/contrib/one-true-awk/awk.1

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  1. .de EX
  2. .nf
  3. .ft CW
  4. ..
  5. .de EE
  6. .br
  7. .fi
  8. .ft 1
  9. ..
  10. awk
  11. .TH AWK 1
  12. .CT 1 files prog_other
  13. .SH NAME
  14. awk \- pattern-directed scanning and processing language
  15. .SH SYNOPSIS
  16. .B awk
  17. [
  18. .BI \-F
  19. .I fs
  20. ]
  21. [
  22. .BI \-v
  23. .I var=value
  24. ]
  25. [
  26. .I 'prog'
  27. |
  28. .BI \-f
  29. .I progfile
  30. ]
  31. [
  32. .I file ...
  33. ]
  34. .SH DESCRIPTION
  35. .I Awk
  36. scans each input
  37. .I file
  38. for lines that match any of a set of patterns specified literally in
  39. .IR prog
  40. or in one or more files
  41. specified as
  42. .B \-f
  43. .IR progfile .
  44. With each pattern
  45. there can be an associated action that will be performed
  46. when a line of a
  47. .I file
  48. matches the pattern.
  49. Each line is matched against the
  50. pattern portion of every pattern-action statement;
  51. the associated action is performed for each matched pattern.
  52. The file name
  53. .B \-
  54. means the standard input.
  55. Any
  56. .IR file
  57. of the form
  58. .I var=value
  59. is treated as an assignment, not a filename,
  60. and is executed at the time it would have been opened if it were a filename.
  61. The option
  62. .B \-v
  63. followed by
  64. .I var=value
  65. is an assignment to be done before
  66. .I prog
  67. is executed;
  68. any number of
  69. .B \-v
  70. options may be present.
  71. The
  72. .B \-F
  73. .IR fs
  74. option defines the input field separator to be the regular expression
  75. .IR fs.
  76. .PP
  77. An input line is normally made up of fields separated by white space,
  78. or by regular expression
  79. .BR FS .
  80. The fields are denoted
  81. .BR $1 ,
  82. .BR $2 ,
  83. \&..., while
  84. .B $0
  85. refers to the entire line.
  86. If
  87. .BR FS
  88. is null, the input line is split into one field per character.
  89. .PP
  90. A pattern-action statement has the form
  91. .IP
  92. .IB pattern " { " action " }
  93. .PP
  94. A missing
  95. .BI { " action " }
  96. means print the line;
  97. a missing pattern always matches.
  98. Pattern-action statements are separated by newlines or semicolons.
  99. .PP
  100. An action is a sequence of statements.
  101. A statement can be one of the following:
  102. .PP
  103. .EX
  104. .ta \w'\f(CWdelete array[expression]'u
  105. .RS
  106. .nf
  107. .ft CW
  108. if(\fI expression \fP)\fI statement \fP\fR[ \fPelse\fI statement \fP\fR]\fP
  109. while(\fI expression \fP)\fI statement\fP
  110. for(\fI expression \fP;\fI expression \fP;\fI expression \fP)\fI statement\fP
  111. for(\fI var \fPin\fI array \fP)\fI statement\fP
  112. do\fI statement \fPwhile(\fI expression \fP)
  113. break
  114. continue
  115. {\fR [\fP\fI statement ... \fP\fR] \fP}
  116. \fIexpression\fP #\fR commonly\fP\fI var = expression\fP
  117. print\fR [ \fP\fIexpression-list \fP\fR] \fP\fR[ \fP>\fI expression \fP\fR]\fP
  118. printf\fI format \fP\fR[ \fP,\fI expression-list \fP\fR] \fP\fR[ \fP>\fI expression \fP\fR]\fP
  119. return\fR [ \fP\fIexpression \fP\fR]\fP
  120. next #\fR skip remaining patterns on this input line\fP
  121. nextfile #\fR skip rest of this file, open next, start at top\fP
  122. delete\fI array\fP[\fI expression \fP] #\fR delete an array element\fP
  123. delete\fI array\fP #\fR delete all elements of array\fP
  124. exit\fR [ \fP\fIexpression \fP\fR]\fP #\fR exit immediately; status is \fP\fIexpression\fP
  125. .fi
  126. .RE
  127. .EE
  128. .DT
  129. .PP
  130. Statements are terminated by
  131. semicolons, newlines or right braces.
  132. An empty
  133. .I expression-list
  134. stands for
  135. .BR $0 .
  136. String constants are quoted \&\f(CW"\ "\fR,
  137. with the usual C escapes recognized within.
  138. Expressions take on string or numeric values as appropriate,
  139. and are built using the operators
  140. .B + \- * / % ^
  141. (exponentiation), and concatenation (indicated by white space).
  142. The operators
  143. .B
  144. ! ++ \-\- += \-= *= /= %= ^= > >= < <= == != ?:
  145. are also available in expressions.
  146. Variables may be scalars, array elements
  147. (denoted
  148. .IB x [ i ] )
  149. or fields.
  150. Variables are initialized to the null string.
  151. Array subscripts may be any string,
  152. not necessarily numeric;
  153. this allows for a form of associative memory.
  154. Multiple subscripts such as
  155. .B [i,j,k]
  156. are permitted; the constituents are concatenated,
  157. separated by the value of
  158. .BR SUBSEP .
  159. .PP
  160. The
  161. .B print
  162. statement prints its arguments on the standard output
  163. (or on a file if
  164. .BI > file
  165. or
  166. .BI >> file
  167. is present or on a pipe if
  168. .BI | cmd
  169. is present), separated by the current output field separator,
  170. and terminated by the output record separator.
  171. .I file
  172. and
  173. .I cmd
  174. may be literal names or parenthesized expressions;
  175. identical string values in different statements denote
  176. the same open file.
  177. The
  178. .B printf
  179. statement formats its expression list according to the format
  180. (see
  181. .IR printf (3)) .
  182. The built-in function
  183. .BI close( expr )
  184. closes the file or pipe
  185. .IR expr .
  186. The built-in function
  187. .BI fflush( expr )
  188. flushes any buffered output for the file or pipe
  189. .IR expr .
  190. .PP
  191. The mathematical functions
  192. .BR exp ,
  193. .BR log ,
  194. .BR sqrt ,
  195. .BR sin ,
  196. .BR cos ,
  197. and
  198. .BR atan2
  199. are built in.
  200. Other built-in functions:
  201. .TF length
  202. .TP
  203. .B length
  204. the length of its argument
  205. taken as a string,
  206. or of
  207. .B $0
  208. if no argument.
  209. .TP
  210. .B rand
  211. random number on (0,1)
  212. .TP
  213. .B srand
  214. sets seed for
  215. .B rand
  216. and returns the previous seed.
  217. .TP
  218. .B int
  219. truncates to an integer value
  220. .TP
  221. .BI substr( s , " m" , " n\fB)
  222. the
  223. .IR n -character
  224. substring of
  225. .I s
  226. that begins at position
  227. .IR m
  228. counted from 1.
  229. .TP
  230. .BI index( s , " t" )
  231. the position in
  232. .I s
  233. where the string
  234. .I t
  235. occurs, or 0 if it does not.
  236. .TP
  237. .BI match( s , " r" )
  238. the position in
  239. .I s
  240. where the regular expression
  241. .I r
  242. occurs, or 0 if it does not.
  243. The variables
  244. .B RSTART
  245. and
  246. .B RLENGTH
  247. are set to the position and length of the matched string.
  248. .TP
  249. .BI split( s , " a" , " fs\fB)
  250. splits the string
  251. .I s
  252. into array elements
  253. .IB a [1] ,
  254. .IB a [2] ,
  255. \&...,
  256. .IB a [ n ] ,
  257. and returns
  258. .IR n .
  259. The separation is done with the regular expression
  260. .I fs
  261. or with the field separator
  262. .B FS
  263. if
  264. .I fs
  265. is not given.
  266. An empty string as field separator splits the string
  267. into one array element per character.
  268. .TP
  269. .BI sub( r , " t" , " s\fB)
  270. substitutes
  271. .I t
  272. for the first occurrence of the regular expression
  273. .I r
  274. in the string
  275. .IR s .
  276. If
  277. .I s
  278. is not given,
  279. .B $0
  280. is used.
  281. .TP
  282. .B gsub
  283. same as
  284. .B sub
  285. except that all occurrences of the regular expression
  286. are replaced;
  287. .B sub
  288. and
  289. .B gsub
  290. return the number of replacements.
  291. .TP
  292. .BI sprintf( fmt , " expr" , " ...\fB )
  293. the string resulting from formatting
  294. .I expr ...
  295. according to the
  296. .IR printf (3)
  297. format
  298. .I fmt
  299. .TP
  300. .BI system( cmd )
  301. executes
  302. .I cmd
  303. and returns its exit status
  304. .TP
  305. .BI tolower( str )
  306. returns a copy of
  307. .I str
  308. with all upper-case characters translated to their
  309. corresponding lower-case equivalents.
  310. .TP
  311. .BI toupper( str )
  312. returns a copy of
  313. .I str
  314. with all lower-case characters translated to their
  315. corresponding upper-case equivalents.
  316. .PD
  317. .PP
  318. The ``function''
  319. .B getline
  320. sets
  321. .B $0
  322. to the next input record from the current input file;
  323. .B getline
  324. .BI < file
  325. sets
  326. .B $0
  327. to the next record from
  328. .IR file .
  329. .B getline
  330. .I x
  331. sets variable
  332. .I x
  333. instead.
  334. Finally,
  335. .IB cmd " | getline
  336. pipes the output of
  337. .I cmd
  338. into
  339. .BR getline ;
  340. each call of
  341. .B getline
  342. returns the next line of output from
  343. .IR cmd .
  344. In all cases,
  345. .B getline
  346. returns 1 for a successful input,
  347. 0 for end of file, and \-1 for an error.
  348. .PP
  349. Patterns are arbitrary Boolean combinations
  350. (with
  351. .BR "! || &&" )
  352. of regular expressions and
  353. relational expressions.
  354. Regular expressions are as in
  355. .IR egrep ;
  356. see
  357. .IR grep (1).
  358. Isolated regular expressions
  359. in a pattern apply to the entire line.
  360. Regular expressions may also occur in
  361. relational expressions, using the operators
  362. .BR ~
  363. and
  364. .BR !~ .
  365. .BI / re /
  366. is a constant regular expression;
  367. any string (constant or variable) may be used
  368. as a regular expression, except in the position of an isolated regular expression
  369. in a pattern.
  370. .PP
  371. A pattern may consist of two patterns separated by a comma;
  372. in this case, the action is performed for all lines
  373. from an occurrence of the first pattern
  374. though an occurrence of the second.
  375. .PP
  376. A relational expression is one of the following:
  377. .IP
  378. .I expression matchop regular-expression
  379. .br
  380. .I expression relop expression
  381. .br
  382. .IB expression " in " array-name
  383. .br
  384. .BI ( expr , expr,... ") in " array-name
  385. .PP
  386. where a relop is any of the six relational operators in C,
  387. and a matchop is either
  388. .B ~
  389. (matches)
  390. or
  391. .B !~
  392. (does not match).
  393. A conditional is an arithmetic expression,
  394. a relational expression,
  395. or a Boolean combination
  396. of these.
  397. .PP
  398. The special patterns
  399. .B BEGIN
  400. and
  401. .B END
  402. may be used to capture control before the first input line is read
  403. and after the last.
  404. .B BEGIN
  405. and
  406. .B END
  407. do not combine with other patterns.
  408. .PP
  409. Variable names with special meanings:
  410. .TF FILENAME
  411. .TP
  412. .B CONVFMT
  413. conversion format used when converting numbers
  414. (default
  415. .BR "%.6g" )
  416. .TP
  417. .B FS
  418. regular expression used to separate fields; also settable
  419. by option
  420. .BI \-F fs.
  421. .TP
  422. .BR NF
  423. number of fields in the current record
  424. .TP
  425. .B NR
  426. ordinal number of the current record
  427. .TP
  428. .B FNR
  429. ordinal number of the current record in the current file
  430. .TP
  431. .B FILENAME
  432. the name of the current input file
  433. .TP
  434. .B RS
  435. input record separator (default newline)
  436. .TP
  437. .B OFS
  438. output field separator (default blank)
  439. .TP
  440. .B ORS
  441. output record separator (default newline)
  442. .TP
  443. .B OFMT
  444. output format for numbers (default
  445. .BR "%.6g" )
  446. .TP
  447. .B SUBSEP
  448. separates multiple subscripts (default 034)
  449. .TP
  450. .B ARGC
  451. argument count, assignable
  452. .TP
  453. .B ARGV
  454. argument array, assignable;
  455. non-null members are taken as filenames
  456. .TP
  457. .B ENVIRON
  458. array of environment variables; subscripts are names.
  459. .PD
  460. .PP
  461. Functions may be defined (at the position of a pattern-action statement) thus:
  462. .IP
  463. .B
  464. function foo(a, b, c) { ...; return x }
  465. .PP
  466. Parameters are passed by value if scalar and by reference if array name;
  467. functions may be called recursively.
  468. Parameters are local to the function; all other variables are global.
  469. Thus local variables may be created by providing excess parameters in
  470. the function definition.
  471. .SH EXAMPLES
  472. .TP
  473. .EX
  474. length($0) > 72
  475. .EE
  476. Print lines longer than 72 characters.
  477. .TP
  478. .EX
  479. { print $2, $1 }
  480. .EE
  481. Print first two fields in opposite order.
  482. .PP
  483. .EX
  484. BEGIN { FS = ",[ \et]*|[ \et]+" }
  485. { print $2, $1 }
  486. .EE
  487. .ns
  488. .IP
  489. Same, with input fields separated by comma and/or blanks and tabs.
  490. .PP
  491. .EX
  492. .nf
  493. { s += $1 }
  494. END { print "sum is", s, " average is", s/NR }
  495. .fi
  496. .EE
  497. .ns
  498. .IP
  499. Add up first column, print sum and average.
  500. .TP
  501. .EX
  502. /start/, /stop/
  503. .EE
  504. Print all lines between start/stop pairs.
  505. .PP
  506. .EX
  507. .nf
  508. BEGIN { # Simulate echo(1)
  509. for (i = 1; i < ARGC; i++) printf "%s ", ARGV[i]
  510. printf "\en"
  511. exit }
  512. .fi
  513. .EE
  514. .SH SEE ALSO
  515. .IR lex (1),
  516. .IR sed (1)
  517. .br
  518. A. V. Aho, B. W. Kernighan, P. J. Weinberger,
  519. .I
  520. The AWK Programming Language,
  521. Addison-Wesley, 1988. ISBN 0-201-07981-X
  522. .SH BUGS
  523. There are no explicit conversions between numbers and strings.
  524. To force an expression to be treated as a number add 0 to it;
  525. to force it to be treated as a string concatenate
  526. \&\f(CW""\fP to it.
  527. .br
  528. The scope rules for variables in functions are a botch;
  529. the syntax is worse.