Provided by: gawk_3.1.8+dfsg-0.1ubuntu1_amd64 bug

NAME

       gawk - pattern scanning and processing language

SYNOPSIS

       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 ...

DESCRIPTION

       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.

OPTION FORMAT

       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.

OPTIONS

       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 them.)

       -O
       --optimize
              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 time.

       -W compat
       -W traditional
       --compat
       --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 information.

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

       -W dump-variables[=file]
       --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
       --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
       --help
       --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]
       --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
       --lint-old
              Provide warnings about constructs that are not portable to the original version  of
              Unix awk.

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

       -W posix
       --posix
              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,
                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]
       --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 function.

       -W re-interval
       --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
       --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 option.

       -W version
       --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.

AWK PROGRAM EXECUTION

       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).

VARIABLES, RECORDS AND FIELDS

       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.

   Records
       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.

   Fields
       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 record.

       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
                   message.

       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 separator.

       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, above.

       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
                   toupper().

       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 available:

                   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 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.

                   PROCINFO["version"] 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 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".

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

   Arrays
       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/.

PATTERNS AND ACTIONS

       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.

   Patterns
       AWK patterns may be one of the following:

              BEGIN
              END
              /regular expression/
              relational expression
              pattern && 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 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
       expression.

   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}
       r{n,}
       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 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  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 characters.)

       [: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 libraries.

       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 supported.

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

       --traditional
              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.

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

   Actions
       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.

   Operators
       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
              break
              continue
              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, 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.  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 variable.

       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 systems.)

       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 problem.

       NOTE: Failure in opening a two-way socket will result 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
       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.

       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
              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 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.

       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 generator.

   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 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.

       mktime(datespec)
                 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 bits.

       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 bits.

       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 "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.

       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.

USER-DEFINED FUNCTIONS

       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.

DYNAMICALLY LOADING NEW FUNCTIONS

       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 aren't willing to redo.

SIGNALS

       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.

EXAMPLES

       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") }'

INTERNATIONALIZATION

       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,

              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 .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 underscores.

       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.

POSIX COMPATIBILITY

       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 developers.)

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

       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).

HISTORICAL FEATURES

       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 line.

       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
       specified.

GNU EXTENSIONS

       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 --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 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 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() function.

       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.

ENVIRONMENT VARIABLES

       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.

       For socket communication, two special environment variables can be  used  to  control  the
       number of retries (GAWK_SOCK_RETRIES), and the interval between retries (GAWK_MSEC_SLEEP).
       The interval is in milliseconds. On systems that do not support usleep(3),  the  value  is
       rounded up to an integral 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.

EXIT STATUS

       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.

SEE ALSO

       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
       http://www.gnu.org/software/gawk/manual.

BUGS

       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.

AUTHORS

       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.

VERSION INFORMATION

       This man page documents gawk, version 3.1.8.

BUG REPORTS

       If  you  find  a  bug  in  gawk,  please send electronic mail to bug-gawk@gnu.org.  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 maintainer.

ACKNOWLEDGEMENTS

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

COPYING PERMISSIONS

       Copyright © 1989, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2001, 2002,  2003,
       2004, 2005, 2007, 2009, 2010 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.