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AWK(1)			       Utility Commands				AWK(1)

       awk - pattern scanning and processing language

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

       Gawk  is	 the  GNU Project's implementation of the AWK programming lan‐
       guage.  In the 4.4BSD distribution, it is installed as  awk.   It  con‐
       forms  to  the  definition  of the language in the POSIX 1003.2 Command
       Language And Utilities Standard.	 This version in turn is based on  the
       description  in	The  AWK  Programming Language, by Aho, Kernighan, and
       Weinberger, with the  additional	 features  defined  in	the  System  V
       Release	4  version  of UNIX awk.  Gawk also provides some GNU-specific

       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 the traditional POSIX one letter options, or
       the  GNU	 style	long options.  POSIX style options start with a single
       ``-'', while GNU long  options  start  with  ``--''.   GNU  style  long
       options	are provided for both GNU-specific features and for POSIX man‐
       dated features.	Other implementations of the AWK language  are	likely
       to only accept the traditional one letter options.

       Following  the  POSIX  standard, gawk-specific options are supplied via
       arguments to the -W option.  Multiple -W options may  be	 supplied,  or
       multiple	 arguments  may	 be supplied together if they are separated by
       commas, or enclosed in quotes and separated by white  space.   Case  is
       ignored	in  arguments  to  the -W option.  Each -W option has a corre‐
       sponding GNU style long option, as detailed below.

       Gawk accepts the following options.

       -F fs
	      Use fs for the input field separator (the value of the FS prede‐
	      fined variable).

       -v 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
	      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.

       -W compat
       --compat	   Run	in  compatibility  mode.   In compatibility mode, gawk
		   behaves identically to UNIX awk; none of  the  GNU-specific
		   extensions  are recognized.	See GNU EXTENSIONS, below, for
		   more information.

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

       -W help
       -W usage
       --usage	   Print  a  relatively short summary of the available options
		   on the standard error output.

       -W lint
       --lint	   Provide warnings about constructs that are dubious or  non-
		   portable to other AWK implementations.
       -W posix
       --posix	   This	 turns on compatibility mode, with the following addi‐
		   tional restrictions:

		   · \x escape sequences are not recognized.

		   · The synonym func for the keyword function is  not	recog‐

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

       -W source=program-text
		   Use program-text as AWK program source code.	  This	option
		   allows  the easy intermixing of library functions (used via
		   the -f and --file options) with source code entered on  the
		   command line.  It is intended primarily for medium to large
		   size AWK programs used in shell scripts.
		   The -W source= form of this option uses  the	 rest  of  the
		   command line argument for program-text; no other options to
		   -W will be recognized in the same argument.

       -W version
       --version   Print version information for this particular copy of  gawk
		   on  the  standard  error 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.

       --	   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  argument  parsing
		   convention used by most other POSIX programs.

       Any other options are flagged as illegal, but are otherwise ignored.

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

	      pattern	{ action statements }
	      function name(parameter list) { statements }

       Gawk first reads the program source from the program-file(s) if	speci‐
       fied,  or  from the first non-option argument on the command line.  The
       -f option may be used multiple times on the command  line.   Gawk  will
       read the program text as if all the program-files 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.
       To use a library function in a file from a program typed in on the com‐
       mand line, specify /dev/tty as one of the program-files, type your pro‐
       gram, and end it with a ^D (control-d).

       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/lib/awk:/usr/local/lib/awk".  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,  gawk  com‐
       piles  the  program  into an internal form.  Next, all variable assign‐
       ments specified via the -v option are performed.	 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  com‐
       mand line, gawk reads the standard input.

       If a filename on the command line has the form var=val it is treated as
       a variable assignment. The variable var will be assigned the value val.
       (This  happens  after  any BEGIN block(s) have been run.)  Command line
       variable assignment is most useful for dynamically assigning values  to
       the  variables  AWK uses to control how input is broken into fields and
       records. It is also useful for controlling state if multiple passes are
       needed over a single data file.

       If  the value of a particular element of ARGV is empty (""), gawk skips
       over it.

       For each line in the input, gawk tests to see if it matches any pattern
       in  the AWK program.  For each pattern that the line matches, the asso‐
       ciated action is executed.  The patterns are tested in the  order  they
       occur in the program.

       Finally,	 after	all  the input is exhausted, gawk executes the code in
       the END block(s) (if any).

       AWK variables are dynamic; they come into existence when they are first
       used.  Their  values  are  either floating-point numbers or strings, or
       both, depending upon how they are used. AWK also	 has  one  dimensional
       arrays;	multiply  dimensioned  arrays  may be simulated.  Several pre-
       defined variables are set as a program runs; these will be described as
       needed and summarized below.

       As each input line is read, gawk splits the line 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.  Otherwise, FS is
       expected to be a full regular expression.  In the special case that  FS
       is  a single blank, fields are separated by runs of blanks and/or tabs.
       Note that the value of IGNORECASE (see  below)  will  also  affect  how
       fields are split when FS is a regular expression.

       If  the	FIELDWIDTHS  variable is set to a space separated list of num‐
       bers, each field is expected to have fixed width, and gawk  will	 split
       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 line may be referenced by its position, $1, $2,
       and so on.  $0 is the whole line. The value of a field may be  assigned
       to as well.  Fields need not be referenced by constants:

	      n = 5
	      print $n

       prints  the  fifth  field in the input line.  The variable NF is set to
       the total number of fields in the input line.

       References to non-existent fields (i.e., fields after $NF) produce  the
       null-string.  However, assigning to a non-existent field (e.g., $(NF+2)
       = 5) will increase the value of NF, create any intervening fields  with
       the  null string as their value, and cause the value of $0 to be recom‐
       puted, with the fields being separated by the value of OFS.

   Built-in Variables
       AWK'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.

       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., ENVI‐
		   RON["HOME"] might be /u/arnold).  Changing this array  does
		   not	affect	the  environment  seen	by programs which gawk
		   spawns via redirection or the system() function.  (This may
		   change in a future version of gawk.)

       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.

       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 separa‐
		   tor.	 The fixed field width facility is still experimental;
		   expect the semantics to change as gawk evolves over time.

       FILENAME	   The name of the current input file.	If no files are speci‐
		   fied on the command line, the value of FILENAME is ``-''.

       FNR	   The input record number in the current input file.

       FS	   The input field separator, a blank by default.

       IGNORECASE  Controls the case-sensitivity  of  all  regular  expression
		   operations.	If  IGNORECASE has a non-zero value, then pat‐
		   tern matching in rules, field splitting  with  FS,  regular
		   expression matching with ~ and !~, and the gsub(), index(),
		   match(), split(), and sub() pre-defined functions will  all
		   ignore  case	 when  doing  regular  expression  operations.
		   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 operations are normally case-sensitive.

       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 blank by default.

       ORS	   The output record separator, a newline by default.

       RS	   The	input  record  separator, a newline by default.	 RS is
		   exceptional in that only the first character of its	string
		   value  is used for separating records.  (This will probably
		   change in a future release of gawk.)	 If RS is set  to  the
		   null	 string,  then	records	 are separated by blank lines.
		   When RS is set to the null string, then the newline charac‐
		   ter	always acts as a field separator, in addition to what‐
		   ever value FS may have.

       RSTART	   The index of the first character matched by match();	 0  if
		   no match.

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

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

       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 associa‐
       tive, 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 array.

       An element may be deleted from an array using the delete statement.

   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 con‐
       text. 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	accom‐
       plished	using atof(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 num‐
       bers 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 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 converted to  a
       string and a string comparison is performed.  Two strings are compared,
       of course, as strings.  According to the POSIX standard,	 even  if  two
       strings	are  numeric strings, a numeric comparison is performed.  How‐
       ever, this is clearly incorrect, and gawk does not do this.

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

       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 will be executed for every single
       line of input.  A missing action is equivalent to

	      { print }

       which prints the entire line.

       Comments	 begin with the ``#'' character, and continue until the end of
       the line.  Blank lines may be used to separate statements.  Normally, a
       statement  ends with a newline, however, this is not the case for lines
       ending in a ``,'', ``{'', ``?'', ``:'', ``&&'', or ``||''.  Lines  end‐
       ing 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 state‐
       ments themselves.

       AWK patterns may be one of the following:

	      /regular expression/
	      relational expression
	      pattern && pattern
	      pattern || pattern
	      pattern ? pattern : pattern
	      ! pattern
	      pattern1, pattern2

       BEGIN and END are two special kinds of patterns which  are  not	tested
       against	the  input.  The action parts of all BEGIN patterns are merged
       as if all the statements had been written in a single BEGIN block. They
       are  executed  before  any of the input is read. Similarly, all the END
       blocks are merged, and executed when all the  input  is	exhausted  (or
       when  an exit statement is executed).  BEGIN and END patterns cannot be
       combined with other patterns in pattern	expressions.   BEGIN  and  END
       patterns cannot have missing action parts.

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

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

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

       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	evalu‐

       The pattern1, pattern2 form of an expression is called a range pattern.
       It matches all input records starting with a  line  that	 matches  pat‐
       tern1,  and continuing until a record that matches pattern2, inclusive.
       It does not combine with any other sort of pattern expression.

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

       c	  matches the non-metacharacter c.

       \c	  matches the literal character c.

       .	  matches any character except newline.

       ^	  matches the beginning of a line or a string.

       $	  matches the end of a line or a string.

       [abc...]	  character class, matches any of the characters abc....

       [^abc...]  negated character class, matches any character except abc...
		  and newline.

       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.

       The escape sequences that are valid in string constants (see below) are
       also legal in regular expressions.

       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 increasing precedence, are

       = += -=
       *= /= %= ^= Assignment. Both absolute  assignment  (var	=  value)  and
		   operator-assignment (the other forms) are supported.

       ?:	   The	C  conditional	expression.  This has the form expr1 ?
		   expr2 : expr3. If expr1 is true, the value of  the  expres‐
		   sion	 is  expr2,  otherwise it is expr3.  Only one of expr2
		   and expr3 is evaluated.

       ||	   Logical OR.

       &&	   Logical AND.

       ~ !~	   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.

       < >
       <= >=
       != ==	   The regular relational operators.

       blank	   String concatenation.

       + -	   Addition and subtraction.

       * / %	   Multiplication, division, and modulus.

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

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

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

       $	   Field reference.

   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]
	      exit [ expression ]
	      { statements }

   I/O Statements
       The input/output statements are as follows:

       close(filename)	     Close file (or pipe, see below).

       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 NF, FNR.

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

       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.

       next file	     Stop processing the current input file.  The next
			     input record read comes from the next input file.
			     FILENAME  is updated, FNR is reset to 1, and pro‐
			     cessing 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.

       print expr-list	     Prints expressions.

       print expr-list >file Prints expressions on file.

       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

       Other input/output redirections are also allowed. For print and printf,
       >>file  appends	output	to the file, while | command writes on a pipe.
       In a similar fashion, command | getline pipes  into  getline.   Getline
       will return 0 on end of file, and -1 on an error.

   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     A decimal number (the integer part).

       %i     Just like %d.

       %e     A floating point number of the form [-]d.ddddddE[+-]dd.

       %f     A floating point number of the form [-]ddd.dddddd.

       %g     Use e or f conversion, whichever is shorter, with nonsignificant
	      zeros suppressed.

       %o     An unsigned octal number (again, an integer).

       %s     A character string.

       %x     An unsigned hexadecimal number (an integer).

       %X     Like %x, but using ABCDEF instead of abcdef.

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

       There are optional, additional parameters that may lie  between	the  %
       and the control letter:

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

       width  The  field  should  be padded to this width. If the number has a
	      leading zero, then the field will be padded with zeros.	Other‐
	      wise it is padded with blanks.

       .prec  A	 number	 indicating  the maximum width of strings or digits to
	      the right of the decimal point.

       The dynamic width and prec capabilities of the ANSI C printf() routines
       are supported.  A * in place of either the width or prec specifications
       will cause their values to be taken from the argument list to printf or

   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).   Other  spe‐
       cial  filenames	provide	 access	 information  about  the  running gawk
       process.	 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 cur‐
		   rent process, in decimal, terminated with a newline.

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

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

       /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"

       These file names may also be used on the	 command  line	to  name  data

   Numeric Functions
       AWK has the following pre-defined arithmetic functions:

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

       cos(expr)   returns the cosine 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 in radians.

       sqrt(expr)  the square root function.

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

   String Functions
       AWK has the following pre-defined string functions:

       gsub(r, s, t)	       for each substring matching the regular expres‐
			       sion  r	in the string t, substitute the string
			       s, and return the number of substitutions.   If
			       t is not supplied, use $0.

       index(s, t)	       returns the index of the string t in the string
			       s, or 0 if t is not present.

       length(s)	       returns the length of  the  string  s,  or  the
			       length of $0 if s is not supplied.

       match(s, r)	       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.

       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.

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

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

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

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

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

   Time Functions
       Since one of the primary uses of AWK programs is processing  log	 files
       that  contain  time  stamp information, gawk provides the following two
       functions for obtaining time stamps and formatting them.

       systime() returns the current time of day  as  the  number  of  seconds
		 since	the Epoch (Midnight UTC, January 1, 1970 on POSIX sys‐

       strftime(format, timestamp)
		 formats timestamp according to the specification  in  format.
		 The  timestamp should be of the same form as returned by sys‐
		 time().  If timestamp is missing, the current time of day  is
		 used.	 See  the specification for the strftime() function in
		 ANSI C for the format conversions that are guaranteed	to  be
		 available.   A public-domain version of strftime(3) and a man
		 page for it are shipped with gawk; if that version  was  used
		 to  build gawk, then all of the conversions described in that
		 man page are available to gawk.

   String Constants
       String constants in AWK are sequences of	 characters  enclosed  between
       double  quotes ("). Within strings, certain escape sequences are recog‐
       nized, 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 fol‐
	    lowing the \x.  As in ANSI C, all following hexadecimal digits are
	    considered part of the escape sequence.  (This feature should tell
	    us something about language design by committee.)  E.g., "\x1B" is
	    the ASCII ESC (escape) character.

       \ddd The character represented by the 1-, 2-, or	 3-digit  sequence  of
	    octal digits. E.g. "\033" is the ASCII ESC (escape) character.

       \c   The literal character c.

       The  escape  sequences may also be used inside constant regular expres‐
       sions (e.g., /[ \t\f\n\r\v]/ matches whitespace characters).

       Functions in AWK are defined as follows:

	      function name(parameter list) { statements }

       Functions are executed when called from within the action parts of reg‐
       ular pattern-action statements. Actual parameters supplied in the func‐
       tion call are used to instantiate the formal parameters declared in the
       function.   Arrays  are passed by reference, other variables are passed
       by value.

       Since functions were not originally part of the AWK language, the  pro‐
       vision 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 & b are local
			     ..... }

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

       The left parenthesis in a function call is required to immediately fol‐
       low 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 parame‐
       ters used as local variables are initialized to the null string and the
       number zero upon function invocation.

       The word func may be used in place of function.

       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 }


       The  AWK Programming Language, Alfred V. Aho, Brian W. Kernighan, Peter
       J. Weinberger, Addison-Wesley, 1988. ISBN 0-201-07981-X.

       The GAWK Manual, Edition 0.15, published by the Free  Software  Founda‐
       tion, 1993.

       A  primary  goal	 for gawk is compatibility with the POSIX standard, as
       well as with the latest version of UNIX awk.  To this end, gawk	incor‐
       porates	the following user visible features which are not described in
       the AWK book, but are part of awk in System V Release 4, and are in the
       POSIX standard.

       The  -v	option for assigning variables before program execution starts
       is new.	The book indicates that command line variable assignment  hap‐
       pens  when  awk	would  otherwise open the argument as a file, which is
       after the BEGIN block is executed.   However,  in  earlier  implementa‐
       tions,  when  such  an  assignment  appeared before any file names, the
       assignment would happen before the BEGIN block was  run.	  Applications
       came  to depend on this ``feature.''  When awk was changed to match its
       documentation, this option was added to	accomodate  applications  that
       depended	 upon the old behavior.	 (This feature was agreed upon by both
       the AT&T and GNU developers.)

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

       When  processing arguments, gawk uses the special option ``--'' to sig‐
       nal the end of arguments, and warns about, but otherwise ignores, unde‐
       fined options.

       The AWK book does not define the return value of srand().  The System V
       Release 4 version of UNIX awk (and the POSIX standard)  has  it	return
       the  seed  it  was  using,  to  allow  keeping  track  of random number
       sequences. Therefore srand() in gawk also returns its current seed.

       Other new features are: The use of multiple -f options (from MKS	 awk);
       the  ENVIRON array; the \a, and \v escape sequences (done originally in
       gawk and fed back into AT&T's version);	the  tolower()	and  toupper()
       built-in	 functions  (from  AT&T); and the ANSI C conversion specifica‐
       tions in printf (done first in AT&T's version).

       Gawk has some extensions to POSIX awk.  They are described in this sec‐
       tion.   All  the	 extensions described here can be disabled by invoking
       gawk with the -W compat option.

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

	      · The \x escape sequence.

	      · The systime() and strftime() functions.

	      · The special file names available for I/O redirection  are  not

	      · The ARGIND and ERRNO variables are not special.

	      · The  IGNORECASE	 variable  and its side-effects are not avail‐

	      · The FIELDWIDTHS variable and fixed width field splitting.

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

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

       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 a file or pipe, respectively.

       When gawk is invoked with the -W compat option, if the fs  argument  to
       the  -F	option	is  ``t'',  then  FS will be set to the tab character.
       Since this is a rather ugly special case, it is not the default	behav‐
       ior.  This behavior also does not occur if -W posix has been specified.

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

	      a = length

       is the same as either of

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

       This  feature  is  marked  as ``deprecated'' in the POSIX standard, and
       gawk will issue a warning about its use if -W lint is specified on  the
       command line.

       The other feature is the use of the continue statement outside the body
       of a while, for, or do  loop.   Traditional  AWK	 implementations  have
       treated such usage as equivalent to the next statement.	Gawk will sup‐
       port this usage if -W posix has not been specified.

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

       If  your	 system	 actually  has	support for /dev/fd and the associated
       /dev/stdin, /dev/stdout, and /dev/stderr files, you may	get  different
       output  from  gawk  than you would get on a system without those files.
       When gawk interprets these files internally, it synchronizes output  to
       the  standard output with output to /dev/stdout, while on a system with
       those files, the output is actually to different	 open  files.	Caveat

       This man page documents gawk, version 2.15.

       Starting	 with  the  2.15  version  of gawk, the -c, -V, -C, -a, and -e
       options of the 2.11 version are no longer recognized.

       The original version of UNIX awk was designed and implemented by Alfred
       Aho,  Peter  Weinberger,	 and  Brian Kernighan of AT&T Bell Labs. Brian
       Kernighan continues to maintain and enhance it.

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

       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.

       Brian Kernighan of Bell Labs provided valuable assistance during	 test‐
       ing and debugging.  We thank him.

Free Software Foundation	 April 15 1993				AWK(1)

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