Operators @subsection The Match-beginning-of-line Operator (@code{^}) @kindex ^ @cindex beginning-of-line operator @cindex anchors This operator can match the empty string either at the beginning of the string or after a newline character. Thus, it is said to @dfn{anchor} the pattern to the beginning of a line. In the cases following, @samp{^} represents this operator. (Otherwise, @samp{^} is ordinary.) @itemize @bullet @item It (the @samp{^}) is first in the pattern, as in @samp{^foo}. @cnindex RE_CONTEXT_INDEP_ANCHORS @r{(and @samp{^})} @item The syntax bit @code{RE_CONTEXT_INDEP_ANCHORS} is set, and it is outside a bracket expression. @cindex open-group operator and @samp{^} @cindex alternation operator and @samp{^} @item It follows an open-group or alternation operator, as in @samp{a\(^b\)} and @samp{a\|^b}. @xref{Grouping Operators}, and @ref{Alternation Operator}. @end itemize These rules imply that some valid patterns containing @samp{^} cannot be matched; for example, @samp{foo^bar} if @code{RE_CONTEXT_INDEP_ANCHORS} is set. @vindex not_bol @r{field in pattern buffer} If the @code{not_bol} field is set in the pattern buffer (@pxref{GNU Pattern Buffers}), then @samp{^} fails to match at the beginning of the string. @xref{POSIX Matching}, for when you might find this useful. @vindex newline_anchor @r{field in pattern buffer} If the @code{newline_anchor} field is set in the pattern buffer, then @samp{^} fails to match after a newline. This is useful when you do not regard the string to be matched as broken into lines. @node Match-end-of-line Operator, , Match-beginning-of-line Operator, Anchoring Operators @subsection The Match-end-of-line Operator (@code{$}) @kindex $ @cindex end-of-line operator @cindex anchors This operator can match the empty string either at the end of the string or before a newline character in the string. Thus, it is said to @dfn{anchor} the pattern to the end of a line. It is always represented by @samp{$}. For example, @samp{foo$} usually matches, e.g., @samp{foo} and, e.g., the first three characters of @samp{foo\nbar}. Its interaction with the syntax bits and pattern buffer fields is exactly the dual of @samp{^}'s; see the previous section. (That is, ``beginning'' becomes ``end'', ``next'' becomes ``previous'', and ``after'' becomes ``before''.) @node GNU Operators, GNU Emacs Operators, Common Operators, Top @chapter GNU Operators Following are operators that @sc{gnu} defines (and @sc{posix} doesn't). @menu * Word Operators:: * Buffer Operators:: @end menu @node Word Operators, Buffer Operators, , GNU Operators @section Word Operators The operators in this section require Regex to recognize parts of words. Regex uses a syntax table to determine whether or not a character is part of a word, i.e., whether or not it is @dfn{word-constituent}. @menu * Non-Emacs Syntax Tables:: * Match-word-boundary Operator:: \b * Match-within-word Operator:: \B * Match-beginning-of-word Operator:: \< * Match-end-of-word Operator:: \> * Match-word-constituent Operator:: \w * Match-non-word-constituent Operator:: \W @end menu @node Non-Emacs Syntax Tables, Match-word-boundary Operator, , Word Operators @subsection Non-Emacs Syntax Tables A @dfn{syntax table} is an array indexed by the characters in your character set. In the @sc{ascii} encoding, therefore, a syntax table has 256 elements. Regex always uses a @code{char *} variable @code{re_syntax_table} as its syntax table. In some cases, it initializes this variable and in others it expects you to initialize it. @itemize @bullet @item If Regex is compiled with the preprocessor symbols @code{emacs} and @code{SYNTAX_TABLE} both undefined, then Regex allocates @code{re_syntax_table} and initializes an element @var{i} either to @code{Sword} (which it defines) if @var{i} is a letter, number, or @samp{_}, or to zero if it's not. @item If Regex is compiled with @code{emacs} undefined but @code{SYNTAX_TABLE} defined, then Regex expects you to define a @code{char *} variable @code{re_syntax_table} to be a valid syntax table. @item @xref{Emacs Syntax Tables}, for what happens when Regex is compiled with the preprocessor symbol @code{emacs} defined. @end itemize @node Match-word-boundary Operator, Match-within-word Operator, Non-Emacs Syntax Tables, Word Operators @subsection The Match-word-boundary Operator (@code{\b}) @cindex @samp{\b} @cindex word boundaries, matching This operator (represented by @samp{\b}) matches the empty string at either the beginning or the end of a word. For example, @samp{\brat\b} matches the separate word @samp{rat}. @node Match-within-word Operator, Match-beginning-of-word Operator, Match-word-boundary Operator, Word Operators @subsection The Match-within-word Operator (@code{\B}) @cindex @samp{\B} This operator (represented by @samp{\B}) matches the empty string within a word. For example, @samp{c\Brat\Be} matches @samp{crate}, but @samp{dirty \Brat} doesn't match @samp{dirty rat}. @node Match-beginning-of-word Operator, Match-end-of-word Operator, Match-within-word Operator, Word Operators @subsection The Match-beginning-of-word Operator (@code{\<}) @cindex @samp{\<} This operator (represented by @samp{\<}) matches the empty string at the beginning of a word. @node Match-end-of-word Operator, Match-word-constituent Operator, Match-beginning-of-word Operator, Word Operators @subsection The Match-end-of-word Operator (@code{\>}) @cindex @samp{\>} This operator (represented by @samp{\>}) matches the empty string at the end of a word. @node Match-word-constituent Operator, Match-non-word-constituent Operator, Match-end-of-word Operator, Word Operators @subsection The Match-word-constituent Operator (@code{\w}) @cindex @samp{\w} This operator (represented by @samp{\w}) matches any word-constituent character. @node Match-non-word-constituent Operator, , Match-word-constituent Operator, Word Operators @subsection The Match-non-word-constituent Operator (@code{\W}) @cindex @samp{\W} This operator (represented by @samp{\W}) matches any character that is not word-constituent. @node Buffer Operators, , Word Operators, GNU Operators @section Buffer Operators Following are operators which work on buffers. In Emacs, a @dfn{buffer} is, naturally, an Emacs buffer. For other programs, Regex considers the entire string to be matched as the buffer. @menu * Match-beginning-of-buffer Operator:: \` * Match-end-of-buffer Operator:: \' @end menu @node Match-beginning-of-buffer Operator, Match-end-of-buffer Operator, , Buffer Operators @subsection The Match-beginning-of-buffer Operator (@code{\`}) @cindex @samp{\`} This operator (represented by @samp{\`}) matches the empty string at the beginning of the buffer. @node Match-end-of-buffer Operator, , Match-beginning-of-buffer Operator, Buffer Operators @subsection The Match-end-of-buffer Operator (@code{\'}) @cindex @samp{\'} This operator (represented by @samp{\'}) matches the empty string at the end of the buffer. @node GNU Emacs Operators, What Gets Matched?, GNU Operators, Top @chapter GNU Emacs Operators Following are operators that @sc{gnu} defines (and @sc{posix} doesn't) that you can use only when Regex is compiled with the preprocessor symbol @code{emacs} defined. @menu * Syntactic Class Operators:: @end menu @node Syntactic Class Operators, , , GNU Emacs Operators @section Syntactic Class Operators The operators in this section require Regex to recognize the syntactic classes of characters. Regex uses a syntax table to determine this. @menu * Emacs Syntax Tables:: * Match-syntactic-class Operator:: \sCLASS * Match-not-syntactic-class Operator:: \SCLASS @end menu @node Emacs Syntax Tables, Match-syntactic-class Operator, , Syntactic Class Operators @subsection Emacs Syntax Tables A @dfn{syntax table} is an array indexed by the characters in your character set. In the @sc{ascii} encoding, therefore, a syntax table has 256 elements. If Regex is compiled with the preprocessor symbol @code{emacs} defined, then Regex expects you to define and initialize the variable @code{re_syntax_table} to be an Emacs syntax table. Emacs' syntax tables are more complicated than Regex's own (@pxref{Non-Emacs Syntax Tables}). @xref{Syntax, , Syntax, emacs, The GNU Emacs User's Manual}, for a description of Emacs' syntax tables. @node Match-syntactic-class Operator, Match-not-syntactic-class Operator, Emacs Syntax Tables, Syntactic Class Operators @subsection The Match-syntactic-class Operator (@code{\s}@var{class}) @cindex @samp{\s} This operator matches any character whose syntactic class is represented by a specified character. @samp{\s@var{class}} represents this operator where @var{class} is the character representing the syntactic class you want. For example, @samp{w} represents the syntactic class of word-constituent characters, so @samp{\sw} matches any word-constituent character. @node Match-not-syntactic-class Operator, , Match-syntactic-class Operator, Syntactic Class Operators @subsection The Match-not-syntactic-class Operator (@code{\S}@var{class}) @cindex @samp{\S} This operator is similar to the match-syntactic-class operator except that it matches any character whose syntactic class is @emph{not} represented by the specified character. @samp{\S@var{class}} represents this operator. For example, @samp{w} represents the syntactic class of word-constituent characters, so @samp{\Sw} matches any character that is not word-constituent. @node What Gets Matched?, Programming with Regex, GNU Emacs Operators, Top @chapter What Gets Matched? Regex usually matches strings according to the ``leftmost longest'' rule; that is, it chooses the longest of the leftmost matches. This does not mean that for a regular expression containing subexpressions that it simply chooses the longest match for each subexpression, left to right; the overall match must also be the longest possible one. For example, @samp{(ac*)(c*d[ac]*)\1} matches @samp{acdacaaa}, not @samp{acdac}, as it would if it were to choose the longest match for the first subexpression. @node Programming with Regex, Copying, What Gets Matched?, Top @chapter Programming with Regex Here we describe how you use the Regex data structures and functions in C programs. Regex has three interfaces: one designed for @sc{gnu}, one compatible with @sc{posix} and one compatible with Berkeley @sc{unix}. @menu * GNU Regex Functions:: * POSIX Regex Functions:: * BSD Regex Functions:: @end menu @node GNU Regex Functions, POSIX Regex Functions, , Programming with Regex @section GNU Regex Functions If you're writing code that doesn't need to be compatible with either @sc{posix} or Berkeley @sc{unix}, you can use these functions. They provide more options than the other interfaces. @menu * GNU Pattern Buffers:: The re_pattern_buffer type. * GNU Regular Expression Compiling:: re_compile_pattern () * GNU Matching:: re_match () * GNU Searching:: re_search () * Matching/Searching with Split Data:: re_match_2 (), re_search_2 () * Searching with Fastmaps:: re_compile_fastmap () * GNU Translate Tables:: The `translate' field. * Using Registers:: The re_registers type and related fns. * Freeing GNU Pattern Buffers:: regfree () @end menu @node GNU Pattern Buffers, GNU Regular Expression Compiling, , GNU Regex Functions @subsection GNU Pattern Buffers @cindex pattern buffer, definition of @tindex re_pattern_buffer @r{definition} @tindex struct re_pattern_buffer @r{definition} To compile, match, or search for a given regular expression, you must supply a pattern buffer. A @dfn{pattern buffer} holds one compiled regular expression.@footnote{Regular expressions are also referred to as ``patterns,'' hence the name ``pattern buffer.''} You can have several different pattern buffers simultaneously, each holding a compiled pattern for a different regular expression. @file{regex.h} defines the pattern buffer @code{struct} as follows: @example /* Space that holds the compiled pattern. It is declared as `unsigned char *' because its elements are sometimes used as array indexes. */ unsigned char *buffer; /* Number of bytes to which `buffer' points. */ unsigned long allocated; /* Number of bytes actually used in `buffer'. */ unsigned long used; /* Syntax setting with which the pattern was compiled. */ reg_syntax_t syntax; /* Pointer to a fastmap, if any, otherwise zero. re_search uses the fastmap, if there is one, to skip over impossible starting points for matches. */ char *fastmap; /* Either a translate table to apply to all characters before comparing them, or zero for no translation. The translation is applied to a pattern when it is compiled and to a string when it is matched. */ char *translate; /* Number of subexpressions found by the compiler. */ size_t re_nsub; /* Zero if this pattern cannot match the empty string, one else. Well, in truth it's used only in `re_search_2', to see whether or not we should use the fastmap, so we don't set this absolutely perfectly; see `re_compile_fastmap' (the `duplicate' case). */ unsigned can_be_null : 1; /* If REGS_UNALLOCATED, allocate space in the `regs' structure for `max (RE_NREGS, re_nsub + 1)' groups. If REGS_REALLOCATE, reallocate space if necessary. If REGS_FIXED, use what's there. */ #define REGS_UNALLOCATED 0 #define REGS_REALLOCATE 1 #define REGS_FIXED 2 unsigned regs_allocated : 2; /* Set to zero when `regex_compile' compiles a pattern; set to one by `re_compile_fastmap' if it updates the fastmap. */ unsigned fastmap_accurate : 1; /* If set, `re_match_2' does not return information about subexpressions. */ unsigned no_sub : 1; /* If set, a beginning-of-line anchor doesn't match at the beginning of the string. */ unsigned not_bol : 1; /* Similarly for an end-of-line anchor. */ unsigned not_eol : 1; /* If true, an anchor at a newline matches. */ unsigned newline_anchor : 1; @end example @node GNU Regular Expression Compiling, GNU Matching, GNU Pattern Buffers, GNU Regex Functions @subsection GNU Regular Expression Compiling In @sc{gnu}, you can both match and search for a given regular expression. To do either, you must first compile it in a pattern buffer (@pxref{GNU Pattern Buffers}). @cindex syntax initialization @vindex re_syntax_options @r{initialization} Regular expressions match according to the syntax with which they were compiled; with @sc{gnu}, you indicate what syntax you want by setting the variable @code{re_syntax_options} (declared in @file{regex.h} and defined in @file{regex.c}) before calling the compiling function, @code{re_compile_pattern} (see below). @xref{Syntax Bits}, and @ref{Predefined Syntaxes}. You can change the value of @code{re_syntax_options} at any time. Usually, however, you set its value once and then never change it. @cindex pattern buffer initialization @code{re_compile_pattern} takes a pattern buffer as an argument. You must initialize the following fields: @table @code @item translate @r{initialization} @item translate @vindex translate @r{initialization} Initialize this to point to a translate table if you want one, or to zero if you don't. We explain translate tables in @ref{GNU Translate Tables}. @item fastmap @vindex fastmap @r{initialization} Initialize this to nonzero if you want a fastmap, or to zero if you don't. @item buffer @itemx allocated @vindex buffer @r{initialization} @vindex allocated @r{initialization} @findex malloc If you want @code{re_compile_pattern} to allocate memory for the compiled pattern, set both of these to zero. If you have an existing block of memory (allocated with @code{malloc}) you want Regex to use, set @code{buffer} to its address and @code{allocated} to its size (in bytes). @code{re_compile_pattern} uses @code{realloc} to extend the space for the compiled pattern as necessary. @end table To compile a pattern buffer, use: @findex re_compile_pattern @example char * re_compile_pattern (const char *@var{regex}, const int @var{regex_size}, struct re_pattern_buffer *@var{pattern_buffer}) @end example @noindent @var{regex} is the regular expression's address, @var{regex_size} is its length, and @var{pattern_buffer} is the pattern buffer's address. If @code{re_compile_pattern} successfully compiles the regular expression, it returns zero and sets @code{*@var{pattern_buffer}} to the compiled pattern. It sets the pattern buffer's fields as follows: @table @code @item buffer @vindex buffer @r{field, set by @code{re_compile_pattern}} to the compiled pattern. @item used @vindex used @r{field, set by @code{re_compile_pattern}} to the number of bytes the compiled pattern in @code{buffer} occupies. @item syntax @vindex syntax @r{field, set by @code{re_compile_pattern}} to the current value of @code{re_syntax_options}. @item re_nsub @vindex re_nsub @r{field, set by @code{re_compile_pattern}} to the number of subexpressions in @var{regex}. @item fastmap_accurate @vindex fastmap_accurate @r{field, set by @code{re_compile_pattern}} to zero on the theory that the pattern you're compiling is different than the one previously compiled into @code{buffer}; in that case (since you can't make a fastmap without a compiled pattern), @code{fastmap} would either contain an incompatible fastmap, or nothing at all. @c xx what else? @end table If @code{re_compile_pattern} can't compile @var{regex}, it returns an error string corresponding to one of the errors listed in @ref{POSIX Regular Expression Compiling}. @node GNU Matching, GNU Searching, GNU Regular Expression Compiling, GNU Regex Functions @subsection GNU Matching @cindex matching with GNU functions Matching the @sc{gnu} way means trying to match as much of a string as possible starting at a position within it you specify. Once you've compiled a pattern into a pattern buffer (@pxref{GNU Regular Expression Compiling}), you can ask the matcher to match that pattern against a string using: @findex re_match @example int re_match (struct re_pattern_buffer *@var{pattern_buffer}, const char *@var{string}, const int @var{size}, const int @var{start}, struct re_registers *@var{regs}) @end example @noindent @var{pattern_buffer} is the address of a pattern buffer containing a compiled pattern. @var{string} is the string you want to match; it can contain newline and null characters. @var{size} is the length of that string. @var{start} is the string index at which you want to begin matching; the first character of @var{string} is at index zero. @xref{Using Registers}, for a explanation of @var{regs}; you can safely pass zero. @code{re_match} matches the regular expression in @var{pattern_buffer} against the string @var{string} according to the syntax in @var{pattern_buffers}'s @code{syntax} field. (@xref{GNU Regular Expression Compiling}, for how to set it.) The function returns @math{-1} if the compiled pattern does not match any part of @var{string} and @math{-2} if an internal error happens; otherwise, it returns how many (possibly zero) characters of @var{string} the pattern matched. An example: suppose @var{pattern_buffer} points to a pattern buffer containing the compiled pattern for @samp{a*}, and @var{string} points to @samp{aaaaab} (whereupon @var{size} should be 6). Then if @var{start} is 2, @code{re_match} returns 3, i.e., @samp{a*} would have matched the last three @samp{a}s in @var{string}. If @var{start} is 0, @code{re_match} returns 5, i.e., @samp{a*} would have matched all the @samp{a}s in @var{string}. If @var{start} is either 5 or 6, it returns zero. If @var{start} is not between zero and @var{size}, then @code{re_match} returns @math{-1}. @node GNU Searching, Matching/Searching with Split Data, GNU Matching, GNU Regex Functions @subsection GNU Searching @cindex searching with GNU functions @dfn{Searching} means trying to match starting at successive positions within a string. The function @code{re_search} does this. Before calling @code{re_search}, you must compile your regular expression. @xref{GNU Regular Expression Compiling}. Here is the function declaration: @findex re_search @example int re_search (struct re_pattern_buffer *@var{pattern_buffer}, const char *@var{string}, const int @var{size}, const int @var{start}, const int @var{range}, struct re_registers *@var{regs}) @end example @noindent @vindex start @r{argument to @code{re_search}} @vindex range @r{argument to @code{re_search}} whose arguments are the same as those to @code{re_match} (@pxref{GNU Matching}) except that the two arguments @var{start} and @var{range} replace @code{re_match}'s argument @var{start}. If @var{range} is positive, then @code{re_search} attempts a match starting first at index @var{start}, then at @math{@var{start} + 1} if that fails, and so on, up to @math{@var{start} + @var{range}}; if @var{range} is negative, then it attempts a match starting first at index @var{start}, then at @math{@var{start} -1} if that fails, and so on. If @var{start} is not between zero and @var{size}, then @code{re_search} returns @math{-1}. When @var{range} is positive, @code{re_search} adjusts @var{range} so that @math{@var{start} + @var{range} - 1} is between zero and @var{size}, if necessary; that way it won't search outside of @var{string}. Similarly, when @var{range} is negative, @code{re_search} adjusts @var{range} so that @math{@var{start} + @var{range} + 1} is between zero and @var{size}, if necessary. If the @code{fastmap} field of @var{pattern_buffer} is zero, @code{re_search} matches starting at consecutive positions; otherwise, it uses @code{fastmap} to make the search more efficient. @xref{Searching with Fastmaps}. If no match is found, @code{re_search} returns @math{-1}. If a match is found, it returns the index where the match began. If an internal error happens, it returns @math{-2}. @node Matching/Searching with Split Data, Searching with Fastmaps, GNU Searching, GNU Regex Functions @subsection Matching and Searching with Split Data Using the functions @code{re_match_2} and @code{re_search_2}, you can match or search in data that is divided into two strings. The function: @findex re_match_2 @example int re_match_2 (struct re_pattern_buffer *@var{buffer}, const char *@var{string1}, const int @var{size1}, const char *@var{string2}, const int @var{size2}, const int @var{start}, struct re_registers *@var{regs}, const int @var{stop}) @end example @noindent is similar to @code{re_match} (@pxref{GNU Matching}) except that you pass @emph{two} data strings and sizes, and an index @var{stop} beyond which you don't want the matcher to try matching. As with @code{re_match}, if it succeeds, @code{re_match_2} returns how many characters of @var{string} it matched. Regard @var{string1} and @var{string2} as concatenated when you set the arguments @var{start} and @var{stop} and use the contents of @var{regs}; @code{re_match_2} never returns a value larger than @math{@var{size1} + @var{size2}}. The function: @findex re_search_2 @example int re_search_2 (struct re_pattern_buffer *@var{buffer}, const char *@var{string1}, const int @var{size1}, const char *@var{string2}, const int @var{size2}, const int @var{start}, const int @var{range}, struct re_registers *@var{regs}, const int @var{stop}) @end example @noindent is similarly related to @code{re_search}. @node Searching with Fastmaps, GNU Translate Tables, Matching/Searching with Split Data, GNU Regex Functions @subsection Searching with Fastmaps @cindex fastmaps If you're searching through a long string, you should use a fastmap. Without one, the searcher tries to match at consecutive positions in the string. Generally, most of the characters in the string could not start a match. It takes much longer to try matching at a given position in the string than it does to check in a table whether or not the character at that position could start a match. A @dfn{fastmap} is such a table. More specifically, a fastmap is an array indexed by the characters in your character set. Under the @sc{ascii} encoding, therefore, a fastmap has 256 elements. If you want the searcher to use a fastmap with a given pattern buffer, you must allocate the array and assign the array's address to the pattern buffer's @code{fastmap} field. You either can compile the fastmap yourself or have @code{re_search} do it for you; when @code{fastmap} is nonzero, it automatically compiles a fastmap the first time you search using a particular compiled pattern. To compile a fastmap yourself, use: @findex re_compile_fastmap @example int re_compile_fastmap (struct re_pattern_buffer *@var{pattern_buffer}) @end example @noindent @var{pattern_buffer} is the address of a pattern buffer. If the character @var{c} could start a match for the pattern, @code{re_compile_fastmap} makes @code{@var{pattern_buffer}->fastmap[@var{c}]} nonzero. It returns @math{0} if it can compile a fastmap and @math{-2} if there is an internal error. For example, if @samp{|} is the alternation operator and @var{pattern_buffer} holds the compiled pattern for @samp{a|b}, then @code{re_compile_fastmap} sets @code{fastmap['a']} and @code{fastmap['b']} (and no others). @code{re_search} uses a fastmap as it moves along in the string: it checks the string's characters until it finds one that's in the fastmap. Then it tries matching at that character. If the match fails, it repeats the process. So, by using a fastmap, @code{re_search} doesn't waste time trying to match at positions in the string that couldn't start a match. If you don't want @code{re_search} to use a fastmap, store zero in the @code{fastmap} field of the pattern buffer before calling @code{re_search}. Once you've initialized a pattern buffer's @code{fastmap} field, you need never do so again---even if you compile a new pattern in it---provided the way the field is set still reflects whether or not you want a fastmap. @code{re_search} will still either do nothing if @code{fastmap} is null or, if it isn't, compile a new fastmap for the new pattern. @node GNU Translate Tables, Using Registers, Searching with Fastmaps, GNU Regex Functions @subsection GNU Translate Tables If you set the @code{translate} field of a pattern buffer to a translate table, then the @sc{gnu} Regex functions to which you've passed that pattern buffer use it to apply a simple transformation to all the regular expression and string characters at which they look. A @dfn{translate table} is an array indexed by the characters in your character set. Under the @sc{ascii} encoding, therefore, a translate table has 256 elements. The array's elements are also characters in your character set. When the Regex functions see a character @var{c}, they use @code{translate[@var{c}]} in its place, with one exception: the character after a @samp{\} is not translated. (This ensures that, the operators, e.g., @samp{\B} and @samp{\b}, are always distinguishable.) For example, a table that maps all lowercase letters to the corresponding uppercase ones would cause the matcher to ignore differences in case.@footnote{A table that maps all uppercase letters to the corresponding lowercase ones would work just as well for this purpose.} Such a table would map all characters except lowercase letters to themselves, and lowercase letters to the corresponding uppercase ones. Under the @sc{ascii} encoding, here's how you could initialize such a table (we'll call it @code{case_fold}): @example for (i = 0; i < 256; i++) case_fold[i] = i; for (i = 'a'; i <= 'z'; i++) case_fold[i] = i - ('a' - 'A'); @end example You tell Regex to use a translate table on a given pattern buffer by assigning that table's address to the @code{translate} field of that buffer. If you don't want Regex to do any translation, put zero into this field. You'll get weird results if you change the table's contents anytime between compiling the pattern buffer, compiling its fastmap, and matching or searching with the pattern buffer. @node Using Registers, Freeing GNU Pattern Buffers, GNU Translate Tables, GNU Regex Functions @subsection Using Registers A group in a regular expression can match a (posssibly empty) substring of the string that regular expression as a whole matched. The matcher remembers the beginning and end of the substring matched by each group. To find out what they matched, pass a nonzero @var{regs} argument to a @sc{gnu} matching or searching function (@pxref{GNU Matching} and @ref{GNU Searching}), i.e., the address of a structure of this type, as defined in @file{regex.h}: @c We don't bother to include this directly from regex.h, @c since it changes so rarely. @example @tindex re_registers @vindex num_regs @r{in @code{struct re_registers}} @vindex start @r{in @code{struct re_registers}} @vindex end @r{in @code{struct re_registers}} struct re_registers @{ unsigned num_regs; regoff_t *start; regoff_t *end; @}; @end example Except for (possibly) the @var{num_regs}'th element (see below), the @var{i}th element of the @code{start} and @code{end} arrays records information about the @var{i}th group in the pattern. (They're declared as C pointers, but this is only because not all C compilers accept zero-length arrays; conceptually, it is simplest to think of them as arrays.) The @code{start} and @code{end} arrays are allocated in various ways, depending on the value of the @code{regs_allocated} @vindex regs_allocated field in the pattern buffer passed to the matcher. The simplest and perhaps most useful is to let the matcher (re)allocate enough space to record information for all the groups in the regular expression. If @code{regs_allocated} is @code{REGS_UNALLOCATED}, @vindex REGS_UNALLOCATED the matcher allocates @math{1 + @var{re_nsub}} (another field in the pattern buffer; @pxref{GNU Pattern Buffers}). The extra element is set to @math{-1}, and sets @code{regs_allocated} to @code{REGS_REALLOCATE}. @vindex REGS_REALLOCATE Then on subsequent calls with the same pattern buffer and @var{regs} arguments, the matcher reallocates more space if necessary. It would perhaps be more logical to make the @code{regs_allocated} field part of the @code{re_registers} structure, instead of part of the pattern buffer. But in that case the caller would be forced to initialize the structure before passing it. Much existing code doesn't do this initialization, and it's arguably better to avoid it anyway. @code{re_compile_pattern} sets @code{regs_allocated} to @code{REGS_UNALLOCATED}, so if you use the GNU regular expression functions, you get this behavior by default. xx document re_set_registers @sc{posix}, on the other hand, requires a different interface: the caller is supposed to pass in a fixed-length array which the matcher fills. Therefore, if @code{regs_allocated} is @code{REGS_FIXED} @vindex REGS_FIXED the matcher simply fills that array. The following examples illustrate the information recorded in the @code{re_registers} structure. (In all of them, @samp{(} represents the open-group and @samp{)} the close-group operator. The first character in the string @var{string} is at index 0.) @c xx i'm not sure this is all true anymore. @itemize @bullet @item If the regular expression has an @w{@var{i}-th} group not contained within another group that matches a substring of @var{string}, then the function sets @code{@w{@var{regs}->}start[@var{i}]} to the index in @var{string} where the substring matched by the @w{@var{i}-th} group begins, and @code{@w{@var{regs}->}end[@var{i}]} to the index just beyond that substring's end. The function sets @code{@w{@var{regs}->}start[0]} and @code{@w{@var{regs}->}end[0]} to analogous information about the entire pattern. For example, when you match @samp{((a)(b))} against @samp{ab}, you get: @itemize @item 0 in @code{@w{@var{regs}->}start[0]} and 2 in @code{@w{@var{regs}->}end[0]} @item 0 in @code{@w{@var{regs}->}start[1]} and 2 in @code{@w{@var{regs}->}end[1]} @item 0 in @code{@w{@var{regs}->}start[2]} and 1 in @code{@w{@var{regs}->}end[2]} @item 1 in @code{@w{@var{regs}->}start[3]} and 2 in @code{@w{@var{regs}->}end[3]} @end itemize @item If a group matches more than once (as it might if followed by, e.g., a repetition operator), then the function reports the information about what the group @emph{last} matched. For example, when you match the pattern @samp{(a)*} against the string @samp{aa}, you get: @itemize @item 0 in @code{@w{@var{regs}->}start[0]} and 2 in @code{@w{@var{regs}->}end[0]} @item 1 in @code{@w{@var{regs}->}start[1]} and 2 in @code{@w{@var{regs}->}end[1]} @end itemize @item If the @w{@var{i}-th} group does not participate in a successful match, e.g., it is an alternative not taken or a repetition operator allows zero repetitions of it, then the function sets @code{@w{@var{regs}->}start[@var{i}]} and @code{@w{@var{regs}->}end[@var{i}]} to @math{-1}. For example, when you match the pattern @samp{(a)*b} against the string @samp{b}, you get: @itemize @item 0 in @code{@w{@var{regs}->}start[0]} and 1 in @code{@w{@var{regs}->}end[0]} @item @math{-1} in @code{@w{@var{regs}->}start[1]} and @math{-1} in @code{@w{@var{regs}->}end[1]} @end itemize @item If the @w{@var{i}-th} group matches a zero-length string, then the function sets @code{@w{@var{regs}->}start[@var{i}]} and @code{@w{@var{regs}->}end[@var{i}]} to the index just beyond that zero-length string. For example, when you match the pattern @samp{(a*)b} against the string @samp{b}, you get: @itemize @item 0 in @code{@w{@var{regs}->}start[0]} and 1 in @code{@w{@var{regs}->}end[0]} @item 0 in @code{@w{@var{regs}->}start[1]} and 0 in @code{@w{@var{regs}->}end[1]} @end itemize @ignore The function sets @code{@w{@var{regs}->}start[0]} and @code{@w{@var{regs}->}end[0]} to analogous information about the entire pattern. For example, when you match the pattern @samp{(a*)} against the empty string, you get: @itemize @item 0 in @code{@w{@var{regs}->}start[0]} and 0 in @code{@w{@var{regs}->}end[0]} @item 0 in @code{@w{@var{regs}->}start[1]} and 0 in @code{@w{@var{regs}->}end[1]} @end itemize @end ignore @item If an @w{@var{i}-th} group contains a @w{@var{j}-th} group in turn not contained within any other group within group @var{i} and the function reports a match of the @w{@var{i}-th} group, then it records in @code{@w{@var{regs}->}start[@var{j}]} and @code{@w{@var{regs}->}end[@var{j}]} the last match (if it matched) of the @w{@var{j}-th} group. For example, when you match the pattern @samp{((a*)b)*} against the string @samp{abb}, @w{group 2} last matches the empty string, so you get what it previously matched: @itemize @item 0 in @code{@w{@var{regs}->}start[0]} and 3 in @code{@w{@var{regs}->}end[0]} @item 2 in @code{@w{@var{regs}->}start[1]} and 3 in @code{@w{@var{regs}->}end[1]} @item 2 in @code{@w{@var{regs}->}start[2]} and 2 in @code{@w{@var{regs}->}end[2]} @end itemize When you match the pattern @samp{((a)*b)*} against the string @samp{abb}, @w{group 2} doesn't participate in the last match, so you get: @itemize @item 0 in @code{@w{@var{regs}->}start[0]} and 3 in @code{@w{@var{regs}->}end[0]} @item 2 in @code{@w{@var{regs}->}start[1]} and 3 in @code{@w{@var{regs}->}end[1]} @item 0 in @code{@w{@var{regs}->}start[2]} and 1 in @code{@w{@var{regs}->}end[2]} @end itemize @item If an @w{@var{i}-th} group contains a @w{@var{j}-th} group in turn not contained within any other group within group @var{i} and the function sets @code{@w{@var{regs}->}start[@var{i}]} and @code{@w{@var{regs}->}end[@var{i}]} to @math{-1}, then it also sets @code{@w{@var{regs}->}start[@var{j}]} and @code{@w{@var{regs}->}end[@var{j}]} to @math{-1}. For example, when you match the pattern @samp{((a)*b)*c} against the string @samp{c}, you get: @itemize @item 0 in @code{@w{@var{regs}->}start[0]} and 1 in @code{@w{@var{regs}->}end[0]} @item @math{-1} in @code{@w{@var{regs}->}start[1]} and @math{-1} in @code{@w{@var{regs}->}end[1]} @item @math{-1} in @code{@w{@var{regs}->}start[2]} and @math{-1} in @code{@w{@var{regs}->}end[2]} @end itemize @end itemize @node Freeing GNU Pattern Buffers, , Using Registers, GNU Regex Functions @subsection Freeing GNU Pattern Buffers To free any allocated fields of a pattern buffer, you can use the @sc{posix} function described in @ref{Freeing POSIX Pattern Buffers}, since the type @code{regex_t}---the type for @sc{posix} pattern buffers---is equivalent to the type @code{re_pattern_buffer}. After freeing a pattern buffer, you need to again compile a regular expression in it (@pxref{GNU Regular Expression Compiling}) before passing it to a matching or searching function. @node POSIX Regex Functions, BSD Regex Functions, GNU Regex Functions, Programming with Regex @section POSIX Regex Functions If you're writing code that has to be @sc{posix} compatible, you'll need to use these functions. Their interfaces are as specified by @sc{posix}, draft 1003.2/D11.2. @menu * POSIX Pattern Buffers:: The regex_t type. * POSIX Regular Expression Compiling:: regcomp () * POSIX Matching:: regexec () * Reporting Errors:: regerror () * Using Byte Offsets:: The regmatch_t type. * Freeing POSIX Pattern Buffers:: regfree () @end menu @node POSIX Pattern Buffers, POSIX Regular Expression Compiling, , POSIX Regex Functions @subsection POSIX Pattern Buffers To compile or match a given regular expression the @sc{posix} way, you must supply a pattern buffer exactly the way you do for @sc{gnu} (@pxref{GNU Pattern Buffers}). @sc{posix} pattern buffers have type @code{regex_t}, which is equivalent to the @sc{gnu} pattern buffer type @code{re_pattern_buffer}. @node POSIX Regular Expression Compiling, POSIX Matching, POSIX Pattern Buffers, POSIX Regex Functions @subsection POSIX Regular Expression Compiling With @sc{posix}, you can only search for a given regular expression; you can't match it. To do this, you must first compile it in a pattern buffer, using @code{regcomp}. @ignore Before calling @code{regcomp}, you must initialize this pattern buffer as you do for @sc{gnu} (@pxref{GNU Regular Expression Compiling}). See below, however, for how to choose a syntax with which to compile. @end ignore To compile a pattern buffer, use: @findex regcomp @example int regcomp (regex_t *@var{preg}, const char *@var{regex}, int @var{cflags}) @end example @noindent @var{preg} is the initialized pattern buffer's address, @var{regex} is the regular expression's address, and @var{cflags} is the compilation flags, which Regex considers as a collection of bits. Here are the valid bits, as defined in @file{regex.h}: @table @code @item REG_EXTENDED @vindex REG_EXTENDED says to use @sc{posix} Extended Regular Expression syntax; if this isn't set, then says to use @sc{posix} Basic Regular Expression syntax. @code{regcomp} sets @var{preg}'s @code{syntax} field accordingly. @item REG_ICASE @vindex REG_ICASE @cindex ignoring case says to ignore case; @code{regcomp} sets @var{preg}'s @code{translate} field to a translate table which ignores case, replacing anything you've put there before. @item REG_NOSUB @vindex REG_NOSUB says to set @var{preg}'s @code{no_sub} field; @pxref{POSIX Matching}, for what this means. @item REG_NEWLINE @vindex REG_NEWLINE says that a: @itemize @bullet @item match-any-character operator (@pxref{Match-any-character Operator}) doesn't match a newline. @item nonmatching list not containing a newline (@pxref{List Operators}) matches a newline. @item match-beginning-of-line operator (@pxref{Match-beginning-of-line Operator}) matches the empty string immediately after a newline, regardless of how @code{REG_NOTBOL} is set (@pxref{POSIX Matching}, for an explanation of @code{REG_NOTBOL}). @item match-end-of-line operator (@pxref{Match-beginning-of-line Operator}) matches the empty string immediately before a newline, regardless of how @code{REG_NOTEOL} is set (@pxref{POSIX Matching}, for an explanation of @code{REG_NOTEOL}). @end itemize @end table If @code{regcomp} successfully compiles the regular expression, it returns zero and sets @code{*@var{pattern_buffer}} to the compiled pattern. Except for @code{syntax} (which it sets as explained above), it also sets the same fields the same way as does the @sc{gnu} compiling function (@pxref{GNU Regular Expression Compiling}). If @code{regcomp} can't compile the regular expression, it returns one of the error codes listed here. (Except when noted differently, the syntax of in all examples below is basic regular expression syntax.) @table @code @comment repetitions @item REG_BADRPT For example, the consecutive repetition operators @samp{**} in @samp{a**} are invalid. As another example, if the syntax is extended regular expression syntax, then the repetition operator @samp{*} with nothing on which to operate in @samp{*} is invalid. @item REG_BADBR For example, the @var{count} @samp{-1} in @samp{a\@{-1} is invalid. @item REG_EBRACE For example, @samp{a\@{1} is missing a close-interval operator. @comment lists @item REG_EBRACK For example, @samp{[a} is missing a close-list operator. @item REG_ERANGE For example, the range ending point @samp{z} that collates lower than does its starting point @samp{a} in @samp{[z-a]} is invalid. Also, the range with the character class @samp{[:alpha:]} as its starting point in @samp{[[:alpha:]-|]}. @item REG_ECTYPE For example, the character class name @samp{foo} in @samp{[[:foo:]} is invalid. @comment groups @item REG_EPAREN For example, @samp{a\)} is missing an open-group operator and @samp{\(a} is missing a close-group operator. @item REG_ESUBREG For example, the back reference @samp{\2} that refers to a nonexistent subexpression in @samp{\(a\)\2} is invalid. @comment unfinished business @item REG_EEND Returned when a regular expression causes no other more specific error. @item REG_EESCAPE For example, the trailing backslash @samp{\} in @samp{a\} is invalid, as is the one in @samp{\}. @comment kitchen sink @item REG_BADPAT For example, in the extended regular expression syntax, the empty group @samp{()} in @samp{a()b} is invalid. @comment internal @item REG_ESIZE Returned when a regular expression needs a pattern buffer larger than 65536 bytes. @item REG_ESPACE Returned when a regular expression makes Regex to run out of memory. @end table @node POSIX Matching, Reporting Errors, POSIX Regular Expression Compiling, POSIX Regex Functions @subsection POSIX Matching Matching the @sc{posix} way means trying to match a null-terminated string starting at its first character. Once you've compiled a pattern into a pattern buffer (@pxref{POSIX Regular Expression Compiling}), you can ask the matcher to match that pattern against a string using: @findex regexec @example int regexec (const regex_t *@var{preg}, const char *@var{string}, size_t @var{nmatch}, regmatch_t @var{pmatch}[], int @var{eflags}) @end example @noindent @var{preg} is the address of a pattern buffer for a compiled pattern. @var{string} is the string you want to match. @xref{Using Byte Offsets}, for an explanation of @var{pmatch}. If you pass zero for @var{nmatch} or you compiled @var{preg} with the compilation flag @code{REG_NOSUB} set, then @code{regexec} will ignore @var{pmatch}; otherwise, you must allocate it to have at least @var{nmatch} elements. @code{regexec} will record @var{nmatch} byte offsets in @var{pmatch}, and set to @math{-1} any unused elements up to @math{@var{pmatch}@code{[@var{nmatch}]} - 1}. @var{eflags} specifies @dfn{execution flags}---namely, the two bits @code{REG_NOTBOL} and @code{REG_NOTEOL} (defined in @file{regex.h}). If you set @code{REG_NOTBOL}, then the match-beginning-of-line operator (@pxref{Match-beginning-of-line Operator}) always fails to match. This lets you match against pieces of a line, as you would need to if, say, searching for repeated instances of a given pattern in a line; it would work correctly for patterns both with and without match-beginning-of-line operators. @code{REG_NOTEOL} works analogously for the match-end-of-line operator (@pxref{Match-end-of-line Operator}); it exists for symmetry. @code{regexec} tries to find a match for @var{preg} in @var{string} according to the syntax in @var{preg}'s @code{syntax} field. (@xref{POSIX Regular Expression Compiling}, for how to set it.) The function returns zero if the compiled pattern matches @var{string} and @code{REG_NOMATCH} (defined in @file{regex.h}) if it doesn't. @node Reporting Errors, Using Byte Offsets, POSIX Matching, POSIX Regex Functions @subsection Reporting Errors If either @code{regcomp} or @code{regexec} fail, they return a nonzero error code, the possibilities for which are defined in @file{regex.h}. @xref{POSIX Regular Expression Compiling}, and @ref{POSIX Matching}, for what these codes mean. To get an error string corresponding to these codes, you can use: @findex regerror @example size_t regerror (int @var{errcode}, const regex_t *@var{preg}, char *@var{errbuf}, size_t @var{errbuf_size}) @end example @noindent @var{errcode} is an error code, @var{preg} is the address of the pattern buffer which provoked the error, @var{errbuf} is the error buffer, and @var{errbuf_size} is @var{errbuf}'s size. @code{regerror} returns the size in bytes of the error string corresponding to @var{errcode} (including its terminating null). If @var{errbuf} and @var{errbuf_size} are nonzero, it also returns in @var{errbuf} the first @math{@var{errbuf_size} - 1} characters of the error string, followed by a null. @var{errbuf_size} must be a nonnegative number less than or equal to the size in bytes of @var{errbuf}. You can call @code{regerror} with a null @var{errbuf} and a zero @var{errbuf_size} to determine how large @var{errbuf} need be to accommodate @code{regerror}'s error string. @node Using Byte Offsets, Freeing POSIX Pattern Buffers, Reporting Errors, POSIX Regex Functions @subsection Using Byte Offsets In @sc{posix}, variables of type @code{regmatch_t} hold analogous information, but are not identical to, @sc{gnu}'s registers (@pxref{Using Registers}). To get information about registers in @sc{posix}, pass to @code{regexec} a nonzero @var{pmatch} of type @code{regmatch_t}, i.e., the address of a structure of this type, defined in @file{regex.h}: @tindex regmatch_t @example typedef struct @{ regoff_t rm_so; regoff_t rm_eo; @} regmatch_t; @end example When reading in @ref{Using Registers}, about how the matching function stores the information into the registers, substitute @var{pmatch} for @var{regs}, @code{@w{@var{pmatch}[@var{i}]->}rm_so} for @code{@w{@var{regs}->}start[@var{i}]} and @code{@w{@var{pmatch}[@var{i}]->}rm_eo} for @code{@w{@var{regs}->}end[@var{i}]}. @node Freeing POSIX Pattern Buffers, , Using Byte Offsets, POSIX Regex Functions @subsection Freeing POSIX Pattern Buffers To free any allocated fields of a pattern buffer, use: @findex regfree @example void regfree (regex_t *@var{preg}) @end example @noindent @var{preg} is the pattern buffer whose allocated fields you want freed. @code{regfree} also sets @var{preg}'s @code{allocated} and @code{used} fields to zero. After freeing a pattern buffer, you need to again compile a regular expression in it (@pxref{POSIX Regular Expression Compiling}) before passing it to the matching function (@pxref{POSIX Matching}). @node BSD Regex Functions, , POSIX Regex Functions, Programming with Regex @section BSD Regex Functions If you're writing code that has to be Berkeley @sc{unix} compatible, you'll need to use these functions whose interfaces are the same as those in Berkeley @sc{unix}. @menu * BSD Regular Expression Compiling:: re_comp () * BSD Searching:: re_exec () @end menu @node BSD Regular Expression Compiling, BSD Searching, , BSD Regex Functions @subsection BSD Regular Expression Compiling With Berkeley @sc{unix}, you can only search for a given regular expression; you can't match one. To search for it, you must first compile it. Before you compile it, you must indicate the regular expression syntax you want it compiled according to by setting the variable @code{re_syntax_options} (declared in @file{regex.h} to some syntax (@pxref{Regular Expression Syntax}). To compile a regular expression use: @findex re_comp @example char * re_comp (char *@var{regex}) @end example @noindent @var{regex} is the address of a null-terminated regular expression. @code{re_comp} uses an internal pattern buffer, so you can use only the most recently compiled pattern buffer. This means that if you want to use a given regular expression that you've already compiled---but it isn't the latest one you've compiled---you'll have to recompile it. If you call @code{re_comp} with the null string (@emph{not} the empty string) as the argument, it doesn't change the contents of the pattern buffer. If @code{re_comp} successfully compiles the regular expression, it returns zero. If it can't compile the regular expression, it returns an error string. @code{re_comp}'s error messages are identical to those of @code{re_compile_pattern} (@pxref{GNU Regular Expression Compiling}). @node BSD Searching, , BSD Regular Expression Compiling, BSD Regex Functions @subsection BSD Searching Searching the Berkeley @sc{unix} way means searching in a string starting at its first character and trying successive positions within it to find a match. Once you've compiled a pattern using @code{re_comp} (@pxref{BSD Regular Expression Compiling}), you can ask Regex to search for that pattern in a string using: @findex re_exec @example int re_exec (char *@var{string}) @end example @noindent @var{string} is the address of the null-terminated string in which you want to search. @code{re_exec} returns either 1 for success or 0 for failure. It automatically uses a @sc{gnu} fastmap (@pxref{Searching with Fastmaps}). @node Copying, Index, Programming with Regex, Top @appendix GNU GENERAL PUBLIC LICENSE @center Version 2, June 1991 @display Copyright @copyright{} 1989, 1991 Free Software Foundation, Inc. 675 Mass Ave, Cambridge, MA 02139, USA Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed. @end display @unnumberedsec Preamble The licenses for most software are designed to take away your freedom to share and change it. By contrast, the GNU General Public License is intended to guarantee your freedom to share and change free software---to make sure the software is free for all its users. This General Public License applies to most of the Free Software Foundation's software and to any other program whose authors commit to using it. (Some other Free Software Foundation software is covered by the GNU Library General Public License instead.) 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If the Program specifies a version number of this License which applies to it and ``any later version'', you have the option of following the terms and conditions either of that version or of any later version published by the Free Software Foundation. If the Program does not specify a version number of this License, you may choose any version ever published by the Free Software Foundation. @item If you wish to incorporate parts of the Program into other free programs whose distribution conditions are different, write to the author to ask for permission. For software which is copyrighted by the Free Software Foundation, write to the Free Software Foundation; we sometimes make exceptions for this. Our decision will be guided by the two goals of preserving the free status of all derivatives of our free software and of promoting the sharing and reuse of software generally. @iftex @heading NO WARRANTY @end iftex @ifinfo @center NO WARRANTY @end ifinfo @item BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM ``AS IS'' WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR OR CORRECTION. @item IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. @end enumerate @iftex @heading END OF TERMS AND CONDITIONS @end iftex @ifinfo @center END OF TERMS AND CONDITIONS @end ifinfo @page @unnumberedsec Appendix: How to Apply These Terms to Your New Programs If you develop a new program, and you want it to be of the greatest possible use to the public, the best way to achieve this is to make it free software which everyone can redistribute and change under these terms. To do so, attach the following notices to the program. It is safest to attach them to the start of each source file to most effectively convey the exclusion of warranty; and each file should have at least the ``copyright'' line and a pointer to where the full notice is found. @smallexample @var{one line to give the program's name and a brief idea of what it does.} Copyright (C) 19@var{yy} @var{name of author} This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. @end smallexample Also add information on how to contact you by electronic and paper mail. If the program is interactive, make it output a short notice like this when it starts in an interactive mode: @smallexample Gnomovision version 69, Copyright (C) 19@var{yy} @var{name of author} Gnomovision comes with ABSOLUTELY NO WARRANTY; for details type `show w'. This is free software, and you are welcome to redistribute it under certain conditions; type `show c' for details. @end smallexample The hypothetical commands @samp{show w} and @samp{show c} should show the appropriate parts of the General Public License. Of course, the commands you use may be called something other than @samp{show w} and @samp{show c}; they could even be mouse-clicks or menu items---whatever suits your program. You should also get your employer (if you work as a programmer) or your school, if any, to sign a ``copyright disclaimer'' for the program, if necessary. Here is a sample; alter the names: @example Yoyodyne, Inc., hereby disclaims all copyright interest in the program `Gnomovision' (which makes passes at compilers) written by James Hacker. @var{signature of Ty Coon}, 1 April 1989 Ty Coon, President of Vice @end example This General Public License does not permit incorporating your program into proprietary programs. If your program is a subroutine library, you may consider it more useful to permit linking proprietary applications with the library. If this is what you want to do, use the GNU Library General Public License instead of this License. @node Index, , Copying, Top @unnumbered Index @printindex cp @contents @bye