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awk(1) - phpMan

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GAWK(1)                                  Utility Commands                                 GAWK(1)

       gawk - pattern scanning and processing language

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

       Gawk  is the GNU Project's implementation of the AWK programming language.  It conforms to
       the definition of the language in the POSIX 1003.1 Standard.   This  version  in  turn  is
       based  on  the  description  in The AWK Programming Language, by Aho, Kernighan, and Wein‐
       berger.  Gawk provides the additional features found  in  the  current  version  of  Brian
       Kernighan's awk and a number of GNU-specific extensions.

       The command line consists of options to gawk itself, the AWK program text (if not supplied
       via the -f or --file options), and values to be made available in the ARGC and  ARGV  pre-
       defined AWK variables.

       When  gawk  is invoked with the --profile option, it starts gathering profiling statistics
       from the execution of the program.  Gawk runs more slowly in this mode, and  automatically
       produces  an  execution  profile  in  the  file  awkprof.out when done.  See the --profile
       option, below.

       Gawk also has an integrated debugger. An interactive debugging session can be  started  by
       supplying  the  --debug  option to the command line. In this mode of execution, gawk loads
       the AWK source code and then prompts for debugging commands.  Gawk can only debug AWK pro‐
       gram  source  provided  with the -f option.  The debugger is documented in GAWK: Effective
       AWK Programming.

       Gawk options may be either traditional POSIX-style one letter options, or  GNU-style  long
       options.  POSIX options start with a single “-”, while long options start with “--”.  Long
       options are provided for both GNU-specific features and for POSIX-mandated features.

       Gawk-specific options are typically used in long-option form.  Arguments to  long  options
       are either joined with the option by an = sign, with no intervening spaces, or they may be
       provided in the next command line argument.  Long options may be abbreviated, as  long  as
       the abbreviation remains unique.

       Additionally,  every  long  option  has a corresponding short option, so that the option's
       functionality may be used from within #!  executable scripts.

       Gawk accepts the following options.   Standard  options  are  listed  first,  followed  by
       options for gawk extensions, listed alphabetically by short option.

       -f program-file
       --file program-file
              Read  the  AWK program source from the file program-file, instead of from the first
              command line argument.  Multiple -f (or --file) options may be used.

       -F fs
       --field-separator fs
              Use fs for the input field separator (the value of the FS predefined variable).

       -v var=val
       --assign var=val
              Assign the value val to the variable var, before execution of the  program  begins.
              Such variable values are available to the BEGIN rule of an AWK program.

              Treat  all  input  data  as  single-byte  characters. In other words, don't pay any
              attention to the locale information when attempting to process strings as multibyte
              characters.  The --posix option overrides this one.

              Run  in  compatibility  mode.   In  compatibility mode, gawk behaves identically to
              Brian Kernighan's awk; none of the GNU-specific extensions are recognized.  See GNU
              EXTENSIONS, below, for more information.

              Print  the  short  version of the GNU copyright information message on the standard
              output and exit successfully.

              Print a sorted list of global variables, their types and final values to file.   If
              no file is provided, gawk uses a file named awkvars.out in the current directory.
              Having  a  list of all the global variables is a good way to look for typographical
              errors in your programs.  You would also use this option if you have a  large  pro‐
              gram  with  a  lot  of functions, and you want to be sure that your functions don't
              inadvertently use global variables that you meant to be local.  (This is a particu‐
              larly easy mistake to make with simple variable names like i, j, and so on.)

              Enable debugging of AWK programs.  By default, the debugger reads commands interac‐
              tively from the terminal.  The optional file argument specifies a file with a  list
              of commands for the debugger to execute non-interactively.

       -e program-text
       --source program-text
              Use program-text as AWK program source code.  This option allows the easy intermix‐
              ing of library functions (used via the -f and  --file  options)  with  source  code
              entered on the command line.  It is intended primarily for medium to large AWK pro‐
              grams used in shell scripts.

       -E file
       --exec file
              Similar to -f, however, this is option is the last one processed.  This  should  be
              used  with  #!   scripts,  particularly  for  CGI applications, to avoid passing in
              options or source code (!) on the command line from a URL.   This  option  disables
              command-line variable assignments.

              Scan  and parse the AWK program, and generate a GNU .pot (Portable Object Template)
              format file on standard output with entries for all localizable strings in the pro‐
              gram.   The  program  itself is not executed.  See the GNU gettext distribution for
              more information on .pot files.

       --help Print a relatively short summary of the available options on the  standard  output.
              (Per the GNU Coding Standards, these options cause an immediate, successful exit.)

       -i include-file
       --include include-file
              Load  an awk source library.  This searches for the library using the AWKPATH envi‐
              ronment variable.  If the initial search fails, another attempt will be made  after
              appending the .awk suffix.  The file will be loaded only once (i.e., duplicates are
              eliminated), and the code does not constitute the main program source.

       -l lib
       --load lib
              Load a shared library lib.  This searches for  the  library  using  the  AWKLIBPATH
              environment  variable.   If  the initial search fails, another attempt will be made
              after appending the default shared library suffix for the  platform.   The  library
              initialization routine is expected to be named dl_load().

       -L [value]
              Provide  warnings  about  constructs  that are dubious or non-portable to other AWK
              implementations.  With an optional argument of fatal, lint  warnings  become  fatal
              errors.   This may be drastic, but its use will certainly encourage the development
              of cleaner AWK programs.  With an optional argument of invalid, only warnings about
              things that are actually invalid are issued. (This is not fully implemented yet.)

              Force  arbitrary precision arithmetic on numbers. This option has no effect if gawk
              is not compiled to use the GNU MPFR and MP libraries.

              Recognize octal and hexadecimal values in input data.  Use this option  with  great

              This  forces  gawk  to  use the locale's decimal point character when parsing input
              data.  Although the POSIX standard requires this behavior, and gawk  does  so  when
              --posix  is  in  effect,  the  default  is to follow traditional behavior and use a
              period as the decimal point, even in locales where the period is  not  the  decimal
              point character.  This option overrides the default behavior, without the full dra‐
              conian strictness of the --posix option.

              Output a pretty printed version of the program to file.  If no  file  is  provided,
              gawk uses a file named awkprof.out in the current directory.

              Enable  optimizations  upon the internal representation of the program.  Currently,
              this includes simple constant-folding, and  tail  call  elimination  for  recursive
              functions. The gawk maintainer hopes to add additional optimizations over time.

              Start  a  profiling session, and send the profiling data to prof-file.  The default
              is awkprof.out.  The profile contains execution counts of  each  statement  in  the
              program in the left margin and function call counts for each user-defined function.

              This turns on compatibility mode, with the following additional restrictions:

              · \x escape sequences are not recognized.

              · Only space and tab act as field separators when FS is set to a single space, new‐
                line does not.

              · You cannot continue lines after ?  and :.

              · The synonym func for the keyword function is not recognized.

              · The operators ** and **= cannot be used in place of ^ and ^=.

              Enable the use of interval expressions in regular expression matching (see  Regular
              Expressions,  below).  Interval expressions were not traditionally available in the
              AWK language.  The POSIX standard added them, to make awk and egrep consistent with
              each  other.   They  are  enabled  by default, but this option remains for use with

              Runs gawk in sandbox mode, disabling the system() function, input redirection  with
              getline,  output redirection with print and printf, and loading dynamic extensions.
              Command execution (through pipelines) is also disabled.  This effectively blocks  a
              script  from  accessing local resources (except for the files specified on the com‐
              mand line).

              Provide warnings about constructs that are not portable to the original version  of
              UNIX awk.

              Print  version information for this particular copy of gawk on the standard output.
              This is useful mainly for knowing if the current copy of gawk on your system is  up
              to  date  with  respect  to  whatever the Free Software Foundation is distributing.
              This is also useful when reporting bugs.  (Per  the  GNU  Coding  Standards,  these
              options cause an immediate, successful exit.)

       --     Signal  the  end  of  options. This is useful to allow further arguments to the AWK
              program itself to start with a “-”.  This provides consistency  with  the  argument
              parsing convention used by most other POSIX programs.

       In  compatibility  mode,  any  other  options  are  flagged  as invalid, but are otherwise
       ignored.  In normal operation, as long as program text has been supplied, unknown  options
       are  passed  on to the AWK program in the ARGV array for processing.  This is particularly
       useful for running AWK programs via the “#!” executable interpreter mechanism.

       For POSIX compatibility, the -W option may be used, followed by the name of a long option.

       An AWK program consists of a sequence of pattern-action statements and  optional  function

              @include "filename"
              @load "filename"
              pattern   { action statements }
              function name(parameter list) { statements }

       Gawk  first reads the program source from the program-file(s) if specified, from arguments
       to --source, or from the first non-option argument  on  the  command  line.   The  -f  and
       --source  options  may be used multiple times on the command line.  Gawk reads the program
       text as if all the program-files and command  line  source  texts  had  been  concatenated
       together.   This  is  useful  for  building  libraries of AWK functions, without having to
       include them in each new AWK program that uses them.  It also provides the ability to  mix
       library functions with command line programs.

       In  addition, lines beginning with @include may be used to include other source files into
       your program, making library use even easier.  This is equivalent to using the -i option.

       Lines beginning with @load may be used to load shared libraries into your  program.   This
       is equivalent to using the -l option.

       The  environment variable AWKPATH specifies a search path to use when finding source files
       named with the -f and -i options.  If this variable does not exist, the  default  path  is
       ".:/usr/local/share/awk".   (The  actual  directory  may vary, depending upon how gawk was
       built and installed.)  If a file name given to the -f option contains a “/” character,  no
       path search is performed.

       The  environment  variable  AWKLIBPATH  specifies a search path to use when finding source
       files named with the -l option.  If this variable does not  exist,  the  default  path  is
       ".:/usr/local/lib/gawk".   (The  actual  directory  may  vary, depending upon how gawk was
       built and installed.)

       Gawk executes AWK programs in the following order.  First, all variable assignments speci‐
       fied  via  the  -v option are performed.  Next, gawk compiles the program into an internal
       form.  Then, gawk executes the code in the BEGIN rule(s) (if any), and  then  proceeds  to
       read each file named in the ARGV array (up to ARGV[ARGC]).  If there are no files named on
       the command line, gawk reads the standard input.

       If a filename on the command line has the form var=val it is treated as a variable assign‐
       ment.   The  variable  var  will be assigned the value val.  (This happens after any BEGIN
       rule(s) have been run.)  Command line variable assignment is most useful  for  dynamically
       assigning  values to the variables AWK uses to control how input is broken into fields and
       records.  It is also useful for controlling state if multiple passes  are  needed  over  a
       single data file.

       If the value of a particular element of ARGV is empty (""), gawk skips over it.

       For  each input file, if a BEGINFILE rule exists, gawk executes the associated code before
       processing the contents of the file. Similarly, gawk executes  the  code  associated  with
       ENDFILE after processing the file.

       For  each record in the input, gawk tests to see if it matches any pattern in the AWK pro‐
       gram.  For each pattern that the record matches, gawk executes the associated action.  The
       patterns are tested in the order they occur in the program.

       Finally,  after  all the input is exhausted, gawk executes the code in the END rule(s) (if

   Command Line Directories
       According to POSIX, files named on the awk command line must be text files.  The  behavior
       is  ``undefined''  if they are not.  Most versions of awk treat a directory on the command
       line as a fatal error.

       Starting with version 4.0 of gawk, a directory on the command line produces a warning, but
       is  otherwise  skipped.   If either of the --posix or --traditional options is given, then
       gawk reverts to treating directories on the command line as a fatal error.

       AWK variables are dynamic; they come into existence when they are first used.  Their  val‐
       ues  are  either  floating-point  numbers or strings, or both, depending upon how they are
       used.  AWK also has one dimensional arrays; arrays with multiple dimensions may  be  simu‐
       lated.  Gawk provides true arrays of arrays; see Arrays, below.  Several pre-defined vari‐
       ables are set as a program runs; these are described as needed and summarized below.

       Normally, records are separated by newline characters.  You can control  how  records  are
       separated by assigning values to the built-in variable RS.  If RS is any single character,
       that character separates records.  Otherwise, RS is a regular  expression.   Text  in  the
       input  that matches this regular expression separates the record.  However, in compatibil‐
       ity mode, only the first character of its string value is used for separating records.  If
       RS  is  set to the null string, then records are separated by blank lines.  When RS is set
       to the null string, the newline character always acts as a field separator, in addition to
       whatever value FS may have.

       As  each  input record is read, gawk splits the record into fields, using the value of the
       FS variable as the field separator.  If FS is a single character, fields are separated  by
       that  character.  If FS is the null string, then each individual character becomes a sepa‐
       rate field.  Otherwise, FS is expected to be a full regular expression.   In  the  special
       case  that FS is a single space, fields are separated by runs of spaces and/or tabs and/or
       newlines.  (But see the section POSIX COMPATIBILITY, below).  NOTE: The value  of  IGNORE‐
       CASE  (see  below)  also affects how fields are split when FS is a regular expression, and
       how records are separated when RS is a regular expression.

       If the FIELDWIDTHS variable is set to a space separated list of  numbers,  each  field  is
       expected  to  have  fixed width, and gawk splits up the record using the specified widths.
       The value of FS is ignored.  Assigning a new value to FS or  FPAT  overrides  the  use  of

       Similarly, if the FPAT variable is set to a string representing a regular expression, each
       field is made up of text that matches that regular expression. In this case,  the  regular
       expression describes the fields themselves, instead of the text that separates the fields.
       Assigning a new value to FS or FIELDWIDTHS overrides the use of FPAT.

       Each field in the input record may be referenced by its position: $1, $2, and so  on.   $0
       is the whole record.  Fields need not be referenced by constants:

              n = 5
              print $n

       prints the fifth field in the input record.

       The variable NF is set to the total number of fields in the input record.

       References  to non-existent fields (i.e., fields after $NF) produce the null-string.  How‐
       ever, assigning to a non-existent field (e.g., $(NF+2) = 5) increases  the  value  of  NF,
       creates  any intervening fields with the null string as their values, and causes the value
       of $0 to be recomputed, with the fields being separated by the value of  OFS.   References
       to  negative  numbered  fields  cause a fatal error.  Decrementing NF causes the values of
       fields past the new value to be lost, and the value of  $0  to  be  recomputed,  with  the
       fields being separated by the value of OFS.

       Assigning  a  value  to an existing field causes the whole record to be rebuilt when $0 is
       referenced.  Similarly, assigning a value to $0 causes the record to be resplit,  creating
       new values for the fields.

   Built-in Variables
       Gawk's built-in variables are:

       ARGC        The number of command line arguments (does not include options to gawk, or the
                   program source).

       ARGIND      The index in ARGV of the current file being processed.

       ARGV        Array of command line arguments.  The array is indexed from 0  to  ARGC  -  1.
                   Dynamically changing the contents of ARGV can control the files used for data.

       BINMODE     On  non-POSIX  systems,  specifies  use  of  “binary”  mode  for all file I/O.
                   Numeric values of 1, 2, or 3, specify that input files, output files,  or  all
                   files,  respectively,  should  use  binary  I/O.  String values of "r", or "w"
                   specify that input files, or output files,  respectively,  should  use  binary
                   I/O.   String  values of "rw" or "wr" specify that all files should use binary
                   I/O.  Any other string value is treated as "rw", but generates a warning  mes‐

       CONVFMT     The conversion format for numbers, "%.6g", by default.

       ENVIRON     An  array  containing  the  values  of  the current environment.  The array is
                   indexed by the environment variables, each element being  the  value  of  that
                   variable (e.g., ENVIRON["HOME"] might be "/home/arnold").  Changing this array
                   does not affect the environment seen by programs which gawk spawns  via  redi‐
                   rection or the system() function.

       ERRNO       If a system error occurs either doing a redirection for getline, during a read
                   for getline, or during a close(), then ERRNO will contain a string  describing
                   the error.  The value is subject to translation in non-English locales.

       FIELDWIDTHS A  whitespace separated list of field widths.  When set, gawk parses the input
                   into fields of fixed width, instead of using the value of the FS  variable  as
                   the field separator.  See Fields, above.

       FILENAME    The  name of the current input file.  If no files are specified on the command
                   line, the value of FILENAME is “-”.  However, FILENAME is undefined inside the
                   BEGIN rule (unless set by getline).

       FNR         The input record number in the current input file.

       FPAT        A  regular expression describing the contents of the fields in a record.  When
                   set, gawk parses the input into fields, where the  fields  match  the  regular
                   expression, instead of using the value of the FS variable as the field separa‐
                   tor.  See Fields, above.

       FS          The input field separator, a space by default.  See Fields, above.

       FUNCTAB     An array whose indices and corresponding values are the names of all the user-
                   defined  or  extension  functions  in  the program.  NOTE: You may not use the
                   delete statement with the FUNCTAB array.

       IGNORECASE  Controls the case-sensitivity of all regular expression and string operations.
                   If IGNORECASE has a non-zero value, then string comparisons and pattern match‐
                   ing in rules, field splitting with FS and FPAT,  record  separating  with  RS,
                   regular  expression matching with ~ and !~, and the gensub(), gsub(), index(),
                   match(), patsplit(), split(), and sub() built-in  functions  all  ignore  case
                   when  doing  regular  expression  operations.  NOTE: Array subscripting is not
                   affected.  However, the asort() and asorti() functions are affected.
                   Thus, if IGNORECASE is not equal to zero, /aB/  matches  all  of  the  strings
                   "ab",  "aB",  "Ab", and "AB".  As with all AWK variables, the initial value of
                   IGNORECASE is zero, so all regular expression and string operations  are  nor‐
                   mally case-sensitive.

       LINT        Provides  dynamic  control  of  the  --lint option from within an AWK program.
                   When true, gawk prints lint warnings. When false, it does not.  When  assigned
                   the  string  value  "fatal",  lint  warnings become fatal errors, exactly like
                   --lint=fatal.  Any other true value just prints warnings.

       NF          The number of fields in the current input record.

       NR          The total number of input records seen so far.

       OFMT        The output format for numbers, "%.6g", by default.

       OFS         The output field separator, a space by default.

       ORS         The output record separator, by default a newline.

       PREC        The working precision of arbitrary precision  floating-point  numbers,  53  by

       PROCINFO    The elements of this array provide access to information about the running AWK
                   program.  On some systems, there  may  be  elements  in  the  array,  "group1"
                   through  "groupn" for some n, which is the number of supplementary groups that
                   the process has.  Use the in operator to test for these elements.  The follow‐
                   ing elements are guaranteed to be available:

                   PROCINFO["egid"]    The value of the getegid(2) system call.

                                       The default time format string for strftime().

                   PROCINFO["euid"]    The value of the geteuid(2) system call.

                   PROCINFO["FS"]      "FS"  if  field  splitting with FS is in effect, "FPAT" if
                                       field splitting with FPAT is in effect,  or  "FIELDWIDTHS"
                                       if field splitting with FIELDWIDTHS is in effect.

                                       A  subarray,  indexed by the names of all identifiers used
                                       in the text of the AWK program.  The values indicate  what
                                       gawk  knows  about  the  identifiers after it has finished
                                       parsing the program; they are not updated while  the  pro‐
                                       gram  runs.  For each identifier, the value of the element
                                       is one of the following:

                                              The identifier is an array.

                                              The identifier is an extension function loaded  via

                                              The identifier is a scalar.

                                              The  identifier  is  untyped  (could  be  used as a
                                              scalar or array, gawk doesn't know yet).

                                       "user" The identifier is a user-defined function.

                   PROCINFO["gid"]     The value of the getgid(2) system call.

                   PROCINFO["pgrpid"]  The process group ID of the current process.

                   PROCINFO["pid"]     The process ID of the current process.

                   PROCINFO["ppid"]    The parent process ID of the current process.

                   PROCINFO["uid"]     The value of the getuid(2) system call.

                                       If this element exists in PROCINFO, then  its  value  con‐
                                       trols  the  order in which array elements are traversed in
                                       for   loops.    Supported   values   are   "@ind_str_asc",
                                       "@ind_num_asc",      "@val_type_asc",      "@val_str_asc",
                                       "@val_num_asc",     "@ind_str_desc",      "@ind_num_desc",
                                       "@val_type_desc",  "@val_str_desc",  "@val_num_desc",  and
                                       "@unsorted".  The value can also be the name of  any  com‐
                                       parison function defined as follows:

                                            function cmp_func(i1, v1, i2, v2)

                                       where  i1  and  i2  are the indices, and v1 and v2 are the
                                       corresponding values of the two elements  being  compared.
                                       It  should return a number less than, equal to, or greater
                                       than 0, depending on how the elements of the array are  to
                                       be ordered.

                   PROCINFO["input", "READ_TIMEOUT"]
                                       The  timeout  in milliseconds for reading data from input,
                                       where input is a redirection string or a filename. A value
                                       of zero or less than zero means no timeout.

                                       The  version  of  the  GNU MPFR library used for arbitrary
                                       precision number support  in  gawk.   This  entry  is  not
                                       present if MPFR support is not compiled into gawk.

                                       The  version of the GNU MP library used for arbitrary pre‐
                                       cision number support in gawk.  This entry is not  present
                                       if MPFR support is not compiled into gawk.

                                       The  maximum  precision  supported by the GNU MPFR library
                                       for  arbitrary  precision  floating-point  numbers.   This
                                       entry  is not present if MPFR support is not compiled into

                                       The minimum precision allowed by the GNU MPFR library  for
                                       arbitrary precision floating-point numbers.  This entry is
                                       not present if MPFR support is not compiled into gawk.

                                       The major version of the extension API.  This entry is not
                                       present if loading dynamic extensions is not available.

                                       The minor version of the extension API.  This entry is not
                                       present if loading dynamic extensions is not available.

                   PROCINFO["version"] the version of gawk.

       ROUNDMODE   The rounding mode to use for arbitrary precision  arithmetic  on  numbers,  by
                   default  "N"  (IEEE-754 roundTiesToEven mode).  The accepted values are "N" or
                   "n" for roundTiesToEven, "U" or "u" for roundTowardPositive, "D"  or  "d"  for
                   roundTowardNegative,  "Z"  or  "z" for roundTowardZero, and if your version of
                   GNU MPFR library supports it, "A" or "a" for roundTiesToAway.

       RS          The input record separator, by default a newline.

       RT          The record terminator.  Gawk sets RT to the input text that matched the  char‐
                   acter or regular expression specified by RS.

       RSTART      The  index  of  the  first character matched by match(); 0 if no match.  (This
                   implies that character indices start at one.)

       RLENGTH     The length of the string matched by match(); -1 if no match.

       SUBSEP      The character used to separate  multiple  subscripts  in  array  elements,  by
                   default "\034".

       SYMTAB      An array whose indices are the names of all currently defined global variables
                   and arrays in the program.  The array may be used for indirect access to  read
                   or write the value of a variable:

                        foo = 5
                        SYMTAB["foo"] = 4
                        print foo    # prints 4

                   The  isarray()  function  may  be  used  to test if an element in SYMTAB is an
                   array.  You may not use the delete statement with the SYMTAB array.

       TEXTDOMAIN  The text domain of the AWK program; used to find  the  localized  translations
                   for the program's strings.

       Arrays  are  subscripted  with  an  expression  between square brackets ([ and ]).  If the
       expression is an expression list (expr, expr ...)  then the array subscript  is  a  string
       consisting of the concatenation of the (string) value of each expression, separated by the
       value of the SUBSEP variable.  This facility is  used  to  simulate  multiply  dimensioned
       arrays.  For example:

              i = "A"; j = "B"; k = "C"
              x[i, j, k] = "hello, world\n"

       assigns  the string "hello, world\n" to the element of the array x which is indexed by the
       string "A\034B\034C".  All arrays in AWK are associative, i.e., indexed by string values.

       The special operator in may be used to test if an array has an index consisting of a  par‐
       ticular value:

              if (val in array)
                   print array[val]

       If the array has multiple subscripts, use (i, j) in array.

       The  in  construct  may  also be used in a for loop to iterate over all the elements of an
       array.  However, the (i, j) in array construct only works in tests, not in for loops.

       An element may be deleted from an array using the delete statement.  The delete  statement
       may  also  be used to delete the entire contents of an array, just by specifying the array
       name without a subscript.

       gawk supports true multidimensional arrays. It does not require that such arrays be ``rec‐
       tangular'' as in C or C++.  For example:

              a[1] = 5
              a[2][1] = 6
              a[2][2] = 7

       NOTE: You may need to tell gawk that an array element is really a subarray in order to use
       it where gawk expects an array (such as in the second argument to split()).   You  can  do
       this  by  creating  an element in the subarray and then deleting it with the delete state‐

   Variable Typing And Conversion
       Variables and fields may be (floating point) numbers, or strings, or both.  How the  value
       of  a  variable is interpreted depends upon its context.  If used in a numeric expression,
       it will be treated as a number; if used as a string it will be treated as a string.

       To force a variable to be treated as a number, add 0 to it; to force it to be treated as a
       string, concatenate it with the null string.

       Uninitialized  variables  have  the  numeric value 0 and the string value "" (the null, or
       empty, string).

       When a string must be converted to a number, the conversion  is  accomplished  using  str‐
       tod(3).   A  number  is  converted  to  a string by using the value of CONVFMT as a format
       string for sprintf(3), with the numeric value of the variable as the  argument.   However,
       even though all numbers in AWK are floating-point, integral values are always converted as
       integers.  Thus, given

              CONVFMT = "%2.2f"
              a = 12
              b = a ""

       the variable b has a string value of "12" and not "12.00".

       NOTE: When operating in POSIX mode (such as with the --posix option), beware  that  locale
       settings  may interfere with the way decimal numbers are treated: the decimal separator of
       the numbers you are feeding to gawk must conform to what your locale would expect, be it a
       comma (,) or a period (.).

       Gawk  performs  comparisons  as  follows:  If two variables are numeric, they are compared
       numerically.  If one value is numeric and the other has a string value that is a  “numeric
       string,” then comparisons are also done numerically.  Otherwise, the numeric value is con‐
       verted to a string and a string comparison is performed.  Two  strings  are  compared,  of
       course, as strings.

       Note  that  string  constants, such as "57", are not numeric strings, they are string con‐
       stants.  The idea of “numeric string” only applies to  fields,  getline  input,  FILENAME,
       ARGV  elements,  ENVIRON  elements and the elements of an array created by split() or pat‐
       split() that are numeric strings.  The basic idea is that user input, and only user input,
       that looks numeric, should be treated that way.

   Octal and Hexadecimal Constants
       You  may use C-style octal and hexadecimal constants in your AWK program source code.  For
       example, the octal value 011 is equal to decimal 9, and  the  hexadecimal  value  0x11  is
       equal to decimal 17.

   String Constants
       String  constants  in AWK are sequences of characters enclosed between double quotes (like
       "value").  Within strings, certain escape sequences are recognized, as in C.  These are:

       \\   A literal backslash.

       \a   The “alert” character; usually the ASCII BEL character.

       \b   Backspace.

       \f   Form-feed.

       \n   Newline.

       \r   Carriage return.

       \t   Horizontal tab.

       \v   Vertical tab.

       \xhex digits
            The character represented by the string of hexadecimal digits following the  \x.   As
            in  ISO  C,  all  following  hexadecimal  digits  are  considered  part of the escape
            sequence.  (This feature should tell us something about language  design  by  commit‐
            tee.)  E.g., "\x1B" is the ASCII ESC (escape) character.

       \ddd The  character represented by the 1-, 2-, or 3-digit sequence of octal digits.  E.g.,
            "\033" is the ASCII ESC (escape) character.

       \c   The literal character c.

       The escape  sequences  may  also  be  used  inside  constant  regular  expressions  (e.g.,
       /[ \t\f\n\r\v]/ matches whitespace characters).

       In  compatibility  mode,  the  characters  represented  by  octal  and  hexadecimal escape
       sequences are treated literally when used in regular expression constants.  Thus,  /a\52b/
       is equivalent to /a\*b/.

       AWK  is  a  line-oriented language.  The pattern comes first, and then the action.  Action
       statements are enclosed in { and }.  Either the pattern may be missing, or the action  may
       be  missing,  but, of course, not both.  If the pattern is missing, the action is executed
       for every single record of input.  A missing action is equivalent to

              { print }

       which prints the entire record.

       Comments begin with the # character, and continue until the end of the line.  Blank  lines
       may  be  used to separate statements.  Normally, a statement ends with a newline, however,
       this is not the case for lines ending in a comma, {, ?, :, &&, or ||.  Lines ending in  do
       or  else  also  have  their  statements automatically continued on the following line.  In
       other cases, a line can be continued by ending it with a “\”, in which case the newline is

       Multiple statements may be put on one line by separating them with a “;”.  This applies to
       both the statements within the action part of a pattern-action pair (the usual case),  and
       to the pattern-action statements themselves.

       AWK patterns may be one of the following:

              /regular expression/
              relational expression
              pattern && pattern
              pattern || pattern
              pattern ? pattern : pattern
              ! pattern
              pattern1, pattern2

       BEGIN  and  END  are two special kinds of patterns which are not tested against the input.
       The action parts of all BEGIN patterns are merged as if all the statements had been  writ‐
       ten  in  a  single  BEGIN rule.  They are executed before any of the input is read.  Simi‐
       larly, all the END rules are merged, and executed when all the input is exhausted (or when
       an exit statement is executed).  BEGIN and END patterns cannot be combined with other pat‐
       terns in pattern expressions.  BEGIN and END patterns cannot have missing action parts.

       BEGINFILE and ENDFILE are additional special patterns whose  bodies  are  executed  before
       reading the first record of each command line input file and after reading the last record
       of each file.  Inside the BEGINFILE rule, the value of ERRNO will be the empty  string  if
       the  file was opened successfully.  Otherwise, there is some problem with the file and the
       code should use nextfile to skip it. If that is not done, gawk produces  its  usual  fatal
       error for files that cannot be opened.

       For  /regular  expression/  patterns,  the associated statement is executed for each input
       record that matches the regular expression.  Regular expressions are the same as those  in
       egrep(1), and are summarized below.

       A  relational  expression  may  use  any  of the operators defined below in the section on
       actions.  These generally test whether certain fields match certain regular expressions.

       The &&, ||, and !  operators are logical AND, logical OR, and logical  NOT,  respectively,
       as  in C.  They do short-circuit evaluation, also as in C, and are used for combining more
       primitive pattern expressions.  As in most languages, parentheses may be  used  to  change
       the order of evaluation.

       The  ?:  operator  is  like the same operator in C.  If the first pattern is true then the
       pattern used for testing is the second pattern, otherwise it is the third.   Only  one  of
       the second and third patterns is evaluated.

       The  pattern1,  pattern2  form of an expression is called a range pattern.  It matches all
       input records starting with a record that matches pattern1, and continuing until a  record
       that  matches  pattern2,  inclusive.   It  does not combine with any other sort of pattern

   Regular Expressions
       Regular expressions are the extended kind found in egrep.  They are composed of characters
       as follows:

       c          Matches the non-metacharacter c.

       \c         Matches the literal character c.

       .          Matches any character including newline.

       ^          Matches the beginning of a string.

       $          Matches the end of a string.

       [abc...]   A  character  list:  matches  any  of the characters abc....  You may include a
                  range of characters by separating them with a dash.

       [^abc...]  A negated character list: matches any character except abc....

       r1|r2      Alternation: matches either r1 or r2.

       r1r2       Concatenation: matches r1, and then r2.

       r+         Matches one or more r's.

       r*         Matches zero or more r's.

       r?         Matches zero or one r's.

       (r)        Grouping: matches r.

       r{n,m}     One or two numbers inside braces denote an interval expression.   If  there  is
                  one  number  in  the  braces,  the preceding regular expression r is repeated n
                  times.  If there are two numbers separated by a comma, r is  repeated  n  to  m
                  times.  If there is one number followed by a comma, then r is repeated at least
                  n times.

       \y         Matches the empty string at either the beginning or the end of a word.

       \B         Matches the empty string within a word.

       \<         Matches the empty string at the beginning of a word.

       \>         Matches the empty string at the end of a word.

       \s         Matches any whitespace character.

       \S         Matches any nonwhitespace character.

       \w         Matches any word-constituent character (letter, digit, or underscore).

       \W         Matches any character that is not word-constituent.

       \`         Matches the empty string at the beginning of a buffer (string).

       \'         Matches the empty string at the end of a buffer.

       The escape sequences that are valid in string constants (see String  Constants)  are  also
       valid in regular expressions.

       Character  classes are a feature introduced in the POSIX standard.  A character class is a
       special notation for describing lists of characters that have a  specific  attribute,  but
       where  the actual characters themselves can vary from country to country and/or from char‐
       acter set to character set.  For example, the notion of what is  an  alphabetic  character
       differs in the USA and in France.

       A character class is only valid in a regular expression inside the brackets of a character
       list.  Character classes consist of [:, a keyword denoting the class, and :].  The charac‐
       ter classes defined by the POSIX standard are:

       [:alnum:]  Alphanumeric characters.

       [:alpha:]  Alphabetic characters.

       [:blank:]  Space or tab characters.

       [:cntrl:]  Control characters.

       [:digit:]  Numeric characters.

       [:graph:]  Characters that are both printable and visible.  (A space is printable, but not
                  visible, while an a is both.)

       [:lower:]  Lowercase alphabetic characters.

       [:print:]  Printable characters (characters that are not control characters.)

       [:punct:]  Punctuation characters (characters that are not letter, digits, control charac‐
                  ters, or space characters).

       [:space:]  Space characters (such as space, tab, and formfeed, to name a few).

       [:upper:]  Uppercase alphabetic characters.

       [:xdigit:] Characters that are hexadecimal digits.

       For  example,  before the POSIX standard, to match alphanumeric characters, you would have
       had to write /[A-Za-z0-9]/.  If your character set had other alphabetic characters in  it,
       this would not match them, and if your character set collated differently from ASCII, this
       might not even match the ASCII alphanumeric characters.  With the POSIX character classes,
       you  can  write  /[[:alnum:]]/,  and this matches the alphabetic and numeric characters in
       your character set, no matter what it is.

       Two additional special sequences can appear in character lists.  These apply to  non-ASCII
       character  sets, which can have single symbols (called collating elements) that are repre‐
       sented with more than one character, as well as several characters that are equivalent for
       collating,  or  sorting, purposes.  (E.g., in French, a plain “e” and a grave-accented “`”
       are equivalent.)

       Collating Symbols
              A collating symbol is a multi-character collating element enclosed in [.   and  .].
              For  example,  if ch is a collating element, then [[.ch.]]  is a regular expression
              that matches this collating element,  while  [ch]  is  a  regular  expression  that
              matches either c or h.

       Equivalence Classes
              An  equivalence  class  is a locale-specific name for a list of characters that are
              equivalent.  The name is enclosed in [= and =].  For example, the name e  might  be
              used  to  represent  all  of “e,” “´,” and “`.”  In this case, [[=e=]] is a regular
              expression that matches any of e, ´, or `.

       These features are very valuable in non-English speaking locales.  The  library  functions
       that  gawk  uses  for regular expression matching currently only recognize POSIX character
       classes; they do not recognize collating symbols or equivalence classes.

       The \y, \B, \<, \>, \s, \S, \w, \W, \`, and \' operators are specific to  gawk;  they  are
       extensions based on facilities in the GNU regular expression libraries.

       The various command line options control how gawk interprets characters in regular expres‐

       No options
              In the default case, gawk provides all the facilities of POSIX regular  expressions
              and the GNU regular expression operators described above.

              Only  POSIX  regular  expressions are supported, the GNU operators are not special.
              (E.g., \w matches a literal w).

              Traditional UNIX awk regular expressions are matched.  The GNU  operators  are  not
              special, and interval expressions are not available.  Characters described by octal
              and hexadecimal escape sequences are treated literally, even if they represent reg‐
              ular expression metacharacters.

              Allow  interval  expressions in regular expressions, even if --traditional has been

       Action statements are enclosed in braces, { and }.  Action statements consist of the usual
       assignment,  conditional,  and looping statements found in most languages.  The operators,
       control statements, and input/output statements available are patterned after those in C.

       The operators in AWK, in order of decreasing precedence, are:

       (...)       Grouping

       $           Field reference.

       ++ --       Increment and decrement, both prefix and postfix.

       ^           Exponentiation (** may also be used, and **= for the assignment operator).

       + - !       Unary plus, unary minus, and logical negation.

       * / %       Multiplication, division, and modulus.

       + -         Addition and subtraction.

       space       String concatenation.

       |   |&      Piped I/O for getline, print, and printf.

       < > <= >= != ==
                   The regular relational operators.

       ~ !~        Regular expression match, negated match.  NOTE: Do not use a constant  regular
                   expression  (/foo/)  on  the left-hand side of a ~ or !~.  Only use one on the
                   right-hand side.  The expression /foo/ ~ exp has the same meaning  as  (($0  ~
                   /foo/) ~ exp).  This is usually not what you want.

       in          Array membership.

       &&          Logical AND.

       ||          Logical OR.

       ?:          The  C  conditional  expression.  This has the form expr1 ? expr2 : expr3.  If
                   expr1 is true, the value of the expression is expr2, otherwise  it  is  expr3.
                   Only one of expr2 and expr3 is evaluated.

       = += -= *= /= %= ^=
                   Assignment.   Both  absolute  assignment (var = value) and operator-assignment
                   (the other forms) are supported.

   Control Statements
       The control statements are as follows:

              if (condition) statement [ else statement ]
              while (condition) statement
              do statement while (condition)
              for (expr1; expr2; expr3) statement
              for (var in array) statement
              delete array[index]
              delete array
              exit [ expression ]
              { statements }
              switch (expression) {
              case value|regex : statement
              [ default: statement ]

   I/O Statements
       The input/output statements are as follows:

       close(file [, how])   Close file, pipe or co-process.  The optional  how  should  only  be
                             used  when  closing  one  end of a two-way pipe to a co-process.  It
                             must be a string value, either "to" or "from".

       getline               Set $0 from next input record; set NF, NR, FNR, RT.

       getline <file         Set $0 from next record of file; set NF, RT.

       getline var           Set var from next input record; set NR, FNR, RT.

       getline var <file     Set var from next record of file, RT.

       command | getline [var]
                             Run command piping the output either into $0 or var, as  above,  and

       command |& getline [var]
                             Run command as a co-process piping the output either into $0 or var,
                             as above, and RT.  Co-processes are a gawk extension.  (command  can
                             also be a socket.  See the subsection Special File Names, below.)

       next                  Stop  processing the current input record.  The next input record is
                             read and processing starts over with the first pattern  in  the  AWK
                             program.  Upon reaching the end of the input data, gawk executes any
                             END rule(s).

       nextfile              Stop processing the current input file.  The next input record  read
                             comes  from  the  next input file.  FILENAME and ARGIND are updated,
                             FNR is reset to 1, and processing starts over with the first pattern
                             in  the  AWK program.  Upon reaching the end of the input data, gawk
                             executes any END rule(s).

       print                 Print the current record.  The output record is terminated with  the
                             value of ORS.

       print expr-list       Print  expressions.   Each  expression  is separated by the value of
                             OFS.  The output record is terminated with the value of ORS.

       print expr-list >file Print expressions on file.  Each  expression  is  separated  by  the
                             value  of  OFS.   The  output record is terminated with the value of

       printf fmt, expr-list Format and print.  See The printf Statement, below.

       printf fmt, expr-list >file
                             Format and print on file.

       system(cmd-line)      Execute the command cmd-line, and return the exit status.  (This may
                             not be available on non-POSIX systems.)

       fflush([file])        Flush any buffers associated with the open output file or pipe file.
                             If file is missing or if it is the null string, then flush all  open
                             output files and pipes.

       Additional output redirections are allowed for print and printf.

       print ... >> file
              Appends output to the file.

       print ... | command
              Writes on a pipe.

       print ... |& command
              Sends data to a co-process or socket.  (See also the subsection Special File Names,

       The getline command returns 1 on success, 0 on end of file, and -1 on an error.   Upon  an
       error, ERRNO is set to a string describing the problem.

       NOTE:  Failure  in opening a two-way socket results in a non-fatal error being returned to
       the calling function. If using a pipe, co-process, or socket to getline, or from print  or
       printf  within  a  loop,  you  must  use close() to create new instances of the command or
       socket.  AWK does not automatically close pipes, sockets, or co-processes when they return

   The printf Statement
       The  AWK  versions  of  the printf statement and sprintf() function (see below) accept the
       following conversion specification formats:

       %c      A single character.  If the argument used for %c is numeric, it is  treated  as  a
               character and printed.  Otherwise, the argument is assumed to be a string, and the
               only first character of that string is printed.

       %d, %i  A decimal number (the integer part).

       %e, %E  A floating point number of the form [-]d.dddddde[+-]dd.   The  %E  format  uses  E
               instead of e.

       %f, %F  A floating point number of the form [-]ddd.dddddd.  If the system library supports
               it, %F is available as well. This is like %f, but uses capital letters for special
               “not a number” and “infinity” values. If %F is not available, gawk uses %f.

       %g, %G  Use  %e  or  %f  conversion,  whichever is shorter, with nonsignificant zeros sup‐
               pressed.  The %G format uses %E instead of %e.

       %o      An unsigned octal number (also an integer).

       %u      An unsigned decimal number (again, an integer).

       %s      A character string.

       %x, %X  An unsigned hexadecimal number (an integer).  The %X format uses ABCDEF instead of

       %%      A single % character; no argument is converted.

       Optional, additional parameters may lie between the % and the control letter:

       count$ Use  the count'th argument at this point in the formatting.  This is called a posi‐
              tional specifier and is intended primarily for use in translated versions of format
              strings, not in the original text of an AWK program.  It is a gawk extension.

       -      The expression should be left-justified within its field.

       space  For  numeric  conversions, prefix positive values with a space, and negative values
              with a minus sign.

       +      The plus sign, used before the width modifier (see below), says to always supply  a
              sign  for numeric conversions, even if the data to be formatted is positive.  The +
              overrides the space modifier.

       #      Use an “alternate form” for certain control letters.   For  %o,  supply  a  leading
              zero.  For %x, and %X, supply a leading 0x or 0X for a nonzero result.  For %e, %E,
              %f and %F, the result always contains a decimal point.  For %g,  and  %G,  trailing
              zeros are not removed from the result.

       0      A  leading  0  (zero)  acts  as a flag, that indicates output should be padded with
              zeroes instead of spaces.  This applies only to the numeric output  formats.   This
              flag only has an effect when the field width is wider than the value to be printed.

       '      A  single quote character instructs gawk to insert the locale's thousands-separator
              character into decimal numbers, and to also use the locale's decimal point  charac‐
              ter  with  floating  point  formats.  This requires correct locale support in the C
              library and in the definition of the current locale.

       width  The field should be padded to this width.  The field is normally padded  with  spa‐
              ces.  With the 0 flag, it is padded with zeroes.

       .prec  A number that specifies the precision to use when printing.  For the %e, %E, %f and
              %F, formats, this specifies the number of digits you want printed to the  right  of
              the  decimal point.  For the %g, and %G formats, it specifies the maximum number of
              significant digits.  For the %d, %i, %o, %u, %x, and %X formats, it  specifies  the
              minimum  number  of  digits  to  print.  For %s, it specifies the maximum number of
              characters from the string that should be printed.

       The dynamic width and prec capabilities of the ISO C printf() routines are supported.  A *
       in  place  of either the width or prec specifications causes their values to be taken from
       the argument list to printf or sprintf().  To use a positional specifier  with  a  dynamic
       width  or  precision,  supply  the  count$ after the * in the format string.  For example,

   Special File Names
       When doing I/O redirection from either print or printf into a file, or via getline from  a
       file,  gawk recognizes certain special filenames internally.  These filenames allow access
       to open file descriptors inherited from gawk's parent process (usually the shell).   These
       file names may also be used on the command line to name data files.  The filenames are:

       -           The standard input.

       /dev/stdin  The standard input.

       /dev/stdout The standard output.

       /dev/stderr The standard error output.

       /dev/fd/n   The file associated with the open file descriptor n.

       These are particularly useful for error messages.  For example:

              print "You blew it!" > "/dev/stderr"

       whereas you would otherwise have to use

              print "You blew it!" | "cat 1>&2"

       The  following  special filenames may be used with the |& co-process operator for creating
       TCP/IP network connections:

              Files for a TCP/IP connection on local port lport to remote host  rhost  on  remote
              port  rport.   Use a port of 0 to have the system pick a port.  Use /inet4 to force
              an IPv4 connection, and /inet6 to force an IPv6 connection.  Plain /inet  uses  the
              system default (most likely IPv4).

              Similar, but use UDP/IP instead of TCP/IP.

   Numeric Functions
       AWK has the following built-in arithmetic functions:

       atan2(y, x)   Return the arctangent of y/x in radians.

       cos(expr)     Return the cosine of expr, which is in radians.

       exp(expr)     The exponential function.

       int(expr)     Truncate to integer.

       log(expr)     The natural logarithm function.

       rand()        Return a random number N, between 0 and 1, such that 0 ≤ N < 1.

       sin(expr)     Return the sine of expr, which is in radians.

       sqrt(expr)    Return the square root of expr.

       srand([expr]) Use  expr  as  the  new seed for the random number generator.  If no expr is
                     provided, use the time of day.  Return the previous seed for the random num‐
                     ber generator.

   String Functions
       Gawk has the following built-in string functions:

       asort(s [, d [, how] ]) Return  the  number  of  elements in the source array s.  Sort the
                               contents of s using gawk's normal rules for comparing values,  and
                               replace  the  indices of the sorted values s with sequential inte‐
                               gers starting with 1. If the optional destination array d is spec‐
                               ified,  first  duplicate  s  into  d, and then sort d, leaving the
                               indices of the source array s unchanged. The optional  string  how
                               controls  the direction and the comparison mode.  Valid values for
                               how are any of the strings valid  for  PROCINFO["sorted_in"].   It
                               can  also  be  the  name  of a user-defined comparison function as
                               described in PROCINFO["sorted_in"].

       asorti(s [, d [, how] ])
                               Return the number of elements in the source array s.  The behavior
                               is  the same as that of asort(), except that the array indices are
                               used for sorting, not the array values.  When done, the  array  is
                               indexed  numerically,  and  the  values  are those of the original
                               indices.  The original values are  lost;  thus  provide  a  second
                               array  if  you  wish to preserve the original.  The purpose of the
                               optional string how is the same as described in asort() above.

       gensub(r, s, h [, t])   Search the target string t for matches of the  regular  expression
                               r.   If  h  is  a  string  beginning with g or G, then replace all
                               matches of r with s.  Otherwise, h is a  number  indicating  which
                               match  of  r  to  replace.   If t is not supplied, use $0 instead.
                               Within the replacement text s, the sequence \n, where n is a digit
                               from  1  to  9, may be used to indicate just the text that matched
                               the n'th parenthesized subexpression.  The sequence \0  represents
                               the  entire  matched  text, as does the character &.  Unlike sub()
                               and gsub(), the modified string is returned as the result  of  the
                               function, and the original target string is not changed.

       gsub(r, s [, t])        For each substring matching the regular expression r in the string
                               t, substitute the string s, and return  the  number  of  substitu‐
                               tions.   If  t  is  not supplied, use $0.  An & in the replacement
                               text is replaced with the text that was actually matched.  Use  \&
                               to  get  a  literal  &.   (This  must be typed as "\\&"; see GAWK:
                               Effective AWK Programming for a fuller discussion of the rules for
                               &'s  and backslashes in the replacement text of sub(), gsub(), and

       index(s, t)             Return the index of the string t in the string s, or 0 if t is not
                               present.   (This implies that character indices start at one.)  It
                               is a fatal error to use a regexp constant for t.

       length([s])             Return the length of the string s, or the length of $0 if s is not
                               supplied.   As  a  non-standard extension, with an array argument,
                               length() returns the number of elements in the array.

       match(s, r [, a])       Return the position in s where the regular expression r occurs, or
                               0  if  r is not present, and set the values of RSTART and RLENGTH.
                               Note that the argument order is the same as for  the  ~  operator:
                               str  ~ re.  If array a is provided, a is cleared and then elements
                               1 through n are filled with the portions of s that match the  cor‐
                               responding  parenthesized subexpression in r.  The 0'th element of
                               a contains the portion of s matched by the entire regular  expres‐
                               sion  r.  Subscripts a[n, "start"], and a[n, "length"] provide the
                               starting index in the string  and  length  respectively,  of  each
                               matching substring.

       patsplit(s, a [, r [, seps] ])
                               Split  the string s into the array a and the separators array seps
                               on the regular expression r, and  return  the  number  of  fields.
                               Element values are the portions of s that matched r.  The value of
                               seps[i] is the separator that appeared in front of a[i+1].   If  r
                               is  omitted,  FPAT  is  used  instead.   The arrays a and seps are
                               cleared first.  Splitting behaves identically to  field  splitting
                               with FPAT, described above.

       split(s, a [, r [, seps] ])
                               Split  the string s into the array a and the separators array seps
                               on the regular expression r, and return the number of fields.   If
                               r  is  omitted,  FS  is  used  instead.  The arrays a and seps are
                               cleared first.  seps[i]  is  the  field  separator  matched  by  r
                               between  a[i]  and  a[i+1].   If r is a single space, then leading
                               whitespace in s goes into the  extra  array  element  seps[0]  and
                               trailing  whitespace  goes  into  the extra array element seps[n],
                               where n is the return value of split(s, a,  r,  seps).   Splitting
                               behaves identically to field splitting, described above.

       sprintf(fmt, expr-list) Print expr-list according to fmt, and return the resulting string.

       strtonum(str)           Examine  str,  and return its numeric value.  If str begins with a
                               leading 0, treat it as an octal number.   If  str  begins  with  a
                               leading  0x  or  0X, treat it as a hexadecimal number.  Otherwise,
                               assume it is a decimal number.

       sub(r, s [, t])         Just like gsub(), but replace only the first matching substring.

       substr(s, i [, n])      Return the at most n-character substring of s starting at i.  If n
                               is omitted, use the rest of s.

       tolower(str)            Return a copy of the string str, with all the uppercase characters
                               in str translated to their corresponding  lowercase  counterparts.
                               Non-alphabetic characters are left unchanged.

       toupper(str)            Return a copy of the string str, with all the lowercase characters
                               in str translated to their corresponding  uppercase  counterparts.
                               Non-alphabetic characters are left unchanged.

       Gawk is multibyte aware.  This means that index(), length(), substr() and match() all work
       in terms of characters, not bytes.

   Time Functions
       Since one of the primary uses of AWK programs is processing log files  that  contain  time
       stamp  information,  gawk  provides  the following functions for obtaining time stamps and
       formatting them.

                 Turn datespec into a time stamp of the same form as returned by  systime(),  and
                 return  the  result.   The datespec is a string of the form YYYY MM DD HH MM SS[
                 DST].  The contents of the string are six or seven numbers representing  respec‐
                 tively  the  full year including century, the month from 1 to 12, the day of the
                 month from 1 to 31, the hour of the day from 0 to 23, the minute from 0  to  59,
                 the  second  from  0 to 60, and an optional daylight saving flag.  The values of
                 these numbers need not be within the ranges specified; for example, an  hour  of
                 -1 means 1 hour before midnight.  The origin-zero Gregorian calendar is assumed,
                 with year 0 preceding year 1 and year -1 preceding year 0.  The time is  assumed
                 to  be in the local timezone.  If the daylight saving flag is positive, the time
                 is assumed to be daylight saving time; if zero, the time is assumed to be  stan‐
                 dard time; and if negative (the default), mktime() attempts to determine whether
                 daylight saving time is in effect for the specified time.  If datespec does  not
                 contain  enough  elements  or  if  the  resulting time is out of range, mktime()
                 returns -1.

       strftime([format [, timestamp[, utc-flag]]])
                 Format timestamp according to the  specification  in  format.   If  utc-flag  is
                 present  and is non-zero or non-null, the result is in UTC, otherwise the result
                 is in local time.  The timestamp should be of the same form as returned by  sys‐
                 time().  If timestamp is missing, the current time of day is used.  If format is
                 missing, a default format equivalent to the output  of  date(1)  is  used.   The
                 default  format is available in PROCINFO["strftime"].  See the specification for
                 the strftime() function in ISO C for the format conversions that are  guaranteed
                 to be available.

       systime() Return  the  current  time  of  day  as  the  number  of seconds since the Epoch
                 (1970-01-01 00:00:00 UTC on POSIX systems).

   Bit Manipulations Functions
       Gawk supplies the following bit manipulation functions.  They work by  converting  double-
       precision  floating point values to uintmax_t integers, doing the operation, and then con‐
       verting the result back to floating point.  The functions are:

       and(v1, v2 [, ...]) Return the bitwise AND of the values provided in  the  argument  list.
                           There must be at least two.

       compl(val)          Return the bitwise complement of val.

       lshift(val, count)  Return the value of val, shifted left by count bits.

       or(v1, v2 [, ...])  Return  the  bitwise  OR  of the values provided in the argument list.
                           There must be at least two.

       rshift(val, count)  Return the value of val, shifted right by count bits.

       xor(v1, v2 [, ...]) Return the bitwise XOR of the values provided in  the  argument  list.
                           There must be at least two.

   Type Function
       The following function is for use with multidimensional arrays.

              Return true if x is an array, false otherwise.

   Internationalization Functions
       The  following  functions may be used from within your AWK program for translating strings
       at run-time.  For full details, see GAWK: Effective AWK Programming.

       bindtextdomain(directory [, domain])
              Specify the directory where gawk looks for the .gmo files, in case they will not or
              cannot  be placed in the ``standard'' locations (e.g., during testing).  It returns
              the directory where domain is ``bound.''
              The default domain is the value of TEXTDOMAIN.  If directory  is  the  null  string
              (""), then bindtextdomain() returns the current binding for the given domain.

       dcgettext(string [, domain [, category]])
              Return  the  translation  of string in text domain domain for locale category cate‐
              gory.  The default value for domain  is  the  current  value  of  TEXTDOMAIN.   The
              default value for category is "LC_MESSAGES".
              If  you  supply a value for category, it must be a string equal to one of the known
              locale categories described in GAWK: Effective AWK Programming.  You must also sup‐
              ply a text domain.  Use TEXTDOMAIN if you want to use the current domain.

       dcngettext(string1, string2, number [, domain [, category]])
              Return the plural form used for number of the translation of string1 and string2 in
              text domain domain for locale category category.  The default value for  domain  is
              the current value of TEXTDOMAIN.  The default value for category is "LC_MESSAGES".
              If  you  supply a value for category, it must be a string equal to one of the known
              locale categories described in GAWK: Effective AWK Programming.  You must also sup‐
              ply a text domain.  Use TEXTDOMAIN if you want to use the current domain.

       Functions in AWK are defined as follows:

              function name(parameter list) { statements }

       Functions  are executed when they are called from within expressions in either patterns or
       actions.  Actual parameters supplied in the function call are used to instantiate the for‐
       mal  parameters declared in the function.  Arrays are passed by reference, other variables
       are passed by value.

       Since functions were not originally part of the AWK  language,  the  provision  for  local
       variables  is  rather clumsy: They are declared as extra parameters in the parameter list.
       The convention is to separate local variables from real parameters by extra spaces in  the
       parameter list.  For example:

              function  f(p, q,     a, b)   # a and b are local

              /abc/     { ... ; f(1, 2) ; ... }

       The  left  parenthesis  in  a function call is required to immediately follow the function
       name, without any intervening whitespace.  This avoids a syntactic ambiguity with the con‐
       catenation  operator.   This  restriction  does not apply to the built-in functions listed

       Functions may call each other and may be recursive.  Function  parameters  used  as  local
       variables are initialized to the null string and the number zero upon function invocation.

       Use  return  expr  to return a value from a function.  The return value is undefined if no
       value is provided, or if the function returns by “falling off” the end.

       As a gawk extension, functions may be called indirectly. To do this, assign  the  name  of
       the  function  to  be  called, as a string, to a variable.  Then use the variable as if it
       were the name of a function, prefixed with an @ sign, like so:
              function  myfunc()
                   print "myfunc called"

              {    ...
                   the_func = "myfunc"
                   @the_func()    # call through the_func to myfunc

       If --lint has been provided, gawk warns about calls to undefined functions at parse  time,
       instead of at run time.  Calling an undefined function at run time is a fatal error.

       The word func may be used in place of function, although this is deprecated.

       You  can  dynamically  add new built-in functions to the running gawk interpreter with the
       @load statement.  The full details are beyond the scope of this  manual  page;  see  GAWK:
       Effective AWK Programming.

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

       String constants are sequences of characters enclosed in double  quotes.   In  non-English
       speaking  environments,  it  is  possible  to mark strings in the AWK program as requiring
       translation to the local natural language. Such strings are marked in the AWK program with
       a leading underscore (“_”).  For example,

              gawk 'BEGIN { print "hello, world" }'

       always prints hello, world.  But,

              gawk 'BEGIN { print _"hello, world" }'

       might print bonjour, monde in France.

       There are several steps involved in producing and running a localizable AWK program.

       1.  Add a BEGIN action to assign a value to the TEXTDOMAIN variable to set the text domain
           to a name associated with your program:

                BEGIN { TEXTDOMAIN = "myprog" }

           This allows gawk to find the .gmo file associated with  your  program.   Without  this
           step,  gawk  uses the messages text domain, which likely does not contain translations
           for your program.

       2.  Mark all strings that should be translated with leading underscores.

       3.  If necessary, use the dcgettext() and/or bindtextdomain() functions in  your  program,
           as appropriate.

       4.  Run  gawk  --gen-pot  -f myprog.awk > myprog.pot to generate a .pot file for your pro‐

       5.  Provide appropriate translations, and build and install the corresponding .gmo files.

       The internationalization features are described in full detail in GAWK: Effective AWK Pro‐

       A primary goal for gawk is compatibility with the POSIX standard, as well as with the lat‐
       est version of Brian Kernighan's awk.  To this end, gawk incorporates the  following  user
       visible  features  which  are  not  described  in  the AWK book, but are part of the Brian
       Kernighan's version of awk, and are in the POSIX standard.

       The book indicates that command line variable assignment happens when awk would  otherwise
       open  the argument as a file, which is after the BEGIN rule is executed.  However, in ear‐
       lier implementations, when such an assignment appeared before any file names, the  assign‐
       ment  would  happen  before  the  BEGIN rule was run.  Applications came to depend on this
       “feature.”  When awk was changed to match its documentation, the -v option  for  assigning
       variables  before  program  execution  was added to accommodate applications that depended
       upon the old behavior.  (This feature was agreed upon by both the  Bell  Laboratories  and
       the GNU developers.)

       When  processing  arguments,  gawk uses the special option “--” to signal the end of argu‐
       ments.  In compatibility mode, it warns about but otherwise ignores undefined options.  In
       normal operation, such arguments are passed on to the AWK program for it to process.

       The  AWK  book  does  not  define  the return value of srand().  The POSIX standard has it
       return the seed it was using, to allow keeping track of random number  sequences.   There‐
       fore srand() in gawk also returns its current seed.

       Other  new features are: The use of multiple -f options (from MKS awk); the ENVIRON array;
       the \a, and \v escape sequences (done originally in gawk and fed back into the Bell  Labo‐
       ratories version); the tolower() and toupper() built-in functions (from the Bell Laborato‐
       ries version); and the ISO C conversion specifications in printf (done first in  the  Bell
       Laboratories version).

       There  is one feature of historical AWK implementations that gawk supports: It is possible
       to call the length() built-in function not only with no argument, but even without  paren‐
       theses!  Thus,

              a = length     # Holy Algol 60, Batman!

       is the same as either of

              a = length()
              a = length($0)

       Using  this feature is poor practice, and gawk issues a warning about its use if --lint is
       specified on the command line.

       Gawk has a too-large number of extensions to POSIX awk.  They are described in  this  sec‐
       tion.   All the extensions described here can be disabled by invoking gawk with the --tra‐
       ditional or --posix options.

       The following features of gawk are not available in POSIX awk.

       · No path search is performed for files named via the -f option.   Therefore  the  AWKPATH
         environment variable is not special.

       · There is no facility for doing file inclusion (gawk's @include mechanism).

       · There  is  no  facility  for dynamically adding new functions written in C (gawk's @load

       · The \x escape sequence.  (Disabled with --posix.)

       · The ability to continue lines after ?  and :.  (Disabled with --posix.)

       · Octal and hexadecimal constants in AWK programs.

       · The ARGIND, BINMODE, ERRNO, LINT, RT and TEXTDOMAIN variables are not special.

       · The IGNORECASE variable and its side-effects are not available.

       · The FIELDWIDTHS variable and fixed-width field splitting.

       · The FPAT variable and field splitting based on field values.

       · The PROCINFO array is not available.

       · The use of RS as a regular expression.

       · The special file names available for I/O redirection are not recognized.

       · The |& operator for creating co-processes.

       · The BEGINFILE and ENDFILE special patterns are not available.

       · The ability to split out individual characters using the null string as the value of FS,
         and as the third argument to split().

       · An optional fourth argument to split() to receive the separator texts.

       · The optional second argument to the close() function.

       · The optional third argument to the match() function.

       · The ability to use positional specifiers with printf and sprintf().

       · The ability to pass an array to length().

       · The and(), asort(), asorti(), bindtextdomain(), compl(), dcgettext(), dcngettext(), gen‐
         sub(), lshift(), mktime(), or(), patsplit(), rshift(), strftime(), strtonum(), systime()
         and xor() functions.

       · Localizable strings.

       The  AWK  book  does  not define the return value of the close() function.  Gawk's close()
       returns the value from fclose(3), or pclose(3), when  closing  an  output  file  or  pipe,
       respectively.   It  returns  the  process's  exit  status when closing an input pipe.  The
       return value is -1 if the named file, pipe or co-process was not opened with  a  redirect‐

       When gawk is invoked with the --traditional option, if the fs argument to the -F option is
       “t”, then FS is set to the tab character.  Note that typing gawk -F\t ...   simply  causes
       the  shell  to  quote  the  “t,” and does not pass “\t” to the -F option.  Since this is a
       rather ugly special case, it is not the default behavior.  This  behavior  also  does  not
       occur  if  --posix has been specified.  To really get a tab character as the field separa‐
       tor, it is best to use single quotes: gawk -F'\t' ....

       The AWKPATH environment variable can be used to provide a list of  directories  that  gawk
       searches  when  looking  for files named via the -f, --file, -i and --include options.  If
       the initial search fails, the path is searched again after appending .awk to the filename.

       The AWKLIBPATH environment variable can be used to provide a list of directories that gawk
       searches when looking for files named via the -l and --load options.

       The  GAWK_READ_TIMEOUT  environment variable can be used to specify a timeout in millisec‐
       onds for reading input from a terminal, pipe or two-way communication including sockets.

       For connection to a remote host via  socket,  GAWK_SOCK_RETRIES  controls  the  number  of
       retries,  and  GAWK_MSEC_SLEEP  and the interval between retries.  The interval is in mil‐
       liseconds. On systems that do not support usleep(3), the value is rounded up to  an  inte‐
       gral number of seconds.

       If  POSIXLY_CORRECT exists in the environment, then gawk behaves exactly as if --posix had
       been specified on the command line.  If --lint has been specified, gawk issues  a  warning
       message to this effect.

       If  the  exit statement is used with a value, then gawk exits with the numeric value given
       to it.

       Otherwise, if there were no problems during execution, gawk exits with the value of the  C
       constant EXIT_SUCCESS.  This is usually zero.

       If  an  error  occurs,  gawk exits with the value of the C constant EXIT_FAILURE.  This is
       usually one.

       If gawk exits because of a fatal error, the exit status is 2.  On non-POSIX systems,  this
       value may be mapped to EXIT_FAILURE.

       This man page documents gawk, version 4.1.

       The  original  version of UNIX awk was designed and implemented by Alfred Aho, Peter Wein‐
       berger, and Brian Kernighan of Bell Laboratories.  Brian Kernighan continues  to  maintain
       and enhance it.

       Paul Rubin and Jay Fenlason, of the Free Software Foundation, wrote gawk, to be compatible
       with the original version of awk distributed in Seventh Edition UNIX.  John Woods contrib‐
       uted  a  number of bug fixes.  David Trueman, with contributions from Arnold Robbins, made
       gawk compatible with the new version of UNIX awk.  Arnold Robbins  is  the  current  main‐

       See  GAWK:  Effective  AWK Programming for a full list of the contributors to gawk and its

       See the README file in the gawk distribution for up-to-date information about  maintainers
       and which ports are currently supported.

       If  you  find  a  bug  in  gawk,  please send electronic mail to bug-gawk AT gnu.org.  Please
       include your operating system and its revision, the version of gawk (from gawk --version),
       which  C compiler you used to compile it, and a test program and data that are as small as
       possible for reproducing the problem.

       Before sending a bug report, please do the following things.  First, verify that you  have
       the  latest  version  of gawk.  Many bugs (usually subtle ones) are fixed at each release,
       and if yours is out of date, the problem may already have been solved.  Second, please see
       if  setting  the  environment  variable  LC_ALL to LC_ALL=C causes things to behave as you
       expect. If so, it's a locale issue, and may or may not really be a bug.   Finally,  please
       read  this man page and the reference manual carefully to be sure that what you think is a
       bug really is, instead of just a quirk in the language.

       Whatever you do, do NOT post a bug report in comp.lang.awk.   While  the  gawk  developers
       occasionally read this newsgroup, posting bug reports there is an unreliable way to report
       bugs.  Instead, please use the electronic mail addresses given above.  Really.

       If you're using a GNU/Linux or BSD-based system, you may wish to submit a  bug  report  to
       the  vendor  of  your  distribution.   That's fine, but please send a copy to the official
       email address as well, since there's no guarantee that the bug report will be forwarded to
       the gawk maintainer.

       The  -F  option  is  not  necessary given the command line variable assignment feature; it
       remains only for backwards compatibility.

       Syntactically invalid single character programs tend to overflow the parse stack, generat‐
       ing  a  rather unhelpful message.  Such programs are surprisingly difficult to diagnose in
       the completely general case, and the effort to do so really is not worth it.

       egrep(1), sed(1), getpid(2), getppid(2),  getpgrp(2),  getuid(2),  geteuid(2),  getgid(2),
       getegid(2), getgroups(2), usleep(3)

       The  AWK  Programming  Language,  Alfred  V. Aho, Brian W. Kernighan, Peter J. Weinberger,
       Addison-Wesley, 1988.  ISBN 0-201-07981-X.

       GAWK: Effective AWK Programming, Edition 4.1, shipped with the gawk source.   The  current
       version of this document is available online at http://www.gnu.org/software/gawk/manual.

       Print and sort the login names of all users:

            BEGIN     { FS = ":" }
                 { print $1 | "sort" }

       Count lines in a file:

                 { nlines++ }
            END  { print nlines }

       Precede each line by its number in the file:

            { print FNR, $0 }

       Concatenate and line number (a variation on a theme):

            { print NR, $0 }

       Run an external command for particular lines of data:

            tail -f access_log |
            awk '/myhome.html/ { system("nmap " $1 ">> logdir/myhome.html") }'

       Brian Kernighan provided valuable assistance during testing and debugging.  We thank him.

       Copyright  © 1989, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2001, 2002, 2003,
       2004, 2005, 2007, 2009, 2010, 2011, 2012, 2013, 2014 Free Software Foundation, Inc.

       Permission is granted to make and distribute verbatim copies of this manual page  provided
       the copyright notice and this permission notice are preserved on all copies.

       Permission  is  granted to copy and distribute modified versions of this manual page under
       the conditions for verbatim copying, provided that the entire resulting  derived  work  is
       distributed under the terms of a permission notice identical to this one.

       Permission is granted to copy and distribute translations of this manual page into another
       language, under the above conditions for modified versions, except  that  this  permission
       notice may be stated in a translation approved by the Foundation.

Free Software Foundation                   Mar 08 2014                                    GAWK(1)

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