1GAWK(1) Utility Commands GAWK(1)
2
6 gawk - pattern scanning and processing language
7
9 gawk [ POSIX or GNU style options ] -f program-file [ -- ] file ...
10 gawk [ POSIX or GNU style options ] [ -- ] program-text file ...
11
13 Gawk is the GNU Project's implementation of the AWK programming lan‐
14 guage. It conforms to the definition of the language in the POSIX
15 1003.1 standard. This version in turn is based on the description in
16 The AWK Programming Language, by Aho, Kernighan, and Weinberger. Gawk
17 provides the additional features found in the current version of Brian
18 Kernighan's awk and numerous GNU-specific extensions.
19 The command line consists of options to gawk itself, the AWK program
21 text (if not supplied via the -f or -i options), and values to be made
22 available in the ARGC and ARGV pre-defined AWK variables.
23 When gawk is invoked with the --profile option, it starts gathering
25 profiling statistics from the execution of the program. Gawk runs more
26 slowly in this mode, and automatically produces an execution profile in
27 the file awkprof.out when done. See the --profile option, below.
28 Gawk also has an integrated debugger. An interactive debugging session
30 can be started by supplying the --debug option to the command line. In
31 this mode of execution, gawk loads the AWK source code and then prompts
32 for debugging commands. Gawk can only debug AWK program source pro‐
33 vided with the -f option. The debugger is documented in GAWK: Effec‐
34 tive AWK Programming.
35
37 Gawk options may be either traditional POSIX-style one letter options,
38 or GNU-style long options. POSIX options start with a single “-”,
39 while long options start with “--”. Long options are provided for both
40 GNU-specific features and for POSIX-mandated features.
41 Gawk-specific options are typically used in long-option form. Argu‐
43 ments to long options are either joined with the option by an = sign,
44 with no intervening spaces, or they may be provided in the next command
45 line argument. Long options may be abbreviated, as long as the abbre‐
46 viation remains unique.
47 Additionally, every long option has a corresponding short option, so
49 that the option's functionality may be used from within #! executable
50 scripts.
51
53 Gawk accepts the following options. Standard options are listed first,
54 followed by options for gawk extensions, listed alphabetically by short
55 option.
56 -f program-file
58 --file program-file
59 Read the AWK program source from the file program-file, instead
60 of from the first command line argument. Multiple -f (or
61 --file) options may be used.
62 -F fs
64 --field-separator fs
65 Use fs for the input field separator (the value of the FS prede‐
66 fined variable).
67 -v var=val
69 --assign var=val
70 Assign the value val to the variable var, before execution of
71 the program begins. Such variable values are available to the
72 BEGIN rule of an AWK program.
73 -b
75 --characters-as-bytes
76 Treat all input data as single-byte characters. In other words,
77 don't pay any attention to the locale information when attempt‐
78 ing to process strings as multibyte characters. The --posix
79 option overrides this one.
80 -c
82 --traditional
83 Run in compatibility mode. In compatibility mode, gawk behaves
84 identically to Brian Kernighan's awk; none of the GNU-specific
85 extensions are recognized. See GNU EXTENSIONS, below, for more
86 information.
87 -C
89 --copyright
90 Print the short version of the GNU copyright information message
91 on the standard output and exit successfully.
92 -d[file]
94 --dump-variables[=file]
95 Print a sorted list of global variables, their types and final
96 values to file. If no file is provided, gawk uses a file named
97 awkvars.out in the current directory.
98 Having a list of all the global variables is a good way to look
99 for typographical errors in your programs. You would also use
100 this option if you have a large program with a lot of functions,
101 and you want to be sure that your functions don't inadvertently
102 use global variables that you meant to be local. (This is a
103 particularly easy mistake to make with simple variable names
104 like i, j, and so on.)
105 -D[file]
107 --debug[=file]
108 Enable debugging of AWK programs. By default, the debugger
109 reads commands interactively from the keyboard (standard input).
110 The optional file argument specifies a file with a list of com‐
111 mands for the debugger to execute non-interactively.
112 -e program-text
114 --source program-text
115 Use program-text as AWK program source code. This option allows
116 the easy intermixing of library functions (used via the -f and
117 -i options) with source code entered on the command line. It is
118 intended primarily for medium to large AWK programs used in
119 shell scripts.
120 -E file
122 --exec file
123 Similar to -f, however, this is option is the last one pro‐
124 cessed. This should be used with #! scripts, particularly for
125 CGI applications, to avoid passing in options or source code (!)
126 on the command line from a URL. This option disables command-
127 line variable assignments.
128 -g
130 --gen-pot
131 Scan and parse the AWK program, and generate a GNU .pot (Porta‐
132 ble Object Template) format file on standard output with entries
133 for all localizable strings in the program. The program itself
134 is not executed. See the GNU gettext distribution for more
135 information on .pot files.
136 -h
138 --help Print a relatively short summary of the available options on the
139 standard output. (Per the GNU Coding Standards, these options
140 cause an immediate, successful exit.)
141 -i include-file
143 --include include-file
144 Load an awk source library. This searches for the library using
145 the AWKPATH environment variable. If the initial search fails,
146 another attempt will be made after appending the .awk suffix.
147 The file will be loaded only once (i.e., duplicates are elimi‐
148 nated), and the code does not constitute the main program
149 source.
150 -l lib
152 --load lib
153 Load a gawk extension from the shared library lib. This
154 searches for the library using the AWKLIBPATH environment vari‐
155 able. If the initial search fails, another attempt will be made
156 after appending the default shared library suffix for the plat‐
157 form. The library initialization routine is expected to be
158 named dl_load().
159 -L [value]
161 --lint[=value]
162 Provide warnings about constructs that are dubious or non-porta‐
163 ble to other AWK implementations. With an optional argument of
164 fatal, lint warnings become fatal errors. This may be drastic,
165 but its use will certainly encourage the development of cleaner
166 AWK programs. With an optional argument of invalid, only warn‐
167 ings about things that are actually invalid are issued. (This is
168 not fully implemented yet.)
169 -M
171 --bignum
172 Force arbitrary precision arithmetic on numbers. This option has
173 no effect if gawk is not compiled to use the GNU MPFR and MP
174 libraries. (In such a case, gawk issues a warning.)
175 -n
177 --non-decimal-data
178 Recognize octal and hexadecimal values in input data. Use this
179 option with great caution!
180 -N
182 --use-lc-numeric
183 Force gawk to use the locale's decimal point character when
184 parsing input data. Although the POSIX standard requires this
185 behavior, and gawk does so when --posix is in effect, the
186 default is to follow traditional behavior and use a period as
187 the decimal point, even in locales where the period is not the
188 decimal point character. This option overrides the default
189 behavior, without the full draconian strictness of the --posix
190 option.
191 -o[file]
193 --pretty-print[=file]
194 Output a pretty printed version of the program to file. If no
195 file is provided, gawk uses a file named awkprof.out in the cur‐
196 rent directory. Implies --no-optimize.
197 -O
199 --optimize
200 Enable gawk's default optimizations upon the internal represen‐
201 tation of the program. Currently, this includes simple con‐
202 stant-folding, and tail call elimination for recursive func‐
203 tions. This option is on by default.
204 -p[prof-file]
206 --profile[=prof-file]
207 Start a profiling session, and send the profiling data to prof-
208 file. The default is awkprof.out. The profile contains execu‐
209 tion counts of each statement in the program in the left margin
210 and function call counts for each user-defined function.
211 Implies --no-optimize.
212 -P
214 --posix
215 This turns on compatibility mode, with the following additional
216 restrictions:
217 · \x escape sequences are not recognized.
219 · You cannot continue lines after ? and :.
221 · The synonym func for the keyword function is not recognized.
223 · The operators ** and **= cannot be used in place of ^ and ^=.
225 -r
227 --re-interval
228 Enable the use of interval expressions in regular expression
229 matching (see Regular Expressions, below). Interval expressions
230 were not traditionally available in the AWK language. The POSIX
231 standard added them, to make awk and egrep consistent with each
232 other. They are enabled by default, but this option remains for
233 use with --traditional.
234 -s
236 --no-optimize
237 Disable gawk's default optimizations upon the internal represen‐
238 tation of the program.
239 -S
241 --sandbox
242 Run gawk in sandbox mode, disabling the system() function, input
243 redirection with getline, output redirection with print and
244 printf, and loading dynamic extensions. Command execution
245 (through pipelines) is also disabled. This effectively blocks a
246 script from accessing local resources, except for the files
247 specified on the command line.
248 -t
250 --lint-old
251 Provide warnings about constructs that are not portable to the
252 original version of UNIX awk.
253 -V
255 --version
256 Print version information for this particular copy of gawk on
257 the standard output. This is useful mainly for knowing if the
258 current copy of gawk on your system is up to date with respect
259 to whatever the Free Software Foundation is distributing. This
260 is also useful when reporting bugs. (Per the GNU Coding Stan‐
261 dards, these options cause an immediate, successful exit.)
262 -- Signal the end of options. This is useful to allow further argu‐
264 ments to the AWK program itself to start with a “-”. This pro‐
265 vides consistency with the argument parsing convention used by
266 most other POSIX programs.
267 In compatibility mode, any other options are flagged as invalid, but
269 are otherwise ignored. In normal operation, as long as program text
270 has been supplied, unknown options are passed on to the AWK program in
271 the ARGV array for processing. This is particularly useful for running
272 AWK programs via the #! executable interpreter mechanism.
273 For POSIX compatibility, the -W option may be used, followed by the
275 name of a long option.
276
278 An AWK program consists of a sequence of optional directives, pattern-
279 action statements, and optional function definitions.
280 @include "filename"
282 @load "filename"
283 pattern { action statements }
284 function name(parameter list) { statements }
285 Gawk first reads the program source from the program-file(s) if speci‐
287 fied, from arguments to --source, or from the first non-option argument
288 on the command line. The -f and --source options may be used multiple
289 times on the command line. Gawk reads the program text as if all the
290 program-files and command line source texts had been concatenated
291 together. This is useful for building libraries of AWK functions,
292 without having to include them in each new AWK program that uses them.
293 It also provides the ability to mix library functions with command line
294 programs.
295 In addition, lines beginning with @include may be used to include other
297 source files into your program, making library use even easier. This
298 is equivalent to using the -i option.
299 Lines beginning with @load may be used to load extension functions into
301 your program. This is equivalent to using the -l option.
302 The environment variable AWKPATH specifies a search path to use when
304 finding source files named with the -f and -i options. If this vari‐
305 able does not exist, the default path is ".:/usr/local/share/awk".
306 (The actual directory may vary, depending upon how gawk was built and
307 installed.) If a file name given to the -f option contains a “/” char‐
308 acter, no path search is performed.
309 The environment variable AWKLIBPATH specifies a search path to use when
311 finding source files named with the -l option. If this variable does
312 not exist, the default path is "/usr/local/lib/gawk". (The actual
313 directory may vary, depending upon how gawk was built and installed.)
314 Gawk executes AWK programs in the following order. First, all variable
316 assignments specified via the -v option are performed. Next, gawk com‐
317 piles the program into an internal form. Then, gawk executes the code
318 in the BEGIN rule(s) (if any), and then proceeds to read each file
319 named in the ARGV array (up to ARGV[ARGC-1]). If there are no files
320 named on the command line, gawk reads the standard input.
321 If a filename on the command line has the form var=val it is treated as
323 a variable assignment. The variable var will be assigned the value
324 val. (This happens after any BEGIN rule(s) have been run.) Command
325 line variable assignment is most useful for dynamically assigning val‐
326 ues to the variables AWK uses to control how input is broken into
327 fields and records. It is also useful for controlling state if multi‐
328 ple passes are needed over a single data file.
329 If the value of a particular element of ARGV is empty (""), gawk skips
331 over it.
332 For each input file, if a BEGINFILE rule exists, gawk executes the
334 associated code before processing the contents of the file. Similarly,
335 gawk executes the code associated with ENDFILE after processing the
336 file.
337 For each record in the input, gawk tests to see if it matches any pat‐
339 tern in the AWK program. For each pattern that the record matches,
340 gawk executes the associated action. The patterns are tested in the
341 order they occur in the program.
342 Finally, after all the input is exhausted, gawk executes the code in
344 the END rule(s) (if any).
345 Command Line Directories
347 According to POSIX, files named on the awk command line must be text
348 files. The behavior is ``undefined'' if they are not. Most versions
349 of awk treat a directory on the command line as a fatal error.
350 Starting with version 4.0 of gawk, a directory on the command line pro‐
352 duces a warning, but is otherwise skipped. If either of the --posix or
353 --traditional options is given, then gawk reverts to treating directo‐
354 ries on the command line as a fatal error.
355
357 AWK variables are dynamic; they come into existence when they are first
358 used. Their values are either floating-point numbers or strings, or
359 both, depending upon how they are used. Additionally, gawk allows
360 variables to have regular-expression type. AWK also has one dimen‐
361 sional arrays; arrays with multiple dimensions may be simulated. Gawk
362 provides true arrays of arrays; see Arrays, below. Several pre-defined
363 variables are set as a program runs; these are described as needed and
364 summarized below.
365 Records
367 Normally, records are separated by newline characters. You can control
368 how records are separated by assigning values to the built-in variable
369 RS. If RS is any single character, that character separates records.
370 Otherwise, RS is a regular expression. Text in the input that matches
371 this regular expression separates the record. However, in compatibil‐
372 ity mode, only the first character of its string value is used for sep‐
373 arating records. If RS is set to the null string, then records are
374 separated by empty lines. When RS is set to the null string, the new‐
375 line character always acts as a field separator, in addition to what‐
376 ever value FS may have.
377 Fields
379 As each input record is read, gawk splits the record into fields, using
380 the value of the FS variable as the field separator. If FS is a single
381 character, fields are separated by that character. If FS is the null
382 string, then each individual character becomes a separate field. Oth‐
383 erwise, FS is expected to be a full regular expression. In the special
384 case that FS is a single space, fields are separated by runs of spaces
385 and/or tabs and/or newlines. NOTE: The value of IGNORECASE (see below)
386 also affects how fields are split when FS is a regular expression, and
387 how records are separated when RS is a regular expression.
388 If the FIELDWIDTHS variable is set to a space-separated list of num‐
390 bers, each field is expected to have fixed width, and gawk splits up
391 the record using the specified widths. Each field width may optionally
392 be preceded by a colon-separated value specifying the number of charac‐
393 ters to skip before the field starts. The value of FS is ignored.
394 Assigning a new value to FS or FPAT overrides the use of FIELDWIDTHS.
395 Similarly, if the FPAT variable is set to a string representing a regu‐
397 lar expression, each field is made up of text that matches that regular
398 expression. In this case, the regular expression describes the fields
399 themselves, instead of the text that separates the fields. Assigning a
400 new value to FS or FIELDWIDTHS overrides the use of FPAT.
401 Each field in the input record may be referenced by its position: $1,
403 $2, and so on. $0 is the whole record. Fields need not be referenced
404 by constants:
405 n = 5
407 print $n
408 prints the fifth field in the input record.
410 The variable NF is set to the total number of fields in the input
412 record.
413 References to non-existent fields (i.e., fields after $NF) produce the
415 null-string. However, assigning to a non-existent field (e.g., $(NF+2)
416 = 5) increases the value of NF, creates any intervening fields with the
417 null string as their values, and causes the value of $0 to be recom‐
418 puted, with the fields being separated by the value of OFS. References
419 to negative numbered fields cause a fatal error. Decrementing NF
420 causes the values of fields past the new value to be lost, and the
421 value of $0 to be recomputed, with the fields being separated by the
422 value of OFS.
423 Assigning a value to an existing field causes the whole record to be
425 rebuilt when $0 is referenced. Similarly, assigning a value to $0
426 causes the record to be resplit, creating new values for the fields.
427 Built-in Variables
429 Gawk's built-in variables are:
430 ARGC The number of command line arguments (does not include
432 options to gawk, or the program source).
433 ARGIND The index in ARGV of the current file being processed.
435 ARGV Array of command line arguments. The array is indexed from
437 0 to ARGC - 1. Dynamically changing the contents of ARGV
438 can control the files used for data.
439 BINMODE On non-POSIX systems, specifies use of “binary” mode for
441 all file I/O. Numeric values of 1, 2, or 3, specify that
442 input files, output files, or all files, respectively,
443 should use binary I/O. String values of "r", or "w" spec‐
444 ify that input files, or output files, respectively, should
445 use binary I/O. String values of "rw" or "wr" specify that
446 all files should use binary I/O. Any other string value is
447 treated as "rw", but generates a warning message.
448 CONVFMT The conversion format for numbers, "%.6g", by default.
450 ENVIRON An array containing the values of the current environment.
452 The array is indexed by the environment variables, each
453 element being the value of that variable (e.g., ENVI‐
454 RON["HOME"] might be "/home/arnold").
455 In POSIX mode, changing this array does not affect the
457 environment seen by programs which gawk spawns via redi‐
458 rection or the system() function. Otherwise, gawk updates
459 its real environment so that programs it spawns see the
460 changes.
461 ERRNO If a system error occurs either doing a redirection for
463 getline, during a read for getline, or during a close(),
464 then ERRNO is set to a string describing the error. The
465 value is subject to translation in non-English locales. If
466 the string in ERRNO corresponds to a system error in the
467 errno(3) variable, then the numeric value can be found in
468 PROCINFO["errno"]. For non-system errors,
469 PROCINFO["errno"] will be zero.
470 FIELDWIDTHS A whitespace-separated list of field widths. When set,
472 gawk parses the input into fields of fixed width, instead
473 of using the value of the FS variable as the field separa‐
474 tor. Each field width may optionally be preceded by a
475 colon-separated value specifying the number of characters
476 to skip before the field starts. See Fields, above.
477 FILENAME The name of the current input file. If no files are speci‐
479 fied on the command line, the value of FILENAME is “-”.
480 However, FILENAME is undefined inside the BEGIN rule
481 (unless set by getline).
482 FNR The input record number in the current input file.
484 FPAT A regular expression describing the contents of the fields
486 in a record. When set, gawk parses the input into fields,
487 where the fields match the regular expression, instead of
488 using the value of the FS variable as the field separator.
489 See Fields, above.
490 FS The input field separator, a space by default. See Fields,
492 above.
493 FUNCTAB An array whose indices and corresponding values are the
495 names of all the user-defined or extension functions in the
496 program. NOTE: You may not use the delete statement with
497 the FUNCTAB array.
498 IGNORECASE Controls the case-sensitivity of all regular expression and
500 string operations. If IGNORECASE has a non-zero value,
501 then string comparisons and pattern matching in rules,
502 field splitting with FS and FPAT, record separating with
503 RS, regular expression matching with ~ and !~, and the gen‐
504 sub(), gsub(), index(), match(), patsplit(), split(), and
505 sub() built-in functions all ignore case when doing regular
506 expression operations. NOTE: Array subscripting is not
507 affected. However, the asort() and asorti() functions are
508 affected.
509 Thus, if IGNORECASE is not equal to zero, /aB/ matches all
510 of the strings "ab", "aB", "Ab", and "AB". As with all AWK
511 variables, the initial value of IGNORECASE is zero, so all
512 regular expression and string operations are normally case-
513 sensitive.
514 LINT Provides dynamic control of the --lint option from within
516 an AWK program. When true, gawk prints lint warnings. When
517 false, it does not. When assigned the string value
518 "fatal", lint warnings become fatal errors, exactly like
519 --lint=fatal. Any other true value just prints warnings.
520 NF The number of fields in the current input record.
522 NR The total number of input records seen so far.
524 OFMT The output format for numbers, "%.6g", by default.
526 OFS The output field separator, a space by default.
528 ORS The output record separator, by default a newline.
530 PREC The working precision of arbitrary precision floating-point
532 numbers, 53 by default.
533 PROCINFO The elements of this array provide access to information
535 about the running AWK program. On some systems, there may
536 be elements in the array, "group1" through "groupn" for
537 some n, which is the number of supplementary groups that
538 the process has. Use the in operator to test for these
539 elements. The following elements are guaranteed to be
540 available:
541 PROCINFO["argv"] The command line arguments as received
543 by gawk at the C-language level. The
544 subscripts start from zero.
545 PROCINFO["egid"] The value of the getegid(2) system
547 call.
548 PROCINFO["errno"] The value of errno(3) when ERRNO is
550 set to the associated error message.
551 PROCINFO["euid"] The value of the geteuid(2) system
553 call.
554 PROCINFO["FS"] "FS" if field splitting with FS is in
556 effect, "FPAT" if field splitting with
557 FPAT is in effect, "FIELDWIDTHS" if
558 field splitting with FIELDWIDTHS is in
559 effect, or "API" if API input parser
560 field splitting is in effect.
561 PROCINFO["gid"] The value of the getgid(2) system
563 call.
564 PROCINFO["identifiers"]
566 A subarray, indexed by the names of
567 all identifiers used in the text of
568 the AWK program. The values indicate
569 what gawk knows about the identifiers
570 after it has finished parsing the pro‐
571 gram; they are not updated while the
572 program runs. For each identifier,
573 the value of the element is one of the
574 following:
575 "array" The identifier is an
577 array.
578 "builtin" The identifier is a built-
580 in function.
581 "extension" The identifier is an
583 extension function loaded
584 via @load or -l.
585 "scalar" The identifier is a
587 scalar.
588 "untyped" The identifier is untyped
590 (could be used as a scalar
591 or array, gawk doesn't
592 know yet).
593 "user" The identifier is a user-
595 defined function.
596 PROCINFO["pgrpid"] The process group ID of the current
598 process.
599 PROCINFO["pid"] The process ID of the current process.
601 PROCINFO["ppid"] The parent process ID of the current
603 process.
604 PROCINFO["strftime"] The default time format string for
606 strftime().
607 PROCINFO["uid"] The value of the getuid(2) system
609 call.
610 PROCINFO["version"] the version of gawk.
612 The following elements are present if loading dynamic
614 extensions is available:
615 PROCINFO["api_major"]
617 The major version of the extension API.
618 PROCINFO["api_minor"]
620 The minor version of the extension API.
621 The following elements are available if MPFR support is
623 compiled into gawk:
624 PROCINFO["gmp_version"]
626 The version of the GNU MP library used for arbitrary
627 precision number support in gawk.
628 PROCINFO["mpfr_version"]
630 The version of the GNU MPFR library used for arbi‐
631 trary precision number support in gawk.
632 PROCINFO["prec_max"]
634 The maximum precision supported by the GNU MPFR
635 library for arbitrary precision floating-point num‐
636 bers.
637 PROCINFO["prec_min"]
639 The minimum precision allowed by the GNU MPFR
640 library for arbitrary precision floating-point num‐
641 bers.
642 The following elements may set by a program to change
644 gawk's behavior:
645 PROCINFO["NONFATAL"]
647 If this exists, then I/O errors for all redirections
648 become nonfatal.
649 PROCINFO["name", "NONFATAL"]
651 Make I/O errors for name be nonfatal.
652 PROCINFO["command", "pty"]
654 Use a pseudo-tty for two-way communication with com‐
655 mand instead of setting up two one-way pipes.
656 PROCINFO["input", "READ_TIMEOUT"]
658 The timeout in milliseconds for reading data from
659 input, where input is a redirection string or a
660 filename. A value of zero or less than zero means no
661 timeout.
662 PROCINFO["input", "RETRY"]
664 If an I/O error that may be retried occurs when
665 reading data from input, and this array entry
666 exists, then getline returns -2 instead of following
667 the default behavior of returning -1 and configuring
668 input to return no further data. An I/O error that
669 may be retried is one where errno(3) has the value
670 EAGAIN, EWOULDBLOCK, EINTR, or ETIMEDOUT. This may
671 be useful in conjunction with PROCINFO["input",
672 "READ_TIMEOUT"] or situations where a file descrip‐
673 tor has been configured to behave in a non-blocking
674 fashion.
675 PROCINFO["sorted_in"]
677 If this element exists in PROCINFO, then its value
678 controls the order in which array elements are tra‐
679 versed in for loops. Supported values are
680 "@ind_str_asc", "@ind_num_asc", "@val_type_asc",
681 "@val_str_asc", "@val_num_asc", "@ind_str_desc",
682 "@ind_num_desc", "@val_type_desc", "@val_str_desc",
683 "@val_num_desc", and "@unsorted". The value can
684 also be the name (as a string) of any comparison
685 function defined as follows:
686 function cmp_func(i1, v1, i2, v2)
688 where i1 and i2 are the indices, and v1 and v2 are
690 the corresponding values of the two elements being
691 compared. It should return a number less than,
692 equal to, or greater than 0, depending on how the
693 elements of the array are to be ordered.
694 ROUNDMODE The rounding mode to use for arbitrary precision arithmetic
696 on numbers, by default "N" (IEEE-754 roundTiesToEven mode).
697 The accepted values are "N" or "n" for roundTiesToEven, "U"
698 or "u" for roundTowardPositive, "D" or "d" for roundToward‐
699 Negative, "Z" or "z" for roundTowardZero, and if your ver‐
700 sion of GNU MPFR library supports it, "A" or "a" for round‐
701 ing away from zero.
702 RS The input record separator, by default a newline.
704 RT The record terminator. Gawk sets RT to the input text that
706 matched the character or regular expression specified by
707 RS.
708 RSTART The index of the first character matched by match(); 0 if
710 no match. (This implies that character indices start at
711 one.)
712 RLENGTH The length of the string matched by match(); -1 if no
714 match.
715 SUBSEP The character used to separate multiple subscripts in array
717 elements, by default "\034".
718 SYMTAB An array whose indices are the names of all currently
720 defined global variables and arrays in the program. The
721 array may be used for indirect access to read or write the
722 value of a variable:
723 foo = 5
725 SYMTAB["foo"] = 4
726 print foo # prints 4
727 The typeof() function may be used to test if an element in
729 SYMTAB is an array. You may not use the delete statement
730 with the SYMTAB array.
731 TEXTDOMAIN The text domain of the AWK program; used to find the local‐
733 ized translations for the program's strings.
734 Arrays
736 Arrays are subscripted with an expression between square brackets ([
737 and ]). If the expression is an expression list (expr, expr ...) then
738 the array subscript is a string consisting of the concatenation of the
739 (string) value of each expression, separated by the value of the SUBSEP
740 variable. This facility is used to simulate multiply dimensioned
741 arrays. For example:
742 i = "A"; j = "B"; k = "C"
744 x[i, j, k] = "hello, world\n"
745 assigns the string "hello, world\n" to the element of the array x which
747 is indexed by the string "A\034B\034C". All arrays in AWK are associa‐
748 tive, i.e., indexed by string values.
749 The special operator in may be used to test if an array has an index
751 consisting of a particular value:
752 if (val in array)
754 print array[val]
755 If the array has multiple subscripts, use (i, j) in array.
757 The in construct may also be used in a for loop to iterate over all the
759 elements of an array. However, the (i, j) in array construct only
760 works in tests, not in for loops.
761 An element may be deleted from an array using the delete statement.
763 The delete statement may also be used to delete the entire contents of
764 an array, just by specifying the array name without a subscript.
765 gawk supports true multidimensional arrays. It does not require that
767 such arrays be ``rectangular'' as in C or C++. For example:
768 a[1] = 5
770 a[2][1] = 6
771 a[2][2] = 7
772 NOTE: You may need to tell gawk that an array element is really a sub‐
774 array in order to use it where gawk expects an array (such as in the
775 second argument to split()). You can do this by creating an element in
776 the subarray and then deleting it with the delete statement.
777 Variable Typing And Conversion
779 Variables and fields may be (floating point) numbers, or strings, or
780 both. They may also be regular expressions. How the value of a vari‐
781 able is interpreted depends upon its context. If used in a numeric
782 expression, it will be treated as a number; if used as a string it will
783 be treated as a string.
784 To force a variable to be treated as a number, add zero to it; to force
786 it to be treated as a string, concatenate it with the null string.
787 Uninitialized variables have the numeric value zero and the string
789 value "" (the null, or empty, string).
790 When a string must be converted to a number, the conversion is accom‐
792 plished using strtod(3). A number is converted to a string by using
793 the value of CONVFMT as a format string for sprintf(3), with the
794 numeric value of the variable as the argument. However, even though
795 all numbers in AWK are floating-point, integral values are always con‐
796 verted as integers. Thus, given
797 CONVFMT = "%2.2f"
799 a = 12
800 b = a ""
801 the variable b has a string value of "12" and not "12.00".
803 NOTE: When operating in POSIX mode (such as with the --posix option),
805 beware that locale settings may interfere with the way decimal numbers
806 are treated: the decimal separator of the numbers you are feeding to
807 gawk must conform to what your locale would expect, be it a comma (,)
808 or a period (.).
809 Gawk performs comparisons as follows: If two variables are numeric,
811 they are compared numerically. If one value is numeric and the other
812 has a string value that is a “numeric string,” then comparisons are
813 also done numerically. Otherwise, the numeric value is converted to a
814 string and a string comparison is performed. Two strings are compared,
815 of course, as strings.
816 Note that string constants, such as "57", are not numeric strings, they
818 are string constants. The idea of “numeric string” only applies to
819 fields, getline input, FILENAME, ARGV elements, ENVIRON elements and
820 the elements of an array created by split() or patsplit() that are
821 numeric strings. The basic idea is that user input, and only user
822 input, that looks numeric, should be treated that way.
823 Octal and Hexadecimal Constants
825 You may use C-style octal and hexadecimal constants in your AWK program
826 source code. For example, the octal value 011 is equal to decimal 9,
827 and the hexadecimal value 0x11 is equal to decimal 17.
828 String Constants
830 String constants in AWK are sequences of characters enclosed between
831 double quotes (like "value"). Within strings, certain escape sequences
832 are recognized, as in C. These are:
833 \\ A literal backslash.
835 \a The “alert” character; usually the ASCII BEL character.
837 \b Backspace.
839 \f Form-feed.
841 \n Newline.
843 \r Carriage return.
845 \t Horizontal tab.
847 \v Vertical tab.
849 \xhex digits
851 The character represented by the string of hexadecimal digits fol‐
852 lowing the \x. Up to two following hexadecimal digits are consid‐
853 ered part of the escape sequence. E.g., "\x1B" is the ASCII ESC
854 (escape) character.
855 \ddd The character represented by the 1-, 2-, or 3-digit sequence of
857 octal digits. E.g., "\033" is the ASCII ESC (escape) character.
858 \c The literal character c.
860 In compatibility mode, the characters represented by octal and hexadec‐
862 imal escape sequences are treated literally when used in regular
863 expression constants. Thus, /a\52b/ is equivalent to /a\*b/.
864 Regexp Constants
866 A regular expression constant is a sequence of characters enclosed
867 between forward slashes (like /value/). Regular expression matching is
868 described more fully below; see Regular Expressions.
869 The escape sequences described earlier may also be used inside constant
871 regular expressions (e.g., /[ \t\f\n\r\v]/ matches whitespace charac‐
872 ters).
873 Gawk provides strongly typed regular expression constants. These are
875 written with a leading @ symbol (like so: @/value/). Such con‐
876 stants may be assigned to scalars (variables, array elements)
877 and passed to user-defined functions. Variables that have been
878 so assigned have regular expression type.
879
881 AWK is a line-oriented language. The pattern comes first, and then the
882 action. Action statements are enclosed in { and }. Either the pattern
883 may be missing, or the action may be missing, but, of course, not both.
884 If the pattern is missing, the action executes for every single record
885 of input. A missing action is equivalent to
886 { print }
888 which prints the entire record.
890 Comments begin with the # character, and continue until the end of the
892 line. Empty lines may be used to separate statements. Normally, a
893 statement ends with a newline, however, this is not the case for lines
894 ending in a comma, {, ?, :, &&, or ||. Lines ending in do or else also
895 have their statements automatically continued on the following line.
896 In other cases, a line can be continued by ending it with a “\”, in
897 which case the newline is ignored.
898 Multiple statements may be put on one line by separating them with a
900 “;”. This applies to both the statements within the action part of a
901 pattern-action pair (the usual case), and to the pattern-action state‐
902 ments themselves.
903 Patterns
905 AWK patterns may be one of the following:
906 BEGIN
908 END
909 BEGINFILE
910 ENDFILE
911 /regular expression/
912 relational expression
913 pattern && pattern
914 pattern || pattern
915 pattern ? pattern : pattern
916 (pattern)
917 ! pattern
918 pattern1, pattern2
919 BEGIN and END are two special kinds of patterns which are not tested
921 against the input. The action parts of all BEGIN patterns are merged
922 as if all the statements had been written in a single BEGIN rule. They
923 are executed before any of the input is read. Similarly, all the END
924 rules are merged, and executed when all the input is exhausted (or when
925 an exit statement is executed). BEGIN and END patterns cannot be com‐
926 bined with other patterns in pattern expressions. BEGIN and END pat‐
927 terns cannot have missing action parts.
928 BEGINFILE and ENDFILE are additional special patterns whose bodies are
930 executed before reading the first record of each command line input
931 file and after reading the last record of each file. Inside the BEGIN‐
932 FILE rule, the value of ERRNO is the empty string if the file was
933 opened successfully. Otherwise, there is some problem with the file
934 and the code should use nextfile to skip it. If that is not done, gawk
935 produces its usual fatal error for files that cannot be opened.
936 For /regular expression/ patterns, the associated statement is executed
938 for each input record that matches the regular expression. Regular
939 expressions are the same as those in egrep(1), and are summarized
940 below.
941 A relational expression may use any of the operators defined below in
943 the section on actions. These generally test whether certain fields
944 match certain regular expressions.
945 The &&, ||, and ! operators are logical AND, logical OR, and logical
947 NOT, respectively, as in C. They do short-circuit evaluation, also as
948 in C, and are used for combining more primitive pattern expressions.
949 As in most languages, parentheses may be used to change the order of
950 evaluation.
951 The ?: operator is like the same operator in C. If the first pattern
953 is true then the pattern used for testing is the second pattern, other‐
954 wise it is the third. Only one of the second and third patterns is
955 evaluated.
956 The pattern1, pattern2 form of an expression is called a range pattern.
958 It matches all input records starting with a record that matches pat‐
959 tern1, and continuing until a record that matches pattern2, inclusive.
960 It does not combine with any other sort of pattern expression.
961 Regular Expressions
963 Regular expressions are the extended kind found in egrep. They are
964 composed of characters as follows:
965 c Matches the non-metacharacter c.
967 \c Matches the literal character c.
969 . Matches any character including newline.
971 ^ Matches the beginning of a string.
973 $ Matches the end of a string.
975 [abc...] A character list: matches any of the characters abc.... You
977 may include a range of characters by separating them with a
978 dash.
979 [^abc...] A negated character list: matches any character except
981 abc....
982 r1|r2 Alternation: matches either r1 or r2.
984 r1r2 Concatenation: matches r1, and then r2.
986 r+ Matches one or more r's.
988 r* Matches zero or more r's.
990 r? Matches zero or one r's.
992 (r) Grouping: matches r.
994 r{n}
996 r{n,}
997 r{n,m} One or two numbers inside braces denote an interval expres‐
998 sion. If there is one number in the braces, the preceding
999 regular expression r is repeated n times. If there are two
1000 numbers separated by a comma, r is repeated n to m times.
1001 If there is one number followed by a comma, then r is
1002 repeated at least n times.
1003 \y Matches the empty string at either the beginning or the end
1005 of a word.
1006 \B Matches the empty string within a word.
1008 \< Matches the empty string at the beginning of a word.
1010 \> Matches the empty string at the end of a word.
1012 \s Matches any whitespace character.
1014 \S Matches any nonwhitespace character.
1016 \w Matches any word-constituent character (letter, digit, or
1018 underscore).
1019 \W Matches any character that is not word-constituent.
1021 \` Matches the empty string at the beginning of a buffer
1023 (string).
1024 \' Matches the empty string at the end of a buffer.
1026 The escape sequences that are valid in string constants (see String
1028 Constants) are also valid in regular expressions.
1029 Character classes are a feature introduced in the POSIX standard. A
1031 character class is a special notation for describing lists of charac‐
1032 ters that have a specific attribute, but where the actual characters
1033 themselves can vary from country to country and/or from character set
1034 to character set. For example, the notion of what is an alphabetic
1035 character differs in the USA and in France.
1036 A character class is only valid in a regular expression inside the
1038 brackets of a character list. Character classes consist of [:, a key‐
1039 word denoting the class, and :]. The character classes defined by the
1040 POSIX standard are:
1041 [:alnum:] Alphanumeric characters.
1043 [:alpha:] Alphabetic characters.
1045 [:blank:] Space or tab characters.
1047 [:cntrl:] Control characters.
1049 [:digit:] Numeric characters.
1051 [:graph:] Characters that are both printable and visible. (A space is
1053 printable, but not visible, while an a is both.)
1054 [:lower:] Lowercase alphabetic characters.
1056 [:print:] Printable characters (characters that are not control char‐
1058 acters.)
1059 [:punct:] Punctuation characters (characters that are not letter, dig‐
1061 its, control characters, or space characters).
1062 [:space:] Space characters (such as space, tab, and formfeed, to name
1064 a few).
1065 [:upper:] Uppercase alphabetic characters.
1067 [:xdigit:] Characters that are hexadecimal digits.
1069 For example, before the POSIX standard, to match alphanumeric charac‐
1071 ters, you would have had to write /[A-Za-z0-9]/. If your character set
1072 had other alphabetic characters in it, this would not match them, and
1073 if your character set collated differently from ASCII, this might not
1074 even match the ASCII alphanumeric characters. With the POSIX character
1075 classes, you can write /[[:alnum:]]/, and this matches the alphabetic
1076 and numeric characters in your character set, no matter what it is.
1077 Two additional special sequences can appear in character lists. These
1079 apply to non-ASCII character sets, which can have single symbols
1080 (called collating elements) that are represented with more than one
1081 character, as well as several characters that are equivalent for col‐
1082 lating, or sorting, purposes. (E.g., in French, a plain “e” and a
1083 grave-accented “e`” are equivalent.)
1084 Collating Symbols
1086 A collating symbol is a multi-character collating element
1087 enclosed in [. and .]. For example, if ch is a collating ele‐
1088 ment, then [[.ch.]] is a regular expression that matches this
1089 collating element, while [ch] is a regular expression that
1090 matches either c or h.
1091 Equivalence Classes
1093 An equivalence class is a locale-specific name for a list of
1094 characters that are equivalent. The name is enclosed in [= and
1095 =]. For example, the name e might be used to represent all of
1096 “e”, “e´”, and “e`”. In this case, [[=e=]] is a regular expres‐
1097 sion that matches any of e, e´, or e`.
1098 These features are very valuable in non-English speaking locales. The
1100 library functions that gawk uses for regular expression matching cur‐
1101 rently only recognize POSIX character classes; they do not recognize
1102 collating symbols or equivalence classes.
1103 The \y, \B, \<, \>, \s, \S, \w, \W, \`, and \' operators are specific
1105 to gawk; they are extensions based on facilities in the GNU regular
1106 expression libraries.
1107 The various command line options control how gawk interprets characters
1109 in regular expressions.
1110 No options
1112 In the default case, gawk provides all the facilities of POSIX
1113 regular expressions and the GNU regular expression operators
1114 described above.
1115 --posix
1117 Only POSIX regular expressions are supported, the GNU operators
1118 are not special. (E.g., \w matches a literal w).
1119 --traditional
1121 Traditional UNIX awk regular expressions are matched. The GNU
1122 operators are not special, and interval expressions are not
1123 available. Characters described by octal and hexadecimal escape
1124 sequences are treated literally, even if they represent regular
1125 expression metacharacters.
1126 --re-interval
1128 Allow interval expressions in regular expressions, even if
1129 --traditional has been provided.
1130 Actions
1132 Action statements are enclosed in braces, { and }. Action statements
1133 consist of the usual assignment, conditional, and looping statements
1134 found in most languages. The operators, control statements, and
1135 input/output statements available are patterned after those in C.
1136 Operators
1138 The operators in AWK, in order of decreasing precedence, are:
1139 (...) Grouping
1141 $ Field reference.
1143 ++ -- Increment and decrement, both prefix and postfix.
1145 ^ Exponentiation (** may also be used, and **= for the
1147 assignment operator).
1148 + - ! Unary plus, unary minus, and logical negation.
1150 * / % Multiplication, division, and modulus.
1152 + - Addition and subtraction.
1154 space String concatenation.
1156 | |& Piped I/O for getline, print, and printf.
1158 < > <= >= == !=
1160 The regular relational operators.
1161 ~ !~ Regular expression match, negated match. NOTE: Do not use
1163 a constant regular expression (/foo/) on the left-hand side
1164 of a ~ or !~. Only use one on the right-hand side. The
1165 expression /foo/ ~ exp has the same meaning as (($0 ~
1166 /foo/) ~ exp). This is usually not what you want.
1167 in Array membership.
1169 && Logical AND.
1171 || Logical OR.
1173 ?: The C conditional expression. This has the form expr1 ?
1175 expr2 : expr3. If expr1 is true, the value of the expres‐
1176 sion is expr2, otherwise it is expr3. Only one of expr2
1177 and expr3 is evaluated.
1178 = += -= *= /= %= ^=
1180 Assignment. Both absolute assignment (var = value) and
1181 operator-assignment (the other forms) are supported.
1182 Control Statements
1184 The control statements are as follows:
1185 if (condition) statement [ else statement ]
1187 while (condition) statement
1188 do statement while (condition)
1189 for (expr1; expr2; expr3) statement
1190 for (var in array) statement
1191 break
1192 continue
1193 delete array[index]
1194 delete array
1195 exit [ expression ]
1196 { statements }
1197 switch (expression) {
1198 case value|regex : statement
1199 ...
1200 [ default: statement ]
1201 }
1202 I/O Statements
1204 The input/output statements are as follows:
1205 close(file [, how]) Close file, pipe or coprocess. The optional how
1207 should only be used when closing one end of a
1208 two-way pipe to a coprocess. It must be a string
1209 value, either "to" or "from".
1210 getline Set $0 from next input record; set NF, NR, FNR,
1212 RT.
1213 getline <file Set $0 from next record of file; set NF, RT.
1215 getline var Set var from next input record; set NR, FNR, RT.
1217 getline var <file Set var from next record of file, RT.
1219 command | getline [var]
1221 Run command piping the output either into $0 or
1222 var, as above, and RT.
1223 command |& getline [var]
1225 Run command as a coprocess piping the output
1226 either into $0 or var, as above, and RT. Copro‐
1227 cesses are a gawk extension. (command can also
1228 be a socket. See the subsection Special File
1229 Names, below.)
1230 next Stop processing the current input record. The
1232 next input record is read and processing starts
1233 over with the first pattern in the AWK program.
1234 Upon reaching the end of the input data, gawk
1235 executes any END rule(s).
1236 nextfile Stop processing the current input file. The next
1238 input record read comes from the next input file.
1239 FILENAME and ARGIND are updated, FNR is reset to
1240 1, and processing starts over with the first pat‐
1241 tern in the AWK program. Upon reaching the end
1242 of the input data, gawk executes any ENDFILE and
1243 END rule(s).
1244 print Print the current record. The output record is
1246 terminated with the value of ORS.
1247 print expr-list Print expressions. Each expression is separated
1249 by the value of OFS. The output record is termi‐
1250 nated with the value of ORS.
1251 print expr-list >file Print expressions on file. Each expression is
1253 separated by the value of OFS. The output record
1254 is terminated with the value of ORS.
1255 printf fmt, expr-list Format and print. See The printf Statement,
1257 below.
1258 printf fmt, expr-list >file
1260 Format and print on file.
1261 system(cmd-line) Execute the command cmd-line, and return the exit
1263 status. (This may not be available on non-POSIX
1264 systems.) See GAWK: Effective AWK Programming
1265 for the full details on the exit status.
1266 fflush([file]) Flush any buffers associated with the open output
1268 file or pipe file. If file is missing or if it
1269 is the null string, then flush all open output
1270 files and pipes.
1271 Additional output redirections are allowed for print and printf.
1273 print ... >> file
1275 Appends output to the file.
1276 print ... | command
1278 Writes on a pipe.
1279 print ... |& command
1281 Sends data to a coprocess or socket. (See also the subsection
1282 Special File Names, below.)
1283 The getline command returns 1 on success, zero on end of file, and -1
1285 on an error. If the errno(3) value indicates that the I/O operation
1286 may be retried, and PROCINFO["input", "RETRY"] is set, then -2 is
1287 returned instead of -1, and further calls to getline may be attempted.
1288 Upon an error, ERRNO is set to a string describing the problem.
1289 NOTE: Failure in opening a two-way socket results in a non-fatal error
1291 being returned to the calling function. If using a pipe, coprocess, or
1292 socket to getline, or from print or printf within a loop, you must use
1293 close() to create new instances of the command or socket. AWK does not
1294 automatically close pipes, sockets, or coprocesses when they return
1295 EOF.
1296 The printf Statement
1298 The AWK versions of the printf statement and sprintf() function (see
1299 below) accept the following conversion specification formats:
1300 %a, %A A floating point number of the form [-]0xh.hhhhp+-dd (C99 hexa‐
1302 decimal floating point format). For %A, uppercase letters are
1303 used instead of lowercase ones.
1304 %c A single character. If the argument used for %c is numeric, it
1306 is treated as a character and printed. Otherwise, the argument
1307 is assumed to be a string, and the only first character of that
1308 string is printed.
1309 %d, %i A decimal number (the integer part).
1311 %e, %E A floating point number of the form [-]d.dddddde[+-]dd. The %E
1313 format uses E instead of e.
1314 %f, %F A floating point number of the form [-]ddd.dddddd. If the sys‐
1316 tem library supports it, %F is available as well. This is like
1317 %f, but uses capital letters for special “not a number” and
1318 “infinity” values. If %F is not available, gawk uses %f.
1319 %g, %G Use %e or %f conversion, whichever is shorter, with nonsignifi‐
1321 cant zeros suppressed. The %G format uses %E instead of %e.
1322 %o An unsigned octal number (also an integer).
1324 %u An unsigned decimal number (again, an integer).
1326 %s A character string.
1328 %x, %X An unsigned hexadecimal number (an integer). The %X format
1330 uses ABCDEF instead of abcdef.
1331 %% A single % character; no argument is converted.
1333 Optional, additional parameters may lie between the % and the control
1335 letter:
1336 count$ Use the count'th argument at this point in the formatting. This
1338 is called a positional specifier and is intended primarily for
1339 use in translated versions of format strings, not in the origi‐
1340 nal text of an AWK program. It is a gawk extension.
1341 - The expression should be left-justified within its field.
1343 space For numeric conversions, prefix positive values with a space,
1345 and negative values with a minus sign.
1346 + The plus sign, used before the width modifier (see below), says
1348 to always supply a sign for numeric conversions, even if the
1349 data to be formatted is positive. The + overrides the space
1350 modifier.
1351 # Use an “alternate form” for certain control letters. For %o,
1353 supply a leading zero. For %x, and %X, supply a leading 0x or
1354 0X for a nonzero result. For %e, %E, %f and %F, the result
1355 always contains a decimal point. For %g, and %G, trailing zeros
1356 are not removed from the result.
1357 0 A leading 0 (zero) acts as a flag, indicating that output should
1359 be padded with zeroes instead of spaces. This applies only to
1360 the numeric output formats. This flag only has an effect when
1361 the field width is wider than the value to be printed.
1362 ' A single quote character instructs gawk to insert the locale's
1364 thousands-separator character into decimal numbers, and to also
1365 use the locale's decimal point character with floating point
1366 formats. This requires correct locale support in the C library
1367 and in the definition of the current locale.
1368 width The field should be padded to this width. The field is normally
1370 padded with spaces. With the 0 flag, it is padded with zeroes.
1371 .prec A number that specifies the precision to use when printing. For
1373 the %e, %E, %f and %F, formats, this specifies the number of
1374 digits you want printed to the right of the decimal point. For
1375 the %g, and %G formats, it specifies the maximum number of sig‐
1376 nificant digits. For the %d, %i, %o, %u, %x, and %X formats, it
1377 specifies the minimum number of digits to print. For %s, it
1378 specifies the maximum number of characters from the string that
1379 should be printed.
1380 The dynamic width and prec capabilities of the ISO C printf() routines
1382 are supported. A * in place of either the width or prec specifications
1383 causes their values to be taken from the argument list to printf or
1384 sprintf(). To use a positional specifier with a dynamic width or pre‐
1385 cision, supply the count$ after the * in the format string. For exam‐
1386 ple, "%3$*2$.*1$s".
1387 Special File Names
1389 When doing I/O redirection from either print or printf into a file, or
1390 via getline from a file, gawk recognizes certain special filenames
1391 internally. These filenames allow access to open file descriptors
1392 inherited from gawk's parent process (usually the shell). These file
1393 names may also be used on the command line to name data files. The
1394 filenames are:
1395 - The standard input.
1397 /dev/stdin The standard input.
1399 /dev/stdout The standard output.
1401 /dev/stderr The standard error output.
1403 /dev/fd/n The file associated with the open file descriptor n.
1405 These are particularly useful for error messages. For example:
1407 print "You blew it!" > "/dev/stderr"
1409 whereas you would otherwise have to use
1411 print "You blew it!" | "cat 1>&2"
1413 The following special filenames may be used with the |& coprocess oper‐
1415 ator for creating TCP/IP network connections:
1416 /inet/tcp/lport/rhost/rport
1418 /inet4/tcp/lport/rhost/rport
1419 /inet6/tcp/lport/rhost/rport
1420 Files for a TCP/IP connection on local port lport to remote host
1421 rhost on remote port rport. Use a port of 0 to have the system
1422 pick a port. Use /inet4 to force an IPv4 connection, and /inet6
1423 to force an IPv6 connection. Plain /inet uses the system
1424 default (most likely IPv4).
1425 /inet/udp/lport/rhost/rport
1427 /inet4/udp/lport/rhost/rport
1428 /inet6/udp/lport/rhost/rport
1429 Similar, but use UDP/IP instead of TCP/IP.
1430 Numeric Functions
1432 AWK has the following built-in arithmetic functions:
1433 atan2(y, x) Return the arctangent of y/x in radians.
1435 cos(expr) Return the cosine of expr, which is in radians.
1437 exp(expr) The exponential function.
1439 int(expr) Truncate to integer.
1441 log(expr) The natural logarithm function.
1443 rand() Return a random number N, between zero and one, such that
1445 0 ≤ N < 1.
1446 sin(expr) Return the sine of expr, which is in radians.
1448 sqrt(expr) Return the square root of expr.
1450 srand([expr]) Use expr as the new seed for the random number generator.
1452 If no expr is provided, use the time of day. Return the
1453 previous seed for the random number generator.
1454 String Functions
1456 Gawk has the following built-in string functions:
1457 asort(s [, d [, how] ]) Return the number of elements in the source
1459 array s. Sort the contents of s using gawk's
1460 normal rules for comparing values, and replace
1461 the indices of the sorted values s with sequen‐
1462 tial integers starting with 1. If the optional
1463 destination array d is specified, first dupli‐
1464 cate s into d, and then sort d, leaving the
1465 indices of the source array s unchanged. The
1466 optional string how controls the direction and
1467 the comparison mode. Valid values for how are
1468 any of the strings valid for
1469 PROCINFO["sorted_in"]. It can also be the name
1470 of a user-defined comparison function as
1471 described in PROCINFO["sorted_in"].
1472 asorti(s [, d [, how] ])
1474 Return the number of elements in the source
1475 array s. The behavior is the same as that of
1476 asort(), except that the array indices are used
1477 for sorting, not the array values. When done,
1478 the array is indexed numerically, and the val‐
1479 ues are those of the original indices. The
1480 original values are lost; thus provide a second
1481 array if you wish to preserve the original.
1482 The purpose of the optional string how is the
1483 same as described previously for asort().
1484 gensub(r, s, h [, t]) Search the target string t for matches of the
1486 regular expression r. If h is a string begin‐
1487 ning with g or G, then replace all matches of r
1488 with s. Otherwise, h is a number indicating
1489 which match of r to replace. If t is not sup‐
1490 plied, use $0 instead. Within the replacement
1491 text s, the sequence \n, where n is a digit
1492 from 1 to 9, may be used to indicate just the
1493 text that matched the n'th parenthesized subex‐
1494 pression. The sequence \0 represents the
1495 entire matched text, as does the character &.
1496 Unlike sub() and gsub(), the modified string is
1497 returned as the result of the function, and the
1498 original target string is not changed.
1499 gsub(r, s [, t]) For each substring matching the regular expres‐
1501 sion r in the string t, substitute the string
1502 s, and return the number of substitutions. If
1503 t is not supplied, use $0. An & in the
1504 replacement text is replaced with the text that
1505 was actually matched. Use \& to get a literal
1506 &. (This must be typed as "\\&"; see GAWK:
1507 Effective AWK Programming for a fuller discus‐
1508 sion of the rules for ampersands and back‐
1509 slashes in the replacement text of sub(),
1510 gsub(), and gensub().)
1511 index(s, t) Return the index of the string t in the string
1513 s, or zero if t is not present. (This implies
1514 that character indices start at one.) It is a
1515 fatal error to use a regexp constant for t.
1516 length([s]) Return the length of the string s, or the
1518 length of $0 if s is not supplied. As a non-
1519 standard extension, with an array argument,
1520 length() returns the number of elements in the
1521 array.
1522 match(s, r [, a]) Return the position in s where the regular
1524 expression r occurs, or zero if r is not
1525 present, and set the values of RSTART and
1526 RLENGTH. Note that the argument order is the
1527 same as for the ~ operator: str ~ re. If array
1528 a is provided, a is cleared and then elements 1
1529 through n are filled with the portions of s
1530 that match the corresponding parenthesized sub‐
1531 expression in r. The zero'th element of a con‐
1532 tains the portion of s matched by the entire
1533 regular expression r. Subscripts a[n,
1534 "start"], and a[n, "length"] provide the start‐
1535 ing index in the string and length respec‐
1536 tively, of each matching substring.
1537 patsplit(s, a [, r [, seps] ])
1539 Split the string s into the array a and the
1540 separators array seps on the regular expression
1541 r, and return the number of fields. Element
1542 values are the portions of s that matched r.
1543 The value of seps[i] is the possibly null sepa‐
1544 rator that appeared after a[i]. The value of
1545 seps[0] is the possibly null leading separator.
1546 If r is omitted, FPAT is used instead. The
1547 arrays a and seps are cleared first. Splitting
1548 behaves identically to field splitting with
1549 FPAT, described above.
1550 split(s, a [, r [, seps] ])
1552 Split the string s into the array a and the
1553 separators array seps on the regular expression
1554 r, and return the number of fields. If r is
1555 omitted, FS is used instead. The arrays a and
1556 seps are cleared first. seps[i] is the field
1557 separator matched by r between a[i] and a[i+1].
1558 If r is a single space, then leading whitespace
1559 in s goes into the extra array element seps[0]
1560 and trailing whitespace goes into the extra
1561 array element seps[n], where n is the return
1562 value of split(s, a, r, seps). Splitting
1563 behaves identically to field splitting,
1564 described above.
1565 sprintf(fmt, expr-list) Print expr-list according to fmt, and return
1567 the resulting string.
1568 strtonum(str) Examine str, and return its numeric value. If
1570 str begins with a leading 0, treat it as an
1571 octal number. If str begins with a leading 0x
1572 or 0X, treat it as a hexadecimal number. Oth‐
1573 erwise, assume it is a decimal number.
1574 sub(r, s [, t]) Just like gsub(), but replace only the first
1576 matching substring. Return either zero or one.
1577 substr(s, i [, n]) Return the at most n-character substring of s
1579 starting at i. If n is omitted, use the rest
1580 of s.
1581 tolower(str) Return a copy of the string str, with all the
1583 uppercase characters in str translated to their
1584 corresponding lowercase counterparts. Non-
1585 alphabetic characters are left unchanged.
1586 toupper(str) Return a copy of the string str, with all the
1588 lowercase characters in str translated to their
1589 corresponding uppercase counterparts. Non-
1590 alphabetic characters are left unchanged.
1591 Gawk is multibyte aware. This means that index(), length(), substr()
1593 and match() all work in terms of characters, not bytes.
1594 Time Functions
1596 Since one of the primary uses of AWK programs is processing log files
1597 that contain time stamp information, gawk provides the following func‐
1598 tions for obtaining time stamps and formatting them.
1599 mktime(datespec [, utc-flag])
1601 Turn datespec into a time stamp of the same form as returned
1602 by systime(), and return the result. The datespec is a
1603 string of the form YYYY MM DD HH MM SS[ DST]. The contents
1604 of the string are six or seven numbers representing respec‐
1605 tively the full year including century, the month from 1 to
1606 12, the day of the month from 1 to 31, the hour of the day
1607 from 0 to 23, the minute from 0 to 59, the second from 0 to
1608 60, and an optional daylight saving flag. The values of
1609 these numbers need not be within the ranges specified; for
1610 example, an hour of -1 means 1 hour before midnight. The
1611 origin-zero Gregorian calendar is assumed, with year 0 pre‐
1612 ceding year 1 and year -1 preceding year 0. If utc-flag is
1613 present and is non-zero or non-null, the time is assumed to
1614 be in the UTC time zone; otherwise, the time is assumed to be
1615 in the local time zone. If the DST daylight saving flag is
1616 positive, the time is assumed to be daylight saving time; if
1617 zero, the time is assumed to be standard time; and if nega‐
1618 tive (the default), mktime() attempts to determine whether
1619 daylight saving time is in effect for the specified time. If
1620 datespec does not contain enough elements or if the resulting
1621 time is out of range, mktime() returns -1.
1622 strftime([format [, timestamp[, utc-flag]]])
1624 Format timestamp according to the specification in format.
1625 If utc-flag is present and is non-zero or non-null, the
1626 result is in UTC, otherwise the result is in local time. The
1627 timestamp should be of the same form as returned by sys‐
1628 time(). If timestamp is missing, the current time of day is
1629 used. If format is missing, a default format equivalent to
1630 the output of date(1) is used. The default format is avail‐
1631 able in PROCINFO["strftime"]. See the specification for the
1632 strftime() function in ISO C for the format conversions that
1633 are guaranteed to be available.
1634 systime() Return the current time of day as the number of seconds since
1636 the Epoch (1970-01-01 00:00:00 UTC on POSIX systems).
1637 Bit Manipulations Functions
1639 Gawk supplies the following bit manipulation functions. They work by
1640 converting double-precision floating point values to uintmax_t inte‐
1641 gers, doing the operation, and then converting the result back to
1642 floating point.
1643 NOTE: Passing negative operands to any of these functions causes a
1645 fatal error.
1646 The functions are:
1648 and(v1, v2 [, ...]) Return the bitwise AND of the values provided in
1650 the argument list. There must be at least two.
1651 compl(val) Return the bitwise complement of val.
1653 lshift(val, count) Return the value of val, shifted left by count
1655 bits.
1656 or(v1, v2 [, ...]) Return the bitwise OR of the values provided in the
1658 argument list. There must be at least two.
1659 rshift(val, count) Return the value of val, shifted right by count
1661 bits.
1662 xor(v1, v2 [, ...]) Return the bitwise XOR of the values provided in
1664 the argument list. There must be at least two.
1665 Type Functions
1667 The following function is for use with multidimensional arrays.
1668 isarray(x)
1670 Return true if x is an array, false otherwise.
1671 You can tell the type of any variable or array element with the follow‐
1673 ing function:
1674 typeof(x)
1676 Return a string indicating the type of x. The string will be
1677 one of "array", "number", "regexp", "string", "strnum", or
1678 "undefined".
1679 Internationalization Functions
1681 The following functions may be used from within your AWK program for
1682 translating strings at run-time. For full details, see GAWK: Effective
1683 AWK Programming.
1684 bindtextdomain(directory [, domain])
1686 Specify the directory where gawk looks for the .gmo files, in
1687 case they will not or cannot be placed in the ``standard'' loca‐
1688 tions (e.g., during testing). It returns the directory where
1689 domain is ``bound.''
1690 The default domain is the value of TEXTDOMAIN. If directory is
1691 the null string (""), then bindtextdomain() returns the current
1692 binding for the given domain.
1693 dcgettext(string [, domain [, category]])
1695 Return the translation of string in text domain domain for
1696 locale category category. The default value for domain is the
1697 current value of TEXTDOMAIN. The default value for category is
1698 "LC_MESSAGES".
1699 If you supply a value for category, it must be a string equal to
1700 one of the known locale categories described in GAWK: Effective
1701 AWK Programming. You must also supply a text domain. Use
1702 TEXTDOMAIN if you want to use the current domain.
1703 dcngettext(string1, string2, number [, domain [, category]])
1705 Return the plural form used for number of the translation of
1706 string1 and string2 in text domain domain for locale category
1707 category. The default value for domain is the current value of
1708 TEXTDOMAIN. The default value for category is "LC_MESSAGES".
1709 If you supply a value for category, it must be a string equal to
1710 one of the known locale categories described in GAWK: Effective
1711 AWK Programming. You must also supply a text domain. Use
1712 TEXTDOMAIN if you want to use the current domain.
1713
1715 Functions in AWK are defined as follows:
1716 function name(parameter list) { statements }
1718 Functions execute when they are called from within expressions in
1720 either patterns or actions. Actual parameters supplied in the function
1721 call are used to instantiate the formal parameters declared in the
1722 function. Arrays are passed by reference, other variables are passed
1723 by value.
1724 Since functions were not originally part of the AWK language, the pro‐
1726 vision for local variables is rather clumsy: They are declared as extra
1727 parameters in the parameter list. The convention is to separate local
1728 variables from real parameters by extra spaces in the parameter list.
1729 For example:
1730 function f(p, q, a, b) # a and b are local
1732 {
1733 ...
1734 }
1735 /abc/ { ... ; f(1, 2) ; ... }
1737 The left parenthesis in a function call is required to immediately fol‐
1739 low the function name, without any intervening whitespace. This avoids
1740 a syntactic ambiguity with the concatenation operator. This restric‐
1741 tion does not apply to the built-in functions listed above.
1742 Functions may call each other and may be recursive. Function parame‐
1744 ters used as local variables are initialized to the null string and the
1745 number zero upon function invocation.
1746 Use return expr to return a value from a function. The return value is
1748 undefined if no value is provided, or if the function returns by “fall‐
1749 ing off” the end.
1750 As a gawk extension, functions may be called indirectly. To do this,
1752 assign the name of the function to be called, as a string, to a vari‐
1753 able. Then use the variable as if it were the name of a function, pre‐
1754 fixed with an @ sign, like so:
1755 function myfunc()
1756 {
1757 print "myfunc called"
1758 ...
1759 }
1760 { ...
1762 the_func = "myfunc"
1763 @the_func() # call through the_func to myfunc
1764 ...
1765 }
1766 As of version 4.1.2, this works with user-defined functions, built-in
1767 functions, and extension functions.
1768 If --lint has been provided, gawk warns about calls to undefined func‐
1770 tions at parse time, instead of at run time. Calling an undefined
1771 function at run time is a fatal error.
1772 The word func may be used in place of function, although this is depre‐
1774 cated.
1775
1777 You can dynamically add new built-in functions to the running gawk
1778 interpreter with the @load statement. The full details are beyond the
1779 scope of this manual page; see GAWK: Effective AWK Programming.
1780
1782 The gawk profiler accepts two signals. SIGUSR1 causes it to dump a
1783 profile and function call stack to the profile file, which is either
1784 awkprof.out, or whatever file was named with the --profile option. It
1785 then continues to run. SIGHUP causes gawk to dump the profile and
1786 function call stack and then exit.
1787
1789 String constants are sequences of characters enclosed in double quotes.
1790 In non-English speaking environments, it is possible to mark strings in
1791 the AWK program as requiring translation to the local natural language.
1792 Such strings are marked in the AWK program with a leading underscore
1793 (“_”). For example,
1794 gawk 'BEGIN { print "hello, world" }'
1796 always prints hello, world. But,
1798 gawk 'BEGIN { print _"hello, world" }'
1800 might print bonjour, monde in France.
1802 There are several steps involved in producing and running a localizable
1804 AWK program.
1805 1. Add a BEGIN action to assign a value to the TEXTDOMAIN variable to
1807 set the text domain to a name associated with your program:
1808 BEGIN { TEXTDOMAIN = "myprog" }
1810 This allows gawk to find the .gmo file associated with your pro‐
1812 gram. Without this step, gawk uses the messages text domain, which
1813 likely does not contain translations for your program.
1814 2. Mark all strings that should be translated with leading under‐
1816 scores.
1817 3. If necessary, use the dcgettext() and/or bindtextdomain() functions
1819 in your program, as appropriate.
1820 4. Run gawk --gen-pot -f myprog.awk > myprog.pot to generate a .pot
1822 file for your program.
1823 5. Provide appropriate translations, and build and install the corre‐
1825 sponding .gmo files.
1826 The internationalization features are described in full detail in GAWK:
1828 Effective AWK Programming.
1829
1831 A primary goal for gawk is compatibility with the POSIX standard, as
1832 well as with the latest version of Brian Kernighan's awk. To this end,
1833 gawk incorporates the following user visible features which are not
1834 described in the AWK book, but are part of the Brian Kernighan's ver‐
1835 sion of awk, and are in the POSIX standard.
1836 The book indicates that command line variable assignment happens when
1838 awk would otherwise open the argument as a file, which is after the
1839 BEGIN rule is executed. However, in earlier implementations, when such
1840 an assignment appeared before any file names, the assignment would hap‐
1841 pen before the BEGIN rule was run. Applications came to depend on this
1842 “feature.” When awk was changed to match its documentation, the -v
1843 option for assigning variables before program execution was added to
1844 accommodate applications that depended upon the old behavior. (This
1845 feature was agreed upon by both the Bell Laboratories and the GNU
1846 developers.)
1847 When processing arguments, gawk uses the special option “--” to signal
1849 the end of arguments. In compatibility mode, it warns about but other‐
1850 wise ignores undefined options. In normal operation, such arguments
1851 are passed on to the AWK program for it to process.
1852 The AWK book does not define the return value of srand(). The POSIX
1854 standard has it return the seed it was using, to allow keeping track of
1855 random number sequences. Therefore srand() in gawk also returns its
1856 current seed.
1857 Other features are: The use of multiple -f options (from MKS awk); the
1859 ENVIRON array; the \a, and \v escape sequences (done originally in gawk
1860 and fed back into the Bell Laboratories version); the tolower() and
1861 toupper() built-in functions (from the Bell Laboratories version); and
1862 the ISO C conversion specifications in printf (done first in the Bell
1863 Laboratories version).
1864
1866 There is one feature of historical AWK implementations that gawk sup‐
1867 ports: It is possible to call the length() built-in function not only
1868 with no argument, but even without parentheses! Thus,
1869 a = length # Holy Algol 60, Batman!
1871 is the same as either of
1873 a = length()
1875 a = length($0)
1876 Using this feature is poor practice, and gawk issues a warning about
1878 its use if --lint is specified on the command line.
1879
1881 Gawk has a too-large number of extensions to POSIX awk. They are
1882 described in this section. All the extensions described here can be
1883 disabled by invoking gawk with the --traditional or --posix options.
1884 The following features of gawk are not available in POSIX awk.
1886 · No path search is performed for files named via the -f option.
1888 Therefore the AWKPATH environment variable is not special.
1889 · There is no facility for doing file inclusion (gawk's @include mecha‐
1891 nism).
1892 · There is no facility for dynamically adding new functions written in
1894 C (gawk's @load mechanism).
1895 · The \x escape sequence.
1897 · The ability to continue lines after ? and :.
1899 · Octal and hexadecimal constants in AWK programs.
1901 · The ARGIND, BINMODE, ERRNO, LINT, PREC, ROUNDMODE, RT and TEXTDOMAIN
1903 variables are not special.
1904 · The IGNORECASE variable and its side-effects are not available.
1906 · The FIELDWIDTHS variable and fixed-width field splitting.
1908 · The FPAT variable and field splitting based on field values.
1910 · The FUNCTAB, SYMTAB, and PROCINFO arrays are not available.
1912 · The use of RS as a regular expression.
1914 · The special file names available for I/O redirection are not recog‐
1916 nized.
1917 · The |& operator for creating coprocesses.
1919 · The BEGINFILE and ENDFILE special patterns are not available.
1921 · The ability to split out individual characters using the null string
1923 as the value of FS, and as the third argument to split().
1924 · An optional fourth argument to split() to receive the separator
1926 texts.
1927 · The optional second argument to the close() function.
1929 · The optional third argument to the match() function.
1931 · The ability to use positional specifiers with printf and sprintf().
1933 · The ability to pass an array to length().
1935 · The and(), asort(), asorti(), bindtextdomain(), compl(), dcgettext(),
1937 dcngettext(), gensub(), lshift(), mktime(), or(), patsplit(),
1938 rshift(), strftime(), strtonum(), systime() and xor() functions.
1939 · Localizable strings.
1941 · Non-fatal I/O.
1943 · Retryable I/O.
1945 The AWK book does not define the return value of the close() function.
1947 Gawk's close() returns the value from fclose(3), or pclose(3), when
1948 closing an output file or pipe, respectively. It returns the process's
1949 exit status when closing an input pipe. The return value is -1 if the
1950 named file, pipe or coprocess was not opened with a redirection.
1951 When gawk is invoked with the --traditional option, if the fs argument
1953 to the -F option is “t”, then FS is set to the tab character. Note
1954 that typing gawk -F\t ... simply causes the shell to quote the “t,”
1955 and does not pass “\t” to the -F option. Since this is a rather ugly
1956 special case, it is not the default behavior. This behavior also does
1957 not occur if --posix has been specified. To really get a tab character
1958 as the field separator, it is best to use single quotes: gawk -F'\t'
1959 ....
1960
1962 The AWKPATH environment variable can be used to provide a list of
1963 directories that gawk searches when looking for files named via the -f,
1964 --file, -i and --include options, and the @include directive. If the
1965 initial search fails, the path is searched again after appending .awk
1966 to the filename.
1967 The AWKLIBPATH environment variable can be used to provide a list of
1969 directories that gawk searches when looking for files named via the -l
1970 and --load options.
1971 The GAWK_READ_TIMEOUT environment variable can be used to specify a
1973 timeout in milliseconds for reading input from a terminal, pipe or two-
1974 way communication including sockets.
1975 For connection to a remote host via socket, GAWK_SOCK_RETRIES controls
1977 the number of retries, and GAWK_MSEC_SLEEP and the interval between
1978 retries. The interval is in milliseconds. On systems that do not sup‐
1979 port usleep(3), the value is rounded up to an integral number of sec‐
1980 onds.
1981 If POSIXLY_CORRECT exists in the environment, then gawk behaves exactly
1983 as if --posix had been specified on the command line. If --lint has
1984 been specified, gawk issues a warning message to this effect.
1985
1987 If the exit statement is used with a value, then gawk exits with the
1988 numeric value given to it.
1989 Otherwise, if there were no problems during execution, gawk exits with
1991 the value of the C constant EXIT_SUCCESS. This is usually zero.
1992 If an error occurs, gawk exits with the value of the C constant
1994 EXIT_FAILURE. This is usually one.
1995 If gawk exits because of a fatal error, the exit status is 2. On non-
1997 POSIX systems, this value may be mapped to EXIT_FAILURE.
1998
2000 This man page documents gawk, version 4.2.
2001
2003 The original version of UNIX awk was designed and implemented by Alfred
2004 Aho, Peter Weinberger, and Brian Kernighan of Bell Laboratories. Brian
2005 Kernighan continues to maintain and enhance it.
2006 Paul Rubin and Jay Fenlason, of the Free Software Foundation, wrote
2008 gawk, to be compatible with the original version of awk distributed in
2009 Seventh Edition UNIX. John Woods contributed a number of bug fixes.
2010 David Trueman, with contributions from Arnold Robbins, made gawk com‐
2011 patible with the new version of UNIX awk. Arnold Robbins is the cur‐
2012 rent maintainer.
2013 See GAWK: Effective AWK Programming for a full list of the contributors
2015 to gawk and its documentation.
2016 See the README file in the gawk distribution for up-to-date information
2018 about maintainers and which ports are currently supported.
2019
2021 If you find a bug in gawk, please send electronic mail to bug-
2022 gawk@gnu.org. Please include your operating system and its revision,
2023 the version of gawk (from gawk --version), which C compiler you used to
2024 compile it, and a test program and data that are as small as possible
2025 for reproducing the problem.
2026 Before sending a bug report, please do the following things. First,
2028 verify that you have the latest version of gawk. Many bugs (usually
2029 subtle ones) are fixed at each release, and if yours is out of date,
2030 the problem may already have been solved. Second, please see if set‐
2031 ting the environment variable LC_ALL to LC_ALL=C causes things to
2032 behave as you expect. If so, it's a locale issue, and may or may not
2033 really be a bug. Finally, please read this man page and the reference
2034 manual carefully to be sure that what you think is a bug really is,
2035 instead of just a quirk in the language.
2036 Whatever you do, do NOT post a bug report in comp.lang.awk. While the
2038 gawk developers occasionally read this newsgroup, posting bug reports
2039 there is an unreliable way to report bugs. Instead, please use the
2040 electronic mail addresses given above. Really.
2041 If you're using a GNU/Linux or BSD-based system, you may wish to submit
2043 a bug report to the vendor of your distribution. That's fine, but
2044 please send a copy to the official email address as well, since there's
2045 no guarantee that the bug report will be forwarded to the gawk main‐
2046 tainer.
2047
2049 The -F option is not necessary given the command line variable assign‐
2050 ment feature; it remains only for backwards compatibility.
2051
2053 egrep(1), sed(1), getpid(2), getppid(2), getpgrp(2), getuid(2),
2054 geteuid(2), getgid(2), getegid(2), getgroups(2), printf(3), strf‐
2055 time(3), usleep(3)
2056 The AWK Programming Language, Alfred V. Aho, Brian W. Kernighan, Peter
2058 J. Weinberger, Addison-Wesley, 1988. ISBN 0-201-07981-X.
2059 GAWK: Effective AWK Programming, Edition 4.2, shipped with the gawk
2061 source. The current version of this document is available online at
2062 https://www.gnu.org/software/gawk/manual.
2063 The GNU gettext documentation, available online at
2065 https://www.gnu.org/software/gettext.
2066
2068 Print and sort the login names of all users:
2069 BEGIN { FS = ":" }
2071 { print $1 | "sort" }
2072 Count lines in a file:
2074 { nlines++ }
2076 END { print nlines }
2077 Precede each line by its number in the file:
2079 { print FNR, $0 }
2081 Concatenate and line number (a variation on a theme):
2083 { print NR, $0 }
2085 Run an external command for particular lines of data:
2087 tail -f access_log |
2089 awk '/myhome.html/ { system("nmap " $1 ">> logdir/myhome.html") }'
2090
2092 Brian Kernighan provided valuable assistance during testing and debug‐
2093 ging. We thank him.
2094
2096 Copyright © 1989, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
2097 2001, 2002, 2003, 2004, 2005, 2007, 2009, 2010, 2011, 2012, 2013, 2014,
2098 2015, 2016, 2017, 2018 Free Software Foundation, Inc.
2099 Permission is granted to make and distribute verbatim copies of this
2101 manual page provided the copyright notice and this permission notice
2102 are preserved on all copies.
2103 Permission is granted to copy and distribute modified versions of this
2105 manual page under the conditions for verbatim copying, provided that
2106 the entire resulting derived work is distributed under the terms of a
2107 permission notice identical to this one.
2108 Permission is granted to copy and distribute translations of this man‐
2110 ual page into another language, under the above conditions for modified
2111 versions, except that this permission notice may be stated in a trans‐
2112 lation approved by the Foundation.
2113Free Software Foundation Mar 22 2018 GAWK(1)