1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
|
.TH REGEXP 7
.SH NAME
regexp \- Plan 9 regular expression notation
.SH DESCRIPTION
This manual page describes the regular expression
syntax used by the Plan 9 regular expression library
.IR regexp (3).
It is the form used by
.IR egrep (1)
before
.I egrep
got complicated.
.PP
A
.I "regular expression"
specifies
a set of strings of characters.
A member of this set of strings is said to be
.I matched
by the regular expression. In many applications
a delimiter character, commonly
.LR / ,
bounds a regular expression.
In the following specification for regular expressions
the word `character' means any character (rune) but newline.
.PP
The syntax for a regular expression
.B e0
is
.IP
.EX
e3: literal | charclass | '.' | '^' | '$' | '(' e0 ')'
e2: e3
| e2 REP
REP: '*' | '+' | '?'
e1: e2
| e1 e2
e0: e1
| e0 '|' e1
.EE
.PP
A
.B literal
is any non-metacharacter, or a metacharacter
(one of
.BR .*+?[]()|\e^$ ),
or the delimiter
preceded by
.LR \e .
.PP
A
.B charclass
is a nonempty string
.I s
bracketed
.BI [ \|s\| ]
(or
.BI [^ s\| ]\fR);
it matches any character in (or not in)
.IR s .
A negated character class never
matches newline.
A substring
.IB a - b\f1,
with
.I a
and
.I b
in ascending
order, stands for the inclusive
range of
characters between
.I a
and
.IR b .
In
.IR s ,
the metacharacters
.LR - ,
.LR ] ,
an initial
.LR ^ ,
and the regular expression delimiter
must be preceded by a
.LR \e ;
other metacharacters
have no special meaning and
may appear unescaped.
.PP
A
.L .
matches any character.
.PP
A
.L ^
matches the beginning of a line;
.L $
matches the end of the line.
.PP
The
.B REP
operators match zero or more
.RB ( * ),
one or more
.RB ( + ),
zero or one
.RB ( ? ),
instances respectively of the preceding regular expression
.BR e2 .
.PP
A concatenated regular expression,
.BR "e1\|e2" ,
matches a match to
.B e1
followed by a match to
.BR e2 .
.PP
An alternative regular expression,
.BR "e0\||\|e1" ,
matches either a match to
.B e0
or a match to
.BR e1 .
.PP
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.
.SH "SEE ALSO"
.IR regexp (3)
|