plan9 man page for regexp

REGEXP(6)							   Games Manual 							 REGEXP(6)

NAME
       regexp - regular expression notation

DESCRIPTION
       A  regular  expression  specifies  a  set  of  strings of characters.  A member of this set of strings is said to be matched by the regular
       expression.  In many applications a delimiter character, commonly bounds a regular expression.  In the following specification for  regular
       expressions the word `character' means any character (rune) but newline.

       The syntax for a regular expression e0 is

	      e3:  literal | charclass | '.' | '^' | '$' | '(' e0 ')'

	      e2:  e3
		|  e2 REP

	      REP: '*' | '+' | '?'

	      e1:  e2
		|  e1 e2

	      e0:  e1
		|  e0 '|' e1

       A literal is any non-metacharacter, or a metacharacter (one of .*+?[]()|^$), or the delimiter preceded by

       A  charclass  is  a  nonempty string s bracketed [s] (or [^s]); it matches any character in (or not in) s.  A negated character class never
       matches newline.  A substring a-b, with a and b in ascending order, stands for the inclusive range of characters between a and  b.   In	s,
       the  metacharacters  an initial and the regular expression delimiter must be preceded by a other metacharacters have no special meaning and
       may appear unescaped.

       A matches any character.

       A matches the beginning of a line; matches the end of the line.

       The REP operators match zero or more (*), one or more (+), zero or one (?), instances respectively of the preceding regular expression e2.

       A concatenated regular expression, e1e2, matches a match to e1 followed by a match to e2.

       An alternative regular expression, e0|e1, matches either a match to e0 or a match to e1.

       A match to any part of a regular expression extends as far as possible without preventing a match to the remainder of the  regular  expres-
       sion.

SEE ALSO
       awk(1), ed(1), sam(1), sed(1), regexp(2)

																	 REGEXP(6)