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1.1 root 1: .TH AWK 1 "18 January 1983"
2: .SH NAME
3: awk \- pattern scanning and processing language
4: .SH SYNOPSIS
5: .B awk
6: [
7: .BI \-F c
8: ]
9: [ prog ] [ file ] ...
10: .SH DESCRIPTION
11: .I Awk
12: scans each input
13: .I file
14: for lines that match any of a set of patterns specified in
15: .IR prog .
16: With each pattern in
17: .I prog
18: there can be an associated action that will be performed
19: when a line of a
20: .I file
21: matches the pattern.
22: The set of patterns may appear literally as
23: .I prog,
24: or in a file
25: specified as
26: .B \-f
27: .IR file .
28: .PP
29: Files are read in order;
30: if there are no files, the standard input is read.
31: The file name `\-'
32: means the standard input.
33: Each line is matched against the
34: pattern portion of every pattern-action statement;
35: the associated action is performed for each matched pattern.
36: .PP
37: An input line is made up of fields separated by white space.
38: (This default can be changed by using FS,
39: .IR "vide infra" ".)"
40: The fields are denoted $1, $2, ... ;
41: $0 refers to the entire line.
42: .PP
43: .PP
44: A pattern-action statement has the form
45: .PP
46: pattern { action }
47: .PP
48: A missing { action } means print the line;
49: a missing pattern always matches.
50: .PP
51: An action is a sequence of statements.
52: A statement can be one of the following:
53: .PP
54: .nf
55: if ( conditional ) statement [ else statement ]
56: while ( conditional ) statement
57: for ( expression ; conditional ; expression ) statement
58: break
59: continue
60: { [ statement ] ... }
61: variable = expression
62: print [ expression-list ] [ >expression ]
63: printf format [ , expression-list ] [ >expression ]
64: next # skip remaining patterns on this input line
65: exit # skip the rest of the input
66: .fi
67: .PP
68: Statements are terminated by
69: semicolons, newlines or right braces.
70: An empty expression-list stands for the whole line.
71: Expressions take on string or numeric values as appropriate,
72: and are built using the operators
73: +, \-, *, /, %, and concatenation (indicated by a blank).
74: The C operators ++, \-\-, +=, \-=, *=, /=, and %=
75: are also available in expressions.
76: Variables may be scalars, array elements
77: (denoted
78: x[i])
79: or fields.
80: Variables are initialized to the null string.
81: Array subscripts may be any string,
82: not necessarily numeric;
83: this allows for a form of associative memory.
84: String constants are quoted "...".
85: .PP
86: The
87: .I print
88: statement prints its arguments on the standard output
89: (or on a file if
90: .I >file
91: is present), separated by the current output field separator,
92: and terminated by the output record separator.
93: The
94: .I printf
95: statement formats its expression list according to the format
96: (see
97: .IR printf (3S)).
98: .PP
99: The built-in function
100: .I length
101: returns the length of its argument
102: taken as a string,
103: or of the whole line if no argument.
104: There are also built-in functions
105: .I exp,
106: .I log,
107: .I sqrt,
108: and
109: .IR int .
110: The last truncates its argument to an integer.
111: .IR substr(s,\ m,\ n)
112: returns the
113: .IR n -character
114: substring of
115: .I s
116: that begins at position
117: .IR m .
118: The function
119: .IR sprintf(fmt,\ expr,\ expr,\ ...)
120: formats the expressions
121: according to the
122: .IR printf (3S)
123: format given by
124: .I fmt
125: and returns the resulting string.
126: .PP
127: Patterns are arbitrary Boolean combinations
128: (!, \(or\(or, &&, and parentheses) of
129: regular expressions and
130: relational expressions.
131: Regular expressions must be surrounded
132: by slashes and are as in
133: .IR egrep .
134: Isolated regular expressions
135: in a pattern apply to the entire line.
136: Regular expressions may also occur in
137: relational expressions.
138: .PP
139: A pattern may consist of two patterns separated by a comma;
140: in this case, the action is performed for all lines
141: between an occurrence of the first pattern
142: and the next occurrence of the second.
143: .PP
144: .nf
145: A relational expression is one of the following:
146: .PP
147: .nf
148: expression matchop regular-expression
149: expression relop expression
150: .PP
151: .fi
152: where a relop is any of the six relational operators in C,
153: and a matchop is either ~ (for contains)
154: or !~ (for does not contain).
155: A conditional is an arithmetic expression,
156: a relational expression,
157: or a Boolean combination
158: of these.
159: .PP
160: The special patterns
161: BEGIN
162: and
163: END
164: may be used to capture control before the first input line is read
165: and after the last.
166: BEGIN must be the first pattern, END the last.
167: .PP
168: A single character
169: .I c
170: may be used to separate the fields by starting
171: the program with
172: .PP
173: BEGIN { FS = "c" }
174: .PP
175: or by using the
176: .BI \-F c
177: option.
178: .PP
179: Other variable names with special meanings
180: include NF, the number of fields in the current record;
181: NR, the ordinal number of the current record;
182: FILENAME, the name of the current input file;
183: OFS, the output field separator (default blank);
184: ORS, the output record separator (default newline);
185: and
186: OFMT, the output format for numbers (default "%.6g").
187: .PP
188: .SH EXAMPLES
189: .PP
190: Print lines longer than 72 characters:
191: .PP
192: .nf
193: length > 72
194: .fi
195: .PP
196: Print first two fields in opposite order:
197: .PP
198: .nf
199: { print $2, $1 }
200: .fi
201: .PP
202: Add up first column, print sum and average:
203: .PP
204: .nf
205: { s += $1 }
206: END { print "sum is", s, " average is", s/NR }
207: .fi
208: .PP
209: Print fields in reverse order:
210: .PP
211: .nf
212: { for (i = NF; i > 0; \-\-i) print $i }
213: .fi
214: .PP
215: Print all lines between start/stop pairs:
216: .PP
217: .nf
218: /start/, /stop/
219: .fi
220: .PP
221: Print all lines whose first field is different from previous one:
222: .PP
223: .nf
224: $1 != prev { print; prev = $1 }
225: .fi
226: .SH SEE ALSO
227: .PP
228: lex(1), sed(1)
229: .br
230: A. V. Aho, B. W. Kernighan, P. J. Weinberger,
231: .I
232: Awk \- a pattern scanning and processing language
233: .SH BUGS
234: There are no explicit conversions between numbers and strings.
235: To force an expression to be treated as a number add 0 to it;
236: to force it to be treated as a string concatenate ""
237: to it.
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