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RedHat 9 (Linux i386) - man page for awk (redhat section 1)

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 1003.2 Command Language  And  Utilities  Stan-
       dard.   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 alphabetically.

       -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 the Bell Laboratories research  version  of  UNIX  awk.	They  are
	      ignored by gawk, since gawk has no pre-defined limits.

       -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 information.

       -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 pro-
	      gram with a lot of functions, and you want to be sure  that  your  functions  don't
	      inadvertently use global variables that you meant to be local.  (This is a particu-
	      larly easy mistake to make with simple variable names like i, j, and so on.)

       -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[=fatal]
	      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.

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

       -W gen-po
	      Scan and parse the AWK program, and generate a GNU .po format file on standard out-
	      put 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 non-decimal-data
	      Recognize  octal	and hexadecimal values in input data.  Use this option with great

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

	      o \x escape sequences are not recognized.

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

	      o You cannot continue lines after ?  and :.

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

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

	      o 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 intermix-
	      ing  of  library	functions  (used  via the -f and --file options) with source code
	      entered on the command line.  It is intended primarily for medium to large AWK pro-
	      grams used in shell scripts.

       -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 is mainly for consistency with the  argu-
	      ment 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
	      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 speci-
       fied via the -v option are performed.  Next, gawk compiles the program  into  an  internal
       form.   Then,  gawk executes the code in the BEGIN 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 assign-
       ment.  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  pro-
       gram.   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
       AWK  variables are dynamic; they come into existence when they are first used.  Their val-
       ues are either floating-point numbers or strings, or both, depending  upon  how	they  are
       used.   AWK  also has one dimensional arrays; arrays with multiple dimensions may be simu-
       lated.  Several pre-defined variables are set as a program runs; these will  be	described
       as needed and summarized below.
       Normally,  records  are	separated by newline characters.  You can control how records are
       separated by assigning values to the built-in variable RS.  If RS is any single character,
       that  character	separates  records.   Otherwise, RS is a regular expression.  Text in the
       input that matches this regular expression separates the record.  However, in  compatibil-
       ity mode, only the first character of its string value is used for separating records.  If
       RS is set to the null string, then records are separated by blank lines.  When RS  is  set
       to the null string, the newline character always acts as a field separator, in addition to
       whatever value FS may have.
       As each input record is read, gawk splits the record into fields, using the value  of  the
       FS  variable as the field separator.  If FS is a single character, fields are separated by
       that character.	If FS is the null string, then each individual character becomes a  sepa-
       rate  field.   Otherwise,  FS is expected to be a full regular expression.  In the special
       case that FS is a single space, fields are separated by runs of spaces and/or tabs  and/or
       newlines.  (But see the discussion of --posix, 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.  How-
       ever, assigning to a non-existent field (e.g., $(NF+2) = 5) increases  the  value  of  NF,
       creates	any  intervening fields with the null string as their 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  mes-
       CONVFMT	   The conversion format for numbers, "%.6g", by default.
       ENVIRON	   An  array  containing  the  values  of  the current environment.  The array is
		   indexed by the environment variables, each element being  the  value  of  that
		   variable  (e.g.,  ENVIRON["HOME"] might be /home/arnold).  Changing this array
		   does not affect the environment seen by programs which gawk spawns  via  redi-
		   rection or the system() function.
       ERRNO	   If a system error occurs either doing a redirection for getline, during a read
		   for getline, or during a close(), then ERRNO will contain a string  describing
		   the error.  The value is subject to translation in non-English locales.
       FIELDWIDTHS A  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 match-
		   ing	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, nor  is  the
		   asort() function.
		   Thus,  if  IGNORECASE  is  not  equal to zero, /aB/ matches all of the strings
		   "ab", "aB", "Ab", and "AB".	As with all AWK variables, the initial	value  of
		   IGNORECASE  is  zero, so all regular expression and string operations are nor-
		   mally case-sensitive.  Under Unix, the full ISO 8859-1 Latin-1  character  set
		   is used when ignoring case.
       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 follow-
		   ing 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  "FIELD-
				      WIDTHS" 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.
       RS	   The input record separator, by default a newline.
       RT	   The	record terminator.  Gawk sets RT to the input text that matched the char-
		   acter or regular expression specified by RS.
       RSTART	   The index of the first character matched by match(); 0  if  no  match.   (This
		   implies that character indices start at one.)
       RLENGTH	   The length of the string matched by match(); -1 if no match.
       SUBSEP	   The	character  used  to  separate  multiple  subscripts in array elements, by
		   default "\034".
       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 in an if or while statement to see 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
       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 str-
       tod(3).	A number is converted to a string by using the	value  of  CONVFMT  as	a  format
       string  for  sprintf(3), with the numeric value of the variable as the argument.  However,
       even though all numbers in AWK are floating-point, integral values are always converted as
       integers.  Thus, given
	      CONVFMT = "%2.2f"
	      a = 12
	      b = a ""
       the variable b has a string value of "12" and not "12.00".
       Gawk  performs  comparisons  as	follows:  If two variables are numeric, they are compared
       numerically.  If one value is numeric and the other has a string value that is a  "numeric
       string," then comparisons are also done numerically.  Otherwise, the numeric value is con-
       verted to a string and a string comparison is performed.  Two  strings  are  compared,  of
       course,	as strings.  Note that the POSIX standard applies the concept of "numeric string"
       everywhere, even to string constants.  However, this is clearly incorrect, and  gawk  does
       not do this.  (Fortunately, this is fixed in the next version of the standard.)
       Note  that  string  constants, such as "57", are not numeric strings, they are string con-
       stants.	The idea of "numeric string" only applies to  fields,  getline	input,	FILENAME,
       ARGV  elements,	ENVIRON elements and the elements of an array created by split() 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 commit-
	    tee.)  E.g., "\x1B" is the ASCII ESC (escape) character.
       \ddd The character represented by the 1-, 2-, or 3-digit sequence of octal digits.   E.g.,
	    "\033" is the ASCII ESC (escape) character.
       \c   The literal character c.
       The  escape  sequences  may  also  be  used  inside  constant  regular  expressions (e.g.,
       /[ \t\f\n\r\v]/ matches whitespace characters).
       In compatibility  mode,	the  characters  represented  by  octal  and  hexadecimal  escape
       sequences  are treated literally when used in regular expression constants.  Thus, /a\52b/
       is equivalent to /a\*b/.
       AWK is a line-oriented language.  The pattern comes first, and then  the  action.   Action
       statements  are enclosed in { and }.  Either the pattern may be missing, or the action may
       be missing, but, of course, not both.  If the pattern is missing, the action  is  executed
       for every single record of input.  A missing action is equivalent to
	      { print }
       which prints the entire record.
       Comments  begin	with  the  "#"	character, and continue until the end of the line.  Blank
       lines may be used to separate statements.  Normally, a statement ends with a newline, how-
       ever, 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 writ-
       ten in a single BEGIN block.  They are executed before any of the input	is  read.   Simi-
       larly,  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
   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 reg-
       ular expressions.

       Character  classes  are a new 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  charac-
       ter differs in the USA and in France.

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

       [:alnum:]  Alphanumeric characters.

       [:alpha:]  Alphabetic characters.

       [:blank:]  Space or tab characters.

       [:cntrl:]  Control characters.

       [:digit:]  Numeric characters.

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

       [:lower:]  Lower-case alphabetic characters.

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

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

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

       [:upper:]  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.

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

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

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

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

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

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

       No options
	      In the default case, gawk 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  charac-
	      ter classes ([[:alnum:]] and so on).  Characters described by octal and hexadecimal
	      escape sequences are treated literally, even if they represent  regular  expression

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

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

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

       (...)	   Grouping

       $	   Field reference.

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

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

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

       * / %	   Multiplication, division, and modulus.

       + -	   Addition and subtraction.

       space	   String concatenation.

       < >
       <= >=
       != ==	   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.

       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

       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.

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

       NOTE: If using a pipe or co-process to getline, or from print or printf within a loop, you
       must use close() to create new instances of the command.  AWK does not automatically close
       pipes 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      A floating point number of the form [-]ddd.dddddd.

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

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

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

       %s      A character string.

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

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

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

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

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

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

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

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

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

       width  The field should be padded to this width.  The field is normally padded  with  spa-
	      ces.  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, 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 sig-
	      nificant digits.	For the %d, %o, %i, %u, %x, and %X formats, it specifies the min-
	      imum number of digits to print.  For %s, it specifies the maximum number of charac-
	      ters 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,

   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 sys-
				    tem 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 dec-
		   imal, 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 get-
		   groups(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 between 0 and 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 pro-
		     vided,  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  con-
			       tents of s are sorted using gawk's normal rules for comparing val-
			       ues, and the indexes 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 indexes of the source array s unchanged.

       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 substitu-
			       tions.  If t is not supplied, use $0.  An  &  in  the  replacement
			       text  is replaced with the text that was actually matched.  Use \&
			       to get a literal &.  (This must	be  typed  as  "\\&";  see  GAWK:
			       Effective AWK Programming for a fuller discussion of the rules for
			       &'s and backslashes in the replacement text of sub(), gsub(),  and

       index(s, t)	       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.

       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 ele-
			       ment  of a contains the portion of s matched by the entire regular
			       expression r.

       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 identi-
			       cally to field splitting, described above.

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

       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

       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 charac-
			       ters in str translated to their corresponding lower-case  counter-
			       parts.  Non-alphabetic characters are left unchanged.

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

   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.

		 Rurns 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 includ-
		 ing 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 mid-
		 night.  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]])
		 Formats timestamp according to  the  specification  in  format.   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 equiva-
		 lent 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  avail-
		 able.	 A  public-domain  version of strftime(3) and a man page for it come with
		 gawk; if that version was used to  build  gawk,  then	all  of  the  conversions
		 described in that man page are available to gawk.

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

       dcngettext(string1 , string2 , number [, domain [, category]])
	      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_MES-
	      If  you  supply a value for category, it must be a string equal to one of the known
	      locale categories described in GAWK: Effective AWK Programming.  You must also sup-
	      ply a text domain.  Use TEXTDOMAIN if you want to use the current domain.

       Functions in AWK are defined as follows:

	      function name(parameter list) { statements }

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

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

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

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

       The  left  parenthesis  in  a function call is required to immediately follow the function
       name, without any intervening white space.  This is to avoid 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 every-
       thing about this feature is likely to change in the next release.  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  --pro-
       file option.  It then continues to run.	SIGHUP causes it 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 }

       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 a corresponding .mo file.

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

       A primary goal for gawk is compatibility with the POSIX standard, as well as with the lat-
       est  version  of UNIX awk.  To this end, gawk incorporates the following user visible fea-
       tures which are not described in the AWK book, but are part of the Bell Laboratories  ver-
       sion 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 ear-
       lier  implementations, when such an assignment appeared before any file names, the assign-
       ment 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  argu-
       ments.  In compatibility mode, it warns about but otherwise ignores undefined options.  In
       normal operation, such arguments are passed on to the AWK program for it to process.

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

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

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

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

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

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

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

       o Octal and hexadecimal constants in AWK programs.

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

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

       o The FIELDWIDTHS variable and fixed-width field splitting.

       o The PROCINFO array is not available.

       o The use of RS as a regular expression.

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

       o The |& operator for creating co-processes.

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

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

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

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

       o The use of delete array to delete the entire contents of an array.

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

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

       o Localizable strings.

       o 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	redirect-

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

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

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

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

       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,

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

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

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

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

       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.  Fred Fish supplied support for the Amiga, Stephen Davies pro-
       vided the Tandem port, and Martin Brown provided the BeOS port.

       This man page documents gawk, version 3.1.0.

       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 two 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  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.

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

       Copyright  (C) 1989, 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2001, 2002 Free
       Software Foundation, Inc.

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

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

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

Free Software Foundation		   Apr 16 2002					  GAWK(1)

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