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regexp9.7 (2227B)

      1 .deEX
      2 .ift .ft5
      3 .nf
      4 ..
      5 .deEE
      6 .ft1
      7 .fi
      8 ..
      9 .TH REGEXP9 7
     10 .SH NAME
     11 regexp \- Plan 9 regular expression notation
     12 .SH DESCRIPTION
     13 This manual page describes the regular expression
     14 syntax used by the Plan 9 regular expression library
     15 .IR regexp9 (3).
     16 It is the form used by
     17 .IR egrep (1)
     18 before
     19 .I egrep
     20 got complicated.
     21 .PP
     22 A 
     23 .I "regular expression"
     24 specifies
     25 a set of strings of characters.
     26 A member of this set of strings is said to be
     27 .I matched
     28 by the regular expression.  In many applications
     29 a delimiter character, commonly
     30 .LR / ,
     31 bounds a regular expression.
     32 In the following specification for regular expressions
     33 the word `character' means any character (rune) but newline.
     34 .PP
     35 The syntax for a regular expression
     36 .B e0
     37 is
     38 .IP
     39 .EX
     40 e3:  literal | charclass | '.' | '^' | '$' | '(' e0 ')'
     41 
     42 e2:  e3
     43   |  e2 REP
     44 
     45 REP: '*' | '+' | '?'
     46 
     47 e1:  e2
     48   |  e1 e2
     49 
     50 e0:  e1
     51   |  e0 '|' e1
     52 .EE
     53 .PP
     54 A
     55 .B literal
     56 is any non-metacharacter, or a metacharacter
     57 (one of
     58 .BR .*+?[]()|\e^$ ),
     59 or the delimiter
     60 preceded by 
     61 .LR \e .
     62 .PP
     63 A
     64 .B charclass
     65 is a nonempty string
     66 .I s
     67 bracketed
     68 .BI [ \|s\| ]
     69 (or
     70 .BI [^ s\| ]\fR);
     71 it matches any character in (or not in)
     72 .IR s .
     73 A negated character class never
     74 matches newline.
     75 A substring 
     76 .IB a - b\f1,
     77 with
     78 .I a
     79 and
     80 .I b
     81 in ascending
     82 order, stands for the inclusive
     83 range of
     84 characters between
     85 .I a
     86 and
     87 .IR b .
     88 In 
     89 .IR s ,
     90 the metacharacters
     91 .LR - ,
     92 .LR ] ,
     93 an initial
     94 .LR ^ ,
     95 and the regular expression delimiter
     96 must be preceded by a
     97 .LR \e ;
     98 other metacharacters 
     99 have no special meaning and
    100 may appear unescaped.
    101 .PP
    102 A 
    103 .L .
    104 matches any character.
    105 .PP
    106 A
    107 .L ^
    108 matches the beginning of a line;
    109 .L $
    110 matches the end of the line.
    111 .PP
    112 The 
    113 .B REP
    114 operators match zero or more
    115 .RB ( * ),
    116 one or more
    117 .RB ( + ),
    118 zero or one
    119 .RB ( ? ),
    120 instances respectively of the preceding regular expression 
    121 .BR e2 .
    122 .PP
    123 A concatenated regular expression,
    124 .BR "e1\|e2" ,
    125 matches a match to 
    126 .B e1
    127 followed by a match to
    128 .BR e2 .
    129 .PP
    130 An alternative regular expression,
    131 .BR "e0\||\|e1" ,
    132 matches either a match to
    133 .B e0
    134 or a match to
    135 .BR e1 .
    136 .PP
    137 A match to any part of a regular expression
    138 extends as far as possible without preventing
    139 a match to the remainder of the regular expression.
    140 .SH "SEE ALSO
    141 .IR regexp9 (3)