regexp(5)						Standards, Environments, and Macros						 regexp(5)

NAME

       regexp, compile, step, advance - simple 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

       extern char *loc1, *loc2, *locs;

       #include <regexp.h>

       char *compile(char *instring, char *expbuf, const char *endfug, int eof);

       int step(const char *string, const char *expbuf);

       int advance(const char *string, const char *expbuf);

DESCRIPTION

       Regular	Expressions  (REs)  provide a mechanism to select specific strings from a set of character strings. The Simple Regular Expressions
       described below differ from the	Internationalized Regular Expressions described on the	regex(5) manual page in the following ways:

	   o	  only Basic Regular Expressions are supported

	   o	  the Internationalization features--character class, equivalence class, and multi-character collation--are not supported.

       The functions step(), advance(), and compile() 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.

       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().

   Basic Regular Expressions
       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 following one-character REs match a single character:

       1.1    An ordinary character ( not one of those discussed in 1.2 below) is a one-character RE that matches itself.

       1.2    A backslash () followed by any special character is a one-character RE that matches the special character itself. The special char-
	      acters are:

	      a.    ., *, [, and  (period, asterisk, left square bracket, and backslash, respectively), which are  always  special,  except  when
		    they appear within square brackets ([]; see 1.4 below).

	      b.    ^  (caret  or  circumflex),  which is special at the beginning of an entire RE (see 4.1 and 4.3 below), or when it immediately
		    follows the left of a pair of square brackets ([]) (see 1.4 below).

	      c.    $ (dollar sign), which is special at the end of an entire RE (see 4.2 below).

	      d.    The character used to bound (that is, delimit) an entire RE, which is special for that RE (for example, see how slash  (/)	is
		    used in the g command, below.)

       1.3    A period (.) is a one-character RE that matches any character except new-line.

       1.4    A  non-empty  string  of	characters  enclosed  in square brackets ([]) is a one-character RE that matches any one character in that
	      string. If, however, the first character of the string is a circumflex (^), the one-character RE matches any character  except  new-
	      line and the remaining characters in the string. The ^ has this special meaning only if it occurs first in the string. The minus (-)
	      may be used to indicate a range of consecutive characters; for example, [0-9] is equivalent to [0123456789]. The - loses	this  spe-
	      cial  meaning if it occurs first (after an initial ^, if any) or last in the string. The right square bracket (]) does not terminate
	      such a string when it is the first character within it (after an initial ^, if any); for example,  []a-f]  matches  either  a  right
	      square bracket (]) or one of the ASCII letters a through f inclusive. The four characters listed in 1.2.a above stand for themselves
	      within such a string of characters.

       The following rules may be used to construct REs from one-character REs:

       2.1    A one-character RE is a RE that matches whatever the one-character RE matches.

       2.2    A one-character RE followed by an asterisk (*) is a RE that matches 0 or more occurrences of the one-character RE. If there  is  any
	      choice, the longest leftmost string that permits a match is chosen.

       2.3    A  one-character	RE  followed by {m}, {m,}, or {m,n} is a RE that matches a range of occurrences of the one-character RE. The
	      values of m and n must be non-negative integers less than 256; {m} matches exactly m occurrences; {m,} matches at least m occur-
	      rences; {m,n} matches any number of occurrences between m and n inclusive. Whenever a choice exists, the RE matches as many occur-
	      rences as possible.

       2.4    The concatenation of REs is a RE that matches the concatenation of the strings matched by each component of the RE.

       2.5    A RE enclosed between the character sequences ( and ) is a RE that matches whatever the unadorned RE matches.

       2.6    The expression 
 matches the same string of characters as was matched by an expression enclosed between ( and )  earlier  in  the
	      same  RE.  Here  n is a digit; the sub-expression specified is that beginning with the n-th occurrence of ( counting from the left.
	      For example, the expression ^(.*)1$ matches a line consisting of two repeated appearances of the same string.

       An RE may be constrained to match words.

       3.1    < constrains a RE to match the beginning of a string or to follow a character that is not a digit, underscore, or letter. The first
	      character matching the RE must be a digit, underscore, or letter.

       3.2    > constrains a RE to match the end of a string or to precede a character that is not a digit, underscore, or letter.

       An entire RE may be constrained to match only an initial segment or final segment of a line (or both).

       4.1    A circumflex (^) at the beginning of an entire RE constrains that RE to match an initial segment of a line.

       4.2    A dollar sign ($) at the end of an entire RE constrains that RE to match a final segment of a line.

       4.3    The construction ^entire RE$ constrains the entire RE to match the entire line.

       The null RE (for example, //) is equivalent to the last RE encountered.

   Addressing with REs
       Addresses are constructed as follows:

	   1.	  The character "." addresses the current line.

	   2.	  The character "$" addresses the last line of the buffer.

	   3.	  A decimal number n addresses the n-th line of the buffer.

	   4.	  'x  addresses  the  line marked with the mark name character x, which must be an ASCII lower-case letter (a-z). Lines are marked
		  with the k command described below.

	   5.	  A RE enclosed by slashes (/) addresses the first line found by searching forward from the line following the current line toward
		  the  end of the buffer and stopping at the first line containing a string matching the RE. If necessary, the search wraps around
		  to the beginning of the buffer and continues up to and including the current line, so that the entire buffer is searched.

	   6.	  A RE enclosed in question marks (?) addresses the first line found by searching backward from the  line  preceding  the  current
		  line	toward	the  beginning of the buffer and stopping at the first line containing a string matching the RE. If necessary, the
		  search wraps around to the end of the buffer and continues up to and including the current line.

	   7.	  An address followed by a plus sign (+) or a minus sign (-) followed by a decimal number specifies  that  address  plus  (respec-
		  tively minus) the indicated number of lines. A shorthand for .+5 is .5.

	   8.	  If  an  address  begins  with  + or -, the addition or subtraction is taken with respect to the current line; for example, -5 is
		  understood to mean .-5.

	   9.	  If an address ends with + or -, then 1 is added to or subtracted from the address, respectively. As a consequence of	this  rule
		  and  of  Rule 8, immediately above, the address - refers to the line preceding the current line. (To maintain compatibility with
		  earlier versions of the editor, the character ^ in addresses is entirely equivalent to -.) Moreover, trailing + and - characters
		  have a cumulative effect, so -- refers to the current line less 2.

	   10.	  For convenience, a comma (,) stands for the address pair 1,$, while a semicolon (;) stands for the pair .,$.

   Characters With Special Meaning
       Characters  that have special meaning except when they appear within square brackets ([]) or are preceded by  are:  ., *, [, . Other spe-
       cial 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  char-
       acter  ^  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 \.

   Macros
       Programs must have the following five macros declared before the #include <regexp.h> statement. These macros are used by the compile() rou-
       tine. The macros GETC, PEEKC, and UNGETC operate on the regular expression given as input to compile().

       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 man-
		      age.

       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.

   compile()
       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 point-
       ers  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. Otherwise it can be used to declare external variables that might be
       used by GETC, PEEKC and UNGETC. (See EXAMPLES below.)

   step(), advance()
       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	0 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 char-
       acter 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.

EXAMPLES

       Example 1 Using Regular Expression Macros and Calls

       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],'');
	  . . .
	       if (step(linebuf, expbuf))
				 succeed;

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.

       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.

SEE ALSO

       regex(5)

SunOS 5.11							    20 May 2002 							 regexp(5)