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OpenSolaris 2009.06 - man page for advance (opensolaris section 5)

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   Inter-
       nationalized  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 com-
       piled 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 characters are:

	      a.    ., *, [, and \ (period, asterisk, left square bracket, and backslash, respec-
		    tively), 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-charac-
	      ter  RE that matches any one character in that string. If, however, the first char-
	      acter 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  indi-
	      cate  a  range  of  consecutive  characters;  for  example,  [0-9] is equivalent to
	      [0123456789]. The - loses this special 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 occurrences; \{m,n\} matches any number of occurrences between m
	      and  n  inclusive.  Whenever a choice exists, the RE matches as many occurrences 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 what-
	      ever the unadorned RE matches.

       2.6    The expression \n 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 con-
	      sisting 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  for-
		  ward	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  deci-
		  mal  number specifies that address plus (respectively minus) the indicated num-
		  ber 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 main-
		  tain 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 special characters, such as  $  have  special
       meaning in more restricted contexts.

       The  character ^ at the beginning of an expression permits a successful match only immedi-
       ately 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 \\.

   Macros
       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().

       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 mem-
		      ory 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.

   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 pointers to input characters. It is sometimes
       used  in  the INIT declaration (see below). Programs which call functions to input charac-
       ters 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 com-
       piled 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 char-
       acter 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  regu-
       lar  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.

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],'\0');
	  . . .
	       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)


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