REGEXP(6)                        Games Manual                        REGEXP(6)

       regexp - regular expression notation

       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

       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 expression.

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