1GAWK(1)                        Utility Commands                        GAWK(1)
2
3
4

NAME

6       gawk - pattern scanning and processing language
7

SYNOPSIS

9       gawk [ POSIX or GNU style options ] -f program-file [ -- ] file ...
10       gawk [ POSIX or GNU style options ] [ -- ] program-text file ...
11

DESCRIPTION

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
20       The command line consists of options to gawk itself,  the  AWK  program
21       text  (if  not supplied via the -f or --include options), and values to
22       be made available in the ARGC and ARGV pre-defined AWK variables.
23
24       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
29       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 and --include options.  The debugger is documented in
34       GAWK: Effective AWK Programming.
35

OPTION FORMAT

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
42       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
48       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

OPTIONS

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
57       -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.  Files read with -f are treated as
62              if they begin with an implicit @namespace "awk" statement.
63
64       -F fs
65       --field-separator fs
66              Use fs for the input field separator (the value of the FS prede‐
67              fined variable).
68
69       -v var=val
70       --assign var=val
71              Assign  the  value  val to the variable var, before execution of
72              the program begins.  Such variable values are available  to  the
73              BEGIN rule of an AWK program.
74
75       -b
76       --characters-as-bytes
77              Treat  all input data as single-byte characters. In other words,
78              don't pay any attention to the locale information when  attempt‐
79              ing  to  process  strings  as multibyte characters.  The --posix
80              option overrides this one.
81
82       -c
83       --traditional
84              Run in compatibility mode.  In compatibility mode, gawk  behaves
85              identically  to  Brian Kernighan's awk; none of the GNU-specific
86              extensions are recognized.  See GNU EXTENSIONS, below, for  more
87              information.
88
89       -C
90       --copyright
91              Print the short version of the GNU copyright information message
92              on the standard output and exit successfully.
93
94       -d[file]
95       --dump-variables[=file]
96              Print a sorted list of global variables, their types  and  final
97              values  to file.  If no file is provided, gawk uses a file named
98              awkvars.out in the current directory.
99              Having a list of all the global variables is a good way to  look
100              for  typographical  errors in your programs.  You would also use
101              this option if you have a large program with a lot of functions,
102              and  you want to be sure that your functions don't inadvertently
103              use global variables that you meant to be  local.   (This  is  a
104              particularly  easy  mistake  to  make with simple variable names
105              like i, j, and so on.)
106
107       -D[file]
108       --debug[=file]
109              Enable debugging of AWK  programs.   By  default,  the  debugger
110              reads commands interactively from the keyboard (standard input).
111              The optional file argument specifies a file with a list of  com‐
112              mands for the debugger to execute non-interactively.
113
114       -e program-text
115       --source program-text
116              Use program-text as AWK program source code.  This option allows
117              the easy intermixing of library functions (used via the  -f  and
118              --include options) with source code entered on the command line.
119              It is intended primarily for medium to large AWK  programs  used
120              in  shell  scripts.  Each argument supplied via -e is treated as
121              if it begins with an implicit @namespace "awk" statement.
122
123       -E file
124       --exec file
125              Similar to -f, however, this is option  is  the  last  one  pro‐
126              cessed.   This should be used with #!  scripts, particularly for
127              CGI applications, to avoid passing in options or source code (!)
128              on  the  command line from a URL.  This option disables command-
129              line variable assignments.
130
131       -g
132       --gen-pot
133              Scan and parse the AWK program, and generate a GNU .pot  (Porta‐
134              ble Object Template) format file on standard output with entries
135              for all localizable strings in the program.  The program  itself
136              is  not  executed.   See  the  GNU gettext distribution for more
137              information on .pot files.
138
139       -h
140       --help Print a relatively short summary of the available options on the
141              standard  output.   (Per the GNU Coding Standards, these options
142              cause an immediate, successful exit.)
143
144       -i include-file
145       --include include-file
146              Load an awk source library.  This searches for the library using
147              the  AWKPATH environment variable.  If the initial search fails,
148              another attempt will be made after appending  the  .awk  suffix.
149              The  file  will be loaded only once (i.e., duplicates are elimi‐
150              nated), and the  code  does  not  constitute  the  main  program
151              source.   Files read with --include are treated as if they begin
152              with an implicit @namespace "awk" statement.
153
154       -l lib
155       --load lib
156              Load a  gawk  extension  from  the  shared  library  lib.   This
157              searches  for the library using the AWKLIBPATH environment vari‐
158              able.  If the initial search fails, another attempt will be made
159              after  appending the default shared library suffix for the plat‐
160              form.  The library initialization  routine  is  expected  to  be
161              named dl_load().
162
163       -L [value]
164       --lint[=value]
165              Provide warnings about constructs that are dubious or non-porta‐
166              ble to other AWK implementations.  With an optional argument  of
167              fatal,  lint warnings become fatal errors.  This may be drastic,
168              but its use will certainly encourage the development of  cleaner
169              AWK  programs.  With an optional argument of invalid, only warn‐
170              ings about things that are actually invalid are issued. (This is
171              not  fully  implemented  yet.)  With an optional argument of no-
172              ext, warnings about gawk extensions are disabled.
173
174       -M
175       --bignum
176              Force arbitrary precision arithmetic on numbers. This option has
177              no  effect  if  gawk is not compiled to use the GNU MPFR and GMP
178              libraries.  (In such a case, gawk issues a warning.)
179
180       -n
181       --non-decimal-data
182              Recognize octal and hexadecimal values in input data.  Use  this
183              option with great caution!
184
185       -N
186       --use-lc-numeric
187              Force  gawk  to  use  the  locale's decimal point character when
188              parsing input data.  Although the POSIX standard  requires  this
189              behavior,  and  gawk  does  so  when  --posix  is in effect, the
190              default is to follow traditional behavior and use  a  period  as
191              the  decimal  point, even in locales where the period is not the
192              decimal point character.   This  option  overrides  the  default
193              behavior,  without  the full draconian strictness of the --posix
194              option.
195
196       -o[file]
197       --pretty-print[=file]
198              Output a pretty printed version of the program to file.   If  no
199              file is provided, gawk uses a file named awkprof.out in the cur‐
200              rent directory.  This option implies --no-optimize.
201
202       -O
203       --optimize
204              Enable gawk's default optimizations upon the internal  represen‐
205              tation  of  the  program.   Currently, this just includes simple
206              constant folding.  This option is on by default.
207
208       -p[prof-file]
209       --profile[=prof-file]
210              Start a profiling session, and send the profiling data to  prof-
211              file.   The default is awkprof.out.  The profile contains execu‐
212              tion counts of each statement in the program in the left  margin
213              and  function  call counts for each user-defined function.  This
214              option implies --no-optimize.
215
216       -P
217       --posix
218              This turns on compatibility mode, with the following  additional
219              restrictions:
220
221              · \x escape sequences are not recognized.
222
223              · You cannot continue lines after ?  and :.
224
225              · The synonym func for the keyword function is not recognized.
226
227              · The operators ** and **= cannot be used in place of ^ and ^=.
228
229       -r
230       --re-interval
231              Enable  the  use  of  interval expressions in regular expression
232              matching (see Regular Expressions, below).  Interval expressions
233              were not traditionally available in the AWK language.  The POSIX
234              standard added them, to make awk and egrep consistent with  each
235              other.  They are enabled by default, but this option remains for
236              use together with --traditional.
237
238       -s
239       --no-optimize
240              Disable gawk's default optimizations upon the internal represen‐
241              tation of the program.
242
243       -S
244       --sandbox
245              Run gawk in sandbox mode, disabling the system() function, input
246              redirection with getline,  output  redirection  with  print  and
247              printf,  and  loading  dynamic  extensions.   Command  execution
248              (through pipelines) is also disabled.  This effectively blocks a
249              script  from  accessing  local  resources,  except for the files
250              specified on the command line.
251
252       -t
253       --lint-old
254              Provide warnings about constructs that are not portable  to  the
255              original version of UNIX awk.
256
257       -V
258       --version
259              Print  version  information  for this particular copy of gawk on
260              the standard output.  This is useful mainly for knowing  if  the
261              current  copy  of gawk on your system is up to date with respect
262              to whatever the Free Software Foundation is distributing.   This
263              is  also  useful when reporting bugs.  (Per the GNU Coding Stan‐
264              dards, these options cause an immediate, successful exit.)
265
266       --     Signal the end of options. This is useful to allow further argu‐
267              ments  to the AWK program itself to start with a “-”.  This pro‐
268              vides consistency with the argument parsing convention  used  by
269              most other POSIX programs.
270
271       In  compatibility  mode,  any other options are flagged as invalid, but
272       are otherwise ignored.  In normal operation, as long  as  program  text
273       has  been supplied, unknown options are passed on to the AWK program in
274       the ARGV array for processing.  This is particularly useful for running
275       AWK programs via the #!  executable interpreter mechanism.
276
277       For  POSIX  compatibility,  the  -W option may be used, followed by the
278       name of a long option.
279

AWK PROGRAM EXECUTION

281       An AWK program consists of a sequence of optional directives,  pattern-
282       action statements, and optional function definitions.
283
284              @include "filename"
285              @load "filename"
286              @namespace "name"
287              pattern   { action statements }
288              function name(parameter list) { statements }
289
290       Gawk  first reads the program source from the program-file(s) if speci‐
291       fied, from arguments to --source, or from the first non-option argument
292       on  the command line.  The -f and --source options may be used multiple
293       times on the command line.  Gawk reads the program text as if  all  the
294       program-files  and  command  line  source  texts  had been concatenated
295       together.  This is useful for  building  libraries  of  AWK  functions,
296       without  having to include them in each new AWK program that uses them.
297       It also provides the ability to mix library functions with command line
298       programs.
299
300       In addition, lines beginning with @include may be used to include other
301       source files into your program, making library use even  easier.   This
302       is equivalent to using the --include option.
303
304       Lines beginning with @load may be used to load extension functions into
305       your program.  This is equivalent to using the --load option.
306
307       The environment variable AWKPATH specifies a search path  to  use  when
308       finding  source files named with the -f and --include options.  If this
309       variable does not exist, the default path is  ".:/usr/local/share/awk".
310       (The  actual  directory may vary, depending upon how gawk was built and
311       installed.)  If a file name given to the -f option contains a “/” char‐
312       acter, no path search is performed.
313
314       The environment variable AWKLIBPATH specifies a search path to use when
315       finding source files named with the --load option.   If  this  variable
316       does not exist, the default path is "/usr/local/lib/gawk".  (The actual
317       directory may vary, depending upon how gawk was built and installed.)
318
319       Gawk executes AWK programs in the following order.  First, all variable
320       assignments specified via the -v option are performed.  Next, gawk com‐
321       piles the program into an internal form.  Then, gawk executes the  code
322       in  the  BEGIN  rule(s)  (if  any), and then proceeds to read each file
323       named in the ARGV array (up to ARGV[ARGC-1]).  If there  are  no  files
324       named on the command line, gawk reads the standard input.
325
326       If a filename on the command line has the form var=val it is treated as
327       a variable assignment.  The variable var will  be  assigned  the  value
328       val.   (This  happens  after any BEGIN rule(s) have been run.)  Command
329       line variable assignment is most useful for dynamically assigning  val‐
330       ues  to  the  variables  AWK  uses  to control how input is broken into
331       fields and records.  It is also useful for controlling state if  multi‐
332       ple passes are needed over a single data file.
333
334       If  the value of a particular element of ARGV is empty (""), gawk skips
335       over it.
336
337       For each input file, if a BEGINFILE  rule  exists,  gawk  executes  the
338       associated  code before processing the contents of the file. Similarly,
339       gawk executes the code associated with  ENDFILE  after  processing  the
340       file.
341
342       For  each record in the input, gawk tests to see if it matches any pat‐
343       tern in the AWK program.  For each pattern  that  the  record  matches,
344       gawk  executes  the  associated action.  The patterns are tested in the
345       order they occur in the program.
346
347       Finally, after all the input is exhausted, gawk executes  the  code  in
348       the END rule(s) (if any).
349
350   Command Line Directories
351       According  to  POSIX,  files named on the awk command line must be text
352       files.  The behavior is ``undefined'' if they are not.   Most  versions
353       of awk treat a directory on the command line as a fatal error.
354
355       Starting with version 4.0 of gawk, a directory on the command line pro‐
356       duces a warning, but is otherwise skipped.  If either of the --posix or
357       --traditional  options is given, then gawk reverts to treating directo‐
358       ries on the command line as a fatal error.
359

VARIABLES, RECORDS AND FIELDS

361       AWK variables are dynamic; they come into existence when they are first
362       used.   Their  values  are either floating-point numbers or strings, or
363       both, depending upon how they  are  used.   Additionally,  gawk  allows
364       variables  to  have  regular-expression  type.  AWK also has one dimen‐
365       sional arrays; arrays with multiple dimensions may be simulated.   Gawk
366       provides true arrays of arrays; see Arrays, below.  Several pre-defined
367       variables are set as a program runs; these are described as needed  and
368       summarized below.
369
370   Records
371       Normally, records are separated by newline characters.  You can control
372       how records are separated by assigning values to the built-in  variable
373       RS.   If  RS is any single character, that character separates records.
374       Otherwise, RS is a regular expression.  Text in the input that  matches
375       this  regular expression separates the record.  However, in compatibil‐
376       ity mode, only the first character of its string value is used for sep‐
377       arating  records.   If  RS  is set to the null string, then records are
378       separated by empty lines.  When RS is set to the null string, the  new‐
379       line  character  always acts as a field separator, in addition to what‐
380       ever value FS may have.
381
382   Fields
383       As each input record is read, gawk splits the record into fields, using
384       the value of the FS variable as the field separator.  If FS is a single
385       character, fields are separated by that character.  If FS is  the  null
386       string,  then each individual character becomes a separate field.  Oth‐
387       erwise, FS is expected to be a full regular expression.  In the special
388       case  that FS is a single space, fields are separated by runs of spaces
389       and/or tabs and/or newlines.  NOTE: The value of IGNORECASE (see below)
390       also  affects how fields are split when FS is a regular expression, and
391       how records are separated when RS is a regular expression.
392
393       If the FIELDWIDTHS variable is set to a space-separated  list  of  num‐
394       bers,  each  field  is expected to have fixed width, and gawk splits up
395       the record using the specified widths.  Each field width may optionally
396       be preceded by a colon-separated value specifying the number of charac‐
397       ters to skip before the field starts.  The  value  of  FS  is  ignored.
398       Assigning a new value to FS or FPAT overrides the use of FIELDWIDTHS.
399
400       Similarly, if the FPAT variable is set to a string representing a regu‐
401       lar expression, each field is made up of text that matches that regular
402       expression.  In  this case, the regular expression describes the fields
403       themselves, instead of the text that separates the fields.  Assigning a
404       new value to FS or FIELDWIDTHS overrides the use of FPAT.
405
406       Each  field  in the input record may be referenced by its position: $1,
407       $2, and so on.  $0 is the whole record, including leading and  trailing
408       whitespace.  Fields need not be referenced by constants:
409
410              n = 5
411              print $n
412
413       prints the fifth field in the input record.
414
415       The  variable  NF  is  set  to  the total number of fields in the input
416       record.
417
418       References to non-existent fields (i.e., fields after $NF) produce  the
419       null string.  However, assigning to a non-existent field (e.g., $(NF+2)
420       = 5) increases the value of NF, creates any intervening fields with the
421       null  string  as  their values, and causes the value of $0 to be recom‐
422       puted, with the fields being separated by the value of OFS.  References
423       to  negative  numbered  fields  cause  a  fatal error.  Decrementing NF
424       causes the values of fields past the new value  to  be  lost,  and  the
425       value  of  $0  to be recomputed, with the fields being separated by the
426       value of OFS.
427
428       Assigning a value to an existing field causes the whole  record  to  be
429       rebuilt  when  $0  is  referenced.   Similarly, assigning a value to $0
430       causes the record to be resplit, creating new values for the fields.
431
432   Built-in Variables
433       Gawk's built-in variables are:
434
435       ARGC        The number of command  line  arguments  (does  not  include
436                   options to gawk, or the program source).
437
438       ARGIND      The index in ARGV of the current file being processed.
439
440       ARGV        Array of command line arguments.  The array is indexed from
441                   0 to ARGC - 1.  Dynamically changing the contents  of  ARGV
442                   can control the files used for data.
443
444       BINMODE     On  non-POSIX  systems,  specifies use of “binary” mode for
445                   all file I/O.  Numeric values of 1, 2, or 3,  specify  that
446                   input  files,  output  files,  or  all files, respectively,
447                   should use binary I/O.  String values of "r", or "w"  spec‐
448                   ify that input files, or output files, respectively, should
449                   use binary I/O.  String values of "rw" or "wr" specify that
450                   all files should use binary I/O.  Any other string value is
451                   treated as "rw", but generates a warning message.
452
453       CONVFMT     The conversion format for numbers, "%.6g", by default.
454
455       ENVIRON     An array containing the values of the current  environment.
456                   The  array  is  indexed  by the environment variables, each
457                   element being the  value  of  that  variable  (e.g.,  ENVI‐
458                   RON["HOME"] might be "/home/arnold").
459
460                   In  POSIX  mode,  changing  this  array does not affect the
461                   environment seen by programs which gawk  spawns  via  redi‐
462                   rection  or the system() function.  Otherwise, gawk updates
463                   its real environment so that programs  it  spawns  see  the
464                   changes.
465
466       ERRNO       If  a  system  error  occurs either doing a redirection for
467                   getline, during a read for getline, or  during  a  close(),
468                   then  ERRNO  is  set to a string describing the error.  The
469                   value is subject to translation in non-English locales.  If
470                   the  string  in  ERRNO corresponds to a system error in the
471                   errno(3) variable, then the numeric value can be  found  in
472                   PROCINFO["errno"].        For       non-system      errors,
473                   PROCINFO["errno"] will be zero.
474
475       FIELDWIDTHS A whitespace-separated list of  field  widths.   When  set,
476                   gawk  parses  the input into fields of fixed width, instead
477                   of using the value of the FS variable as the field  separa‐
478                   tor.   Each  field  width  may  optionally be preceded by a
479                   colon-separated value specifying the number  of  characters
480                   to skip before the field starts.  See Fields, above.
481
482       FILENAME    The name of the current input file.  If no files are speci‐
483                   fied on the command line, the value  of  FILENAME  is  “-”.
484                   However,  FILENAME  is  undefined  inside  the  BEGIN  rule
485                   (unless set by getline).
486
487       FNR         The input record number in the current input file.
488
489       FPAT        A regular expression describing the contents of the  fields
490                   in  a record.  When set, gawk parses the input into fields,
491                   where the fields match the regular expression,  instead  of
492                   using  the value of FS as the field separator.  See Fields,
493                   above.
494
495       FS          The input field separator, a space by default.  See Fields,
496                   above.
497
498       FUNCTAB     An  array  whose  indices  and corresponding values are the
499                   names of all the user-defined or extension functions in the
500                   program.   NOTE:  You may not use the delete statement with
501                   the FUNCTAB array.
502
503       IGNORECASE  Controls the case-sensitivity of all regular expression and
504                   string  operations.   If  IGNORECASE  has a non-zero value,
505                   then string comparisons  and  pattern  matching  in  rules,
506                   field  splitting  with  FS and FPAT, record separating with
507                   RS, regular expression matching with ~ and !~, and the gen‐
508                   sub(),  gsub(),  index(), match(), patsplit(), split(), and
509                   sub() built-in functions all ignore case when doing regular
510                   expression  operations.   NOTE:  Array  subscripting is not
511                   affected.  However, the asort() and asorti() functions  are
512                   affected.
513                   Thus,  if IGNORECASE is not equal to zero, /aB/ matches all
514                   of the strings "ab", "aB", "Ab", and "AB".  As with all AWK
515                   variables,  the initial value of IGNORECASE is zero, so all
516                   regular expression and string operations are normally case-
517                   sensitive.
518
519       LINT        Provides  dynamic  control of the --lint option from within
520                   an AWK program.  When true, gawk prints lint warnings. When
521                   false,  it  does  not.   The  values allowed for the --lint
522                   option may also be assigned to LINT, with the same effects.
523                   Any other true value just prints warnings.
524
525       NF          The number of fields in the current input record.
526
527       NR          The total number of input records seen so far.
528
529       OFMT        The output format for numbers, "%.6g", by default.
530
531       OFS         The output field separator, a space by default.
532
533       ORS         The output record separator, by default a newline.
534
535       PREC        The working precision of arbitrary precision floating-point
536                   numbers, 53 by default.
537
538       PROCINFO    The elements of this array provide  access  to  information
539                   about  the running AWK program.  On some systems, there may
540                   be elements in the array,  "group1"  through  "groupn"  for
541                   some  n,  which  is the number of supplementary groups that
542                   the process has.  Use the in operator  to  test  for  these
543                   elements.   The  following  elements  are  guaranteed to be
544                   available:
545
546                   PROCINFO["argv"]     The command line arguments as received
547                                        by  gawk at the C-language level.  The
548                                        subscripts start from zero.
549
550                   PROCINFO["egid"]     The value  of  the  getegid(2)  system
551                                        call.
552
553                   PROCINFO["errno"]    The  value  of  errno(3) when ERRNO is
554                                        set to the associated error message.
555
556                   PROCINFO["euid"]     The value  of  the  geteuid(2)  system
557                                        call.
558
559                   PROCINFO["FS"]       "FS"  if field splitting with FS is in
560                                        effect, "FPAT" if field splitting with
561                                        FPAT  is  in  effect, "FIELDWIDTHS" if
562                                        field splitting with FIELDWIDTHS is in
563                                        effect,  or  "API" if API input parser
564                                        field splitting is in effect.
565
566                   PROCINFO["gid"]      The  value  of  the  getgid(2)  system
567                                        call.
568
569                   PROCINFO["identifiers"]
570                                        A  subarray,  indexed  by the names of
571                                        all identifiers used in  the  text  of
572                                        the  AWK program.  The values indicate
573                                        what gawk knows about the  identifiers
574                                        after it has finished parsing the pro‐
575                                        gram; they are not updated  while  the
576                                        program  runs.   For  each identifier,
577                                        the value of the element is one of the
578                                        following:
579
580                                        "array"     The   identifier   is   an
581                                                    array.
582
583                                        "builtin"   The identifier is a built-
584                                                    in function.
585
586                                        "extension" The   identifier   is   an
587                                                    extension function  loaded
588                                                    via @load or --load.
589
590                                        "scalar"    The    identifier   is   a
591                                                    scalar.
592
593                                        "untyped"   The identifier is  untyped
594                                                    (could be used as a scalar
595                                                    or  array,  gawk   doesn't
596                                                    know yet).
597
598                                        "user"      The  identifier is a user-
599                                                    defined function.
600
601                   PROCINFO["pgrpid"]   The value  of  the  getpgrp(2)  system
602                                        call.
603
604                   PROCINFO["pid"]      The  value  of  the  getpid(2)  system
605                                        call.
606
607                   PROCINFO["platform"] A string indicating the  platform  for
608                                        which  gawk  was  compiled.  It is one
609                                        of:
610
611                                        "djgpp", "mingw"
612                                               Microsoft Windows, using either
613                                               DJGPP, or MinGW, respectively.
614
615                                        "os2"  OS/2.
616
617                                        "posix"
618                                               GNU/Linux,  Cygwin,  Mac  OS X,
619                                               and legacy Unix systems.
620
621                                        "vms"  OpenVMS or Vax/VMS.
622
623                   PROCINFO["ppid"]     The value  of  the  getppid(2)  system
624                                        call.
625
626                   PROCINFO["strftime"] The  default  time  format  string for
627                                        strftime().    Changing   its    value
628                                        affects  how  strftime()  formats time
629                                        values when called with no arguments.
630
631                   PROCINFO["uid"]      The  value  of  the  getuid(2)  system
632                                        call.
633
634                   PROCINFO["version"]  The version of gawk.
635
636                   The  following  elements  are  present  if  loading dynamic
637                   extensions is available:
638
639                   PROCINFO["api_major"]
640                          The major version of the extension API.
641
642                   PROCINFO["api_minor"]
643                          The minor version of the extension API.
644
645                   The following elements are available  if  MPFR  support  is
646                   compiled into gawk:
647
648                   PROCINFO["gmp_version"]
649                          The  version  of  the GNU GMP library used for arbi‐
650                          trary precision number support in gawk.
651
652                   PROCINFO["mpfr_version"]
653                          The version of the GNU MPFR library used  for  arbi‐
654                          trary precision number support in gawk.
655
656                   PROCINFO["prec_max"]
657                          The  maximum  precision  supported  by  the GNU MPFR
658                          library for arbitrary precision floating-point  num‐
659                          bers.
660
661                   PROCINFO["prec_min"]
662                          The  minimum  precision  allowed  by  the  GNU  MPFR
663                          library for arbitrary precision floating-point  num‐
664                          bers.
665
666                   The  following  elements  may  set  by  a program to change
667                   gawk's behavior:
668
669                   PROCINFO["NONFATAL"]
670                          If this exists, then I/O errors for all redirections
671                          become nonfatal.
672
673                   PROCINFO["name", "NONFATAL"]
674                          Make I/O errors for name be nonfatal.
675
676                   PROCINFO["command", "pty"]
677                          Use a pseudo-tty for two-way communication with com‐
678                          mand instead of setting up two one-way pipes.
679
680                   PROCINFO["input", "READ_TIMEOUT"]
681                          The timeout in milliseconds for  reading  data  from
682                          input,  where  input  is  a  redirection string or a
683                          filename. A value of zero or less than zero means no
684                          timeout.
685
686                   PROCINFO["input", "RETRY"]
687                          If  an  I/O  error  that  may be retried occurs when
688                          reading  data  from  input,  and  this  array  entry
689                          exists, then getline returns -2 instead of following
690                          the default behavior of returning -1 and configuring
691                          input  to return no further data.  An I/O error that
692                          may be retried is one where errno(3) has  the  value
693                          EAGAIN,  EWOULDBLOCK, EINTR, or ETIMEDOUT.  This may
694                          be  useful  in  conjunction  with  PROCINFO["input",
695                          "READ_TIMEOUT"]   or  in  situations  where  a  file
696                          descriptor has been configured to behave in  a  non-
697                          blocking fashion.
698
699                   PROCINFO["sorted_in"]
700                          If  this  element exists in PROCINFO, then its value
701                          controls the order in which array elements are  tra‐
702                          versed   in   for   loops.    Supported  values  are
703                          "@ind_str_asc",   "@ind_num_asc",   "@val_type_asc",
704                          "@val_str_asc",   "@val_num_asc",   "@ind_str_desc",
705                          "@ind_num_desc", "@val_type_desc",  "@val_str_desc",
706                          "@val_num_desc",  and  "@unsorted".   The  value can
707                          also be the name (as a  string)  of  any  comparison
708                          function defined as follows:
709
710                               function cmp_func(i1, v1, i2, v2)
711
712                          where  i1  and i2 are the indices, and v1 and v2 are
713                          the corresponding values of the two  elements  being
714                          compared.   It  should  return  a  number less than,
715                          equal to, or greater than 0, depending  on  how  the
716                          elements of the array are to be ordered.
717
718       ROUNDMODE   The rounding mode to use for arbitrary precision arithmetic
719                   on numbers, by default "N" (IEEE-754 roundTiesToEven mode).
720                   The accepted values are:
721
722                   "A" or "a"
723                          for  rounding away from zero.  These are only avail‐
724                          able if your version of the GNU  MPFR  library  sup‐
725                          ports rounding away from zero.
726
727                   "D" or "d" for roundTowardNegative.
728
729                   "N" or "n" for roundTiesToEven.
730
731                   "U" or "u" for roundTowardPositive.
732
733                   "Z" or "z" for roundTowardZero.
734
735       RS          The input record separator, by default a newline.
736
737       RT          The record terminator.  Gawk sets RT to the input text that
738                   matched the character or regular  expression  specified  by
739                   RS.
740
741       RSTART      The  index  of the first character matched by match(); 0 if
742                   no match.  (This implies that character  indices  start  at
743                   one.)
744
745       RLENGTH     The  length  of  the  string  matched  by match(); -1 if no
746                   match.
747
748       SUBSEP      The string used to separate multiple  subscripts  in  array
749                   elements, by default "\034".
750
751       SYMTAB      An  array  whose  indices  are  the  names of all currently
752                   defined global variables and arrays in  the  program.   The
753                   array  may be used for indirect access to read or write the
754                   value of a variable:
755
756                        foo = 5
757                        SYMTAB["foo"] = 4
758                        print foo    # prints 4
759
760                   The typeof() function may be used to test if an element  in
761                   SYMTAB  is  an array.  You may not use the delete statement
762                   with the SYMTAB array, nor assign to elements with an index
763                   that is not a variable name.
764
765       TEXTDOMAIN  The text domain of the AWK program; used to find the local‐
766                   ized translations for the program's strings.
767
768   Arrays
769       Arrays are subscripted with an expression between  square  brackets  ([
770       and ]).  If the expression is an expression list (expr, expr ...)  then
771       the array subscript is a string consisting of the concatenation of  the
772       (string) value of each expression, separated by the value of the SUBSEP
773       variable.  This facility  is  used  to  simulate  multiply  dimensioned
774       arrays.  For example:
775
776              i = "A"; j = "B"; k = "C"
777              x[i, j, k] = "hello, world\n"
778
779       assigns the string "hello, world\n" to the element of the array x which
780       is indexed by the string "A\034B\034C".  All arrays in AWK are associa‐
781       tive, i.e., indexed by string values.
782
783       The  special  operator  in may be used to test if an array has an index
784       consisting of a particular value:
785
786              if (val in array)
787                   print array[val]
788
789       If the array has multiple subscripts, use (i, j) in array.
790
791       The in construct may also be used in a for loop to iterate over all the
792       elements  of  an  array.   However,  the (i, j) in array construct only
793       works in tests, not in for loops.
794
795       An element may be deleted from an array  using  the  delete  statement.
796       The  delete statement may also be used to delete the entire contents of
797       an array, just by specifying the array name without a subscript.
798
799       gawk supports true multidimensional arrays. It does  not  require  that
800       such arrays be ``rectangular'' as in C or C++.  For example:
801
802              a[1] = 5
803              a[2][1] = 6
804              a[2][2] = 7
805
806       NOTE:  You may need to tell gawk that an array element is really a sub‐
807       array in order to use it where gawk expects an array (such  as  in  the
808       second argument to split()).  You can do this by creating an element in
809       the subarray and then deleting it with the delete statement.
810
811   Namespaces
812       Gawk provides a simple namespace facility to help work around the  fact
813       that all variables in AWK are global.
814
815       A  qualified name consists of a two simple identifiers joined by a dou‐
816       ble colon (::).  The left-hand identifier represents the namespace  and
817       the  right-hand identifier is the variable within it.  All simple (non-
818       qualified) names are considered to be in the ``current'' namespace; the
819       default  namespace  is  awk.   However,  simple  identifiers consisting
820       solely of uppercase letters are forced into the awk namespace, even  if
821       the current namespace is different.
822
823       You change the current namespace with an @namespace "name" directive.
824
825       The  standard  predefined  builtin  function  names  may not be used as
826       namespace names.  The names of additional functions  provided  by  gawk
827       may be used as namespace names or as simple identifiers in other names‐
828       paces.  For more details, see GAWK: Effective AWK Programming.
829
830   Variable Typing And Conversion
831       Variables and fields may be (floating point) numbers,  or  strings,  or
832       both.   They  may also be regular expressions. How the value of a vari‐
833       able is interpreted depends upon its context.  If  used  in  a  numeric
834       expression, it will be treated as a number; if used as a string it will
835       be treated as a string.
836
837       To force a variable to be treated as a number, add zero to it; to force
838       it to be treated as a string, concatenate it with the null string.
839
840       Uninitialized  variables  have  the  numeric  value zero and the string
841       value "" (the null, or empty, string).
842
843       When a string must be converted to a number, the conversion  is  accom‐
844       plished  using  strtod(3).   A number is converted to a string by using
845       the value of CONVFMT as  a  format  string  for  sprintf(3),  with  the
846       numeric  value  of  the variable as the argument.  However, even though
847       all numbers in AWK are floating-point, integral values are always  con‐
848       verted as integers.  Thus, given
849
850              CONVFMT = "%2.2f"
851              a = 12
852              b = a ""
853
854       the variable b has a string value of "12" and not "12.00".
855
856       NOTE:  When  operating in POSIX mode (such as with the --posix option),
857       beware that locale settings may interfere with the way decimal  numbers
858       are  treated:  the  decimal separator of the numbers you are feeding to
859       gawk must conform to what your locale would expect, be it a  comma  (,)
860       or a period (.).
861
862       Gawk  performs  comparisons  as  follows: If two variables are numeric,
863       they are compared numerically.  If one value is numeric and  the  other
864       has  a  string  value  that is a “numeric string,” then comparisons are
865       also done numerically.  Otherwise, the numeric value is converted to  a
866       string and a string comparison is performed.  Two strings are compared,
867       of course, as strings.
868
869       Note that string constants, such as "57", are not numeric strings, they
870       are  string  constants.   The  idea of “numeric string” only applies to
871       fields, getline input, FILENAME, ARGV elements,  ENVIRON  elements  and
872       the  elements  of  an  array  created by split() or patsplit() that are
873       numeric strings.  The basic idea is that  user  input,  and  only  user
874       input, that looks numeric, should be treated that way.
875
876   Octal and Hexadecimal Constants
877       You may use C-style octal and hexadecimal constants in your AWK program
878       source code.  For example, the octal value 011 is equal to  decimal  9,
879       and the hexadecimal value 0x11 is equal to decimal 17.
880
881   String Constants
882       String  constants  in  AWK are sequences of characters enclosed between
883       double quotes (like "value").  Within strings, certain escape sequences
884       are recognized, as in C.  These are:
885
886       \\   A literal backslash.
887
888       \a   The “alert” character; usually the ASCII BEL character.
889
890       \b   Backspace.
891
892       \f   Form-feed.
893
894       \n   Newline.
895
896       \r   Carriage return.
897
898       \t   Horizontal tab.
899
900       \v   Vertical tab.
901
902       \xhex digits
903            The character represented by the string of hexadecimal digits fol‐
904            lowing the \x.  Up to two following hexadecimal digits are consid‐
905            ered  part  of the escape sequence.  E.g., "\x1B" is the ASCII ESC
906            (escape) character.
907
908       \ddd The character represented by the 1-, 2-, or  3-digit  sequence  of
909            octal digits.  E.g., "\033" is the ASCII ESC (escape) character.
910
911       \c   The literal character c.
912
913       In compatibility mode, the characters represented by octal and hexadec‐
914       imal escape sequences  are  treated  literally  when  used  in  regular
915       expression constants.  Thus, /a\52b/ is equivalent to /a\*b/.
916
917   Regexp Constants
918       A  regular  expression  constant  is  a sequence of characters enclosed
919       between forward slashes (like /value/).  Regular expression matching is
920       described more fully below; see Regular Expressions.
921
922       The escape sequences described earlier may also be used inside constant
923       regular expressions (e.g., /[ \t\f\n\r\v]/ matches  whitespace  charac‐
924       ters).
925
926       Gawk  provides  strongly  typed regular expression constants. These are
927       written with a leading @ symbol (like so:  @/value/).   Such  constants
928       may  be  assigned  to scalars (variables, array elements) and passed to
929       user-defined functions. Variables that have been so assigned have regu‐
930       lar expression type.
931

PATTERNS AND ACTIONS

933       AWK is a line-oriented language.  The pattern comes first, and then the
934       action.  Action statements are enclosed in { and }.  Either the pattern
935       may be missing, or the action may be missing, but, of course, not both.
936       If the pattern is missing, the action executes for every single  record
937       of input.  A missing action is equivalent to
938
939              { print }
940
941       which prints the entire record.
942
943       Comments  begin with the # character, and continue until the end of the
944       line.  Empty lines may be used to  separate  statements.   Normally,  a
945       statement  ends with a newline, however, this is not the case for lines
946       ending in a comma, {, ?, :, &&, or ||.  Lines ending in do or else also
947       have  their  statements  automatically continued on the following line.
948       In other cases, a line can be continued by ending it  with  a  “\”,  in
949       which  case  the  newline  is ignored.  However, a “\” after a # is not
950       special.
951
952       Multiple statements may be put on one line by separating  them  with  a
953       “;”.   This  applies to both the statements within the action part of a
954       pattern-action pair (the usual case), and to the pattern-action  state‐
955       ments themselves.
956
957   Patterns
958       AWK patterns may be one of the following:
959
960              BEGIN
961              END
962              BEGINFILE
963              ENDFILE
964              /regular expression/
965              relational expression
966              pattern && pattern
967              pattern || pattern
968              pattern ? pattern : pattern
969              (pattern)
970              ! pattern
971              pattern1, pattern2
972
973       BEGIN  and  END  are two special kinds of patterns which are not tested
974       against the input.  The action parts of all BEGIN patterns  are  merged
975       as if all the statements had been written in a single BEGIN rule.  They
976       are executed before any of the input is read.  Similarly, all  the  END
977       rules are merged, and executed when all the input is exhausted (or when
978       an exit statement is executed).  BEGIN and END patterns cannot be  com‐
979       bined  with  other patterns in pattern expressions.  BEGIN and END pat‐
980       terns cannot have missing action parts.
981
982       BEGINFILE and ENDFILE are additional special patterns whose actions are
983       executed  before  reading  the  first record of each command-line input
984       file and after reading the last record of each file.  Inside the BEGIN‐
985       FILE  rule,  the  value  of  ERRNO  is the empty string if the file was
986       opened successfully.  Otherwise, there is some problem  with  the  file
987       and  the code should use nextfile to skip it. If that is not done, gawk
988       produces its usual fatal error for files that cannot be opened.
989
990       For /regular expression/ patterns, the associated statement is executed
991       for  each  input  record  that matches the regular expression.  Regular
992       expressions are the same as  those  in  egrep(1),  and  are  summarized
993       below.
994
995       A  relational  expression may use any of the operators defined below in
996       the section on actions.  These generally test  whether  certain  fields
997       match certain regular expressions.
998
999       The  &&,  ||, and !  operators are logical AND, logical OR, and logical
1000       NOT, respectively, as in C.  They do short-circuit evaluation, also  as
1001       in  C,  and  are used for combining more primitive pattern expressions.
1002       As in most languages, parentheses may be used to change  the  order  of
1003       evaluation.
1004
1005       The  ?:  operator is like the same operator in C.  If the first pattern
1006       is true then the pattern used for testing is the second pattern, other‐
1007       wise  it  is  the  third.  Only one of the second and third patterns is
1008       evaluated.
1009
1010       The pattern1, pattern2 form of an expression is called a range pattern.
1011       It  matches  all input records starting with a record that matches pat‐
1012       tern1, and continuing until a record that matches pattern2,  inclusive.
1013       It does not combine with any other sort of pattern expression.
1014
1015   Regular Expressions
1016       Regular  expressions  are  the  extended kind found in egrep.  They are
1017       composed of characters as follows:
1018
1019       c          Matches the non-metacharacter c.
1020
1021       \c         Matches the literal character c.
1022
1023       .          Matches any character including newline.
1024
1025       ^          Matches the beginning of a string.
1026
1027       $          Matches the end of a string.
1028
1029       [abc...]   A character list: matches any of the characters abc....  You
1030                  may  include a range of characters by separating them with a
1031                  dash.  To include a literal dash in the list, put  it  first
1032                  or last.
1033
1034       [^abc...]  A  negated  character  list:  matches  any  character except
1035                  abc....
1036
1037       r1|r2      Alternation: matches either r1 or r2.
1038
1039       r1r2       Concatenation: matches r1, and then r2.
1040
1041       r+         Matches one or more r's.
1042
1043       r*         Matches zero or more r's.
1044
1045       r?         Matches zero or one r's.
1046
1047       (r)        Grouping: matches r.
1048
1049       r{n}
1050       r{n,}
1051       r{n,m}     One or two numbers inside braces denote an interval  expres‐
1052                  sion.   If  there is one number in the braces, the preceding
1053                  regular expression r is repeated n times.  If there are  two
1054                  numbers  separated  by  a comma, r is repeated n to m times.
1055                  If there is one number  followed  by  a  comma,  then  r  is
1056                  repeated at least n times.
1057
1058       \y         Matches  the empty string at either the beginning or the end
1059                  of a word.
1060
1061       \B         Matches the empty string within a word.
1062
1063       \<         Matches the empty string at the beginning of a word.
1064
1065       \>         Matches the empty string at the end of a word.
1066
1067       \s         Matches any whitespace character.
1068
1069       \S         Matches any nonwhitespace character.
1070
1071       \w         Matches any word-constituent character  (letter,  digit,  or
1072                  underscore).
1073
1074       \W         Matches any character that is not word-constituent.
1075
1076       \`         Matches  the  empty  string  at  the  beginning  of a buffer
1077                  (string).
1078
1079       \'         Matches the empty string at the end of a buffer.
1080
1081       The escape sequences that are valid in  string  constants  (see  String
1082       Constants) are also valid in regular expressions.
1083
1084       Character  classes  are  a feature introduced in the POSIX standard.  A
1085       character class is a special notation for describing lists  of  charac‐
1086       ters  that  have  a specific attribute, but where the actual characters
1087       themselves can vary from country to country and/or from  character  set
1088       to  character  set.   For  example, the notion of what is an alphabetic
1089       character differs in the USA and in France.
1090
1091       A character class is only valid in  a  regular  expression  inside  the
1092       brackets  of a character list.  Character classes consist of [:, a key‐
1093       word denoting the class, and :].  The character classes defined by  the
1094       POSIX standard are:
1095
1096       [:alnum:]  Alphanumeric characters.
1097
1098       [:alpha:]  Alphabetic characters.
1099
1100       [:blank:]  Space or tab characters.
1101
1102       [:cntrl:]  Control characters.
1103
1104       [:digit:]  Numeric characters.
1105
1106       [:graph:]  Characters that are both printable and visible.  (A space is
1107                  printable, but not visible, while an a is both.)
1108
1109       [:lower:]  Lowercase alphabetic characters.
1110
1111       [:print:]  Printable characters (characters that are not control  char‐
1112                  acters.)
1113
1114       [:punct:]  Punctuation characters (characters that are not letter, dig‐
1115                  its, control characters, or space characters).
1116
1117       [:space:]  Space characters (such as space, tab, and formfeed, to  name
1118                  a few).
1119
1120       [:upper:]  Uppercase alphabetic characters.
1121
1122       [:xdigit:] Characters that are hexadecimal digits.
1123
1124       For  example,  before the POSIX standard, to match alphanumeric charac‐
1125       ters, you would have had to write /[A-Za-z0-9]/.  If your character set
1126       had  other  alphabetic characters in it, this would not match them, and
1127       if your character set collated differently from ASCII, this  might  not
1128       even match the ASCII alphanumeric characters.  With the POSIX character
1129       classes, you can write /[[:alnum:]]/, and this matches  the  alphabetic
1130       and numeric characters in your character set, no matter what it is.
1131
1132       Two  additional special sequences can appear in character lists.  These
1133       apply to non-ASCII  character  sets,  which  can  have  single  symbols
1134       (called  collating  elements)  that  are represented with more than one
1135       character, as well as several characters that are equivalent  for  col‐
1136       lating,  or  sorting,  purposes.   (E.g.,  in French, a plain “e” and a
1137       grave-accented “e`” are equivalent.)
1138
1139       Collating Symbols
1140              A  collating  symbol  is  a  multi-character  collating  element
1141              enclosed  in [.  and .].  For example, if ch is a collating ele‐
1142              ment, then [[.ch.]]  is a regular expression that  matches  this
1143              collating  element,  while  [ch]  is  a  regular expression that
1144              matches either c or h.
1145
1146       Equivalence Classes
1147              An equivalence class is a locale-specific name  for  a  list  of
1148              characters  that are equivalent.  The name is enclosed in [= and
1149              =].  For example, the name e might be used to represent  all  of
1150              “e”,  “e´”,  and “e`”.  In this case, [[=e=]] is a regular expres‐
1151              sion that matches any of e, e´, or e`.
1152
1153       These features are very valuable in non-English speaking locales.   The
1154       library  functions  that gawk uses for regular expression matching cur‐
1155       rently only recognize POSIX character classes; they  do  not  recognize
1156       collating symbols or equivalence classes.
1157
1158       The  \y,  \B, \<, \>, \s, \S, \w, \W, \`, and \' operators are specific
1159       to gawk; they are extensions based on facilities  in  the  GNU  regular
1160       expression libraries.
1161
1162       The various command line options control how gawk interprets characters
1163       in regular expressions.
1164
1165       No options
1166              In the default case, gawk provides all the facilities  of  POSIX
1167              regular  expressions  and  the  GNU regular expression operators
1168              described above.
1169
1170       --posix
1171              Only POSIX regular expressions are supported, the GNU  operators
1172              are not special.  (E.g., \w matches a literal w).
1173
1174       --traditional
1175              Traditional  UNIX  awk regular expressions are matched.  The GNU
1176              operators are not special,  and  interval  expressions  are  not
1177              available.  Characters described by octal and hexadecimal escape
1178              sequences are treated literally, even if they represent  regular
1179              expression metacharacters.
1180
1181       --re-interval
1182              Allow  interval  expressions  in  regular  expressions,  even if
1183              --traditional has been provided.
1184
1185   Actions
1186       Action statements are enclosed in braces, { and }.   Action  statements
1187       consist  of  the  usual assignment, conditional, and looping statements
1188       found in  most  languages.   The  operators,  control  statements,  and
1189       input/output statements available are patterned after those in C.
1190
1191   Operators
1192       The operators in AWK, in order of decreasing precedence, are:
1193
1194       (...)       Grouping
1195
1196       $           Field reference.
1197
1198       ++ --       Increment and decrement, both prefix and postfix.
1199
1200       ^           Exponentiation  (**  may  also  be  used,  and  **= for the
1201                   assignment operator).
1202
1203       + - !       Unary plus, unary minus, and logical negation.
1204
1205       * / %       Multiplication, division, and modulus.
1206
1207       + -         Addition and subtraction.
1208
1209       space       String concatenation.
1210
1211       |   |&      Piped I/O for getline, print, and printf.
1212
1213       < > <= >= == !=
1214                   The regular relational operators.
1215
1216       ~ !~        Regular expression match, negated match.  NOTE: Do not  use
1217                   a constant regular expression (/foo/) on the left-hand side
1218                   of a ~ or !~.  Only use one on the  right-hand  side.   The
1219                   expression  /foo/  ~  exp  has  the  same meaning as (($0 ~
1220                   /foo/) ~ exp).  This is usually not what you want.
1221
1222       in          Array membership.
1223
1224       &&          Logical AND.
1225
1226       ||          Logical OR.
1227
1228       ?:          The C conditional expression.  This has the  form  expr1  ?
1229                   expr2  : expr3.  If expr1 is true, the value of the expres‐
1230                   sion is expr2, otherwise it is expr3.  Only  one  of  expr2
1231                   and expr3 is evaluated.
1232
1233       = += -= *= /= %= ^=
1234                   Assignment.   Both  absolute  assignment  (var = value) and
1235                   operator-assignment (the other forms) are supported.
1236
1237   Control Statements
1238       The control statements are as follows:
1239
1240              if (condition) statement [ else statement ]
1241              while (condition) statement
1242              do statement while (condition)
1243              for (expr1; expr2; expr3) statement
1244              for (var in array) statement
1245              break
1246              continue
1247              delete array[index]
1248              delete array
1249              exit [ expression ]
1250              { statements }
1251              switch (expression) {
1252              case value|regex : statement
1253              ...
1254              [ default: statement ]
1255              }
1256
1257   I/O Statements
1258       The input/output statements are as follows:
1259
1260       close(file [, how])   Close file, pipe or coprocess.  The optional  how
1261                             should  only  be  used  when closing one end of a
1262                             two-way pipe to a coprocess.  It must be a string
1263                             value, either "to" or "from".
1264
1265       getline               Set  $0  from  the next input record; set NF, NR,
1266                             FNR, RT.
1267
1268       getline <file         Set $0 from the next record of file; set NF, RT.
1269
1270       getline var           Set var from the next input record; set NR,  FNR,
1271                             RT.
1272
1273       getline var <file     Set var from the next record of file; set RT.
1274
1275       command | getline [var]
1276                             Run  command, piping the output either into $0 or
1277                             var, as above, and RT.
1278
1279       command |& getline [var]
1280                             Run command as  a  coprocess  piping  the  output
1281                             either  into $0 or var, as above, and RT.  Copro‐
1282                             cesses are a gawk extension.   (The  command  can
1283                             also  be  a  socket.   See the subsection Special
1284                             File Names, below.)
1285
1286       next                  Stop processing the current input  record.   Read
1287                             the  next  input record and start processing over
1288                             with the first pattern in the AWK program.   Upon
1289                             reaching  the  end of the input data, execute any
1290                             END rule(s).
1291
1292       nextfile              Stop processing the current input file.  The next
1293                             input record read comes from the next input file.
1294                             Update FILENAME and ARGIND, reset FNR to  1,  and
1295                             start  processing  over with the first pattern in
1296                             the AWK program.  Upon reaching the  end  of  the
1297                             input data, execute any ENDFILE and END rule(s).
1298
1299       print                 Print  the  current record.  The output record is
1300                             terminated with the value of ORS.
1301
1302       print expr-list       Print expressions.  Each expression is  separated
1303                             by the value of OFS.  The output record is termi‐
1304                             nated with the value of ORS.
1305
1306       print expr-list >file Print expressions on file.   Each  expression  is
1307                             separated by the value of OFS.  The output record
1308                             is terminated with the value of ORS.
1309
1310       printf fmt, expr-list Format and  print.   See  The  printf  Statement,
1311                             below.
1312
1313       printf fmt, expr-list >file
1314                             Format and print on file.
1315
1316       system(cmd-line)      Execute the command cmd-line, and return the exit
1317                             status.  (This may not be available on  non-POSIX
1318                             systems.)   See  GAWK:  Effective AWK Programming
1319                             for the full details on the exit status.
1320
1321       fflush([file])        Flush any buffers associated with the open output
1322                             file  or  pipe file.  If file is missing or if it
1323                             is the null string, then flush  all  open  output
1324                             files and pipes.
1325
1326       Additional output redirections are allowed for print and printf.
1327
1328       print ... >> file
1329              Append output to the file.
1330
1331       print ... | command
1332              Write on a pipe.
1333
1334       print ... |& command
1335              Send  data  to  a coprocess or socket.  (See also the subsection
1336              Special File Names, below.)
1337
1338       The getline command returns 1 on success, zero on end of file,  and  -1
1339       on  an  error.   If the errno(3) value indicates that the I/O operation
1340       may be retried, and PROCINFO["input",  "RETRY"]  is  set,  then  -2  is
1341       returned  instead of -1, and further calls to getline may be attempted.
1342       Upon an error, ERRNO is set to a string describing the problem.
1343
1344       NOTE: Failure in opening a two-way socket results in a non-fatal  error
1345       being  returned to the calling function. If using a pipe, coprocess, or
1346       socket to getline, or from print or printf within a loop, you must  use
1347       close() to create new instances of the command or socket.  AWK does not
1348       automatically close pipes, sockets, or  coprocesses  when  they  return
1349       EOF.
1350
1351   The printf Statement
1352       The  AWK  versions  of the printf statement and sprintf() function (see
1353       below) accept the following conversion specification formats:
1354
1355       %a, %A  A floating point number of the form [-]0xh.hhhhp+-dd (C99 hexa‐
1356               decimal  floating point format).  For %A, uppercase letters are
1357               used instead of lowercase ones.
1358
1359       %c      A single character.  If the argument used for %c is numeric, it
1360               is treated as a character and printed.  Otherwise, the argument
1361               is assumed to be a string, and the only first character of that
1362               string is printed.
1363
1364       %d, %i  A decimal number (the integer part).
1365
1366       %e, %E  A floating point number of the form [-]d.dddddde[+-]dd.  The %E
1367               format uses E instead of e.
1368
1369       %f, %F  A floating point number of the form [-]ddd.dddddd.  If the sys‐
1370               tem  library supports it, %F is available as well. This is like
1371               %f, but uses capital letters for special  “not  a  number”  and
1372               “infinity” values. If %F is not available, gawk uses %f.
1373
1374       %g, %G  Use %e or %f conversion, whichever is shorter, with nonsignifi‐
1375               cant zeros suppressed.  The %G format uses %E instead of %e.
1376
1377       %o      An unsigned octal number (also an integer).
1378
1379       %u      An unsigned decimal number (again, an integer).
1380
1381       %s      A character string.
1382
1383       %x, %X  An unsigned hexadecimal number (an  integer).   The  %X  format
1384               uses ABCDEF instead of abcdef.
1385
1386       %%      A single % character; no argument is converted.
1387
1388       Optional,  additional  parameters may lie between the % and the control
1389       letter:
1390
1391       count$ Use the count'th argument at this point in the formatting.  This
1392              is  called  a positional specifier and is intended primarily for
1393              use in translated versions of format strings, not in the  origi‐
1394              nal text of an AWK program.  It is a gawk extension.
1395
1396       -      The expression should be left-justified within its field.
1397
1398       space  For  numeric  conversions,  prefix positive values with a space,
1399              and negative values with a minus sign.
1400
1401       +      The plus sign, used before the width modifier (see below),  says
1402              to  always  supply  a  sign for numeric conversions, even if the
1403              data to be formatted is positive.  The  +  overrides  the  space
1404              modifier.
1405
1406       #      Use  an  “alternate  form” for certain control letters.  For %o,
1407              supply a leading zero.  For %x, and %X, supply a leading  0x  or
1408              0X  for  a  nonzero  result.   For %e, %E, %f and %F, the result
1409              always contains a decimal point.  For %g, and %G, trailing zeros
1410              are not removed from the result.
1411
1412       0      A leading 0 (zero) acts as a flag, indicating that output should
1413              be padded with zeroes instead of spaces.  This applies  only  to
1414              the  numeric  output formats.  This flag only has an effect when
1415              the field width is wider than the value to be printed.
1416
1417       '      A single quote character instructs gawk to insert  the  locale's
1418              thousands-separator  character into decimal numbers, and to also
1419              use the locale's decimal point  character  with  floating  point
1420              formats.   This requires correct locale support in the C library
1421              and in the definition of the current locale.
1422
1423       width  The field should be padded to this width.  The field is normally
1424              padded with spaces.  With the 0 flag, it is padded with zeroes.
1425
1426       .prec  A number that specifies the precision to use when printing.  For
1427              the %e, %E, %f and %F, formats, this  specifies  the  number  of
1428              digits  you want printed to the right of the decimal point.  For
1429              the %g, and %G formats, it specifies the maximum number of  sig‐
1430              nificant digits.  For the %d, %i, %o, %u, %x, and %X formats, it
1431              specifies the minimum number of digits to  print.   For  the  %s
1432              format,  it  specifies the maximum number of characters from the
1433              string that should be printed.
1434
1435       The dynamic width and prec capabilities of the ISO C printf()  routines
1436       are supported.  A * in place of either the width or prec specifications
1437       causes their values to be taken from the argument  list  to  printf  or
1438       sprintf().   To use a positional specifier with a dynamic width or pre‐
1439       cision, supply the count$ after the * in the format string.  For  exam‐
1440       ple, "%3$*2$.*1$s".
1441
1442   Special File Names
1443       When  doing I/O redirection from either print or printf into a file, or
1444       via getline from a file,  gawk  recognizes  certain  special  filenames
1445       internally.   These  filenames  allow  access  to open file descriptors
1446       inherited from gawk's parent process (usually the shell).   These  file
1447       names  may  also  be  used on the command line to name data files.  The
1448       filenames are:
1449
1450       -           The standard input.
1451
1452       /dev/stdin  The standard input.
1453
1454       /dev/stdout The standard output.
1455
1456       /dev/stderr The standard error output.
1457
1458       /dev/fd/n   The file associated with the open file descriptor n.
1459
1460       These are particularly useful for error messages.  For example:
1461
1462              print "You blew it!" > "/dev/stderr"
1463
1464       whereas you would otherwise have to use
1465
1466              print "You blew it!" | "cat 1>&2"
1467
1468       The following special filenames may be used with the |& coprocess oper‐
1469       ator for creating TCP/IP network connections:
1470
1471       /inet/tcp/lport/rhost/rport
1472       /inet4/tcp/lport/rhost/rport
1473       /inet6/tcp/lport/rhost/rport
1474              Files for a TCP/IP connection on local port lport to remote host
1475              rhost on remote port rport.  Use a port of 0 to have the  system
1476              pick a port.  Use /inet4 to force an IPv4 connection, and /inet6
1477              to force an  IPv6  connection.   Plain  /inet  uses  the  system
1478              default (most likely IPv4).  Usable only with the |& two-way I/O
1479              operator.
1480
1481       /inet/udp/lport/rhost/rport
1482       /inet4/udp/lport/rhost/rport
1483       /inet6/udp/lport/rhost/rport
1484              Similar, but use UDP/IP instead of TCP/IP.
1485
1486   Numeric Functions
1487       AWK has the following built-in arithmetic functions:
1488
1489       atan2(y, x)   Return the arctangent of y/x in radians.
1490
1491       cos(expr)     Return the cosine of expr, which is in radians.
1492
1493       exp(expr)     The exponential function.
1494
1495       int(expr)     Truncate to integer.
1496
1497       log(expr)     The natural logarithm function.
1498
1499       rand()        Return a random number N, between zero and one, such that
1500                     0 ≤ N < 1.
1501
1502       sin(expr)     Return the sine of expr, which is in radians.
1503
1504       sqrt(expr)    Return the square root of expr.
1505
1506       srand([expr]) Use expr as the new seed for the random number generator.
1507                     If no expr is provided, use the time of day.  Return  the
1508                     previous seed for the random number generator.
1509
1510   String Functions
1511       Gawk has the following built-in string functions:
1512
1513       asort(s [, d [, how] ]) Return  the  number  of  elements in the source
1514                               array s.  Sort the contents of s  using  gawk's
1515                               normal  rules for comparing values, and replace
1516                               the indices of the sorted values s with sequen‐
1517                               tial  integers starting with 1. If the optional
1518                               destination array d is specified, first  dupli‐
1519                               cate  s  into  d,  and then sort d, leaving the
1520                               indices of the source array  s  unchanged.  The
1521                               optional  string how controls the direction and
1522                               the comparison mode.  Valid values for how  are
1523                               any     of     the     strings     valid    for
1524                               PROCINFO["sorted_in"].  It can also be the name
1525                               of   a   user-defined  comparison  function  as
1526                               described in PROCINFO["sorted_in"].
1527
1528       asorti(s [, d [, how] ])
1529                               Return the number of  elements  in  the  source
1530                               array  s.   The behavior is the same as that of
1531                               asort(), except that the array indices are used
1532                               for  sorting, not the array values.  When done,
1533                               the array is indexed numerically, and the  val‐
1534                               ues  are  those  of  the original indices.  The
1535                               original values are lost; thus provide a second
1536                               array  if  you  wish  to preserve the original.
1537                               The purpose of the optional string how  is  the
1538                               same as described previously for asort().
1539
1540       gensub(r, s, h [, t])   Search  the  target string t for matches of the
1541                               regular expression r.  If h is a string  begin‐
1542                               ning with g or G, then replace all matches of r
1543                               with s.  Otherwise, h is  a  number  indicating
1544                               which  match of r to replace.  If t is not sup‐
1545                               plied, use $0 instead.  Within the  replacement
1546                               text  s,  the  sequence  \n, where n is a digit
1547                               from 1 to 9, may be used to indicate  just  the
1548                               text that matched the n'th parenthesized subex‐
1549                               pression.   The  sequence  \0  represents   the
1550                               entire  matched  text, as does the character &.
1551                               Unlike sub() and gsub(), the modified string is
1552                               returned as the result of the function, and the
1553                               original target string is not changed.
1554
1555       gsub(r, s [, t])        For each substring matching the regular expres‐
1556                               sion  r  in the string t, substitute the string
1557                               s, and return the number of substitutions.   If
1558                               t  is  not  supplied,  use  $0.   An  &  in the
1559                               replacement text is replaced with the text that
1560                               was  actually matched.  Use \& to get a literal
1561                               &.  (This must be typed  as  "\\&";  see  GAWK:
1562                               Effective  AWK Programming for a fuller discus‐
1563                               sion of the  rules  for  ampersands  and  back‐
1564                               slashes  in  the  replacement  text  of  sub(),
1565                               gsub(), and gensub().)
1566
1567       index(s, t)             Return the index of the string t in the  string
1568                               s,  or zero if t is not present.  (This implies
1569                               that character indices start at one.)  It is  a
1570                               fatal error to use a regexp constant for t.
1571
1572       length([s])             Return  the  length  of  the  string  s, or the
1573                               length of $0 if s is not supplied.  As  a  non-
1574                               standard  extension,  with  an  array argument,
1575                               length() returns the number of elements in  the
1576                               array.
1577
1578       match(s, r [, a])       Return  the  position  in  s  where the regular
1579                               expression r  occurs,  or  zero  if  r  is  not
1580                               present,  and  set  the  values  of  RSTART and
1581                               RLENGTH.  Note that the argument order  is  the
1582                               same as for the ~ operator: str ~ re.  If array
1583                               a is provided, a is cleared and then elements 1
1584                               through  n  are  filled  with the portions of s
1585                               that match the corresponding parenthesized sub‐
1586                               expression in r.  The zero'th element of a con‐
1587                               tains the portion of s matched  by  the  entire
1588                               regular    expression   r.    Subscripts   a[n,
1589                               "start"], and a[n, "length"] provide the start‐
1590                               ing  index  in  the  string  and length respec‐
1591                               tively, of each matching substring.
1592
1593       patsplit(s, a [, r [, seps] ])
1594                               Split the string s into the  array  a  and  the
1595                               separators array seps on the regular expression
1596                               r, and return the number  of  fields.   Element
1597                               values  are  the  portions of s that matched r.
1598                               The value of seps[i] is the possibly null sepa‐
1599                               rator  that  appeared after a[i].  The value of
1600                               seps[0] is the possibly null leading separator.
1601                               If  r  is  omitted,  FPAT is used instead.  The
1602                               arrays a and seps are cleared first.  Splitting
1603                               behaves  identically  to  field  splitting with
1604                               FPAT, described above.
1605
1606       split(s, a [, r [, seps] ])
1607                               Split the string s into the  array  a  and  the
1608                               separators array seps on the regular expression
1609                               r, and return the number of fields.   If  r  is
1610                               omitted,  FS is used instead.  The arrays a and
1611                               seps are cleared first.  seps[i] is  the  field
1612                               separator matched by r between a[i] and a[i+1].
1613                               If r is a single space, then leading whitespace
1614                               in  s goes into the extra array element seps[0]
1615                               and trailing whitespace  goes  into  the  extra
1616                               array  element  seps[n],  where n is the return
1617                               value  of  split(s,  a,  r,  seps).   Splitting
1618                               behaves   identically   to   field   splitting,
1619                               described above.  In particular, if r is a sin‐
1620                               gle-character  string,  that string acts as the
1621                               separator, even if it happens to be  a  regular
1622                               expression metacharacter.
1623
1624       sprintf(fmt, expr-list) Print  expr-list  according  to fmt, and return
1625                               the resulting string.
1626
1627       strtonum(str)           Examine str, and return its numeric value.   If
1628                               str  begins  with  a  leading 0, treat it as an
1629                               octal number.  If str begins with a leading  0x
1630                               or  0X, treat it as a hexadecimal number.  Oth‐
1631                               erwise, assume it is a decimal number.
1632
1633       sub(r, s [, t])         Just like gsub(), but replace  only  the  first
1634                               matching substring.  Return either zero or one.
1635
1636       substr(s, i [, n])      Return  the  at most n-character substring of s
1637                               starting at i.  If n is omitted, use  the  rest
1638                               of s.
1639
1640       tolower(str)            Return  a  copy of the string str, with all the
1641                               uppercase characters in str translated to their
1642                               corresponding   lowercase  counterparts.   Non-
1643                               alphabetic characters are left unchanged.
1644
1645       toupper(str)            Return a copy of the string str, with  all  the
1646                               lowercase characters in str translated to their
1647                               corresponding  uppercase  counterparts.    Non-
1648                               alphabetic characters are left unchanged.
1649
1650       Gawk  is  multibyte aware.  This means that index(), length(), substr()
1651       and match() all work in terms of characters, not bytes.
1652
1653   Time Functions
1654       Since one of the primary uses of AWK programs is processing  log  files
1655       that  contain time stamp information, gawk provides the following func‐
1656       tions for obtaining time stamps and formatting them.
1657
1658       mktime(datespec [, utc-flag])
1659                 Turn datespec into a time stamp of the same form as  returned
1660                 by  systime(),  and  return  the  result.   The datespec is a
1661                 string of the form YYYY MM DD HH MM SS[ DST].   The  contents
1662                 of  the  string are six or seven numbers representing respec‐
1663                 tively the full year including century, the month from  1  to
1664                 12,  the  day  of the month from 1 to 31, the hour of the day
1665                 from 0 to 23, the minute from 0 to 59, the second from  0  to
1666                 60,  and  an  optional  daylight  saving flag.  The values of
1667                 these numbers need not be within the  ranges  specified;  for
1668                 example,  an  hour  of  -1 means 1 hour before midnight.  The
1669                 origin-zero Gregorian calendar is assumed, with year  0  pre‐
1670                 ceding  year  1 and year -1 preceding year 0.  If utc-flag is
1671                 present and is non-zero or non-null, the time is  assumed  to
1672                 be in the UTC time zone; otherwise, the time is assumed to be
1673                 in the local time zone.  If the DST daylight saving  flag  is
1674                 positive,  the time is assumed to be daylight saving time; if
1675                 zero, the time is assumed to be standard time; and  if  nega‐
1676                 tive  (the  default),  mktime() attempts to determine whether
1677                 daylight saving time is in effect for the specified time.  If
1678                 datespec does not contain enough elements or if the resulting
1679                 time is out of range, mktime() returns -1.
1680
1681       strftime([format [, timestamp[, utc-flag]]])
1682                 Format timestamp according to the  specification  in  format.
1683                 If  utc-flag  is  present  and  is  non-zero or non-null, the
1684                 result is in UTC, otherwise the result is in local time.  The
1685                 timestamp  should  be  of  the  same form as returned by sys‐
1686                 time().  If timestamp is missing, the current time of day  is
1687                 used.   If  format is missing, a default format equivalent to
1688                 the output of date(1) is used.  The default format is  avail‐
1689                 able  in PROCINFO["strftime"].  See the specification for the
1690                 strftime() function in ISO C for the format conversions  that
1691                 are guaranteed to be available.
1692
1693       systime() Return the current time of day as the number of seconds since
1694                 the Epoch (1970-01-01 00:00:00 UTC on POSIX systems).
1695
1696   Bit Manipulations Functions
1697       Gawk supplies the following bit manipulation functions.  They  work  by
1698       converting  double-precision  floating  point values to uintmax_t inte‐
1699       gers, doing the operation, and  then  converting  the  result  back  to
1700       floating point.
1701
1702       NOTE:  Passing  negative  operands  to  any of these functions causes a
1703       fatal error.
1704
1705       The functions are:
1706
1707       and(v1, v2 [, ...]) Return the bitwise AND of the  values  provided  in
1708                           the argument list.  There must be at least two.
1709
1710       compl(val)          Return the bitwise complement of val.
1711
1712       lshift(val, count)  Return  the  value  of  val,  shifted left by count
1713                           bits.
1714
1715       or(v1, v2 [, ...])  Return the bitwise OR of the values provided in the
1716                           argument list.  There must be at least two.
1717
1718       rshift(val, count)  Return  the  value  of  val, shifted right by count
1719                           bits.
1720
1721       xor(v1, v2 [, ...]) Return the bitwise XOR of the  values  provided  in
1722                           the argument list.  There must be at least two.
1723
1724   Type Functions
1725       The  following  functions  provide type related information about their
1726       arguments.
1727
1728       isarray(x) Return true if x is an array, false otherwise.   This  func‐
1729                  tion is mainly for use with the elements of multidimensional
1730                  arrays and with function parameters.
1731
1732       typeof(x)  Return a string indicating the type of x.  The  string  will
1733                  be  one  of "array", "number", "regexp", "string", "strnum",
1734                  "unassigned", or "undefined".
1735
1736   Internationalization Functions
1737       The following functions may be used from within your  AWK  program  for
1738       translating strings at run-time.  For full details, see GAWK: Effective
1739       AWK Programming.
1740
1741       bindtextdomain(directory [, domain])
1742              Specify the directory where gawk looks for the  .gmo  files,  in
1743              case they will not or cannot be placed in the ``standard'' loca‐
1744              tions (e.g., during testing).  It returns  the  directory  where
1745              domain is ``bound.''
1746              The  default domain is the value of TEXTDOMAIN.  If directory is
1747              the null string (""), then bindtextdomain() returns the  current
1748              binding for the given domain.
1749
1750       dcgettext(string [, domain [, category]])
1751              Return  the  translation  of  string  in  text domain domain for
1752              locale category category.  The default value for domain  is  the
1753              current  value of TEXTDOMAIN.  The default value for category is
1754              "LC_MESSAGES".
1755              If you supply a value for category, it must be a string equal to
1756              one  of the known locale categories described in GAWK: Effective
1757              AWK Programming.  You must  also  supply  a  text  domain.   Use
1758              TEXTDOMAIN if you want to use the current domain.
1759
1760       dcngettext(string1, string2, number [, domain [, category]])
1761              Return  the  plural  form  used for number of the translation of
1762              string1 and string2 in text domain domain  for  locale  category
1763              category.   The default value for domain is the current value of
1764              TEXTDOMAIN.  The default value for category is "LC_MESSAGES".
1765              If you supply a value for category, it must be a string equal to
1766              one  of the known locale categories described in GAWK: Effective
1767              AWK Programming.  You must  also  supply  a  text  domain.   Use
1768              TEXTDOMAIN if you want to use the current domain.
1769

USER-DEFINED FUNCTIONS

1771       Functions in AWK are defined as follows:
1772
1773              function name(parameter list) { statements }
1774
1775       Functions  execute  when  they  are  called  from within expressions in
1776       either patterns or actions.  Actual parameters supplied in the function
1777       call  are  used  to  instantiate  the formal parameters declared in the
1778       function.  Arrays are passed by reference, other variables  are  passed
1779       by value.
1780
1781       Since  functions were not originally part of the AWK language, the pro‐
1782       vision for local variables is rather clumsy: They are declared as extra
1783       parameters  in the parameter list.  The convention is to separate local
1784       variables from real parameters by extra spaces in the  parameter  list.
1785       For example:
1786
1787              function  f(p, q,     a, b)   # a and b are local
1788              {
1789                   ...
1790              }
1791
1792              /abc/     { ... ; f(1, 2) ; ... }
1793
1794       The left parenthesis in a function call is required to immediately fol‐
1795       low the function name, without any intervening whitespace.  This avoids
1796       a  syntactic  ambiguity with the concatenation operator.  This restric‐
1797       tion does not apply to the built-in functions listed above.
1798
1799       Functions may call each other and may be recursive.   Function  parame‐
1800       ters used as local variables are initialized to the null string and the
1801       number zero upon function invocation.
1802
1803       Use return expr to return a value from a function.  The return value is
1804       undefined if no value is provided, or if the function returns by “fall‐
1805       ing off” the end.
1806
1807       As a gawk extension, functions may be called indirectly.  To  do  this,
1808       assign  the  name of the function to be called, as a string, to a vari‐
1809       able.  Then use the variable as if it were the name of a function, pre‐
1810       fixed with an @ sign, like so:
1811              function myfunc()
1812              {
1813                   print "myfunc called"
1814                   ...
1815              }
1816
1817              {    ...
1818                   the_func = "myfunc"
1819                   @the_func()    # call through the_func to myfunc
1820                   ...
1821              }
1822       As  of  version 4.1.2, this works with user-defined functions, built-in
1823       functions, and extension functions.
1824
1825       If --lint has been provided, gawk warns about calls to undefined  func‐
1826       tions  at  parse  time,  instead  of at run time.  Calling an undefined
1827       function at run time is a fatal error.
1828
1829       The word func may be used in place of function, although this is depre‐
1830       cated.
1831

DYNAMICALLY LOADING NEW FUNCTIONS

1833       You  can  dynamically add new functions written in C or C++ to the run‐
1834       ning gawk interpreter with the @load statement.  The full  details  are
1835       beyond  the scope of this manual page; see GAWK: Effective AWK Program‐
1836       ming.
1837

SIGNALS

1839       The gawk profiler accepts two signals.  SIGUSR1 causes  it  to  dump  a
1840       profile  and  function  call stack to the profile file, which is either
1841       awkprof.out, or whatever file was named with the --profile option.   It
1842       then  continues  to  run.   SIGHUP  causes gawk to dump the profile and
1843       function call stack and then exit.
1844

INTERNATIONALIZATION

1846       String constants are sequences of characters enclosed in double quotes.
1847       In non-English speaking environments, it is possible to mark strings in
1848       the AWK program as requiring translation to the local natural language.
1849       Such  strings  are  marked in the AWK program with a leading underscore
1850       (“_”).  For example,
1851
1852              gawk 'BEGIN { print "hello, world" }'
1853
1854       always prints hello, world.  But,
1855
1856              gawk 'BEGIN { print _"hello, world" }'
1857
1858       might print bonjour, monde in France.
1859
1860       There are several steps involved in producing and running a localizable
1861       AWK program.
1862
1863       1.  Add  a BEGIN action to assign a value to the TEXTDOMAIN variable to
1864           set the text domain to a name associated with your program:
1865
1866                BEGIN { TEXTDOMAIN = "myprog" }
1867
1868           This allows gawk to find the .gmo file associated  with  your  pro‐
1869           gram.  Without this step, gawk uses the messages text domain, which
1870           likely does not contain translations for your program.
1871
1872       2.  Mark all strings that should  be  translated  with  leading  under‐
1873           scores.
1874
1875       3.  If necessary, use the dcgettext() and/or bindtextdomain() functions
1876           in your program, as appropriate.
1877
1878       4.  Run gawk --gen-pot -f myprog.awk > myprog.pot to  generate  a  .pot
1879           file for your program.
1880
1881       5.  Provide  appropriate translations, and build and install the corre‐
1882           sponding .gmo files.
1883
1884       The internationalization features are described in full detail in GAWK:
1885       Effective AWK Programming.
1886

POSIX COMPATIBILITY

1888       A  primary  goal  for gawk is compatibility with the POSIX standard, as
1889       well as with the latest version of Brian Kernighan's awk.  To this end,
1890       gawk  incorporates  the  following  user visible features which are not
1891       described in the AWK book, but are part of the Brian  Kernighan's  ver‐
1892       sion of awk, and are in the POSIX standard.
1893
1894       The  book  indicates that command line variable assignment happens when
1895       awk would otherwise open the argument as a file,  which  is  after  the
1896       BEGIN rule is executed.  However, in earlier implementations, when such
1897       an assignment appeared before any file names, the assignment would hap‐
1898       pen before the BEGIN rule was run.  Applications came to depend on this
1899       “feature.”  When awk was changed to match  its  documentation,  the  -v
1900       option  for  assigning  variables before program execution was added to
1901       accommodate applications that depended upon the  old  behavior.   (This
1902       feature  was  agreed  upon by both the Bell Laboratories developers and
1903       the GNU developers.)
1904
1905       When processing arguments, gawk uses the special option “--” to  signal
1906       the end of arguments.  In compatibility mode, it warns about but other‐
1907       wise ignores undefined options.  In normal  operation,  such  arguments
1908       are passed on to the AWK program for it to process.
1909
1910       The  AWK  book  does not define the return value of srand().  The POSIX
1911       standard has it return the seed it was using, to allow keeping track of
1912       random  number  sequences.   Therefore srand() in gawk also returns its
1913       current seed.
1914
1915       Other features are: The use of multiple -f options (from MKS awk);  the
1916       ENVIRON array; the \a, and \v escape sequences (done originally in gawk
1917       and fed back into the Bell Laboratories  version);  the  tolower()  and
1918       toupper()  built-in functions (from the Bell Laboratories version); and
1919       the ISO C conversion specifications in printf (done first in  the  Bell
1920       Laboratories version).
1921

HISTORICAL FEATURES

1923       There  is  one feature of historical AWK implementations that gawk sup‐
1924       ports: It is possible to call the length() built-in function  not  only
1925       with no argument, but even without parentheses!  Thus,
1926
1927              a = length     # Holy Algol 60, Batman!
1928
1929       is the same as either of
1930
1931              a = length()
1932              a = length($0)
1933
1934       Using  this  feature  is poor practice, and gawk issues a warning about
1935       its use if --lint is specified on the command line.
1936

GNU EXTENSIONS

1938       Gawk has a too-large number of  extensions  to  POSIX  awk.   They  are
1939       described  in  this  section.  All the extensions described here can be
1940       disabled by invoking gawk with the --traditional or --posix options.
1941
1942       The following features of gawk are not available in POSIX awk.
1943
1944       · No path search is performed  for  files  named  via  the  -f  option.
1945         Therefore the AWKPATH environment variable is not special.
1946
1947       · There is no facility for doing file inclusion (gawk's @include mecha‐
1948         nism).
1949
1950       · There is no facility for dynamically adding new functions written  in
1951         C (gawk's @load mechanism).
1952
1953       · The \x escape sequence.
1954
1955       · The ability to continue lines after ?  and :.
1956
1957       · Octal and hexadecimal constants in AWK programs.
1958
1959       · The  ARGIND, BINMODE, ERRNO, LINT, PREC, ROUNDMODE, RT and TEXTDOMAIN
1960         variables are not special.
1961
1962       · The IGNORECASE variable and its side-effects are not available.
1963
1964       · The FIELDWIDTHS variable and fixed-width field splitting.
1965
1966       · The FPAT variable and field splitting based on field values.
1967
1968       · The FUNCTAB, SYMTAB, and PROCINFO arrays are not available.
1969
1970       · The use of RS as a regular expression.
1971
1972       · The special file names available for I/O redirection are  not  recog‐
1973         nized.
1974
1975       · The |& operator for creating coprocesses.
1976
1977       · The BEGINFILE and ENDFILE special patterns are not available.
1978
1979       · The  ability to split out individual characters using the null string
1980         as the value of FS, and as the third argument to split().
1981
1982       · An optional fourth argument  to  split()  to  receive  the  separator
1983         texts.
1984
1985       · The optional second argument to the close() function.
1986
1987       · The optional third argument to the match() function.
1988
1989       · The ability to use positional specifiers with printf and sprintf().
1990
1991       · The ability to pass an array to length().
1992
1993       · The and(), asort(), asorti(), bindtextdomain(), compl(), dcgettext(),
1994         dcngettext(),  gensub(),  lshift(),   mktime(),   or(),   patsplit(),
1995         rshift(), strftime(), strtonum(), systime() and xor() functions.
1996
1997       · Localizable strings.
1998
1999       · Non-fatal I/O.
2000
2001       · Retryable I/O.
2002
2003       The  AWK book does not define the return value of the close() function.
2004       Gawk's close() returns the value from  fclose(3),  or  pclose(3),  when
2005       closing an output file or pipe, respectively.  It returns the process's
2006       exit status when closing an input pipe.  The return value is -1 if  the
2007       named file, pipe or coprocess was not opened with a redirection.
2008
2009       When  gawk is invoked with the --traditional option, if the fs argument
2010       to the -F option is “t”, then FS is set to  the  tab  character.   Note
2011       that  typing  gawk  -F\t ...  simply causes the shell to quote the “t,”
2012       and does not pass “\t” to the -F option.  Since this is a  rather  ugly
2013       special  case, it is not the default behavior.  This behavior also does
2014       not occur if --posix has been specified.  To really get a tab character
2015       as  the  field  separator, it is best to use single quotes: gawk -F'\t'
2016       ....
2017

ENVIRONMENT VARIABLES

2019       The AWKPATH environment variable can be  used  to  provide  a  list  of
2020       directories that gawk searches when looking for files named via the -f,
2021       --file, -i and --include options, and the @include directive.   If  the
2022       initial  search  fails, the path is searched again after appending .awk
2023       to the filename.
2024
2025       The AWKLIBPATH environment variable can be used to provide  a  list  of
2026       directories  that gawk searches when looking for files named via the -l
2027       and --load options.
2028
2029       The GAWK_READ_TIMEOUT environment variable can be  used  to  specify  a
2030       timeout in milliseconds for reading input from a terminal, pipe or two-
2031       way communication including sockets.
2032
2033       For connection to a remote host via socket, GAWK_SOCK_RETRIES  controls
2034       the  number  of  retries,  and  GAWK_MSEC_SLEEP  the  interval  between
2035       retries.  The interval is in milliseconds. On systems that do not  sup‐
2036       port  usleep(3),  the value is rounded up to an integral number of sec‐
2037       onds.
2038
2039       If POSIXLY_CORRECT exists in the environment, then gawk behaves exactly
2040       as  if  --posix  had been specified on the command line.  If --lint has
2041       been specified, gawk issues a warning message to this effect.
2042

EXIT STATUS

2044       If the exit statement is used with a value, then gawk  exits  with  the
2045       numeric value given to it.
2046
2047       Otherwise,  if there were no problems during execution, gawk exits with
2048       the value of the C constant EXIT_SUCCESS.  This is usually zero.
2049
2050       If an error occurs, gawk  exits  with  the  value  of  the  C  constant
2051       EXIT_FAILURE.  This is usually one.
2052
2053       If  gawk exits because of a fatal error, the exit status is 2.  On non-
2054       POSIX systems, this value may be mapped to EXIT_FAILURE.
2055

VERSION INFORMATION

2057       This man page documents gawk, version 5.1.
2058

AUTHORS

2060       The original version of UNIX awk was designed and implemented by Alfred
2061       Aho, Peter Weinberger, and Brian Kernighan of Bell Laboratories.  Brian
2062       Kernighan continues to maintain and enhance it.
2063
2064       Paul Rubin and Jay Fenlason, of the  Free  Software  Foundation,  wrote
2065       gawk,  to be compatible with the original version of awk distributed in
2066       Seventh Edition UNIX.  John Woods contributed a number  of  bug  fixes.
2067       David  Trueman,  with contributions from Arnold Robbins, made gawk com‐
2068       patible with the new version of UNIX awk.  Arnold Robbins is  the  cur‐
2069       rent maintainer.
2070
2071       See GAWK: Effective AWK Programming for a full list of the contributors
2072       to gawk and its documentation.
2073
2074       See the README file in the gawk distribution for up-to-date information
2075       about maintainers and which ports are currently supported.
2076

BUG REPORTS

2078       If   you   find   a  bug  in  gawk,  please  send  electronic  mail  to
2079       bug-gawk@gnu.org.  Please include your operating system and  its  revi‐
2080       sion,  the  version of gawk (from gawk --version), which C compiler you
2081       used to compile it, and a test program and data that are  as  small  as
2082       possible for reproducing the problem.
2083
2084       Before  sending  a  bug report, please do the following things.  First,
2085       verify that you have the latest version of gawk.   Many  bugs  (usually
2086       subtle  ones)  are  fixed at each release, and if yours is out of date,
2087       the problem may already have been solved.  Second, please see  if  set‐
2088       ting  the  environment  variable  LC_ALL  to  LC_ALL=C causes things to
2089       behave as you expect. If so, it's a locale issue, and may  or  may  not
2090       really  be a bug.  Finally, please read this man page and the reference
2091       manual carefully to be sure that what you think is  a  bug  really  is,
2092       instead of just a quirk in the language.
2093
2094       Whatever  you do, do NOT post a bug report in comp.lang.awk.  While the
2095       gawk developers occasionally read this newsgroup, posting  bug  reports
2096       there is an unreliable way to report bugs.  Similarly, do NOT use a web
2097       forum (such as Stack Overflow) for reporting bugs.  Instead, please use
2098       the electronic mail addresses given above.  Really.
2099
2100       If you're using a GNU/Linux or BSD-based system, you may wish to submit
2101       a bug report to the vendor of  your  distribution.   That's  fine,  but
2102       please send a copy to the official email address as well, since there's
2103       no guarantee that the bug report will be forwarded to  the  gawk  main‐
2104       tainer.
2105

BUGS

2107       The  -F option is not necessary given the command line variable assign‐
2108       ment feature; it remains only for backwards compatibility.
2109

SEE ALSO

2111       egrep(1),  sed(1),  getpid(2),   getppid(2),   getpgrp(2),   getuid(2),
2112       geteuid(2),   getgid(2),  getegid(2),  getgroups(2),  printf(3),  strf‐
2113       time(3), usleep(3)
2114
2115       The AWK Programming Language, Alfred V. Aho, Brian W. Kernighan,  Peter
2116       J. Weinberger, Addison-Wesley, 1988.  ISBN 0-201-07981-X.
2117
2118       GAWK:  Effective  AWK  Programming,  Edition 5.1, shipped with the gawk
2119       source.  The current version of this document is  available  online  at
2120       https://www.gnu.org/software/gawk/manual.
2121
2122       The     GNU     gettext     documentation,    available    online    at
2123       https://www.gnu.org/software/gettext.
2124

EXAMPLES

2126       Print and sort the login names of all users:
2127
2128            BEGIN     { FS = ":" }
2129                 { print $1 | "sort" }
2130
2131       Count lines in a file:
2132
2133                 { nlines++ }
2134            END  { print nlines }
2135
2136       Precede each line by its number in the file:
2137
2138            { print FNR, $0 }
2139
2140       Concatenate and line number (a variation on a theme):
2141
2142            { print NR, $0 }
2143
2144       Run an external command for particular lines of data:
2145
2146            tail -f access_log |
2147            awk '/myhome.html/ { system("nmap " $1 ">> logdir/myhome.html") }'
2148

ACKNOWLEDGEMENTS

2150       Brian Kernighan provided valuable assistance during testing and  debug‐
2151       ging.  We thank him.
2152

COPYING PERMISSIONS

2154       Copyright © 1989, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999,
2155       2001, 2002, 2003, 2004, 2005, 2007, 2009, 2010, 2011, 2012, 2013, 2014,
2156       2015, 2016, 2017, 2018, 2019, 2020, Free Software Foundation, Inc.
2157
2158       Permission  is  granted  to make and distribute verbatim copies of this
2159       manual page provided the copyright notice and  this  permission  notice
2160       are preserved on all copies.
2161
2162       Permission  is granted to copy and distribute modified versions of this
2163       manual page under the conditions for verbatim  copying,  provided  that
2164       the  entire  resulting derived work is distributed under the terms of a
2165       permission notice identical to this one.
2166
2167       Permission is granted to copy and distribute translations of this  man‐
2168       ual page into another language, under the above conditions for modified
2169       versions, except that this permission notice may be stated in a  trans‐
2170       lation approved by the Foundation.
2171
2172
2173
2174Free Software Foundation          Mar 23 2020                          GAWK(1)
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