Home Man
Today's Posts

Linux & Unix Commands - Search Man Pages
Man Page or Keyword Search:
Select Section of Man Page:
Select Man Page Repository:

Linux 2.6 - man page for nawk (linux 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 1003.1 Standard.   This  version  in  turn  is
       based  on  the  description  in The AWK Programming Language, by Aho, Kernighan, and Wein-
       berger, 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-spe-
       cific 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.  (Cur-
	      rent 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 addi-
	      tional 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 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 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 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 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

       -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 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 dra-
	      conian 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

	      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  are  described  as
       needed and summarized below.

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

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

       If  the	FIELDWIDTHS  variable  is set to a space separated list of numbers, each field is
       expected to have fixed width, and gawk splits up the record using  the  specified  widths.
       The value of FS is ignored.  Assigning a new value to FS 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.	 However,
		   the asort() and asorti() functions are affected.
		   Thus,  if  IGNORECASE  is  not  equal to zero, /aB/ matches all of the strings
		   "ab", "aB", "Ab", and "AB".	As with all AWK variables, the initial	value  of
		   IGNORECASE  is  zero, so all regular expression and string operations are nor-
		   mally case-sensitive.  Under Unix, the full ISO 8859-1 Latin-1  character  set
		   is  used  when  ignoring  case.   As of gawk 3.1.4, the case equivalencies are
		   fully locale-aware, based on the C <ctype.h> facilities such as isalpha(), and

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

       NF	   The number of fields in the current input record.

       NR	   The total number of input records seen so far.

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

       OFS	   The output field separator, a space by default.

       ORS	   The output record separator, by default a newline.

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

		   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  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 to test if an array has an index consisting of a par-
       ticular value.

	      if (val in array)
		   print array[val]

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

       The in construct may also be used in a for loop to iterate over all  the  elements  of  an

       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".

       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 sepa-
       rator of the numbers you are feeding to gawk  must  conform  to	what  your  locale  would
       expect, be it a comma (,) or a period (.).

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

       Note  that  string  constants, such as "57", are not numeric strings, they are string con-
       stants.	The idea of "numeric string" only applies to  fields,  getline	input,	FILENAME,
       ARGV  elements,	ENVIRON elements and the elements of an array created by split() 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 feature introduced in the POSIX standard.  A character class is a
       special notation for describing lists of characters that have a	specific  attribute,  but
       where  the actual characters themselves can vary from country to country and/or from char-
       acter set to character set.  For example, the notion of what is	an  alphabetic	character
       differs in the USA and in France.

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

       [:alnum:]  Alphanumeric characters.

       [:alpha:]  Alphabetic characters.

       [:blank:]  Space or tab characters.

       [:cntrl:]  Control characters.

       [:digit:]  Numeric characters.

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

       [:lower:]  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, no matter what it is.

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

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

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

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

       The \y, \B, \<, \>, \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.

       | |&	   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 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 or socket.  (See also the subsection Special File Names,

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

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

   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  sup-
	       pressed.  The %G format uses %E instead of %e.

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

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

       %s      A character string.

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

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

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

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

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

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

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

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

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

       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, %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,

   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 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 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 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 behav-
			       ior 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	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.  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 ele-
			       ment of a contains the portion of s matched by the entire  regular
			       expression  r.	Subscripts a[n, "start"], and a[n, "length"] pro-
			       vide 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 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.

       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 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[, 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  sys-
		 time().  If timestamp is missing, the current time of day is used.  If format is
		 missing, a default format equivalent to the output of date(1) is used.  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 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 avoids a syntactic ambiguity with the
       concatenation operator.	This restriction does not apply to the built-in functions  listed

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

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

       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 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 --pro-
       file option.  It then continues to run.	SIGHUP causes pgawk to dump the profile and func-
       tion 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

       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 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  or
       --posix options.

       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 ability to pass an array to length().

       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(), asorti(), bindtextdomain(), compl(), dcgettext(), dcngettext(), gen-
	 sub(), lshift(), mktime(), or(), rshift(), strftime(), strtonum(), systime()  and  xor()

       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' ....

       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),

       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, 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.  Andreas Buening now maintains the OS/2 port.  Fred Fish sup-
       plied support for the Amiga, and Martin Brown provided the BeOS port.  Stephen Davies pro-
       vided  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 bug-gawk@gnu.org.  Please
       include your operating system and its revision, the version of gawk (from gawk --version),
       what  C	compiler you used to compile it, and a test program and data that are as small as
       possible for reproducing the problem.

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

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

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

       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,
       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.

Free Software Foundation		   Apr 20 2010					  GAWK(1)

All times are GMT -4. The time now is 03:17 PM.

Unix & Linux Forums Content Copyrightę1993-2018. All Rights Reserved.
Show Password

Not a Forum Member?
Forgot Password?