129 lines
2 KiB
Text
129 lines
2 KiB
Text
.TH REGEXP 6
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.SH NAME
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regexp \- regular expression notation
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.SH DESCRIPTION
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A
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.I "regular expression"
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specifies
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a set of strings of characters.
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A member of this set of strings is said to be
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.I matched
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by the regular expression. In many applications
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a delimiter character, commonly
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.LR / ,
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bounds a regular expression.
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In the following specification for regular expressions
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the word `character' means any character (rune) but newline.
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.PP
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The syntax for a regular expression
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.B e0
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is
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.IP
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.EX
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e3: literal | charclass | '.' | '^' | '$' | '(' e0 ')'
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e2: e3
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| e2 REP
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REP: '*' | '+' | '?'
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e1: e2
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| e1 e2
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e0: e1
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| e0 '|' e1
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.EE
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.PP
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A
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.B literal
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is any non-metacharacter, or a metacharacter
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(one of
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.BR .*+?[]()|\e^$ ),
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or the delimiter
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preceded by
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.LR \e .
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.PP
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A
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.B charclass
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is a nonempty string
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.I s
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bracketed
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.BI [ \|s\| ]
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(or
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.BI [^ s\| ]\fR);
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it matches any character in (or not in)
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.IR s .
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A negated character class never
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matches newline.
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A substring
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.IB a - b\f1,
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with
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.I a
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and
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.I b
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in ascending
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order, stands for the inclusive
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range of
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characters between
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.I a
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and
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.IR b .
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In
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.IR s ,
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the metacharacters
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.LR - ,
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.LR ] ,
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an initial
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.LR ^ ,
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and the regular expression delimiter
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must be preceded by a
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.LR \e ;
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other metacharacters
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have no special meaning and
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may appear unescaped.
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.PP
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A
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.L .
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matches any character.
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.PP
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A
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.L ^
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matches the beginning of a line;
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.L $
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matches the end of the line.
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.PP
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The
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.B REP
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operators match zero or more
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.RB ( * ),
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one or more
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.RB ( + ),
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zero or one
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.RB ( ? ),
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instances respectively of the preceding regular expression
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.BR e2 .
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.PP
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A concatenated regular expression,
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.BR "e1\|e2" ,
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matches a match to
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.B e1
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followed by a match to
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.BR e2 .
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.PP
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An alternative regular expression,
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.BR "e0\||\|e1" ,
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matches either a match to
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.B e0
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or a match to
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.BR e1 .
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.PP
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A match to any part of a regular expression
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extends as far as possible without preventing
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a match to the remainder of the regular expression.
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.SH "SEE ALSO"
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.IR awk (1),
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.IR ed (1),
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.IR grep (1),
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.IR sam (1),
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.IR sed (1),
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.IR regexp (2)
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