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regexp(5)							     regexp(5)

NAME
     regexp:  compile, step, advance - regular expression compile and match
     routines

SYNOPSIS
     #define INIT declarations
     #define GETC(void) getc code
     #define PEEKC(void) peekc code
     #define UNGETC(void) ungetc code
     #define RETURN(ptr) return code
     #define ERROR(val) error code
     #include <regexp.h>
     char *compile(char *instring, char *expbuf, char *endbuf, int eof);
     int step(char *string, char *expbuf);
     int advance(char *string, char *expbuf);
     extern char *loc1, *loc2, *locs;

DESCRIPTION
     These functions are general purpose regular expression matching routines
     to be used in programs that perform regular expression matching.  These
     functions are defined by the regexp.h header file.

     The functions step and advance do pattern matching given a character
     string and a compiled regular expression as input.

     The function compile takes as input a regular expression as defined below
     and produces a compiled expression that can be used with step or advance.

     A regular expression specifies a set of character strings.	 A member of
     this set of strings is said to be matched by the regular expression.
     Some characters have special meaning when used in a regular expression;
     other characters stand for themselves.

     The regular expressions available for use with the regexp functions are
     constructed as follows:

     Expression	 Meaning

     c		 the character c where c is not a special character.

     \c		 the character c where c is any character, except a digit in
		 the range 1-9.

     ^		 the beginning of the line being compared.

     $		 the end of the line being compared.

									Page 1

regexp(5)							     regexp(5)

     .		 any character in the input.

     [s]	 any character in the set s, where s is a sequence of
		 characters and/or a range of characters, for example, [c-c].

     [^s]	 any character not in the set s, where s is defined as above.

     r*		 zero or more successive occurrences of the regular expression
		 r.  The longest leftmost match is chosen.

     rx		 the occurrence of regular expression r followed by the
		 occurrence of regular expression x.  (Concatenation)

     r\{m,n\}	 any number of m through n successive occurrences of the
		 regular expression r.	The regular expression r\{m\} matches
		 exactly m occurrences; r\{m,\} matches at least m
		 occurrences.

     \(r\)	 the regular expression r.  When \n (where n is a number
		 greater than zero) appears in a constructed regular
		 expression, it stands for the regular expression x where x is
		 the nth regular expression enclosed in \( and \) that
		 appeared earlier in the constructed regular expression.  For
		 example, \(r\)x\(y\)z\2 is the concatenation of regular
		 expressions rxyzy.

     Characters that have special meaning except when they appear within
     square brackets ([]) or are preceded by \ are:  ., *, [, \.  Other
     special characters, such as $ have special meaning in more restricted
     contexts.

     The character ^ at the beginning of an expression permits a successful
     match only immediately after a newline, and the character $ at the end of
     an expression requires a trailing newline.

     Two characters have special meaning only when used within square
     brackets.	The character - denotes a range, [c-c], unless it is just
     after the open bracket or before the closing bracket, [-c] or [c-] in
     which case it has no special meaning.  When used within brackets, the
     character ^ has the meaning complement of if it immediately follows the
     open bracket (example: [^c]); elsewhere between brackets (example: [c^])
     it stands for the ordinary character ^.

     The special meaning of the \ operator can be escaped only by preceding it
     with another \, for example, \\.

     Programs must have the following five macros declared before the #include
     regexp.h statement.  These macros are used by the compile routine.	 The
     macros GETC, PEEKC, and UNGETC operate on the regular expression given as
     input to compile.

									Page 2

regexp(5)							     regexp(5)

     GETC	    This macro returns the value of the next character (byte)
		    in the regular expression pattern.	Successive calls to
		    GETC should return successive characters of the regular
		    expression.

     PEEKC	    This macro returns the next character (byte) in the
		    regular expression.	 Immediately successive calls to PEEKC
		    should return the same character, which should also be the
		    next character returned by GETC.

     UNGETC	    This macro causes the argument c to be returned by the
		    next call to GETC and PEEKC.  No more than one character
		    of pushback is ever needed and this character is
		    guaranteed to be the last character read by GETC.  The
		    return value of the macro UNGETC(c) is always ignored.

     RETURN(ptr)    This macro is used on normal exit of the compile routine.
		    The value of the argument ptr is a pointer to the
		    character after the last character of the compiled regular
		    expression.	 This is useful to programs which have memory
		    allocation to manage.

     ERROR(val)	    This macro is the abnormal return from the compile
		    routine.  The argument val is an error number [see ERRORS
		    below for meanings].  This call should never return.

     The syntax of the compile routine is as follows:

	  compile(instring, expbuf, endbuf, eof)

     The first parameter, instring, is never used explicitly by the compile
     routine but is useful for programs that pass down different pointers to
     input characters.	It is sometimes used in the INIT declaration (see
     below).  Programs which call functions to input characters or have
     characters in an external array can pass down a value of (char *)0 for
     this parameter.

     The next parameter, expbuf, is a character pointer.  It points to the
     place where the compiled regular expression will be placed.

     The parameter endbuf is one more than the highest address where the
     compiled regular expression may be placed.	 If the compiled expression
     cannot fit in (endbuf-expbuf) bytes, a call to ERROR(50) is made.

     The parameter eof is the character which marks the end of the regular
     expression.  This character is usually a /.

     Each program that includes the regexp.h header file must have a #define
     statement for INIT.  It is used for dependent declarations and
     initializations.  Most often it is used to set a register variable to
     point to the beginning of the regular expression so that this register
     variable can be used in the declarations for GETC, PEEKC, and UNGETC.

									Page 3

regexp(5)							     regexp(5)

     Otherwise it can be used to declare external variables that might be used
     by GETC, PEEKC and UNGETC.	 [See EXAMPLE below.]

     The first parameter to the step and advance functions is a pointer to a
     string of characters to be checked for a match.  This string should be
     null terminated.

     The second parameter, expbuf, is the compiled regular expression which
     was obtained by a call to the function compile.

     The function step returns non-zero if some substring of string matches
     the regular expression in expbuf and zero if there is no match.  If there
     is a match, two external character pointers are set as a side effect to
     the call to step.	The variable loc1 points to the first character that
     matched the regular expression; the variable loc2 points to the character
     after the last character that matches the regular expression.  Thus if
     the regular expression matches the entire input string, loc1 will point
     to the first character of string and loc2 will point to the null at the
     end of string.

     The function advance returns non-zero if the initial substring of string
     matches the regular expression in expbuf.	If there is a match, an
     external character pointer, loc2, is set as a side effect.	 The variable
     loc2 points to the next character in string after the last character that
     matched.

     When advance encounters a * or \{ \} sequence in the regular expression,
     it will advance its pointer to the string to be matched as far as
     possible and will recursively call itself trying to match the rest of the
     string to the rest of the regular expression.  As long as there is no
     match, advance will back up along the string until it finds a match or
     reaches the point in the string that initially matched the	 * or \{ \}.
     It is sometimes desirable to stop this backing up before the initial
     point in the string is reached.  If the external character pointer locs
     is equal to the point in the string at sometime during the backing up
     process, advance will break out of the loop that backs up and will return
     zero.

     The external variables circf, sed, and nbra are reserved.

DIAGNOSTICS
     The function compile uses the macro RETURN on success and the macro ERROR
     on failure (see above).  The functions step and advance return non-zero
     on a successful match and zero if there is no match.  Errors are:

	  11   range endpoint too large.

	  16   bad number.

	  25   \ digit out of range.

									Page 4

regexp(5)							     regexp(5)

	  36   illegal or missing delimiter.

	  41   no remembered search string.

	  42   \( \) imbalance.

	  43   too many \(.

	  44   more than 2 numbers given in \{ \}.

	  45   } expected after \.

	  46   first number exceeds second in \{ \}.

	  49   [ ] imbalance.

	  50   regular expression overflow.

EXAMPLE
     The following is an example of how the regular expression macros and
     calls might be defined by an application program:

	  #define INIT	     register char *sp = instring;
	  #define GETC	     (*sp++)
	  #define PEEKC	     (*sp)
	  #define UNGETC(c)  (--sp)
	  #define RETURN(*c) return;
	  #define ERROR(c)   regerr
	  #include <regexp.h>
	   . . .
		(void) compile(*argv, expbuf, &expbuf[ESIZE],'\0');
	   . . .
		if (step(linebuf, expbuf))
				  succeed;

									Page 5

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