1AWK(1) General Commands Manual AWK(1)
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6 awk - pattern scanning and processing language
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9 awk [ -Fc ] [ prog ] [ file ] ...
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12 Awk scans each input file for lines that match any of a set of patterns
13 specified in prog. With each pattern in prog there can be an associ‐
14 ated action that will be performed when a line of a file matches the
15 pattern. The set of patterns may appear literally as prog, or in a
16 file specified as -f file.
17 Files are read in order; if there are no files, the standard input is
19 read. The file name `-' means the standard input. Each line is
20 matched against the pattern portion of every pattern-action statement;
21 the associated action is performed for each matched pattern.
22 An input line is made up of fields separated by white space. (This
24 default can be changed by using FS, vide infra.) The fields are
25 denoted $1, $2, ... ; $0 refers to the entire line.
26 A pattern-action statement has the form
28 pattern { action }
30 A missing { action } means print the line; a missing pattern always
32 matches.
33 An action is a sequence of statements. A statement can be one of the
35 following:
36 if ( conditional ) statement [ else statement ]
38 while ( conditional ) statement
39 for ( expression ; conditional ; expression ) statement
40 break
41 continue
42 { [ statement ] ... }
43 variable = expression
44 print [ expression-list ] [ >expression ]
45 printf format [ , expression-list ] [ >expression ]
46 next # skip remaining patterns on this input line
47 exit # skip the rest of the input
48 Statements are terminated by semicolons, newlines or right braces. An
50 empty expression-list stands for the whole line. Expressions take on
51 string or numeric values as appropriate, and are built using the opera‐
52 tors +, -, *, /, %, and concatenation (indicated by a blank). The C
53 operators ++, --, +=, -=, *=, /=, and %= are also available in expres‐
54 sions. Variables may be scalars, array elements (denoted x[i]) or
55 fields. Variables are initialized to the null string. Array sub‐
56 scripts may be any string, not necessarily numeric; this allows for a
57 form of associative memory. String constants are quoted "...".
58 The print statement prints its arguments on the standard output (or on
60 a file if >file is present), separated by the current output field sep‐
61 arator, and terminated by the output record separator. The printf
62 statement formats its expression list according to the format (see
63 printf(3)).
64 The built-in function length returns the length of its argument taken
66 as a string, or of the whole line if no argument. There are also
67 built-in functions exp, log, sqrt, and int. The last truncates its
68 argument to an integer. substr(s, m, n) returns the n-character sub‐
69 string of s that begins at position m. The function
70 sprintf(fmt, expr, expr, ...) formats the expressions according to the
71 printf(3) format given by fmt and returns the resulting string.
72 Patterns are arbitrary Boolean combinations (!, ||, &&, and parenthe‐
74 ses) of regular expressions and relational expressions. Regular
75 expressions must be surrounded by slashes and are as in egrep. Iso‐
76 lated regular expressions in a pattern apply to the entire line. Regu‐
77 lar expressions may also occur in relational expressions.
78 A pattern may consist of two patterns separated by a comma; in this
80 case, the action is performed for all lines between an occurrence of
81 the first pattern and the next occurrence of the second.
82 A relational expression is one of the following:
84 expression matchop regular-expression
86 expression relop expression
87 where a relop is any of the six relational operators in C, and a
89 matchop is either ~ (for contains) or !~ (for does not contain). A
90 conditional is an arithmetic expression, a relational expression, or a
91 Boolean combination of these.
92 The special patterns BEGIN and END may be used to capture control
94 before the first input line is read and after the last. BEGIN must be
95 the first pattern, END the last.
96 A single character c may be used to separate the fields by starting the
98 program with
99 BEGIN { FS = "c" }
101 or by using the -Fc option.
103 Other variable names with special meanings include NF, the number of
105 fields in the current record; NR, the ordinal number of the current
106 record; FILENAME, the name of the current input file; OFS, the output
107 field separator (default blank); ORS, the output record separator
108 (default newline); and OFMT, the output format for numbers (default
109 "%.6g").
110
112 Print lines longer than 72 characters:
113 length > 72
115 Print first two fields in opposite order:
117 { print $2, $1 }
119 Add up first column, print sum and average:
121 { s += $1 }
123 END { print "sum is", s, " average is", s/NR }
124 Print fields in reverse order:
126 { for (i = NF; i > 0; --i) print $i }
128 Print all lines between start/stop pairs:
130 /start/, /stop/
132 Print all lines whose first field is different from previous one:
134 $1 != prev { print; prev = $1 }
136
138 lex(1), sed(1)
139 A. V. Aho, B. W. Kernighan, P. J. Weinberger, Awk - a pattern scanning
140 and processing language
141
143 There are no explicit conversions between numbers and strings. To
144 force an expression to be treated as a number add 0 to it; to force it
145 to be treated as a string concatenate "" to it.
146 AWK(1)