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Plan 9 - man page for regexp (plan9 section 6)

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REGEXP(6)										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 regu-
       lar 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 expression.

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

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