GAWK(1)                                                        Utility Commands                                                        GAWK(1)


       gawk - pattern scanning and processing language


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

       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 them.)

              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
              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 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]
              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
              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 option.

       -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 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 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

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

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

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

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

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

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

       c          matches the non-metacharacter c.

       \c         matches the literal character c.

       .          matches any character including newline.

       ^          matches the beginning of a string.

       $          matches the end of a string.

       [abc...]   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 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.

              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, 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

       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

       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.

                 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

       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.


       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 aren't 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,

              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.


       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).


       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


       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.


       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.


       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.


       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 3.1.8.


       If you find a bug in gawk, please send electronic mail to  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.


       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, 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.

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