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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 reg-
       ular expression matching routines to be used in programs  that  perform
       regular  expression  matching. These functions are defined by the <&lt;reg-
       exp.h>&gt; header.

       The functions step() and advance() do pattern matching given a  charac-
       ter 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 characters 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 con-
                secutive 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 occur-
                       rences;  \{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  con-
                       catenation  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 \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 consisting  of
                       two repeated appearances of the same string.



       An RE may be constrained to match words.

       3.1             \<&lt;  constrains  a RE to match the beginning of a string
                       or to follow a character that is not  a  digit,  under-
                       score,  or  letter. The first character matching the RE
                       must be a digit, underscore, or letter.



       3.2             \>&gt; 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 con-
                       strains 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 (respectively
           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 under-
           stood 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 pre-
           ceding  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 con-
       texts.

       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 brack-
       ets.  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 charac-
       ter ^ 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 <&lt;regexp.h>&gt; 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  guar-
                       anteed  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() rou-
                       tine. The value of the argument ptr is a pointer to the
                       character after the last character of the compiled reg-
                       ular  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.



   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 com-
       pile() routine but is useful for  programs  that  pass  down  different
       pointers to input characters. It is sometimes used in the INIT declara-
       tion (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  <&lt;regexp.h>&gt;  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 vari-
       able loc2 points to the next character in string after the last charac-
       ter that matched.

       When  advance() encounters a * or \{ \} sequence in the regular expres-
       sion, 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 <&lt;regexp.h>&gt;
        . . .
             (void) compile(*argv, expbuf, &&amp;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 5.10                        20 May 2002                        regexp(5)