This is Info file regex.info, produced by Makeinfo-1.55 from the input file regex.texi. 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. 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.  File: regex.info, Node: Syntactic Class Operators, Up: GNU Emacs Operators 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  File: regex.info, Node: Emacs Syntax Tables, Next: Match-syntactic-class Operator, Up: Syntactic Class Operators Emacs Syntax Tables ------------------- A "syntax table" is an array indexed by the characters in your character set. In the ASCII encoding, therefore, a syntax table has 256 elements. If Regex is compiled with the preprocessor symbol `emacs' defined, then Regex expects you to define and initialize the variable `re_syntax_table' to be an Emacs syntax table. Emacs' syntax tables are more complicated than Regex's own (*note Non-Emacs Syntax Tables::.). *Note Syntax: (emacs)Syntax, for a description of Emacs' syntax tables.  File: regex.info, Node: Match-syntactic-class Operator, Next: Match-not-syntactic-class Operator, Prev: Emacs Syntax Tables, Up: Syntactic Class Operators The Match-syntactic-class Operator (`\s'CLASS) ---------------------------------------------- This operator matches any character whose syntactic class is represented by a specified character. `\sCLASS' represents this operator where CLASS is the character representing the syntactic class you want. For example, `w' represents the syntactic class of word-constituent characters, so `\sw' matches any word-constituent character.  File: regex.info, Node: Match-not-syntactic-class Operator, Prev: Match-syntactic-class Operator, Up: Syntactic Class Operators The Match-not-syntactic-class Operator (`\S'CLASS) -------------------------------------------------- This operator is similar to the match-syntactic-class operator except that it matches any character whose syntactic class is *not* represented by the specified character. `\SCLASS' represents this operator. For example, `w' represents the syntactic class of word-constituent characters, so `\Sw' matches any character that is not word-constituent.  File: regex.info, Node: What Gets Matched?, Next: Programming with Regex, Prev: GNU Emacs Operators, Up: Top 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, `(ac*)(c*d[ac]*)\1' matches `acdacaaa', not `acdac', as it would if it were to choose the longest match for the first subexpression.  File: regex.info, Node: Programming with Regex, Next: Copying, Prev: What Gets Matched?, Up: Top 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 GNU, one compatible with POSIX and one compatible with Berkeley UNIX. * Menu: * GNU Regex Functions:: * POSIX Regex Functions:: * BSD Regex Functions::  File: regex.info, Node: GNU Regex Functions, Next: POSIX Regex Functions, Up: Programming with Regex GNU Regex Functions =================== If you're writing code that doesn't need to be compatible with either POSIX or Berkeley 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 ()  File: regex.info, Node: GNU Pattern Buffers, Next: GNU Regular Expression Compiling, Up: GNU Regex Functions GNU Pattern Buffers ------------------- To compile, match, or search for a given regular expression, you must supply a pattern buffer. A "pattern buffer" holds one compiled regular expression.(1) You can have several different pattern buffers simultaneously, each holding a compiled pattern for a different regular expression. `regex.h' defines the pattern buffer `struct' as follows: /* 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; ---------- Footnotes ---------- (1) Regular expressions are also referred to as "patterns," hence the name "pattern buffer."  File: regex.info, Node: GNU Regular Expression Compiling, Next: GNU Matching, Prev: GNU Pattern Buffers, Up: GNU Regex Functions GNU Regular Expression Compiling -------------------------------- In GNU, you can both match and search for a given regular expression. To do either, you must first compile it in a pattern buffer (*note GNU Pattern Buffers::.). Regular expressions match according to the syntax with which they were compiled; with GNU, you indicate what syntax you want by setting the variable `re_syntax_options' (declared in `regex.h' and defined in `regex.c') before calling the compiling function, `re_compile_pattern' (see below). *Note Syntax Bits::, and *Note Predefined Syntaxes::. You can change the value of `re_syntax_options' at any time. Usually, however, you set its value once and then never change it. `re_compile_pattern' takes a pattern buffer as an argument. You must initialize the following fields: `translate initialization' `translate' Initialize this to point to a translate table if you want one, or to zero if you don't. We explain translate tables in *Note GNU Translate Tables::. `fastmap' Initialize this to nonzero if you want a fastmap, or to zero if you don't. `buffer' `allocated' If you want `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 `malloc') you want Regex to use, set `buffer' to its address and `allocated' to its size (in bytes). `re_compile_pattern' uses `realloc' to extend the space for the compiled pattern as necessary. To compile a pattern buffer, use: char * re_compile_pattern (const char *REGEX, const int REGEX_SIZE, struct re_pattern_buffer *PATTERN_BUFFER) REGEX is the regular expression's address, REGEX_SIZE is its length, and PATTERN_BUFFER is the pattern buffer's address. If `re_compile_pattern' successfully compiles the regular expression, it returns zero and sets `*PATTERN_BUFFER' to the compiled pattern. It sets the pattern buffer's fields as follows: `buffer' to the compiled pattern. `used' to the number of bytes the compiled pattern in `buffer' occupies. `syntax' to the current value of `re_syntax_options'. `re_nsub' to the number of subexpressions in REGEX. `fastmap_accurate' to zero on the theory that the pattern you're compiling is different than the one previously compiled into `buffer'; in that case (since you can't make a fastmap without a compiled pattern), `fastmap' would either contain an incompatible fastmap, or nothing at all. If `re_compile_pattern' can't compile REGEX, it returns an error string corresponding to one of the errors listed in *Note POSIX Regular Expression Compiling::.  File: regex.info, Node: GNU Matching, Next: GNU Searching, Prev: GNU Regular Expression Compiling, Up: GNU Regex Functions GNU Matching ------------ Matching the 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 (*note GNU Regular Expression Compiling::.), you can ask the matcher to match that pattern against a string using: int re_match (struct re_pattern_buffer *PATTERN_BUFFER, const char *STRING, const int SIZE, const int START, struct re_registers *REGS) PATTERN_BUFFER is the address of a pattern buffer containing a compiled pattern. STRING is the string you want to match; it can contain newline and null characters. SIZE is the length of that string. START is the string index at which you want to begin matching; the first character of STRING is at index zero. *Note Using Registers::, for a explanation of REGS; you can safely pass zero. `re_match' matches the regular expression in PATTERN_BUFFER against the string STRING according to the syntax in PATTERN_BUFFERS's `syntax' field. (*Note GNU Regular Expression Compiling::, for how to set it.) The function returns -1 if the compiled pattern does not match any part of STRING and -2 if an internal error happens; otherwise, it returns how many (possibly zero) characters of STRING the pattern matched. An example: suppose PATTERN_BUFFER points to a pattern buffer containing the compiled pattern for `a*', and STRING points to `aaaaab' (whereupon SIZE should be 6). Then if START is 2, `re_match' returns 3, i.e., `a*' would have matched the last three `a's in STRING. If START is 0, `re_match' returns 5, i.e., `a*' would have matched all the `a's in STRING. If START is either 5 or 6, it returns zero. If START is not between zero and SIZE, then `re_match' returns -1.  File: regex.info, Node: GNU Searching, Next: Matching/Searching with Split Data, Prev: GNU Matching, Up: GNU Regex Functions GNU Searching ------------- "Searching" means trying to match starting at successive positions within a string. The function `re_search' does this. Before calling `re_search', you must compile your regular expression. *Note GNU Regular Expression Compiling::. Here is the function declaration: int re_search (struct re_pattern_buffer *PATTERN_BUFFER, const char *STRING, const int SIZE, const int START, const int RANGE, struct re_registers *REGS) whose arguments are the same as those to `re_match' (*note GNU Matching::.) except that the two arguments START and RANGE replace `re_match''s argument START. If RANGE is positive, then `re_search' attempts a match starting first at index START, then at START + 1 if that fails, and so on, up to START + RANGE; if RANGE is negative, then it attempts a match starting first at index START, then at START -1 if that fails, and so on. If START is not between zero and SIZE, then `re_search' returns -1. When RANGE is positive, `re_search' adjusts RANGE so that START + RANGE - 1 is between zero and SIZE, if necessary; that way it won't search outside of STRING. Similarly, when RANGE is negative, `re_search' adjusts RANGE so that START + RANGE + 1 is between zero and SIZE, if necessary. If the `fastmap' field of PATTERN_BUFFER is zero, `re_search' matches starting at consecutive positions; otherwise, it uses `fastmap' to make the search more efficient. *Note Searching with Fastmaps::. If no match is found, `re_search' returns -1. If a match is found, it returns the index where the match began. If an internal error happens, it returns -2.  File: regex.info, Node: Matching/Searching with Split Data, Next: Searching with Fastmaps, Prev: GNU Searching, Up: GNU Regex Functions Matching and Searching with Split Data -------------------------------------- Using the functions `re_match_2' and `re_search_2', you can match or search in data that is divided into two strings. The function: int re_match_2 (struct re_pattern_buffer *BUFFER, const char *STRING1, const int SIZE1, const char *STRING2, const int SIZE2, const int START, struct re_registers *REGS, const int STOP) is similar to `re_match' (*note GNU Matching::.) except that you pass *two* data strings and sizes, and an index STOP beyond which you don't want the matcher to try matching. As with `re_match', if it succeeds, `re_match_2' returns how many characters of STRING it matched. Regard STRING1 and STRING2 as concatenated when you set the arguments START and STOP and use the contents of REGS; `re_match_2' never returns a value larger than SIZE1 + SIZE2. The function: int re_search_2 (struct re_pattern_buffer *BUFFER, const char *STRING1, const int SIZE1, const char *STRING2, const int SIZE2, const int START, const int RANGE, struct re_registers *REGS, const int STOP) is similarly related to `re_search'.  File: regex.info, Node: Searching with Fastmaps, Next: GNU Translate Tables, Prev: Matching/Searching with Split Data, Up: GNU Regex Functions Searching with 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 "fastmap" is such a table. More specifically, a fastmap is an array indexed by the characters in your character set. Under the 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 `fastmap' field. You either can compile the fastmap yourself or have `re_search' do it for you; when `fastmap' is nonzero, it automatically compiles a fastmap the first time you search using a particular compiled pattern. To compile a fastmap yourself, use: int re_compile_fastmap (struct re_pattern_buffer *PATTERN_BUFFER) PATTERN_BUFFER is the address of a pattern buffer. If the character C could start a match for the pattern, `re_compile_fastmap' makes `PATTERN_BUFFER->fastmap[C]' nonzero. It returns 0 if it can compile a fastmap and -2 if there is an internal error. For example, if `|' is the alternation operator and PATTERN_BUFFER holds the compiled pattern for `a|b', then `re_compile_fastmap' sets `fastmap['a']' and `fastmap['b']' (and no others). `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, `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 `re_search' to use a fastmap, store zero in the `fastmap' field of the pattern buffer before calling `re_search'. Once you've initialized a pattern buffer's `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. `re_search' will still either do nothing if `fastmap' is null or, if it isn't, compile a new fastmap for the new pattern.  File: regex.info, Node: GNU Translate Tables, Next: Using Registers, Prev: Searching with Fastmaps, Up: GNU Regex Functions GNU Translate Tables -------------------- If you set the `translate' field of a pattern buffer to a translate table, then the 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 "translate table" is an array indexed by the characters in your character set. Under the 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 C, they use `translate[C]' in its place, with one exception: the character after a `\' is not translated. (This ensures that, the operators, e.g., `\B' and `\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.(1) Such a table would map all characters except lowercase letters to themselves, and lowercase letters to the corresponding uppercase ones. Under the ASCII encoding, here's how you could initialize such a table (we'll call it `case_fold'): for (i = 0; i < 256; i++) case_fold[i] = i; for (i = 'a'; i <= 'z'; i++) case_fold[i] = i - ('a' - 'A'); You tell Regex to use a translate table on a given pattern buffer by assigning that table's address to the `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. ---------- Footnotes ---------- (1) A table that maps all uppercase letters to the corresponding lowercase ones would work just as well for this purpose.  File: regex.info, Node: Using Registers, Next: Freeing GNU Pattern Buffers, Prev: GNU Translate Tables, Up: GNU Regex Functions 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 REGS argument to a GNU matching or searching function (*note GNU Matching::. and *Note GNU Searching::), i.e., the address of a structure of this type, as defined in `regex.h': struct re_registers { unsigned num_regs; regoff_t *start; regoff_t *end; }; Except for (possibly) the NUM_REGS'th element (see below), the Ith element of the `start' and `end' arrays records information about the Ith 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 `start' and `end' arrays are allocated in various ways, depending on the value of the `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 `regs_allocated' is `REGS_UNALLOCATED', the matcher allocates 1 + RE_NSUB (another field in the pattern buffer; *note GNU Pattern Buffers::.). The extra element is set to -1, and sets `regs_allocated' to `REGS_REALLOCATE'. Then on subsequent calls with the same pattern buffer and REGS arguments, the matcher reallocates more space if necessary. It would perhaps be more logical to make the `regs_allocated' field part of the `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. `re_compile_pattern' sets `regs_allocated' to `REGS_UNALLOCATED', so if you use the GNU regular expression functions, you get this behavior by default. xx document re_set_registers 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 `regs_allocated' is `REGS_FIXED' the matcher simply fills that array. The following examples illustrate the information recorded in the `re_registers' structure. (In all of them, `(' represents the open-group and `)' the close-group operator. The first character in the string STRING is at index 0.) * If the regular expression has an I-th group not contained within another group that matches a substring of STRING, then the function sets `REGS->start[I]' to the index in STRING where the substring matched by the I-th group begins, and `REGS->end[I]' to the index just beyond that substring's end. The function sets `REGS->start[0]' and `REGS->end[0]' to analogous information about the entire pattern. For example, when you match `((a)(b))' against `ab', you get: * 0 in `REGS->start[0]' and 2 in `REGS->end[0]' * 0 in `REGS->start[1]' and 2 in `REGS->end[1]' * 0 in `REGS->start[2]' and 1 in `REGS->end[2]' * 1 in `REGS->start[3]' and 2 in `REGS->end[3]' * 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 *last* matched. For example, when you match the pattern `(a)*' against the string `aa', you get: * 0 in `REGS->start[0]' and 2 in `REGS->end[0]' * 1 in `REGS->start[1]' and 2 in `REGS->end[1]' * If the 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 `REGS->start[I]' and `REGS->end[I]' to -1. For example, when you match the pattern `(a)*b' against the string `b', you get: * 0 in `REGS->start[0]' and 1 in `REGS->end[0]' * -1 in `REGS->start[1]' and -1 in `REGS->end[1]' * If the I-th group matches a zero-length string, then the function sets `REGS->start[I]' and `REGS->end[I]' to the index just beyond that zero-length string. For example, when you match the pattern `(a*)b' against the string `b', you get: * 0 in `REGS->start[0]' and 1 in `REGS->end[0]' * 0 in `REGS->start[1]' and 0 in `REGS->end[1]' * If an I-th group contains a J-th group in turn not contained within any other group within group I and the function reports a match of the I-th group, then it records in `REGS->start[J]' and `REGS->end[J]' the last match (if it matched) of the J-th group. For example, when you match the pattern `((a*)b)*' against the string `abb', group 2 last matches the empty string, so you get what it previously matched: * 0 in `REGS->start[0]' and 3 in `REGS->end[0]' * 2 in `REGS->start[1]' and 3 in `REGS->end[1]' * 2 in `REGS->start[2]' and 2 in `REGS->end[2]' When you match the pattern `((a)*b)*' against the string `abb', group 2 doesn't participate in the last match, so you get: * 0 in `REGS->start[0]' and 3 in `REGS->end[0]' * 2 in `REGS->start[1]' and 3 in `REGS->end[1]' * 0 in `REGS->start[2]' and 1 in `REGS->end[2]' * If an I-th group contains a J-th group in turn not contained within any other group within group I and the function sets `REGS->start[I]' and `REGS->end[I]' to -1, then it also sets `REGS->start[J]' and `REGS->end[J]' to -1. For example, when you match the pattern `((a)*b)*c' against the string `c', you get: * 0 in `REGS->start[0]' and 1 in `REGS->end[0]' * -1 in `REGS->start[1]' and -1 in `REGS->end[1]' * -1 in `REGS->start[2]' and -1 in `REGS->end[2]'  File: regex.info, Node: Freeing GNU Pattern Buffers, Prev: Using Registers, Up: GNU Regex Functions Freeing GNU Pattern Buffers --------------------------- To free any allocated fields of a pattern buffer, you can use the POSIX function described in *Note Freeing POSIX Pattern Buffers::, since the type `regex_t'--the type for POSIX pattern buffers--is equivalent to the type `re_pattern_buffer'. After freeing a pattern buffer, you need to again compile a regular expression in it (*note GNU Regular Expression Compiling::.) before passing it to a matching or searching function.  File: regex.info, Node: POSIX Regex Functions, Next: BSD Regex Functions, Prev: GNU Regex Functions, Up: Programming with Regex POSIX Regex Functions ===================== If you're writing code that has to be POSIX compatible, you'll need to use these functions. Their interfaces are as specified by 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 ()  File: regex.info, Node: POSIX Pattern Buffers, Next: POSIX Regular Expression Compiling, Up: POSIX Regex Functions POSIX Pattern Buffers --------------------- To compile or match a given regular expression the POSIX way, you must supply a pattern buffer exactly the way you do for GNU (*note GNU Pattern Buffers::.). POSIX pattern buffers have type `regex_t', which is equivalent to the GNU pattern buffer type `re_pattern_buffer'.  File: regex.info, Node: POSIX Regular Expression Compiling, Next: POSIX Matching, Prev: POSIX Pattern Buffers, Up: POSIX Regex Functions POSIX Regular Expression Compiling ---------------------------------- With 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 `regcomp'. To compile a pattern buffer, use: int regcomp (regex_t *PREG, const char *REGEX, int CFLAGS) PREG is the initialized pattern buffer's address, REGEX is the regular expression's address, and CFLAGS is the compilation flags, which Regex considers as a collection of bits. Here are the valid bits, as defined in `regex.h': `REG_EXTENDED' says to use POSIX Extended Regular Expression syntax; if this isn't set, then says to use POSIX Basic Regular Expression syntax. `regcomp' sets PREG's `syntax' field accordingly. `REG_ICASE' says to ignore case; `regcomp' sets PREG's `translate' field to a translate table which ignores case, replacing anything you've put there before. `REG_NOSUB' says to set PREG's `no_sub' field; *note POSIX Matching::., for what this means. `REG_NEWLINE' says that a: * match-any-character operator (*note Match-any-character Operator::.) doesn't match a newline. * nonmatching list not containing a newline (*note List Operators::.) matches a newline. * match-beginning-of-line operator (*note Match-beginning-of-line Operator::.) matches the empty string immediately after a newline, regardless of how `REG_NOTBOL' is set (*note POSIX Matching::., for an explanation of `REG_NOTBOL'). * match-end-of-line operator (*note Match-beginning-of-line Operator::.) matches the empty string immediately before a newline, regardless of how `REG_NOTEOL' is set (*note POSIX Matching::., for an explanation of `REG_NOTEOL'). If `regcomp' successfully compiles the regular expression, it returns zero and sets `*PATTERN_BUFFER' to the compiled pattern. Except for `syntax' (which it sets as explained above), it also sets the same fields the same way as does the GNU compiling function (*note GNU Regular Expression Compiling::.). If `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.) `REG_BADRPT' For example, the consecutive repetition operators `**' in `a**' are invalid. As another example, if the syntax is extended regular expression syntax, then the repetition operator `*' with nothing on which to operate in `*' is invalid. `REG_BADBR' For example, the COUNT `-1' in `a\{-1' is invalid. `REG_EBRACE' For example, `a\{1' is missing a close-interval operator. `REG_EBRACK' For example, `[a' is missing a close-list operator. `REG_ERANGE' For example, the range ending point `z' that collates lower than does its starting point `a' in `[z-a]' is invalid. Also, the range with the character class `[:alpha:]' as its starting point in `[[:alpha:]-|]'. `REG_ECTYPE' For example, the character class name `foo' in `[[:foo:]' is invalid. `REG_EPAREN' For example, `a\)' is missing an open-group operator and `\(a' is missing a close-group operator. `REG_ESUBREG' For example, the back reference `\2' that refers to a nonexistent subexpression in `\(a\)\2' is invalid. `REG_EEND' Returned when a regular expression causes no other more specific error. `REG_EESCAPE' For example, the trailing backslash `\' in `a\' is invalid, as is the one in `\'. `REG_BADPAT' For example, in the extended regular expression syntax, the empty group `()' in `a()b' is invalid. `REG_ESIZE' Returned when a regular expression needs a pattern buffer larger than 65536 bytes. `REG_ESPACE' Returned when a regular expression makes Regex to run out of memory.  File: regex.info, Node: POSIX Matching, Next: Reporting Errors, Prev: POSIX Regular Expression Compiling, Up: POSIX Regex Functions POSIX Matching -------------- Matching the 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 (*note POSIX Regular Expression Compiling::.), you can ask the matcher to match that pattern against a string using: int regexec (const regex_t *PREG, const char *STRING, size_t NMATCH, regmatch_t PMATCH[], int EFLAGS) PREG is the address of a pattern buffer for a compiled pattern. STRING is the string you want to match. *Note Using Byte Offsets::, for an explanation of PMATCH. If you pass zero for NMATCH or you compiled PREG with the compilation flag `REG_NOSUB' set, then `regexec' will ignore PMATCH; otherwise, you must allocate it to have at least NMATCH elements. `regexec' will record NMATCH byte offsets in PMATCH, and set to -1 any unused elements up to PMATCH`[NMATCH]' - 1. EFLAGS specifies "execution flags"--namely, the two bits `REG_NOTBOL' and `REG_NOTEOL' (defined in `regex.h'). If you set `REG_NOTBOL', then the match-beginning-of-line operator (*note 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. `REG_NOTEOL' works analogously for the match-end-of-line operator (*note Match-end-of-line Operator::.); it exists for symmetry. `regexec' tries to find a match for PREG in STRING according to the syntax in PREG's `syntax' field. (*Note POSIX Regular Expression Compiling::, for how to set it.) The function returns zero if the compiled pattern matches STRING and `REG_NOMATCH' (defined in `regex.h') if it doesn't.  File: regex.info, Node: Reporting Errors, Next: Using Byte Offsets, Prev: POSIX Matching, Up: POSIX Regex Functions Reporting Errors ---------------- If either `regcomp' or `regexec' fail, they return a nonzero error code, the possibilities for which are defined in `regex.h'. *Note POSIX Regular Expression Compiling::, and *Note POSIX Matching::, for what these codes mean. To get an error string corresponding to these codes, you can use: size_t regerror (int ERRCODE, const regex_t *PREG, char *ERRBUF, size_t ERRBUF_SIZE) ERRCODE is an error code, PREG is the address of the pattern buffer which provoked the error, ERRBUF is the error buffer, and ERRBUF_SIZE is ERRBUF's size. `regerror' returns the size in bytes of the error string corresponding to ERRCODE (including its terminating null). If ERRBUF and ERRBUF_SIZE are nonzero, it also returns in ERRBUF the first ERRBUF_SIZE - 1 characters of the error string, followed by a null. eRRBUF_SIZE must be a nonnegative number less than or equal to the size in bytes of ERRBUF. You can call `regerror' with a null ERRBUF and a zero ERRBUF_SIZE to determine how large ERRBUF need be to accommodate `regerror''s error string.  File: regex.info, Node: Using Byte Offsets, Next: Freeing POSIX Pattern Buffers, Prev: Reporting Errors, Up: POSIX Regex Functions Using Byte Offsets ------------------ In POSIX, variables of type `regmatch_t' hold analogous information, but are not identical to, GNU's registers (*note Using Registers::.). To get information about registers in POSIX, pass to `regexec' a nonzero PMATCH of type `regmatch_t', i.e., the address of a structure of this type, defined in `regex.h': typedef struct { regoff_t rm_so; regoff_t rm_eo; } regmatch_t; When reading in *Note Using Registers::, about how the matching function stores the information into the registers, substitute PMATCH for REGS, `PMATCH[I]->rm_so' for `REGS->start[I]' and `PMATCH[I]->rm_eo' for `REGS->end[I]'.  File: regex.info, Node: Freeing POSIX Pattern Buffers, Prev: Using Byte Offsets, Up: POSIX Regex Functions Freeing POSIX Pattern Buffers ----------------------------- To free any allocated fields of a pattern buffer, use: void regfree (regex_t *PREG) PREG is the pattern buffer whose allocated fields you want freed. `regfree' also sets PREG's `allocated' and `used' fields to zero. After freeing a pattern buffer, you need to again compile a regular expression in it (*note POSIX Regular Expression Compiling::.) before passing it to the matching function (*note POSIX Matching::.).  File: regex.info, Node: BSD Regex Functions, Prev: POSIX Regex Functions, Up: Programming with Regex BSD Regex Functions =================== If you're writing code that has to be Berkeley UNIX compatible, you'll need to use these functions whose interfaces are the same as those in Berkeley UNIX. * Menu: * BSD Regular Expression Compiling:: re_comp () * BSD Searching:: re_exec ()  File: regex.info, Node: BSD Regular Expression Compiling, Next: BSD Searching, Up: BSD Regex Functions BSD Regular Expression Compiling -------------------------------- With Berkeley 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 `re_syntax_options' (declared in `regex.h' to some syntax (*note Regular Expression Syntax::.). To compile a regular expression use: char * re_comp (char *REGEX) REGEX is the address of a null-terminated regular expression. `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 `re_comp' with the null string (*not* the empty string) as the argument, it doesn't change the contents of the pattern buffer. If `re_comp' successfully compiles the regular expression, it returns zero. If it can't compile the regular expression, it returns an error string. `re_comp''s error messages are identical to those of `re_compile_pattern' (*note GNU Regular Expression Compiling::.).  File: regex.info, Node: BSD Searching, Prev: BSD Regular Expression Compiling, Up: BSD Regex Functions BSD Searching ------------- Searching the Berkeley 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 `re_comp' (*note BSD Regular Expression Compiling::.), you can ask Regex to search for that pattern in a string using: int re_exec (char *STRING) STRING is the address of the null-terminated string in which you want to search. `re_exec' returns either 1 for success or 0 for failure. It automatically uses a GNU fastmap (*note Searching with Fastmaps::.).