Man Linux: Main Page and Category List


       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 ...

       pgawk [ POSIX or GNU style options ] -f program-file [ -- ] file ...
       pgawk [ 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  Weinberger,  with
       the additional features found in the System V Release 4 version of UNIX
       awk.  Gawk also provides more recent Bell Laboratories awk  extensions,
       and a number of GNU-specific extensions.

       Pgawk  is  the profiling version of gawk.  It is identical in every way
       to gawk, except that programs run more  slowly,  and  it  automatically
       produces  an  execution profile in the file awkprof.out when done.  See
       the --profile option, below.

       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.


       Gawk options may be either traditional POSIX  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.

       Following  the  POSIX  standard, gawk-specific options are supplied via
       arguments to the -W option.  Multiple -W options may be  supplied  Each
       -W   option  has  a  corresponding  long  option,  as  detailed  below.
       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.


       Gawk accepts the following options, listed by frequency.

       -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 block of an AWK program.

       -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.

       -mf NNN
       -mr NNN
              Set various memory limits to the value NNN.  The f flag sets the
              maximum number of fields, and the r flag sets the maximum record
              size.  These two flags and the -m option  are  from  an  earlier
              version  of  the Bell Laboratories research version of UNIX awk.
              They are ignored by gawk, since gawk has no pre-defined  limits.
              (Current  versions of the Bell Laboratories awk no longer accept

              Enable optimizations upon the  internal  representation  of  the
              program.  Currently, this includes just simple constant-folding.
              The gawk maintainer hopes to add additional  optimizations  over

       -W compat
       -W traditional
              Run  in compatibility mode.  In compatibility mode, gawk behaves
              identically to UNIX awk; none of the GNU-specific extensions are
              recognized.   The  use  of  --traditional  is preferred over the
              other forms of this option.  See GNU EXTENSIONS, below, for more

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

       -W dump-variables[=file]
              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 program 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
              particularly  easy  mistake  to  make with simple variable names
              like i, j, and so on.)

       -W exec 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.

       -W gen-po
              Scan and parse the AWK program, and generate a  GNU  .po  format
              file on standard output with entries for all localizable strings
              in the program.  The program itself is not  executed.   See  the
              GNU gettext distribution for more information on .po files.

       -W help
       -W usage
              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.)

       -W lint[=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.)

       -W lint-old
              Provide  warnings  about constructs that are not portable to the
              original version of Unix awk.

       -W non-decimal-data
              Recognize octal and hexadecimal values in input data.  Use  this
              option with great caution!

       -W posix
              This  turns on compatibility mode, with the following additional

              · \x escape sequences are not recognized.

              · Only space and tab act as field separators when FS is set to a
                single space, newline 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 ^=.

              · The fflush() function is not available.

       -W profile[=prof_file]
              Send profiling data to prof_file.  The default  is  awkprof.out.
              When  run  with  gawk,  the  profile  is just a “pretty printed”
              version of the  program.   When  run  with  pgawk,  the  profile
              contains  execution  counts  of each statement in the program in
              the left margin and function call counts for  each  user-defined

       -W re-interval
              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.   However, their use is likely to break old AWK programs,
              so gawk only provides them  if  they  are  requested  with  this
              option, or when --posix is specified.

       -W source program-text
       --source program-text
              Use program-text as AWK program source code.  This option allows
              the easy intermixing 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  programs  used
              in shell scripts.

       -W use-lc-numeric
              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 draconian strictness of the --posix

       -W version
              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.


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

              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.

       The  environment  variable  AWKPATH specifies a search path to use when
       finding source files named with the -f option.  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.

       Gawk executes AWK programs in the following order.  First, all variable
       assignments  specified  via  the  -v  option are performed.  Next, gawk
       compiles the program into an internal form.  Then,  gawk  executes  the
       code  in  the  BEGIN  block(s) (if any), and then proceeds to read each
       file named in the ARGV array.  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 assignment.  The variable var will  be  assigned  the  value
       val.   (This  happens after any BEGIN block(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 record in the input, gawk tests  to  see  if  it  matches  any
       pattern  in the AWK program.  For each pattern that the record matches,
       the associated action is executed.  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 block(s) (if any).


       AWK variables are dynamic; they come into existence when they are first
       used.   Their  values  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 simulated.  Several pre-
       defined variables 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
       compatibility 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  separate 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 IGNORECASE (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  overrides  the  use  of  FIELDWIDTHS,  and
       restores the default behavior.

       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

       References to non-existent fields (i.e. fields after $NF)  produce  the
       null-string.  However, 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  value,  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

       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 redirection 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 white-space separated list  of  fieldwidths.   When  set,
                   gawk  parses  the input into fields of fixed width, instead
                   of using  the  value  of  the  FS  variable  as  the  field

       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 block
                   (unless set by getline).

       FNR         The input record number in the current input file.

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

       IGNORECASE  Controls the case-sensitivity of all regular expression and
                   string operations.  If IGNORECASE  has  a  non-zero  value,
                   then  string  comparisons  and  pattern  matching in rules,
                   field splitting with FS, record separating with RS, regular
                   expression  matching  with  ~  and  !~,  and  the gensub(),
                   gsub(),  index(),  match(),  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 normally case-
                   sensitive.    Under  Unix,  the  full  ISO  8859-1  Latin-1
                   character set is used  when  ignoring  case.   As  of  gawk
                   3.1.4, the case equivalencies are fully locale-aware, based
                   on the  C  <ctype.h>  facilities  such  as  isalpha(),  and

       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.

       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 following  elements  are  guaranteed  to  be

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

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

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

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

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

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

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

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

                                      The version of gawk.  This is  available
                                      from version 3.1.4 and later.

       RS          The input record separator, by default a newline.

       RT          The record terminator.  Gawk sets RT to the input text that
                   matched the character or regular  expression  specified  by

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

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

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

       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 particular 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.

       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.

   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.

       When  a  string  must  be  converted  to  a  number,  the conversion is
       accomplished using strtod(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".

       When operating in POSIX mode (such as with  the  --posix  command  line
       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 converted 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 constants.  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() that are  numeric  strings.
       The  basic  idea  is  that  user input, and only user input, that looks
       numeric, should be treated that way.

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

   Octal and Hexadecimal Constants
       Starting  with  version  3.1  of  gawk  , 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  (").   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 ANSI C, all following hexadecimal digits
            are considered part of the escape sequence.  (This feature  should
            tell  us  something  about  language  design by committee.)  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 “,”, {, ?, :, &&, 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 will be ignored.

       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 written in a single BEGIN block.
       They are executed before any of the input is read.  Similarly, all  the
       END blocks 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  patterns  in pattern expressions.  BEGIN and END
       patterns cannot have missing action parts.

       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

       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

       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...]   character list, matches any of the characters abc....

       [^abc...]  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.
                  Interval expressions are only available if either --posix or
                  --re-interval is specified on the command line.

       \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.

       \w         matches  any  word-constituent  character (letter, digit, or

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

       \‘         matches the empty  string  at  the  beginning  of  a  buffer

       \’         matches the empty string at the end of a buffer.

       The escape sequences that are valid in string constants (see below) 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
       character 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 character 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:]  Lower-case alphabetic characters.

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

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

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

       [:upper:]  Upper-case 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 represented 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 e`.

       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, \<, \>, \w, \W, \‘, and \’ operators are specific to gawk;
       they are extensions based on facilities in the GNU  regular  expression

       The various command line options control how gawk interprets characters
       in regular expressions.

       No options
              In the default case, gawk provide all the  facilities  of  POSIX
              regular  expressions  and  the  GNU regular expression operators
              described  above.   However,  interval   expressions   are   not

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

              Traditional  Unix  awk regular expressions are matched.  The GNU
              operators  are  not  special,  interval  expressions   are   not
              available,   and   neither   are  the  POSIX  character  classes
              ([[:alnum:]] and so on).   Characters  described  by  octal  and
              hexadecimal escape sequences are treated literally, even if they
              represent regular expression metacharacters.

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

       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 was intended.

       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 }

   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.

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

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

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

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

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

       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.
                             If the end of the input data is reached, the  END
                             block(s), if any, are executed.

       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. If the end of the
                             input data is reached, the END block(s), if  any,
                             are executed.

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

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

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

       printf fmt, expr-list Format and print.

       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

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

       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, below.)

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

       NOTE:  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 EOF.

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

       %c      An ASCII 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 suppressed.  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 abcdef.

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

       NOTE: When using the integer format-control letters for values that are
       outside the range of a C long integer, gawk switches to the %0f  format
       specifier.  If  --lint is provided on the command line gawk warns about
       this.  Other versions of awk may print invalid values or  do  something
       else entirely.

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

       count$ Use the count’th argument at this point in the formatting.  This
              is  called  a positional 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

       #      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  even  to
              non-numeric  output  formats.  This flag only has an effect when
              the field width is wider than the value to be printed.

       width  The field should be padded to this width.  The field is normally
              padded  with  spaces.  If the 0 flag has been used, 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, %o, %i, %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 ANSI 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, "%3$*2$.*1$s".

   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:

       /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.

       /inet/tcp/lport/rhost/rport  File for 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.

       /inet/udp/lport/rhost/rport  Similar, but use UDP/IP instead of TCP/IP.

       /inet/raw/lport/rhost/rport  Reserved for future use.

       Other special filenames provide access to information about the running
       gawk  process.   These  filenames  are  now obsolete.  Use the PROCINFO
       array to obtain the information they provide.  The filenames are:

       /dev/pid    Reading this file returns the process  ID  of  the  current
                   process, in decimal, terminated with a newline.

       /dev/ppid   Reading  this  file  returns  the  parent process ID of the
                   current process, in decimal, terminated with a newline.

       /dev/pgrpid Reading this file returns  the  process  group  ID  of  the
                   current process, in decimal, terminated with a newline.

       /dev/user   Reading this file returns a single record terminated with a
                   newline.  The fields are separated with spaces.  $1 is  the
                   value  of the getuid(2) system call, $2 is the value of the
                   geteuid(2) system call, $3 is the value  of  the  getgid(2)
                   system  call,  and $4 is the value of the getegid(2) system
                   call.  If there are any additional  fields,  they  are  the
                   group  IDs  returned  by getgroups(2).  Multiple groups may
                   not be supported on all systems.

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

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

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

       exp(expr)     The exponential function.

       int(expr)     Truncates to integer.

       log(expr)     The natural logarithm function.

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

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

       sqrt(expr)    The square root function.

       srand([expr]) Uses  expr as a new seed for the random number generator.
                     If no expr is provided, the time of  day  is  used.   The
                     return  value  is the previous seed for the random number

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

       asort(s [, d])          Returns the number of elements  in  the  source
                               array  s.   The  contents of s are sorted using
                               gawk’s normal rules for comparing  values,  and
                               the  indices  of  the  sorted  values  of s are
                               replaced with sequential integers starting with
                               1.  If  the  optional  destination  array  d is
                               specified, then s is first duplicated  into  d,
                               and  then  d  is sorted, leaving the indices of
                               the source array s unchanged.

       asorti(s [, d])         Returns 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.

       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, $0 is  used  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
                               substitutions.  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 gensub().)

       index(s, t)             Returns 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.)

       length([s])             Returns  the  length  of  the  string s, or the
                               length of $0 if s is  not  supplied.   Starting
                               with   version   3.1.5,   as   a   non-standard
                               extension, with  an  array  argument,  length()
                               returns the number of elements in the array.

       match(s, r [, a])       Returns  the  position  in  s where the regular
                               expression r occurs, or 0 if r is not  present,
                               and  sets  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  corresponding   parenthesized
                               subexpression  in  r.   The  0’th  element of a
                               contains the portion of s matched by the entire
                               regular    expression   r.    Subscripts   a[n,
                               "start"],  and  a[n,  "length"]   provide   the
                               starting   index   in  the  string  and  length
                               respectively, of each matching substring.

       split(s, a [, r])       Splits the string s into the  array  a  on  the
                               regular expression r, and returns the number of
                               fields.  If r is omitted, FS is  used  instead.
                               The   array  a  is  cleared  first.   Splitting
                               behaves   identically   to   field   splitting,
                               described above.

       sprintf(fmt, expr-list) Prints  expr-list according to fmt, and returns
                               the resulting string.

       strtonum(str)           Examines str, and returns  its  numeric  value.
                               If  str  begins  with  a  leading 0, strtonum()
                               assumes that str is an octal  number.   If  str
                               begins  with  a  leading  0x  or 0X, strtonum()
                               assumes that str is a hexadecimal number.

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

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

       tolower(str)            Returns  a copy of the string str, with all the
                               upper-case  characters  in  str  translated  to
                               their  corresponding  lower-case  counterparts.
                               Non-alphabetic characters are left unchanged.

       toupper(str)            Returns a copy of the string str, with all  the
                               lower-case  characters  in  str  translated  to
                               their  corresponding  upper-case  counterparts.
                               Non-alphabetic characters are left unchanged.

       As of version 3.1.5, gawk is multibyte aware.  This means that index(),
       length(), substr() and match() all work in  terms  of  characters,  not

   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.

                 Turns datespec into a time stamp of the same form as returned
                 by systime().  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  respectively  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,  and 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 standard 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]]])
                 Formats  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
                 systime().   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.  See the specification for
                 the strftime() function in ANSI C for the format  conversions
                 that are guaranteed to be available.

       systime() Returns  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
       Starting with version 3.1  of  gawk,  the  following  bit  manipulation
       functions  are  available.   They  work  by converting double-precision
       floating point values to uintmax_t integers, doing the  operation,  and
       then converting the result back to floating point.  The functions are:

       and(v1, v2)         Return the bitwise AND of the values provided by v1
                           and v2.

       compl(val)          Return the bitwise complement of val.

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

       or(v1, v2)          Return  the bitwise OR of the values provided by v1
                           and v2.

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

       xor(v1, v2)         Return the bitwise XOR of the values provided by v1
                           and v2.

   Internationalization Functions
       Starting with version 3.1 of gawk, 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])
              Specifies the directory where gawk looks for the .mo  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]])
              Returns  the  translation  of  string  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
              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  supply  a  text  domain.   Use
              TEXTDOMAIN if you want to use the current domain.

       dcngettext(string1 , string2 , number [, domain [, category]])
              Returns  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  supply  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 formal 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  white  space.   This
       avoids  a  syntactic  ambiguity  with the concatenation operator.  This
       restriction does not apply to the built-in functions listed above.

       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.

       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.


       Beginning with version 3.1 of gawk, you can dynamically add new  built-
       in  functions  to  the  running gawk interpreter.  The full details are
       beyond  the  scope  of  this  manual  page;  see  GAWK:  Effective  AWK
       Programming for the details.

       extension(object, function)
               Dynamically  link  the  shared object file named by object, and
               invoke function in  that  object,  to  perform  initialization.
               These  should  both  be provided as strings.  Returns the value
               returned by function.

       This function  is  provided  and  documented  in  GAWK:  Effective  AWK
       Programming,  but  everything  about  this  feature is likely to change
       eventually.  We STRONGLY recommend that you do not use this feature for
       anything that you arent willing to redo.


       pgawk  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 pgawk to dump the profile and function
       call stack and then exit.


       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") }


       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  native  natural
       language. Such strings are marked in the AWK  program  with  a  leading
       underscore (“_”).  For example,

              gawkBEGIN { print "hello, world" }’

       always prints hello, world.  But,

              gawkBEGIN { 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 .mo 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

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

       4.  Run  gawk --gen-po -f myprog.awk > myprog.po to generate a .po file
           for your program.

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

       The internationalization features are described in full detail in GAWK:
       Effective AWK Programming.


       A primary goal for gawk is compatibility with the  POSIX  standard,  as
       well  as  with  the  latest  version  of  UNIX  awk.  To this end, gawk
       incorporates  the  following  user  visible  features  which  are   not
       described  in  the  AWK  book,  but  are  part of the Bell Laboratories
       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 block is executed.  However,  in  earlier  implementations,  when
       such an assignment appeared before any file names, the assignment would
       happen before the BEGIN block 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

       The  -W  option  for implementation specific features is from the POSIX

       When processing arguments, gawk uses the special option “--” to  signal
       the  end  of  arguments.   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.   Therefore 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 Laboratories  version);  the  tolower()
       and  toupper() built-in functions (from the Bell Laboratories version);
       and the ANSI C conversion specifications in printf (done first  in  the
       Bell Laboratories version).


       There  are  two  features  of  historical AWK implementations that gawk
       supports.  First, it is possible to call the length() built-in function
       not only with no argument, but even without parentheses!  Thus,

              a = length     # Holy Algol 60, Batman!

       is the same as either of

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

       This  feature is marked as “deprecated” in the POSIX standard, and gawk
       issues a warning about its use if --lint is specified  on  the  command

       The  other  feature  is  the  use  of  either the continue or the break
       statements outside the body of a while, for, or do  loop.   Traditional
       AWK  implementations  have treated such usage as equivalent to the next
       statement.   Gawk  supports  this  usage  if  --traditional  has   been


       Gawk  has  a  number of extensions to POSIX awk.  They are described in
       this section.  All the extensions described here  can  be  disabled  by
       invoking gawk with the --traditional 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.

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

       · The fflush() function.  (Disabled with --posix.)

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

       · Octal and hexadecimal constants in AWK programs.

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

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

       · The FIELDWIDTHS variable and fixed-width field splitting.

       · 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

       · The |& operator for creating co-processes.

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

       · 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 use of delete array to delete the entire contents of an array.

       · The use of nextfile to abandon processing of the current input  file.

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

       · Localizable strings.

       · Adding  new  built-in  functions  dynamically  with  the  extension()

       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 redirection.

       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 separator, it is best to use single  quotes:  gawk  -F\t....

       If  gawk is configured with the --enable-switch option to the configure
       command, then it accepts an additional control-flow statement:
              switch (expression) {
              case value|regex : statement
              [ default: statement ]

       If gawk is configured with the --disable-directories-fatal option, then
       it   will   silently  skip  directories  named  on  the  command  line.
       Otherwise, it will do so only if invoked with the --traditional option.


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

       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.


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

       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 3.0, published by the Free
       Software Foundation, 2001.  The current version  of  this  document  is
       available online at


       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, generating 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.


       The original version of UNIX awk was designed and implemented by Alfred
       Aho, Peter Weinberger, 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 contributed 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 maintainer.

       The initial DOS port was done  by  Conrad  Kwok  and  Scott  Garfinkle.
       Scott Deifik is the current DOS maintainer.  Pat Rankin did the port to
       VMS, and Michal Jaegermann did the port to the Atari ST.  The  port  to
       OS/2  was  done  by  Kai  Uwe  Rommel, with contributions and help from
       Darrel Hankerson.  Andreas Buening now maintains the OS/2  port.   Fred
       Fish supplied support for the Amiga, and Martin Brown provided the BeOS
       port.  Stephen Davies provided the original Tandem  port,  and  Matthew
       Woehlke  provided  changes  for Tandem’s POSIX-compliant systems.  Ralf
       Wildenhues now maintains that port.

       See the README file in the gawk distribution  for  current  information
       about maintainers and which ports are currently supported.


       This man page documents gawk, version 3.1.7.


       If  you  find  a  bug  in  gawk,  please  send  electronic mail to bug-  Please include your operating system and  its  revision,
       the  version of gawk (from gawk --version), what 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.

       If you’re using a GNU/Linux system 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  will  be  forwarded to the gawk


       Brian Kernighan  of  Bell  Laboratories  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 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.