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1.1 root 1: .TH AWK 1
2: .CT 1 files prog_other
3: .SH NAME
4: awk \- pattern-directed scanning and processing language
5: .SH SYNOPSIS
6: .B awk
7: [
8: .BI -F fs
9: ]
10: [
11: .BI -v
12: .I var=value
13: ] ...
14: [
15: .B -f
16: ]
17: .I prog
18: [
19: .I file ...
20: ]
21: .SH DESCRIPTION
22: .I Awk
23: scans each input
24: .I file
25: for lines that match any of a set of patterns in
26: .IR prog ,
27: which may appear as one literal argument or as one or more
28: file names each preceded by
29: .BR -f .
30: With each pattern
31: may be associated an action to be performed
32: when a line of a
33: .I file
34: matches the pattern.
35: Each line is matched against the
36: pattern portion of every pattern-action statement in order;
37: the associated action is performed for each matched pattern.
38: The file name
39: .L -
40: means the standard input.
41: Any
42: .IR file
43: of the form
44: .I var=value
45: is treated as an assignment, not a filename,
46: and is executed at the time it would have been opened if it were a filename.
47: Option
48: .B -v
49: designates an assignment to be done before
50: .I prog
51: is executed.
52: .PP
53: An input line is made up of fields separated by white space,
54: or by regular expression
55: .BR FS .
56: The fields are denoted
57: .BR $1 ,
58: .BR $2 ,
59: \&..., while
60: .B $0
61: refers to the entire line.
62: .PP
63: A pattern-action statement has the form
64: .IP
65: .IB pattern " { " action " }
66: .PP
67: A missing
68: .BI { " action " }
69: means print the line;
70: a missing pattern always matches.
71: Pattern-action statements are separated by newlines or semicolons.
72: .PP
73: An action is a sequence of statements.
74: A statement can be one of the following:
75: .PP
76: .EX
77: .ta \w'\f(CWdelete array[expression]'u
78: if(\fI expression \fP)\fI statement \fP\fR[ \fPelse\fI statement \fP\fR]\fP
79: while(\fI expression \fP)\fI statement\fP
80: for(\fI expression \fP;\fI expression \fP;\fI expression \fP)\fI statement\fP
81: for(\fI var \fPin\fI array \fP)\fI statement\fP
82: do\fI statement \fPwhile(\fI expression \fP)
83: break
84: continue
85: {\fR [\fP\fI statement ... \fP\fR] \fP}
86: \fIexpression\fP #\fR commonly\fP\fI var = expression\fP
87: print\fR [ \fP\fIexpression-list \fP\fR] \fP\fR[ \fP>\fI expression \fP\fR]\fP
88: printf\fI format \fP\fR[ \fP,\fI expression-list \fP\fR] \fP\fR[ \fP>\fI expression \fP\fR]\fP
89: return\fR [ \fP\fIexpression \fP\fR]\fP
90: next #\fR skip remaining patterns on this input line\fP
91: delete\fI array\fP[\fI expression \fP] #\fR delete an array element\fP
92: exit\fR [ \fP\fIexpression \fP\fR]\fP #\fR exit immediately; status is \fP\fIexpression\fP
93: .EE
94: .DT
95: .PP
96: Statements are terminated by
97: semicolons, newlines or right braces.
98: An empty
99: .I expression-list
100: stands for
101: .BR $0 .
102: String constants are quoted \&\f(CW"\ "\fR,
103: with the usual C escapes recognized within.
104: Expressions take on string or numeric values as appropriate,
105: and are built using the operators
106: .B + - * / % ^
107: (exponentiation), and concatenation (indicated by white space).
108: The operators
109: .B
110: ! ++ -- += -= *= /= %= ^= > >= < <= == != && || ?:
111: are also available in expressions.
112: Variables may be scalars, array elements
113: (denoted
114: .IB x [ i ] )
115: or fields.
116: Variables are initialized to the null string.
117: Array subscripts may be any string,
118: not necessarily numeric;
119: this allows for a form of associative memory.
120: Multiple subscripts such as
121: .B [i,j,k]
122: are permitted; the constituents are concatenated,
123: separated by the value of
124: .BR SUBSEP .
125: .PP
126: The
127: .B print
128: statement prints its arguments on the standard output
129: (or on a file if
130: .BI > file
131: or
132: .BI >> file
133: is present or on a pipe if
134: .BI | cmd
135: is present), separated by the current output field separator,
136: and terminated by the output record separator.
137: .I file
138: and
139: .I cmd
140: may be literal names or parenthesized expressions;
141: identical string values in different statements denote
142: the same open file.
143: The
144: .B printf
145: statement formats its expression list according to the format
146: (see
147: .IR printf (3)) .
148: The built-in function
149: .BI close( expr )
150: closes the file or pipe
151: .IR expr .
152: .PP
153: The mathematical functions
154: .BR exp ,
155: .BR log ,
156: .BR sqrt ,
157: .BR sin ,
158: .BR cos ,
159: and
160: .BR atan2
161: are built in.
162: Other built-in functions:
163: .TF length
164: .TP
165: .B length
166: the length of its argument
167: taken as a string,
168: or of
169: .B $0
170: if no argument.
171: .TP
172: .B rand
173: random number on (0,1)
174: .TP
175: .B srand
176: sets seed for
177: .B rand
178: and returns the previous seed.
179: .TP
180: .B int
181: truncates to an integer value
182: .TP
183: .BI substr( s , " m" , " n\fB)
184: the
185: .IR n -character
186: substring of
187: .I s
188: that begins at position
189: .IR m
190: counted from 1.
191: .TP
192: .BI index( s , " t" )
193: the position in
194: .I s
195: where the string
196: .I t
197: occurs, or 0 if it does not.
198: .TP
199: .BI match( s , " r" )
200: the position in
201: .I s
202: where the regular expression
203: .I r
204: occurs, or 0 if it does not.
205: The variables
206: .B RSTART
207: and
208: .B RLENGTH
209: are set to the position and length of the matched string.
210: .TP
211: .BI split( s , " a" , " fs\fB)
212: splits the string
213: .I s
214: into array elements
215: .IB a [1] ,
216: .IB a [2] ,
217: \&...,
218: .IB a [ n ] ,
219: and returns
220: .IR n .
221: The separation is done with the regular expression
222: .I fs
223: or with the field separator
224: .B FS
225: if
226: .I fs
227: is not given.
228: .TP
229: .BI sub( r , " t" , " s\fB)
230: substitutes
231: .I t
232: for the first occurrence of the regular expression
233: .I r
234: in the string
235: .IR s .
236: If
237: .I s
238: is not given,
239: .B $0
240: is used.
241: .TP
242: .B gsub
243: same as
244: .B sub
245: except that all occurrences of the regular expression
246: are replaced;
247: .B sub
248: and
249: .B gsub
250: return the number of replacements.
251: .TP
252: .BI sprintf( fmt , " expr" , " ...\fB )
253: the string resulting from formatting
254: .I expr ...
255: according to the
256: .IR printf (3)
257: format
258: .I fmt
259: .TP
260: .BI system( cmd )
261: executes
262: .I cmd
263: and returns its exit status
264: .PD
265: .PP
266: The ``function''
267: .B getline
268: sets
269: .B $0 to
270: the next input record from the current input file;
271: .B getline
272: .BI < file
273: sets
274: .B $0
275: to the next record from
276: .IR file .
277: .B getline
278: .I x
279: sets variable
280: .I x
281: instead.
282: Finally,
283: .IB cmd " | getline
284: pipes the output of
285: .I cmd
286: into
287: .BR getline ;
288: each call of
289: .B getline
290: returns the next line of output from
291: .IR cmd .
292: In all cases,
293: .B getline
294: returns 1 for a successful input,
295: 0 for end of file, and \-1 for an error.
296: .PP
297: Patterns are arbitrary Boolean combinations
298: (with
299: .BR "! || &&" )
300: of regular expressions and
301: relational expressions.
302: Regular expressions are as in
303: .IR egrep ;
304: see
305: .IR gre (1).
306: Isolated regular expressions
307: in a pattern apply to the entire line.
308: Regular expressions may also occur in
309: relational expressions, using the operators
310: .BR ~
311: and
312: .BR !~ .
313: .BI / re /
314: is a constant regular expression;
315: any string (constant or variable) may be used
316: as a regular expression, except in the position of an isolated regular expression
317: in a pattern.
318: .PP
319: A pattern may consist of two patterns separated by a comma;
320: in this case, the action is performed for all lines
321: from an occurrence of the first pattern
322: though an occurrence of the second.
323: .PP
324: A relational expression is one of the following:
325: .IP
326: .I expression matchop regular-expression
327: .br
328: .I expression relop expression
329: .br
330: .IB expression " in " array-name
331: .br
332: .BI ( expr , expr,... ") in " array-name
333: .PP
334: where a relop is any of the six relational operators in C,
335: and a matchop is either
336: .B ~
337: (matches)
338: or
339: .B !~
340: (does not match).
341: A conditional is an arithmetic expression,
342: a relational expression,
343: or a Boolean combination
344: of these.
345: .PP
346: The special patterns
347: .B BEGIN
348: and
349: .B END
350: may be used to capture control before the first input line is read
351: and after the last.
352: .B BEGIN
353: and
354: .B END
355: do not combine with other patterns.
356: .PP
357: Variable names with special meanings:
358: .TF FILENAME
359: .TP
360: .B FS
361: regular expression used to separate fields; also settable
362: by option
363: .BI -F fs.
364: .TP
365: .BR NF
366: number of fields in the current record
367: .TP
368: .B NR
369: ordinal number of the current record
370: .TP
371: .B FNR
372: ordinal number of the current record in the current file
373: .TP
374: .B FILENAME
375: the name of the current input file
376: .TP
377: .B RS
378: input record separator (default newline)
379: .TP
380: .B OFS
381: output field separator (default blank)
382: .TP
383: .B ORS
384: output record separator (default newline)
385: .TP
386: .B OFMT
387: output format for numbers (default
388: .BR "%.6g" )
389: .TP
390: .B SUBSEP
391: separates multiple subscripts (default 034)
392: .TP
393: .B ARGC
394: argument count, assignable
395: .TP
396: .B ARGV
397: argument array, assignable;
398: non-null members are taken as filenames
399: .TP
400: .B ENVIRON
401: array of environment variables; subscripts are names.
402: .PD
403: .PP
404: Functions may be defined (at the position of a pattern-action statement) thus:
405: .IP
406: .L
407: function foo(a, b, c) { ...; return x }
408: .PP
409: Parameters are passed by value if scalar and by reference if array name;
410: functions may be called recursively.
411: Parameters are local to the function; all other variables are global.
412: Thus local variables may be created by providing excess parameters in
413: the function definition.
414: .SH EXAMPLES
415: .TP
416: .L
417: length > 72
418: Print lines longer than 72 characters.
419: .TP
420: .L
421: { print $2, $1 }
422: Print first two fields in opposite order.
423: .PP
424: .EX
425: BEGIN { FS = ",[ \et]*|[ \et]+" }
426: { print $2, $1 }
427: .EE
428: .ns
429: .IP
430: Same, with input fields separated by comma and/or blanks and tabs.
431: .PP
432: .EX
433: { s += $1 }
434: END { print "sum is", s, " average is", s/NR }
435: .EE
436: .ns
437: .IP
438: Add up first column, print sum and average.
439: .TP
440: .L
441: /start/, /stop/
442: Print all lines between start/stop pairs.
443: .PP
444: .EX
445: BEGIN { # Simulate echo(1)
446: for (i = 1; i < ARGC; i++) printf "%s ", ARGV[i]
447: printf "\en"
448: exit }
449: .EE
450: .SH SEE ALSO
451: .IR gre (1),
452: .IR lex (1),
453: .IR sed (1)
454: .br
455: A. V. Aho, B. W. Kernighan, P. J. Weinberger,
456: .I
457: The AWK Programming Language,
458: Addison-Wesley, 1988.
459: .SH BUGS
460: There are no explicit conversions between numbers and strings.
461: To force an expression to be treated as a number add 0 to it;
462: to force it to be treated as a string concatenate
463: \&\f(CW""\fP to it.
464: .br
465: The scope rules for variables in functions are a botch;
466: the syntax is worse.
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