Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages

  
 
  

home | help
AWK(1P)			   POSIX Programmer's Manual		       AWK(1P)

PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface	may differ (consult the	 corresponding
       Linux  manual page for details of Linux behavior), or the interface may
       not be implemented on Linux.

NAME
       awk - pattern scanning and processing language

SYNOPSIS
       awk [-F ERE][-v assignment] ... program [argument ...]

       awk [-F ERE] -f progfile	...  [-v assignment] ...[argument ...]

DESCRIPTION
       The awk utility shall execute programs written in the  awk  programming
       language,  which	 is  specialized for textual data manipulation.	An awk
       program is a sequence of	patterns and corresponding actions. When input
       is read that matches a pattern, the action associated with that pattern
       is carried out.

       Input shall be interpreted as a sequence	 of  records.  By  default,  a
       record  is  a  line,  less  its	terminating <newline>, but this	can be
       changed by using	the RS built-in	variable. Each record of  input	 shall
       be  matched  in turn against each pattern in the	program. For each pat-
       tern matched, the associated action shall be executed.

       The awk utility shall interpret each input  record  as  a  sequence  of
       fields  where,  by  default, a field is a string	of non-	<blank>s. This
       default white-space field delimiter can be  changed  by	using  the  FS
       built-in	 variable  or  -F  ERE.	The awk	utility	shall denote the first
       field in	a record $1, the second	$2, and	so on.	The  symbol  $0	 shall
       refer to	the entire record; setting any other field causes the re-eval-
       uation of $0. Assigning to $0 shall  reset  the	values	of  all	 other
       fields and the NF built-in variable.

OPTIONS
       The  awk	 utility  shall	 conform  to  the  Base	 Definitions volume of
       IEEE Std	1003.1-2001, Section 12.2, Utility Syntax Guidelines.

       The following options shall be supported:

       -F  ERE
	      Define the input field separator	to  be	the  extended  regular
	      expression  ERE,	before	any input is read; see Regular Expres-
	      sions .

       -f  progfile
	      Specify the pathname of the file progfile	containing an awk pro-
	      gram.  If	 multiple  instances of	this option are	specified, the
	      concatenation of the files specified as progfile	in  the	 order
	      specified	shall be the awk program. The awk program can alterna-
	      tively be	specified in the command line as a single argument.

       -v  assignment
	      The application shall ensure that	the assignment argument	is  in
	      the  same	 form as an assignment operand.	The specified variable
	      assignment shall occur  prior  to	 executing  the	 awk  program,
	      including	 the  actions associated with BEGIN patterns (if any).
	      Multiple occurrences of this option can be specified.

OPERANDS
       The following operands shall be supported:

       program
	      If no -f option is specified, the	first operand to awk shall  be
	      the  text	 of  the awk program. The application shall supply the
	      program operand as a single argument to awk. If  the  text  does
	      not  end	in  a <newline>, awk shall interpret the text as if it
	      did.

       argument
	      Either of	the following two types	of argument can	be intermixed:

       file
	      A	 pathname  of a	file that contains the input to	be read, which
	      is matched against the set of patterns in	 the  program.	If  no
	      file  operands  are  specified, or if a file operand is '-', the
	      standard input shall be used.

       assignment
	      An operand that begins with an underscore	or alphabetic  charac-
	      ter  from	 the portable character	set (see the table in the Base
	      Definitions volume of IEEE Std 1003.1-2001, Section 6.1,	Porta-
	      ble  Character Set), followed by a sequence of underscores, dig-
	      its, and alphabetics from	the portable character	set,  followed
	      by the '=' character, shall specify a variable assignment	rather
	      than a pathname. The characters before  the  '='	represent  the
	      name  of	an  awk	variable; if that name is an awk reserved word
	      (see Grammar ) the behavior is undefined.	The characters follow-
	      ing  the	equal sign shall be interpreted	as if they appeared in
	      the awk program preceded and followed by a double-quote (	 '  )'
	      character,  as a STRING token (see Grammar ), except that	if the
	      last character is	an unescaped backslash,	 it  shall  be	inter-
	      preted as	a literal backslash rather than	as the first character
	      of the sequence "\"" . The variable shall	be assigned the	 value
	      of  that STRING token and, if appropriate, shall be considered a
	      numeric string (see Expressions in awk  ),  the  variable	 shall
	      also  be	assigned its numeric value. Each such variable assign-
	      ment shall occur just prior to the processing of	the  following
	      file, if any. Thus, an assignment	before the first file argument
	      shall be executed	after the BEGIN	actions	 (if  any),  while  an
	      assignment  after	 the last file argument	shall occur before the
	      END actions (if any). If there are no  file  arguments,  assign-
	      ments shall be executed before processing	the standard input.

STDIN
       The  standard  input  shall be used only	if no file operands are	speci-
       fied, or	if a file operand is '-' ; see the INPUT FILES section.	If the
       awk  program  contains  no  actions and no patterns, but	is otherwise a
       valid awk program, standard input and any file operands	shall  not  be
       read and	awk shall exit with a return status of zero.

INPUT FILES
       Input  files to the awk program from any	of the following sources shall
       be text files:

	* Any file operands or their equivalents, achieved  by	modifying  the
	  awk variables	ARGV and ARGC

	* Standard input in the	absence	of any file operands

	* Arguments to the getline function

       Whether	the  variable  RS  is set to a value other than	a <newline> or
       not, for	these files, implementations shall support records  terminated
       with  the  specified  separator	up to {LINE_MAX} bytes and may support
       longer records.

       If -f progfile is specified, the	 application  shall  ensure  that  the
       files named by each of the progfile option-arguments are	text files and
       their concatenation, in the same	order as they appear in	the arguments,
       is an awk program.

ENVIRONMENT VARIABLES
       The following environment variables shall affect	the execution of awk:

       LANG   Provide  a  default value	for the	internationalization variables
	      that are unset or	null. (See  the	 Base  Definitions  volume  of
	      IEEE Std 1003.1-2001,  Section  8.2,  Internationalization Vari-
	      ables for	the precedence of internationalization variables  used
	      to determine the values of locale	categories.)

       LC_ALL If  set  to a non-empty string value, override the values	of all
	      the other	internationalization variables.

       LC_COLLATE
	      Determine	the locale for the  behavior  of  ranges,  equivalence
	      classes,	and  multi-character collating elements	within regular
	      expressions and in comparisons of	string values.

       LC_CTYPE
	      Determine	the locale for	the  interpretation  of	 sequences  of
	      bytes  of	 text  data as characters (for example,	single-byte as
	      opposed to multi-byte characters in arguments and	input  files),
	      the  behavior  of	 character classes within regular expressions,
	      the identification of characters as letters, and the mapping  of
	      uppercase	 and  lowercase	characters for the toupper and tolower
	      functions.

       LC_MESSAGES
	      Determine	the locale that	should be used to  affect  the	format
	      and contents of diagnostic messages written to standard error.

       LC_NUMERIC
	      Determine	 the  radix  character	used when interpreting numeric
	      input, performing	conversions between numeric and	string values,
	      and  formatting numeric output. Regardless of locale, the	period
	      character	(the decimal-point character of	the POSIX  locale)  is
	      the  decimal-point  character  recognized	in processing awk pro-
	      grams (including assignments in command line arguments).

       NLSPATH
	      Determine	the location of	message	catalogs for the processing of
	      LC_MESSAGES .

       PATH   Determine	 the search path when looking for commands executed by
	      system(expr), or input and output	pipes; see  the	 Base  Defini-
	      tions  volume  of	 IEEE Std 1003.1-2001,	Chapter	8, Environment
	      Variables.

       In addition, all	environment variables shall be	visible	 via  the  awk
       variable	ENVIRON.

ASYNCHRONOUS EVENTS
       Default.

STDOUT
       The nature of the output	files depends on the awk program.

STDERR
       The standard error shall	be used	only for diagnostic messages.

OUTPUT FILES
       The nature of the output	files depends on the awk program.

EXTENDED DESCRIPTION
   Overall Program Structure
       An awk program is composed of pairs of the form:

	      pattern {	action }

       Either the pattern or the action	(including the enclosing brace charac-
       ters) can be omitted.

       A missing pattern shall match any record	of input, and a	missing	action
       shall be	equivalent to:

	      {	print }

       Execution of the	awk program shall start	by first executing the actions
       associated with all BEGIN patterns in the order they occur in the  pro-
       gram. Then each file operand (or	standard input if no files were	speci-
       fied) shall be processed	in turn	by reading data	from the file until  a
       record separator	is seen	( <newline> by default). Before	the first ref-
       erence to a field in the	record is evaluated, the record	shall be split
       into  fields,  according	to the rules in	Regular	Expressions, using the
       value of	FS that	was current at the time	the record was read. Each pat-
       tern in the program then	shall be evaluated in the order	of occurrence,
       and the action associated with each pattern that	 matches  the  current
       record  executed.  The  action for a matching pattern shall be executed
       before evaluating subsequent patterns. Finally, the actions  associated
       with  all END patterns shall be executed	in the order they occur	in the
       program.

   Expressions in awk
       Expressions describe computations used in patterns and actions.	In the
       following  table,  valid	expression operations are given	in groups from
       highest precedence first	to lowest precedence last,  with  equal-prece-
       dence operators grouped between horizontal lines. In expression evalua-
       tion, where the grammar is formally ambiguous, higher precedence	opera-
       tors  shall be evaluated	before lower precedence	operators. In this ta-
       ble expr, expr1,	expr2,	and  expr3  represent  any  expression,	 while
       lvalue  represents  any entity that can be assigned to (that is,	on the
       left side of an assignment operator). The precise syntax	of expressions
       is given	in Grammar .

		 Table:	Expressions in Decreasing Precedence in	awk

    Syntax		  Name			    Type of Result   Associativity
    ( expr )		  Grouping		    Type of expr     N/A
    $expr		  Field	reference	    String	     N/A
    ++ lvalue		  Pre-increment		    Numeric	     N/A
    -- lvalue		  Pre-decrement		    Numeric	     N/A
    lvalue ++		  Post-increment	    Numeric	     N/A
    lvalue --		  Post-decrement	    Numeric	     N/A
    expr ^ expr		  Exponentiation	    Numeric	     Right
    ! expr		  Logical not		    Numeric	     N/A
    + expr		  Unary	plus		    Numeric	     N/A
    - expr		  Unary	minus		    Numeric	     N/A
    expr * expr		  Multiplication	    Numeric	     Left

    expr / expr		  Division		    Numeric	     Left
    expr % expr		  Modulus		    Numeric	     Left
    expr + expr		  Addition		    Numeric	     Left
    expr - expr		  Subtraction		    Numeric	     Left
    expr expr		  String concatenation	    String	     Left
    expr _ expr		  Less than		    Numeric	     None
    expr _= expr	  Less than or equal to	    Numeric	     None
    expr != expr	  Not equal to		    Numeric	     None
    expr == expr	  Equal	to		    Numeric	     None
    expr _ expr		  Greater than		    Numeric	     None
    expr _= expr	  Greater than or equal	to  Numeric	     None
    expr ~ expr		  ERE match		    Numeric	     None
    expr !~ expr	  ERE non-match		    Numeric	     None
    expr in array	  Array	membership	    Numeric	     Left
    ( index ) in array	  Multi-dimension array	    Numeric	     Left
			  membership
    expr __ expr	  Logical AND		    Numeric	     Left
    expr || expr	  Logical OR		    Numeric	     Left
    expr1 ? expr2 : expr3 Conditional expression    Type of selected Right
						    expr2 or expr3
    lvalue ^= expr	  Exponentiation assignment Numeric	     Right
    lvalue %= expr	  Modulus assignment	    Numeric	     Right
    lvalue *= expr	  Multiplication assignment Numeric	     Right
    lvalue /= expr	  Division assignment	    Numeric	     Right
    lvalue += expr	  Addition assignment	    Numeric	     Right
    lvalue -= expr	  Subtraction assignment    Numeric	     Right
    lvalue = expr	  Assignment		    Type of expr     Right

       Each  expression	 shall have either a string value, a numeric value, or
       both. Except as stated for specific contexts, the value of  an  expres-
       sion  shall  be implicitly converted to the type	needed for the context
       in which	it is used. A string value shall be  converted	to  a  numeric
       value  by the equivalent	of the following calls to functions defined by
       the ISO C standard:

	      setlocale(LC_NUMERIC, "");
	      numeric_value = atof(string_value);

       A numeric value that is exactly equal to	the value of an	 integer  (see
       Concepts	 Derived  from	the  ISO  C Standard ) shall be	converted to a
       string by the equivalent	of a call to the sprintf function (see	String
       Functions  )  with  the string "%d" as the fmt argument and the numeric
       value being converted as	the first and only expr	 argument.  Any	 other
       numeric	value  shall  be  converted to a string	by the equivalent of a
       call to the sprintf function with the value of the variable CONVFMT  as
       the fmt argument	and the	numeric	value being converted as the first and
       only expr argument. The result of the conversion	is unspecified if  the
       value  of  CONVFMT  is  not a floating-point format specification. This
       volume  of  IEEE	Std 1003.1-2001	 specifies  no	explicit   conversions
       between	numbers	and strings. An	application can	force an expression to
       be treated as a number by adding	zero to	it, or	can  force  it	to  be
       treated as a string by concatenating the	null string ( "" ) to it.

       A  string  value	 shall be considered a numeric string if it comes from
       one of the following:

	1. Field variables

	2. Input from the getline() function

	3. FILENAME

	4. ARGV	array elements

	5. ENVIRON array elements

	6. Array elements created by the split() function

	7. A command line variable assignment

	8. Variable assignment from another numeric string variable

       and after all the following conversions have been applied, the  result-
       ing string would	lexically be recognized	as a NUMBER token as described
       by the lexical conventions in Grammar :

	* All leading and trailing <blank>s are	discarded.

	* If the first non- <blank> is '+' or '-', it is discarded.

	* Changing each	occurrence of the decimal  point  character  from  the
	  current locale to a period.

       If a '-'	character is ignored in	the preceding description, the numeric
       value of	the numeric string shall be the	negation of the	numeric	 value
       of  the	recognized  NUMBER token.  Otherwise, the numeric value	of the
       numeric string shall be the numeric  value  of  the  recognized	NUMBER
       token.  Whether	or  not	a string is a numeric string shall be relevant
       only in contexts	where that term	is used	in this	section.

       When an expression is used in a Boolean context,	if it  has  a  numeric
       value,  a  value	 of zero shall be treated as false and any other value
       shall be	treated	as true. Otherwise, a string value of the null	string
       shall be	treated	as false and any other value shall be treated as true.
       A Boolean context shall be one of the following:

	* The first subexpression of a conditional expression

	* An expression	operated on by logical NOT, logical AND, or logical OR

	* The second expression	of a for statement

	* The expression of an if statement

	* The  expression of the while clause in either	a while	or do... while
	  statement

	* An expression	used as	a pattern (as in Overall Program Structure)

       All arithmetic shall follow the semantics of floating-point  arithmetic
       as specified by the ISO C standard (see Concepts	Derived	from the ISO C
       Standard	).

       The value of the	expression:

	      expr1 ^ expr2

       shall be	equivalent to the value	returned by the	ISO C  standard	 func-
       tion call:

	      pow(expr1, expr2)

       The expression:

	      lvalue ^=	expr

       shall be	equivalent to the ISO C	standard expression:

	      lvalue = pow(lvalue, expr)

       except  that  lvalue  shall  be	evaluated  only	once. The value	of the
       expression:

	      expr1 % expr2

       shall be	equivalent to the value	returned by the	ISO C  standard	 func-
       tion call:

	      fmod(expr1, expr2)

       The expression:

	      lvalue %=	expr

       shall be	equivalent to the ISO C	standard expression:

	      lvalue = fmod(lvalue, expr)

       except that lvalue shall	be evaluated only once.

       Variables and fields shall be set by the	assignment statement:

	      lvalue = expression

       and the type of expression shall	determine the resulting	variable type.
       The assignment includes the arithmetic assignments ( "+=", "-=",	 "*=",
       "/=",  "%=",  "^=",  "++",  "--"	) all of which shall produce a numeric
       result. The left-hand side of an	assignment and the target of increment
       and  decrement operators	can be one of a	variable, an array with	index,
       or a field selector.

       The awk language	supplies arrays	that are used for storing  numbers  or
       strings.	 Arrays	 need  not be declared.	They shall initially be	empty,
       and their sizes shall change dynamically. The  subscripts,  or  element
       identifiers,  are  strings, providing a type of associative array capa-
       bility. An array	name followed by a subscript  within  square  brackets
       can be used as an lvalue	and thus as an expression, as described	in the
       grammar;	see Grammar . Unsubscripted array names	can be	used  in  only
       the following contexts:

	* A parameter in a function definition or function call

	* The  NAME  token following any use of	the keyword in as specified in
	  the grammar (see Grammar ); if the name used in this context is  not
	  an array name, the behavior is undefined

       A  valid	 array	index  shall  consist  of  one or more comma-separated
       expressions, similar to the way in which	multi-dimensional  arrays  are
       indexed	in  some programming languages.	 Because awk arrays are	really
       one-dimensional,	such a comma-separated list shall be  converted	 to  a
       single  string  by  concatenating  the  string  values  of the separate
       expressions, each separated from	the other by the value of  the	SUBSEP
       variable.   Thus,  the  following two index operations shall be equiva-
       lent:

	      var[expr1, expr2,	... exprn]

	      var[expr1	SUBSEP expr2 SUBSEP ...	SUBSEP exprn]

       The application shall ensure that a multi-dimensioned index  used  with
       the  in operator	is parenthesized. The in operator, which tests for the
       existence of a particular array element,	shall not cause	 that  element
       to  exist.  Any	other  reference  to a nonexistent array element shall
       automatically create it.

       Comparisons (with the '<', "<=",	"!=", "==", '>', and  ">="  operators)
       shall  be  made	numerically  if	 both  operands	are numeric, if	one is
       numeric and the other has a string value	that is	a numeric  string,  or
       if one is numeric and the other has the uninitialized value. Otherwise,
       operands	shall be converted to strings as required and a	string compar-
       ison  shall  be	made using the locale-specific collation sequence. The
       value of	the comparison expression shall	be 1 if	the relation is	 true,
       or 0 if the relation is false.

   Variables and Special Variables
       Variables  can be used in an awk	program	by referencing them.  With the
       exception of function parameters	(see User-Defined  Functions  ),  they
       are not explicitly declared. Function parameter names shall be local to
       the function; all other variable	names shall be global. The  same  name
       shall  not be used as both a function parameter name and	as the name of
       a function or a special awk variable. The same name shall not  be  used
       both  as	 a  variable name with global scope and	as the name of a func-
       tion. The same name shall not be	used within the	same scope both	 as  a
       scalar  variable	 and  as an array.  Uninitialized variables, including
       scalar variables, array elements, and field variables,  shall  have  an
       uninitialized  value.  An uninitialized value shall have	both a numeric
       value of	zero and a string value	of the	empty  string.	Evaluation  of
       variables  with	an  uninitialized  value, to either string or numeric,
       shall be	determined by the context in which they	are used.

       Field variables shall be	designated by a	'$' followed by	 a  number  or
       numerical  expression. The effect of the	field number expression	evalu-
       ating to	anything other than a  non-negative  integer  is  unspecified;
       uninitialized  variables	 or  string  values  need  not be converted to
       numeric values in this context. New field variables can be  created  by
       assigning  a value to them.  References to nonexistent fields (that is,
       fields after $NF), shall	evaluate to the	uninitialized value. Such ref-
       erences	shall  not create new fields. However, assigning to a nonexis-
       tent field (for example,	$(NF+2)=5) shall increase  the	value  of  NF;
       create  any  intervening	fields with the	uninitialized value; and cause
       the value of $0 to be recomputed, with the fields  being	 separated  by
       the  value  of OFS. Each	field variable shall have a string value or an
       uninitialized value when	 created.   Field  variables  shall  have  the
       uninitialized value when	created	from $0	using FS and the variable does
       not contain any characters. If appropriate, the field variable shall be
       considered a numeric string (see	Expressions in awk ).

       Implementations	shall  support	the  following other special variables
       that are	set by awk:

       ARGC   The number of elements in	the ARGV array.

       ARGV   An array of command line arguments, excluding  options  and  the
	      program argument,	numbered from zero to ARGC-1.

       The arguments in	ARGV can be modified or	added to; ARGC can be altered.
       As each input file ends,	awk shall treat	the next non-null  element  of
       ARGV,  up to the	current	value of ARGC-1, inclusive, as the name	of the
       next input file.	Thus, setting an element of ARGV to null means that it
       shall not be treated as an input	file. The name '-' indicates the stan-
       dard input. If an argument matches the format of	an assignment operand,
       this  argument  shall  be  treated  as an assignment rather than	a file
       argument.

       CONVFMT
	      The printf format	for converting numbers to strings (except  for
	      output statements, where OFMT is used); "%.6g" by	default.

       ENVIRON
	      An array representing the	value of the environment, as described
	      in the exec functions defined in the System Interfaces volume of
	      IEEE Std 1003.1-2001.  The indices of the	array shall be strings
	      consisting of the	names of the environment  variables,  and  the
	      value  of	each array element shall be a string consisting	of the
	      value of that variable. If appropriate, the environment variable
	      shall  be	considered a numeric string (see Expressions in	awk );
	      the array	element	shall also have	its numeric value.

       In all cases where the behavior of awk is affected by environment vari-
       ables  (including the environment of any	commands that awk executes via
       the system function or via pipeline redirections	with the print	state-
       ment,  the  printf statement, or	the getline function), the environment
       used shall be the environment at	the time awk began  executing;	it  is
       implementation-defined whether any modification of ENVIRON affects this
       environment.

       FILENAME
	      A	pathname of the	current	input file. Inside a BEGIN action  the
	      value  is	undefined. Inside an END action	the value shall	be the
	      name of the last input file processed.

       FNR    The ordinal number of the	current	record in  the	current	 file.
	      Inside  a	 BEGIN	action	the value shall	be zero. Inside	an END
	      action the value shall be	the number of  the  last  record  pro-
	      cessed in	the last file processed.

       FS     Input  field separator regular expression; a <space> by default.

       NF     The number of fields in  the  current  record.  Inside  a	 BEGIN
	      action,  the  use	 of  NF	is undefined unless a getline function
	      without a	var argument is	executed previously.   Inside  an  END
	      action,  NF  shall  retain  the value it had for the last	record
	      read, unless a subsequent, redirected, getline function  without
	      a	var argument is	performed prior	to entering the	END action.

       NR     The  ordinal  number  of	the  current  record from the start of
	      input.  Inside a BEGIN action the	value shall be zero. Inside an
	      END action the value shall be the	number of the last record pro-
	      cessed.

       OFMT   The printf format	for converting numbers to  strings  in	output
	      statements  (see	Output	Statements  );	"%.6g" by default. The
	      result of	the conversion is unspecified if the value of OFMT  is
	      not a floating-point format specification.

       OFS    The print	statement output field separation; <space> by default.

       ORS    The print	statement output  record  separator;  a	 <newline>  by
	      default.

       RLENGTH
	      The length of the	string matched by the match function.

       RS     The first	character of the string	value of RS shall be the input
	      record separator;	a <newline> by default.	If  RS	contains  more
	      than one character, the results are unspecified.	If RS is null,
	      then records are separated by sequences consisting  of  a	 <new-
	      line>  plus  one	or more	blank lines, leading or	trailing blank
	      lines shall not result in	empty records at the beginning or  end
	      of the input, and	a <newline> shall always be a field separator,
	      no matter	what the value of FS is.

       RSTART The starting position of the string matched by the  match	 func-
	      tion,  numbering	from 1.	This shall always be equivalent	to the
	      return value of the match	function.

       SUBSEP The subscript separator string for multi-dimensional arrays; the
	      default value is implementation-defined.

   Regular Expressions
       The awk utility shall make use of the extended regular expression nota-
       tion (see the Base Definitions volume of	IEEE Std 1003.1-2001,  Section
       9.4,  Extended  Regular Expressions) except that	it shall allow the use
       of C-language conventions for escaping special  characters  within  the
       EREs,  as  specified  in	 the  table  in	the Base Definitions volume of
       IEEE Std	1003.1-2001, Chapter 5,	File Format  Notation  (  '\\',	 '\a',
       '\b',  '\f',  '\n',  '\r',  '\t', '\v' )	and the	following table; these
       escape sequences	shall be recognized both inside	 and  outside  bracket
       expressions.  Note that records need not	be separated by	<newline>s and
       string constants	can contain <newline>s,	so even	the "\n"  sequence  is
       valid  in  awk EREs. Using a slash character within an ERE requires the
       escaping	shown in the following table.

			   Table: Escape Sequences in awk

       Escape
       Sequence	Description		       Meaning
       \"	Backslash quotation-mark       Quotation-mark character
       \/	Backslash slash		       Slash character
       \ddd	A backslash character followed The character whose encoding
		by the longest sequence	of     is represented by the one,
		one, two, or three octal-digit two, or three-digit octal
		characters (01234567). If all  integer.	Multi-byte characters
		of the digits are 0 (that is,  require multiple, concatenated
		representation of the NUL      escape sequences	of this	type,
		character), the	behavior is    including the leading '\' for
		undefined.		       each byte.
       \c	A backslash character followed Undefined
		by any character not described
		in this	table or in the	table
		in the Base Definitions	volume
		of IEEE	Std 1003.1-2001, Chap-
		ter 5, File Format Notation (
		'\\', '\a', '\b', '\f',	'\n',
		'\r', '\t', '\v' ).

       A  regular expression can be matched against a specific field or	string
       by using	one of the two regular expression matching operators, '~'  and
       "!~"  .	These  operators shall interpret their right-hand operand as a
       regular expression and their left-hand operand as a string. If the reg-
       ular  expression	 matches the string, the '~' expression	shall evaluate
       to a value of 1,	and the	"!~" expression	shall evaluate to a  value  of
       0. (The regular expression matching operation is	as defined by the term
       matched in the Base Definitions volume of IEEE Std 1003.1-2001, Section
       9.1,  Regular  Expression Definitions, where a match occurs on any part
       of the string unless the	regular	expression is limited with the circum-
       flex or dollar sign special characters.)	If the regular expression does
       not match the string, the '~' expression	shall evaluate to a  value  of
       0,  and	the  "!~"  expression  shall  evaluate to a value of 1.	If the
       right-hand operand is any expression other than the lexical token  ERE,
       the  string value of the	expression shall be interpreted	as an extended
       regular expression, including the escape	conventions  described	above.
       Note that these same escape conventions shall also be applied in	deter-
       mining the value	of a string literal (the lexical  token	 STRING),  and
       thus  shall  be	applied	a second time when a string literal is used in
       this context.

       When an ERE token appears as an expression in any context other than as
       the  right-hand	of  the	'~' or "!~" operator or	as one of the built-in
       function	arguments described below, the value of	the resulting  expres-
       sion shall be the equivalent of:

	      $0 ~ /ere/

       The ere argument	to the gsub, match, sub	functions, and the fs argument
       to the split function (see String Functions ) shall be  interpreted  as
       extended	 regular  expressions. These can be either ERE tokens or arbi-
       trary expressions, and shall be interpreted in the same manner  as  the
       right-hand side of the '~' or "!~" operator.

       An  extended regular expression can be used to separate fields by using
       the -F ERE option or by assigning a string containing the expression to
       the built-in variable FS. The default value of the FS variable shall be
       a single	<space>. The following describes FS behavior:

	1. If FS is a null string, the behavior	is unspecified.

	2. If FS is a single character:

	    a. If FS is	<space>, skip leading and  trailing  <blank>s;	fields
	       shall be	delimited by sets of one or more <blank>s.

	    b. Otherwise,  if  FS  is  any  other character c, fields shall be
	       delimited by each single	occurrence of c.

	3. Otherwise, the string value of FS shall  be	considered  to	be  an
	   extended regular expression.	Each occurrence	of a sequence matching
	   the extended	regular	expression shall delimit fields.

       Except for the '~' and "!~" operators, and in the gsub,	match,	split,
       and  sub	 built-in  functions,  ERE  matching  shall  be	based on input
       records;	that is, record	separator characters (the first	 character  of
       the  value of the variable RS, <newline>	by default) cannot be embedded
       in the expression, and no expression shall match	the  record  separator
       character.  If the record separator is not <newline>, <newline>s	embed-
       ded in the expression can be matched. For the '~' and  "!~"  operators,
       and  in	those  four built-in functions,	ERE matching shall be based on
       text strings; that is,  any  character  (including  <newline>  and  the
       record  separator)  can	be embedded in the pattern, and	an appropriate
       pattern shall match any character. However, in all  awk	ERE  matching,
       the  use	of one or more NUL characters in the pattern, input record, or
       text string produces undefined results.

   Patterns
       A pattern is any	valid expression, a range specified by two expressions
       separated  by a comma, or one of	the two	special	patterns BEGIN or END.

   Special Patterns
       The awk utility shall recognize two special patterns,  BEGIN  and  END.
       Each BEGIN pattern shall	be matched once	and its	associated action exe-
       cuted before the	first record of	input is read (except possibly by  use
       of  the	getline	function-see Input/Output and General Functions	- in a
       prior BEGIN action) and before command line assignment  is  done.  Each
       END  pattern  shall  be matched once and	its associated action executed
       after the last record of	input has been read. These two patterns	 shall
       have associated actions.

       BEGIN and END shall not combine with other patterns. Multiple BEGIN and
       END patterns shall be allowed. The actions associated  with  the	 BEGIN
       patterns	 shall	be  executed in	the order specified in the program, as
       are the END actions. An END pattern can precede a BEGIN	pattern	 in  a
       program.

       If  an awk program consists of only actions with	the pattern BEGIN, and
       the BEGIN action	contains no getline function, awk shall	 exit  without
       reading	its  input when	the last statement in the last BEGIN action is
       executed. If an awk program consists of only actions with  the  pattern
       END or only actions with	the patterns BEGIN and END, the	input shall be
       read before the statements in the END actions are executed.

   Expression Patterns
       An expression pattern shall be evaluated	as if it were an expression in
       a  Boolean context. If the result is true, the pattern shall be consid-
       ered to match, and the associated action	(if any) shall be executed. If
       the result is false, the	action shall not be executed.

   Pattern Ranges
       A  pattern  range  consists of two expressions separated	by a comma; in
       this case, the action shall be performed	 for  all  records  between  a
       match  of  the  first  expression and the following match of the	second
       expression, inclusive. At this point, the pattern range can be repeated
       starting	at input records subsequent to the end of the matched range.

   Actions
       An  action is a sequence	of statements as shown in the grammar in Gram-
       mar . Any single	statement can be replaced by a statement list enclosed
       in  braces. The application shall ensure	that statements	in a statement
       list are	separated by <newline>s	or semicolons. Statements in a	state-
       ment list shall be executed sequentially	in the order that they appear.

       The expression acting as	the conditional	in an if  statement  shall  be
       evaluated  and  if  it is non-zero or non-null, the following statement
       shall be	executed; otherwise, if	else is	present, the statement follow-
       ing the else shall be executed.

       The  if,	 while,	 do...	while, for, break, and continue	statements are
       based on	the ISO	C standard (see	Concepts Derived from the ISO C	 Stan-
       dard  ),	 except	 that  the  Boolean  expressions  shall	 be treated as
       described in Expressions	in awk , and except in the case	of:

	      for (variable in array)

       which shall iterate, assigning each index of array to  variable	in  an
       unspecified  order.  The	results	of adding new elements to array	within
       such a for loop are undefined. If a break or continue statement	occurs
       outside of a loop, the behavior is undefined.

       The  delete  statement shall remove an individual array element.	 Thus,
       the following code deletes an entire array:

	      for (index in array)
		  delete array[index]

       The next	statement shall	cause all further processing  of  the  current
       input  record  to  be  abandoned.  The  behavior	is undefined if	a next
       statement appears or is invoked in a BEGIN or END action.

       The exit	statement shall	invoke all END actions in the order  in	 which
       they occur in the program source	and then terminate the program without
       reading further input. An exit statement	inside	an  END	 action	 shall
       terminate  the  program without further execution of END	actions. If an
       expression is specified in an exit statement, its numeric  value	 shall
       be  the exit status of awk, unless subsequent errors are	encountered or
       a subsequent exit statement with	an expression is executed.

   Output Statements
       Both print and printf statements	shall  write  to  standard  output  by
       default.	 The output shall be written to	the location specified by out-
       put_redirection if one is supplied, as follows:

	      >	expression>> expression| expression

       In all cases, the expression shall be evaluated	to  produce  a	string
       that is used as a pathname into which to	write (for '>' or ">>" ) or as
       a command to be executed	(for '|' ). Using the first two	forms, if  the
       file  of	 that name is not currently open, it shall be opened, creating
       it if necessary and using the first form, truncating the	file. The out-
       put  then  shall	 be  appended to the file. As long as the file remains
       open, subsequent	calls in which expression evaluates to the same	string
       value  shall  simply  append  output to the file. The file remains open
       until the close function	(see Input/Output and General Functions	 )  is
       called with an expression that evaluates	to the same string value.

       The third form shall write output onto a	stream piped to	the input of a
       command.	The stream shall be created if no  stream  is  currently  open
       with  the  value	of expression as its command name.  The	stream created
       shall be	equivalent to one created by a call to	the  popen()  function
       defined	in  the	 System	Interfaces volume of IEEE Std 1003.1-2001 with
       the value of expression as the command argument and a value of w	as the
       mode  argument. As long as the stream remains open, subsequent calls in
       which expression	evaluates to the same string value shall write	output
       to  the	existing  stream. The stream shall remain open until the close
       function	(see Input/Output and General Functions	) is  called  with  an
       expression  that	evaluates to the same string value.  At	that time, the
       stream shall be closed as if by a call to the pclose() function defined
       in the System Interfaces	volume of IEEE Std 1003.1-2001.

       As  described in	detail by the grammar in Grammar , these output	state-
       ments shall take	a comma-separated list of expressions referred	to  in
       the  grammar by the non-terminal	symbols	expr_list, print_expr_list, or
       print_expr_list_opt. This list is referred to here  as  the  expression
       list, and each member is	referred to as an expression argument.

       The  print  statement shall write the value of each expression argument
       onto the	indicated output stream	separated by the current output	 field
       separator (see variable OFS above), and terminated by the output	record
       separator (see variable ORS above). All expression arguments  shall  be
       taken  as  strings, being converted if necessary; this conversion shall
       be as described in Expressions in awk , with  the  exception  that  the
       printf format in	OFMT shall be used instead of the value	in CONVFMT. An
       empty expression	list shall stand for the whole input record ($0).

       The printf statement shall produce output based on a  notation  similar
       to  the File Format Notation used to describe file formats in this vol-
       ume  of	IEEE Std 1003.1-2001  (see  the	 Base  Definitions  volume  of
       IEEE Std	1003.1-2001,  Chapter  5, File Format Notation).  Output shall
       be produced as specified	with the  first	 expression  argument  as  the
       string  format  and subsequent expression arguments as the strings arg1
       to argn,	inclusive, with	the following exceptions:

	1. The format shall be an actual character string rather than a	graph-
	   ical	 representation.  Therefore, it	cannot contain empty character
	   positions. The <space> in the format	string,	in any	context	 other
	   than	 a  flag of a conversion specification,	shall be treated as an
	   ordinary character that is copied to	the output.

	2. If the character set	contains a ' ' character  and  that  character
	   appears  in	the  format string, it shall be	treated	as an ordinary
	   character that is copied to the output.

	3. The escape sequences	beginning with a backslash character shall  be
	   treated  as sequences of ordinary characters	that are copied	to the
	   output. Note	that these same	sequences shall	be  interpreted	 lexi-
	   cally  by  awk  when	they appear in literal strings,	but they shall
	   not be treated specially by the printf statement.

	4. A field width or precision can be specified as  the	'*'  character
	   instead  of a digit string. In this case the	next argument from the
	   expression list shall be fetched and	its numeric value taken	as the
	   field width or precision.

	5. The implementation shall not	precede	or follow output from the d or
	   u conversion	specifier characters with <blank>s  not	 specified  by
	   the format string.

	6. The	implementation	shall not precede output from the o conversion
	   specifier character with leading zeros not specified	by the	format
	   string.

	7. For	the  c	conversion  specifier character: if the	argument has a
	   numeric value, the character	whose encoding is that value shall  be
	   output.  If the value is zero or is not the encoding	of any charac-
	   ter in the character	set, the behavior is undefined.	If  the	 argu-
	   ment	 does  not  have  a  numeric value, the	first character	of the
	   string value	shall be output; if the	string does  not  contain  any
	   characters, the behavior is undefined.

	8. For	each  conversion  specification	that consumes an argument, the
	   next	expression argument shall be evaluated.	With the exception  of
	   the	c conversion specifier character, the value shall be converted
	   (according to the rules specified in	Expressions in awk  )  to  the
	   appropriate type for	the conversion specification.

	9. If  there  are insufficient expression arguments to satisfy all the
	   conversion specifications in	the format  string,  the  behavior  is
	   undefined.

       10. If  any  character  sequence	in the format string begins with a '%'
	   character, but does not form	a valid	conversion specification,  the
	   behavior is unspecified.

       Both print and printf can output	at least {LINE_MAX} bytes.

   Functions
       The  awk	 language  has	a  variety  of built-in	functions: arithmetic,
       string, input/output, and general.

   Arithmetic Functions
       The arithmetic functions, except	for int, shall be based	on  the	 ISO C
       standard	 (see Concepts Derived from the	ISO C Standard ). The behavior
       is undefined in cases where the ISO C standard specifies	that an	 error
       be  returned  or	 that  the behavior is undefined. Although the grammar
       (see Grammar ) permits built-in functions to appear with	 no  arguments
       or  parentheses,	 unless	 the  argument or parentheses are indicated as
       optional	in the following list (by  displaying  them  within  the  "[]"
       brackets), such use is undefined.

       atan2(y,x)
	      Return arctangent	of y/x in radians in the range [-pi,pi].

       cos(x) Return cosine of x, where	x is in	radians.

       sin(x) Return sine of x,	where x	is in radians.

       exp(x) Return the exponential function of x.

       log(x) Return the natural logarithm of x.

       sqrt(x)
	      Return the square	root of	x.

       int(x) Return the argument truncated to an integer. Truncation shall be
	      toward 0 when x>0.

       rand() Return a random number n,	such that 0<=n<1.

       srand([expr])
	      Set the seed value for rand to expr or use the time  of  day  if
	      expr is omitted. The previous seed value shall be	returned.

   String Functions
       The string functions in the following list shall	be supported. Although
       the grammar (see	Grammar	) permits built-in functions to	appear with no
       arguments  or parentheses, unless the argument or parentheses are indi-
       cated as	optional in the	following list (by displaying them within  the
       "[]" brackets), such use	is undefined.

       gsub(ere, repl[,	in])
	      Behave  like  sub	 (see below), except that it shall replace all
	      occurrences of the  regular  expression  (like  the  ed  utility
	      global  substitute) in $0	or in the in argument, when specified.

       index(s,	t)
	      Return the position, in characters, numbering from 1, in	string
	      s	 where	string t first occurs, or zero if it does not occur at
	      all.

       length[([s])]
	      Return the length, in characters,	of its	argument  taken	 as  a
	      string, or of the	whole record, $0, if there is no argument.

       match(s,	ere)
	      Return  the position, in characters, numbering from 1, in	string
	      s	where the extended regular expression ere occurs, or  zero  if
	      it  does	not  occur at all. RSTART shall	be set to the starting
	      position (which is the same as the returned value), zero	if  no
	      match  is	 found;	 RLENGTH  shall	 be  set  to the length	of the
	      matched string, -1 if no match is	found.

       split(s,	a[, fs	])
	      Split the	string s into array elements a[1],  a[2],  ...,	 a[n],
	      and  return n. All elements of the array shall be	deleted	before
	      the split	is performed. The separation shall be  done  with  the
	      ERE  fs  or with the field separator FS if fs is not given. Each
	      array element shall have a string	value  when  created  and,  if
	      appropriate,  the	 array	element	 shall be considered a numeric
	      string (see Expressions in awk ).	The effect of a	null string as
	      the value	of fs is unspecified.

       sprintf(fmt, expr, expr,	...)
	      Format  the  expressions according to the	printf format given by
	      fmt and return the resulting string.

       sub(ere,	repl[, in  ])
	      Substitute the string repl in place of the first instance	of the
	      extended regular expression ERE in string	in and return the num-
	      ber of substitutions. An ampersand (  '&'	 )  appearing  in  the
	      string repl shall	be replaced by the string from in that matches
	      the ERE. An ampersand preceded with a backslash (	'\' ) shall be
	      interpreted as the literal ampersand character. An occurrence of
	      two consecutive backslashes shall	be interpreted as just a  sin-
	      gle literal backslash character. Any other occurrence of a back-
	      slash (for example, preceding  any  other	 character)  shall  be
	      treated as a literal backslash character.	Note that if repl is a
	      string literal (the lexical token	STRING;	 see  Grammar  ),  the
	      handling	of  the	 ampersand  character occurs after any lexical
	      processing, including any	lexical	backslash escape sequence pro-
	      cessing. If in is	specified and it is not	an lvalue (see Expres-
	      sions in awk ), the behavior is undefined. If in is omitted, awk
	      shall use	the current record ($0)	in its place.

       substr(s, m[, n	])
	      Return  the  at  most  n-character substring of s	that begins at
	      position m, numbering from 1. If n is omitted, or	if n specifies
	      more  characters	than are left in the string, the length	of the
	      substring	shall be limited by the	length of the string s.

       tolower(s)
	      Return a string based on the string s. Each character in s  that
	      is  an  uppercase	 letter	specified to have a tolower mapping by
	      the LC_CTYPE category of the current locale shall	be replaced in
	      the  returned  string  by	 the lowercase letter specified	by the
	      mapping. Other  characters  in  s	 shall	be  unchanged  in  the
	      returned string.

       toupper(s)
	      Return  a	string based on	the string s. Each character in	s that
	      is a lowercase letter specified to have a	toupper	mapping	by the
	      LC_CTYPE	category  of  the  current  locale  is replaced	in the
	      returned string by the uppercase letter specified	 by  the  map-
	      ping.  Other  characters	in  s  are  unchanged  in the returned
	      string.

       All of the preceding functions that take	ERE as a  parameter  expect  a
       pattern	or  a string valued expression that is a regular expression as
       defined in Regular Expressions .

   Input/Output	and General Functions
       The input/output	and general functions are:

       close(expression)
	      Close the	file or	pipe opened by a print or printf statement  or
	      a	 call  to  getline with	the same string-valued expression. The
	      limit on the number of open expression arguments is  implementa-
	      tion-defined.  If	 the  close was	successful, the	function shall
	      return zero; otherwise, it shall return non-zero.

       expression |  getline [var]
	      Read a record of input from a stream piped from the output of  a
	      command.	 The stream shall be created if	no stream is currently
	      open with	the value of  expression  as  its  command  name.  The
	      stream  created  shall be	equivalent to one created by a call to
	      the popen() function with	the value of expression	as the command
	      argument	and  a value of	r as the mode argument.	As long	as the
	      stream remains open, subsequent calls in which expression	evalu-
	      ates to the same string value shall read subsequent records from
	      the stream. The stream shall remain open until the  close	 func-
	      tion  is	called	with  an expression that evaluates to the same
	      string value. At that time, the stream shall be closed as	if  by
	      a	 call  to  the pclose()	function. If var is omitted, $0	and NF
	      shall be set; otherwise, var shall be set	and,  if  appropriate,
	      it  shall	be considered a	numeric	string (see Expressions	in awk
	      ).

       The getline operator can	 form  ambiguous  constructs  when  there  are
       unparenthesized	operators  (including  concatenate) to the left	of the
       '|' (to the beginning of	the expression	containing  getline).  In  the
       context	of  the	 '$'  operator,	 '|' shall behave as if	it had a lower
       precedence than '$' . The  result  of  evaluating  other	 operators  is
       unspecified,  and  conforming  applications shall parenthesize properly
       all such	usages.

       getline
	      Set $0 to	the next input record from  the	 current  input	 file.
	      This form	of getline shall set the NF, NR, and FNR variables.

       getline	var
	      Set variable var to the next input record	from the current input
	      file and,	if appropriate,	var  shall  be	considered  a  numeric
	      string (see Expressions in awk ).	This form of getline shall set
	      the FNR and NR variables.

       getline [var]  <	expression
	      Read the next record of input from a named file. The  expression
	      shall  be	 evaluated to produce a	string that is used as a path-
	      name. If the file	of that	name is	not currently open,  it	 shall
	      be  opened. As long as the stream	remains	open, subsequent calls
	      in which expression evaluates to the  same  string  value	 shall
	      read  subsequent	records	 from  the file. The file shall	remain
	      open until the close function is called with an expression  that
	      evaluates	to the same string value. If var is omitted, $0	and NF
	      shall be set; otherwise, var shall be set	and,  if  appropriate,
	      it  shall	be considered a	numeric	string (see Expressions	in awk
	      ).

       The getline operator can	 form  ambiguous  constructs  when  there  are
       unparenthesized	binary	operators (including concatenate) to the right
       of the '<' (up to the end of the	expression  containing	the  getline).
       The  result of evaluating such a	construct is unspecified, and conform-
       ing applications	shall parenthesize properly all	such usages.

       system(expression)
	      Execute the command given	by expression in a  manner  equivalent
	      to the system() function defined in the System Interfaces	volume
	      of IEEE Std 1003.1-2001 and return the exit status of  the  com-
	      mand.

       All forms of getline shall return 1 for successful input, zero for end-
       of-file,	and -1 for an error.

       Where strings are used as the name of a file or pipeline, the  applica-
       tion shall ensure that the strings are textually	identical.  The	termi-
       nology "same string value"  implies  that  "equivalent  strings",  even
       those that differ only by <space>s, represent different files.

   User-Defined	Functions
       The  awk	 language also provides	user-defined functions.	Such functions
       can be defined as:

	      function name([parameter,	...]) {	statements }

       A function can be referred to anywhere in an awk	program;  in  particu-
       lar,  its  use  can  precede its	definition. The	scope of a function is
       global.

       Function	parameters, if present,	can be either scalars or  arrays;  the
       behavior	 is  undefined	if an array name is passed as a	parameter that
       the function uses as a scalar, or if a scalar expression	is passed as a
       parameter that the function uses	as an array. Function parameters shall
       be passed by value if scalar and	by reference if	array name.

       The number of parameters	in the function	definition need	not match  the
       number of parameters in the function call. Excess formal	parameters can
       be used as local	variables. If fewer arguments are supplied in a	 func-
       tion  call  than	 are  in the function definition, the extra parameters
       that are	used in	the function body as scalars  shall  evaluate  to  the
       uninitialized value until they are otherwise initialized, and the extra
       parameters that are used	in  the	 function  body	 as  arrays  shall  be
       treated	as  uninitialized  arrays  where each element evaluates	to the
       uninitialized value until otherwise initialized.

       When invoking a function, no white space	 can  be  placed  between  the
       function	name and the opening parenthesis. Function calls can be	nested
       and recursive calls can be made upon functions. Upon  return  from  any
       nested  or  recursive  function	call, the values of all	of the calling
       function's parameters shall be unchanged, except	for  array  parameters
       passed  by  reference.  The  return  statement  can be used to return a
       value. If a return statement appears outside of a function  definition,
       the behavior is undefined.

       In  the	function  definition,  <newline>s shall	be optional before the
       opening brace and after the closing  brace.  Function  definitions  can
       appear  anywhere	in the program where a pattern-action pair is allowed.

   Grammar
       The grammar in this section and the lexical conventions in the  follow-
       ing  section  shall  together describe the syntax for awk programs. The
       general conventions for this style of grammar are described in  Grammar
       Conventions  .  A  valid	program	can be represented as the non-terminal
       symbol program in the grammar. This formal syntax shall take precedence
       over the	preceding text syntax description.

	      %token NAME NUMBER STRING	ERE
	      %token FUNC_NAME	 /* Name followed by '(' without white space. */

	      /* Keywords  */
	      %token	   Begin   End
	      /*	  'BEGIN' 'END'				   */

	      %token	   Break   Continue   Delete   Do   Else
	      /*	  'break' 'continue' 'delete' 'do' 'else'  */

	      %token	   Exit	  For	Function   If	In
	      /*	  'exit' 'for' 'function' 'if' 'in'	   */

	      %token	   Next	  Print	  Printf   Return   While
	      /*	  'next' 'print' 'printf' 'return' 'while' */

	      /* Reserved function names */
	      %token BUILTIN_FUNC_NAME
			  /* One token for the following:
			   * atan2 cos sin exp log sqrt	int rand srand
			   * gsub index	length match split sprintf sub
			   * substr tolower toupper close system
			   */
	      %token GETLINE
			  /* Syntactically different from other	built-ins. */

	      /* Two-character tokens. */
	      %token ADD_ASSIGN	SUB_ASSIGN MUL_ASSIGN DIV_ASSIGN MOD_ASSIGN POW_ASSIGN
	      /*     '+='	'-='	   '*='	      '/='	 '%='	    '^=' */

	      %token OR	  AND  NO_MATCH	  EQ   LE   GE	 NE   INCR  DECR  APPEND
	      /*     '||' '&&' '!~' '==' '<=' '>=' '!='	'++'  '--'  '>>'   */

	      /* One-character tokens. */
	      %token '{' '}' '(' ')' '[' ']' ',' ';' NEWLINE
	      %token '+' '-' '*' '%' '^' '!' '>' '<' '|' '?' ':' '~' '$' '='

	      %start program
	      %%

	      program	       : item_list
			       | actionless_item_list
			       ;

	      item_list	       : newline_opt
			       | actionless_item_list item terminator
			       | item_list	      item terminator
			       | item_list	    action terminator
			       ;

	      actionless_item_list : item_list		  pattern terminator
			       | actionless_item_list pattern terminator
			       ;

	      item	       : pattern action
			       | Function NAME	    '('	param_list_opt ')'
				     newline_opt action
			       | Function FUNC_NAME '('	param_list_opt ')'
				     newline_opt action
			       ;

	      param_list_opt   : /* empty */
			       | param_list
			       ;

	      param_list       : NAME
			       | param_list ','	NAME
			       ;

	      pattern	       : Begin
			       | End
			       | expr
			       | expr ',' newline_opt expr
			       ;

	      action	       : '{' newline_opt			     '}'
			       | '{' newline_opt terminated_statement_list   '}'
			       | '{' newline_opt unterminated_statement_list '}'
			       ;

	      terminator       : terminator ';'
			       | terminator NEWLINE
			       |	    ';'
			       |	    NEWLINE
			       ;

	      terminated_statement_list	: terminated_statement
			       | terminated_statement_list terminated_statement
			       ;

	      unterminated_statement_list : unterminated_statement
			       | terminated_statement_list unterminated_statement
			       ;

	      terminated_statement : action newline_opt
			       | If '('	expr ')' newline_opt terminated_statement
			       | If '('	expr ')' newline_opt terminated_statement
				     Else newline_opt terminated_statement
			       | While '(' expr	')' newline_opt	terminated_statement
			       | For '(' simple_statement_opt ';'
				    expr_opt ';' simple_statement_opt ')' newline_opt
				    terminated_statement
			       | For '(' NAME In NAME ')' newline_opt
				    terminated_statement
			       | ';' newline_opt
			       | terminatable_statement	NEWLINE	newline_opt
			       | terminatable_statement	';'	newline_opt
			       ;

	      unterminated_statement : terminatable_statement
			       | If '('	expr ')' newline_opt unterminated_statement
			       | If '('	expr ')' newline_opt terminated_statement
				    Else newline_opt unterminated_statement
			       | While '(' expr	')' newline_opt	unterminated_statement
			       | For '(' simple_statement_opt ';'
				expr_opt ';' simple_statement_opt ')' newline_opt
				    unterminated_statement
			       | For '(' NAME In NAME ')' newline_opt
				    unterminated_statement
			       ;

	      terminatable_statement : simple_statement
			       | Break
			       | Continue
			       | Next
			       | Exit expr_opt
			       | Return	expr_opt
			       | Do newline_opt	terminated_statement While '(' expr ')'
			       ;

	      simple_statement_opt : /*	empty */
			       | simple_statement
			       ;

	      simple_statement : Delete	NAME '[' expr_list ']'
			       | expr
			       | print_statement
			       ;

	      print_statement  : simple_print_statement
			       | simple_print_statement	output_redirection
			       ;

	      simple_print_statement : Print  print_expr_list_opt
			       | Print	'(' multiple_expr_list ')'
			       | Printf	print_expr_list
			       | Printf	'(' multiple_expr_list ')'
			       ;

	      output_redirection : '>'	  expr
			       | APPEND	expr
			       | '|'	expr
			       ;

	      expr_list_opt    : /* empty */
			       | expr_list
			       ;

	      expr_list	       : expr
			       | multiple_expr_list
			       ;

	      multiple_expr_list : expr	',' newline_opt	expr
			       | multiple_expr_list ','	newline_opt expr
			       ;

	      expr_opt	       : /* empty */
			       | expr
			       ;

	      expr	       : unary_expr
			       | non_unary_expr
			       ;

	      unary_expr       : '+' expr
			       | '-' expr
			       | unary_expr '^'	     expr
			       | unary_expr '*'	     expr
			       | unary_expr '/'	     expr
			       | unary_expr '%'	     expr
			       | unary_expr '+'	     expr
			       | unary_expr '-'	     expr
			       | unary_expr	     non_unary_expr
			       | unary_expr '<'	     expr
			       | unary_expr LE	     expr
			       | unary_expr NE	     expr
			       | unary_expr EQ	     expr
			       | unary_expr '>'	     expr
			       | unary_expr GE	     expr
			       | unary_expr '~'	     expr
			       | unary_expr NO_MATCH expr
			       | unary_expr In NAME
			       | unary_expr AND	newline_opt expr
			       | unary_expr OR	newline_opt expr
			       | unary_expr '?'	expr ':' expr
			       | unary_input_function
			       ;

	      non_unary_expr   : '(' expr ')'
			       | '!' expr
			       | non_unary_expr	'^'	 expr
			       | non_unary_expr	'*'	 expr
			       | non_unary_expr	'/'	 expr
			       | non_unary_expr	'%'	 expr
			       | non_unary_expr	'+'	 expr
			       | non_unary_expr	'-'	 expr
			       | non_unary_expr		 non_unary_expr
			       | non_unary_expr	'<'	 expr
			       | non_unary_expr	LE	 expr
			       | non_unary_expr	NE	 expr
			       | non_unary_expr	EQ	 expr
			       | non_unary_expr	'>'	 expr
			       | non_unary_expr	GE	 expr
			       | non_unary_expr	'~'	 expr
			       | non_unary_expr	NO_MATCH expr
			       | non_unary_expr	In NAME
			       | '(' multiple_expr_list	')' In NAME
			       | non_unary_expr	AND newline_opt	expr
			       | non_unary_expr	OR  newline_opt	expr
			       | non_unary_expr	'?' expr ':' expr
			       | NUMBER
			       | STRING
			       | lvalue
			       | ERE
			       | lvalue	INCR
			       | lvalue	DECR
			       | INCR lvalue
			       | DECR lvalue
			       | lvalue	POW_ASSIGN expr
			       | lvalue	MOD_ASSIGN expr
			       | lvalue	MUL_ASSIGN expr
			       | lvalue	DIV_ASSIGN expr
			       | lvalue	ADD_ASSIGN expr
			       | lvalue	SUB_ASSIGN expr
			       | lvalue	'=' expr
			       | FUNC_NAME '(' expr_list_opt ')'
				    /* no white	space allowed before '(' */
			       | BUILTIN_FUNC_NAME '(' expr_list_opt ')'
			       | BUILTIN_FUNC_NAME
			       | non_unary_input_function
			       ;

	      print_expr_list_opt : /* empty */
			       | print_expr_list
			       ;

	      print_expr_list  : print_expr
			       | print_expr_list ',' newline_opt print_expr
			       ;

	      print_expr       : unary_print_expr
			       | non_unary_print_expr
			       ;

	      unary_print_expr : '+' print_expr
			       | '-' print_expr
			       | unary_print_expr '^'	   print_expr
			       | unary_print_expr '*'	   print_expr
			       | unary_print_expr '/'	   print_expr
			       | unary_print_expr '%'	   print_expr
			       | unary_print_expr '+'	   print_expr
			       | unary_print_expr '-'	   print_expr
			       | unary_print_expr	   non_unary_print_expr
			       | unary_print_expr '~'	   print_expr
			       | unary_print_expr NO_MATCH print_expr
			       | unary_print_expr In NAME
			       | unary_print_expr AND newline_opt print_expr
			       | unary_print_expr OR  newline_opt print_expr
			       | unary_print_expr '?' print_expr ':' print_expr
			       ;

	      non_unary_print_expr : '(' expr ')'
			       | '!' print_expr
			       | non_unary_print_expr '^'      print_expr
			       | non_unary_print_expr '*'      print_expr
			       | non_unary_print_expr '/'      print_expr
			       | non_unary_print_expr '%'      print_expr
			       | non_unary_print_expr '+'      print_expr
			       | non_unary_print_expr '-'      print_expr
			       | non_unary_print_expr	       non_unary_print_expr
			       | non_unary_print_expr '~'      print_expr
			       | non_unary_print_expr NO_MATCH print_expr
			       | non_unary_print_expr In NAME
			       | '(' multiple_expr_list	')' In NAME
			       | non_unary_print_expr AND newline_opt print_expr
			       | non_unary_print_expr OR  newline_opt print_expr
			       | non_unary_print_expr '?' print_expr ':' print_expr
			       | NUMBER
			       | STRING
			       | lvalue
			       | ERE
			       | lvalue	INCR
			       | lvalue	DECR
			       | INCR lvalue
			       | DECR lvalue
			       | lvalue	POW_ASSIGN print_expr
			       | lvalue	MOD_ASSIGN print_expr
			       | lvalue	MUL_ASSIGN print_expr
			       | lvalue	DIV_ASSIGN print_expr
			       | lvalue	ADD_ASSIGN print_expr
			       | lvalue	SUB_ASSIGN print_expr
			       | lvalue	'=' print_expr
			       | FUNC_NAME '(' expr_list_opt ')'
				   /* no white space allowed before '('	*/
			       | BUILTIN_FUNC_NAME '(' expr_list_opt ')'
			       | BUILTIN_FUNC_NAME
			       ;

	      lvalue	       : NAME
			       | NAME '[' expr_list ']'
			       | '$' expr
			       ;

	      non_unary_input_function : simple_get
			       | simple_get '<'	expr
			       | non_unary_expr	'|' simple_get
			       ;

	      unary_input_function : unary_expr	'|' simple_get
			       ;

	      simple_get       : GETLINE
			       | GETLINE lvalue
			       ;

	      newline_opt      : /* empty */
			       | newline_opt NEWLINE
			       ;

       This grammar has	several	ambiguities that shall be resolved as follows:

	* Operator precedence and  associativity  shall	 be  as	 described  in
	  Expressions in Decreasing Precedence in awk .

	* In  case  of	ambiguity,  an	else shall be associated with the most
	  immediately preceding	if that	would satisfy the grammar.

	* In some contexts, a slash ( '/' ) that is used to  surround  an  ERE
	  could	 also be the division operator.	This shall be resolved in such
	  a way	that wherever the division operator could appear, a  slash  is
	  assumed  to  be  the	division operator. (There is no	unary division
	  operator.)

       One convention that might not be	obvious	from  the  formal  grammar  is
       where  <newline>s  are acceptable. There	are several obvious placements
       such as terminating a statement,	and a backslash	can be used to	escape
       <newline>s  between any lexical tokens. In addition, <newline>s without
       backslashes can follow a	comma, an open brace, logical AND  operator  (
       "&&" ), logical OR operator ( "||" ), the do keyword, the else keyword,
       and the closing parenthesis of an if,  for,  or	while  statement.  For
       example:

	      {	print  $1,
		       $2 }

   Lexical Conventions
       The lexical conventions for awk programs, with respect to the preceding
       grammar,	shall be as follows:

	1. Except as noted, awk	shall recognize	the longest possible token  or
	   delimiter beginning at a given point.

	2. A comment shall consist of any characters beginning with the	number
	   sign	character and terminated by, but excluding the next occurrence
	   of,	a  <newline>. Comments shall have no effect, except to delimit
	   lexical tokens.

	3. The <newline> shall be recognized as	the token NEWLINE.

	4. A backslash character immediately followed  by  a  <newline>	 shall
	   have	no effect.

	5. The	token  STRING shall represent a	string constant. A string con-
	   stant shall begin with the character	' .' Within a string constant,
	   a  backslash	 character  shall  be  considered  to  begin an	escape
	   sequence as specified in the	table in the Base  Definitions	volume
	   of  IEEE Std	1003.1-2001,  Chapter  5, File Format Notation ( '\\',
	   '\a', '\b', '\f', '\n', '\r', '\t', '\v' ). In addition, the	escape
	   sequences  in  Expressions in Decreasing Precedence in awk shall be
	   recognized. A <newline> shall not occur within a string constant. A
	   string  constant  shall be terminated by the	first unescaped	occur-
	   rence of the	character '' after the one that	begins the string con-
	   stant.  The	value  of  the	string	shall  be  the sequence	of all
	   unescaped characters	and values of escape  sequences	 between,  but
	   not including, the two delimiting ''	characters.

	6. The	token  ERE represents an extended regular expression constant.
	   An ERE constant shall begin with the	slash  character.   Within  an
	   ERE constant, a backslash character shall be	considered to begin an
	   escape sequence as specified	in the table in	the  Base  Definitions
	   volume of IEEE Std 1003.1-2001, Chapter 5, File Format Notation. In
	   addition, the escape	sequences in Expressions in Decreasing	Prece-
	   dence in awk	shall be recognized. The application shall ensure that
	   a <newline> does not	occur within an	ERE constant. An ERE  constant
	   shall  be terminated	by the first unescaped occurrence of the slash
	   character after the one that	begins the ERE constant. The  extended
	   regular  expression	represented  by	 the ERE constant shall	be the
	   sequence of all unescaped characters	and values of escape sequences
	   between, but	not including, the two delimiting slash	characters.

	7. A <blank> shall have	no effect, except to delimit lexical tokens or
	   within STRING or ERE	tokens.

	8. The token NUMBER shall represent a numeric constant.	Its  form  and
	   numeric value shall be equivalent to	either of the tokens floating-
	   constant or integer-constant	as specified by	 the  ISO C  standard,
	   with	the following exceptions:

	    a. An  integer  constant cannot begin with 0x or include the hexa-
	       decimal digits 'a', 'b',	'c', 'd', 'e',	'f',  'A',  'B',  'C',
	       'D', 'E', or 'F'	.

	    b. The  value  of  an  integer  constant beginning with 0 shall be
	       taken in	decimal	rather than octal.

	    c. An integer constant cannot include a suffix ( 'u', 'U', 'l', or
	       'L' ).

	    d. A floating constant cannot include a suffix ( 'f', 'F', 'l', or
	       'L' ).

       If the value is too large or too	small to be  representable  (see  Con-
       cepts Derived from the ISO C Standard ),	the behavior is	undefined.

	9. A  sequence of underscores, digits, and alphabetics from the	porta-
	   ble	character  set	 (see	the   Base   Definitions   volume   of
	   IEEE	Std 1003.1-2001,  Section 6.1, Portable	Character Set),	begin-
	   ning	with an	underscore or alphabetic, shall	be considered a	 word.

       10. The	following words	are keywords that shall	be recognized as indi-
	   vidual tokens; the name of the token	is the same as the keyword:

		  BEGIN	     delete   END    function	in	printf
		  break	     do	      exit   getline	next	return
		  continue   else     for    if		print	while

       11. The following words are names of built-in functions	and  shall  be
	   recognized as the token BUILTIN_FUNC_NAME:

		  atan2	  gsub	   log	   split     sub       toupper
		  close	  index	   match   sprintf   substr
		  cos	  int	   rand	   sqrt	     system
		  exp	  length   sin	   srand     tolower

       The  above-listed  keywords and names of	built-in functions are consid-
       ered reserved words.

       12. The token NAME shall	consist	of a word that is not a	keyword	 or  a
	   name	 of a built-in function	and is not followed immediately	(with-
	   out any delimiters) by the '(' character.

       13. The token FUNC_NAME shall consist of	a word that is not  a  keyword
	   or a	name of	a built-in function, followed immediately (without any
	   delimiters) by the '(' character. The '(' character	shall  not  be
	   included as part of the token.

       14. The	following  two-character  sequences shall be recognized	as the
	   named tokens:

		      Token Name   Sequence   Token Name   Sequence
		      ADD_ASSIGN   +=	      NO_MATCH	   !~
		      SUB_ASSIGN   -=	      EQ	   ==
		      MUL_ASSIGN   *=	      LE	   <=
		      DIV_ASSIGN   /=	      GE	   >=
		      MOD_ASSIGN   %=	      NE	   !=
		      POW_ASSIGN   ^=	      INCR	   ++
		      OR	   ||	      DECR	   --
		      AND	   &&	      APPEND	   >>

       15. The following single	characters shall be recognized as tokens whose
	   names are the character:

	   <newline> { } ( ) [ ] , ; + - * % ^ ! > < | ? : ~ $ =

       There  is  a lexical ambiguity between the token	ERE and	the tokens '/'
       and DIV_ASSIGN. When an input sequence begins with a slash character in
       any syntactic context where the token '/' or DIV_ASSIGN could appear as
       the next	token in a valid program, the longer of	those two tokens  that
       can  be	recognized shall be recognized.	In any other syntactic context
       where the token ERE could appear	as the next token in a valid  program,
       the token ERE shall be recognized.

EXIT STATUS
       The following exit values shall be returned:

	0     All input	files were processed successfully.

       >0     An error occurred.

       The  exit  status  can  be  altered within the program by using an exit
       expression.

CONSEQUENCES OF	ERRORS
       If any file operand is specified	and the	named file cannot be accessed,
       awk  shall  write  a diagnostic message to standard error and terminate
       without any further action.

       If the program specified	by either the program operand  or  a  progfile
       operand	is  not	 a  valid  awk	program	 (as specified in the EXTENDED
       DESCRIPTION section), the behavior is undefined.

       The following sections are informative.

APPLICATION USAGE
       The index, length, match, and substr functions should not  be  confused
       with  similar  functions	 in  the ISO C standard; the awk versions deal
       with characters,	while the ISO C	standard deals with bytes.

       Because the concatenation operation is represented by adjacent  expres-
       sions  rather  than  an explicit	operator, it is	often necessary	to use
       parentheses to enforce the proper evaluation precedence.

EXAMPLES
       The awk program specified in the	command	line is	most easily  specified
       within single-quotes (for example, programs commonly contain characters
       that are	special	to the shell, including	double-quotes.	In  the	 cases
       where  an  awk  program contains	single-quote characters, it is usually
       easiest to specify most of the program as strings within	 single-quotes
       concatenated  by	 the  shell  with  quoted single-quote characters. For
       example:

	      awk '/'\''/ { print "quote:", $0 }'

       prints all lines	from the  standard  input  containing  a  single-quote
       character, prefixed with	quote:.

       The following are examples of simple awk	programs:

	1. Write  to  the standard output all input lines for which field 3 is
	   greater than	5:

	   $3 >	5

	2. Write every tenth line:

	   (NR % 10) ==	0

	3. Write any line with a substring matching the	regular	expression:

	   /(G|D)(2[0-9][[:alpha:]]*)/

	4. Print any line with a substring containing a	'G' or	'D',  followed
	   by  a sequence of digits and	characters.  This example uses charac-
	   ter classes digit and alpha to match	language-independent digit and
	   alphabetic characters respectively:

	   /(G|D)([[:digit:][:alpha:]]*)/

	5. Write  any  line  in	 which	the  second  field matches the regular
	   expression and the fourth field does	not:

	   $2 ~	/xyz/ && $4 !~ /xyz/

	6. Write any line in which the second field contains a backslash:

	   $2 ~	/\\/

	7. Write any line in which the second field contains a backslash. Note
	   that	 backslash escapes are interpreted twice; once in lexical pro-
	   cessing of the string and once in processing	 the  regular  expres-
	   sion:

	   $2 ~	"\\\\"

	8. Write the second to the last	and the	last field in each line. Sepa-
	   rate	the fields by a	colon:

	   {OFS=":";print $(NF-1), $NF}

	9. Write the line number and number of fields in each line. The	 three
	   strings  representing the line number, the colon, and the number of
	   fields are concatenated and that string is written to standard out-
	   put:

	   {print NR ":" NF}

       10. Write lines longer than 72 characters:

	   length($0) >	72

       11. Write the first two fields in opposite order	separated by OFS:

	   { print $2, $1 }

       12. Same,  with	input  fields  separated  by  a	 comma or <space>s and
	   <tab>s, or both:

	   BEGIN { FS =	",[ \t]*|[ \t]+" }
		 { print $2, $1	}

       13. Add up the first column, print sum, and average:

		{s += $1 }
	   END	 {print	"sum is	", s, "	average	is", s/NR}

       14. Write fields	in reverse order, one per line	(many  lines  out  for
	   each	line in):

	   { for (i = NF; i > 0; --i) print $i }

       15. Write all lines between occurrences of the strings start and	stop:

	   /start/, /stop/

       16. Write  all  lines  whose first field	is different from the previous
	   one:

	   $1 != prev {	print; prev = $1 }

       17. Simulate echo:

	   BEGIN  {
		   for (i = 1; i < ARGC; ++i)
		   printf("%s%s", ARGV[i], i==ARGC-1?"\n":" ")
	   }

       18. Write the path prefixes contained in	the PATH environment variable,
	   one per line:

	   BEGIN  {
		   n = split (ENVIRON["PATH"], path, ":")
		   for (i = 1; i <= n; ++i)
		   print path[i]
	   }

       19. If there is a file named input containing page headers of the form:

	   Page	#

       and a file named	program	that contains:

	      /Page/   { $2 = n++; }
		       { print }

       then the	command	line:

	      awk -f program n=5 input

       prints the file input, filling in page numbers starting at 5.

RATIONALE
       This description	is based on the	new awk, "nawk", (see  the  referenced
       The  AWK	 Programming  Language), which introduced a number of new fea-
       tures to	the historical awk:

	1. New keywords: delete, do, function, return

	2. New built-in	functions: atan2, close, cos, gsub, match, rand,  sin,
	   srand, sub, system

	3. New predefined variables: FNR, ARGC,	ARGV, RSTART, RLENGTH, SUBSEP

	4. New expression operators: ?,	:, ,, ^

	5. The	FS  variable  and  the third argument to split,	now treated as
	   extended regular expressions.

	6. The operator	precedence, changed to more closely match the  C  lan-
	   guage.  Two examples	of code	that operate differently are:

	   while ( n /=	10 > 1)	...
	   if (!"wk" ~ /bwk/) ...

       Several features	have been added	based on newer implementations of awk:

	* Multiple instances of	-f progfile are	permitted.

	* The new option -v assignment.

	* The new predefined variable ENVIRON.

	* New built-in functions toupper and tolower.

	* More formatting capabilities are added to printf to match the	 ISO C
	  standard.

       The  overall awk	syntax has always been based on	the C language,	with a
       few features from the shell command language and	other sources. Because
       of this,	it is not completely compatible	with any other language, which
       has caused confusion for	some users.  It	is not the intent of the stan-
       dard developers to address such issues.	A few relatively minor changes
       toward making the language more compatible with the ISO C standard were
       made;  most  of	these  changes	are based on similar changes in	recent
       implementations,	as described above. There  remain  several  C-language
       conventions  that  are not in awk. One of the notable ones is the comma
       operator, which is commonly used	to specify multiple expressions	in the
       C  language  for	statement. Also, there are various places where	awk is
       more restrictive	than the C language regarding the type	of  expression
       that  can  be used in a given context. These limitations	are due	to the
       different features that the awk language	does provide.

       Regular expressions in awk have been extended somewhat from  historical
       implementations	to  make  them	a  pure	 superset  of extended regular
       expressions, as defined by IEEE Std 1003.1-2001 (see the	 Base  Defini-
       tions  volume  of  IEEE Std 1003.1-2001,	 Section 9.4, Extended Regular
       Expressions).  The main extensions  are	internationalization  features
       and  interval expressions.  Historical implementations of awk have long
       supported backslash escape sequences as an extension to extended	 regu-
       lar expressions,	and this extension has been retained despite inconsis-
       tency with other	utilities. The number of escape	 sequences  recognized
       in  both	extended regular expressions and strings has varied (generally
       increasing with time)  among  implementations.  The  set	 specified  by
       IEEE Std	1003.1-2001  includes  most sequences known to be supported by
       popular implementations and by the ISO C	standard. One sequence that is
       not  supported  is hexadecimal value escapes beginning with '\x'	. This
       would allow values expressed in more than 9 bits	to be used within  awk
       as in the ISO C standard. However, because this syntax has a non-deter-
       ministic	length,	it does	not permit the subsequent character  to	 be  a
       hexadecimal  digit. This	limitation can be dealt	with in	the C language
       by the use of lexical string concatenation. In the awk  language,  con-
       catenation  could  also be a solution for strings, but not for extended
       regular expressions (either lexical ERE tokens or strings used  dynami-
       cally  as regular expressions). Because of this limitation, the feature
       has not been added to IEEE Std 1003.1-2001.

       When a string variable is used in a context where an  extended  regular
       expression normally appears (where the lexical token ERE	is used	in the
       grammar)	the string does	not contain the	literal	slashes.

       Some versions of	awk allow the form:

	      func name(args, ... ) { statements }

       This has	been deprecated	by the authors of the language,	who asked that
       it not be specified.

       Historical  implementations of awk produce an error if a	next statement
       is executed in a	BEGIN action, and cause	awk to	terminate  if  a  next
       statement is executed in	an END action. This behavior has not been doc-
       umented,	and it was not believed	that it	was necessary  to  standardize
       it.

       The  specification  of conversions between string and numeric values is
       much more detailed than in the documentation of historical  implementa-
       tions or	in the referenced The AWK Programming Language.	 Although most
       of the behavior is designed to be intuitive, the	details	are  necessary
       to  ensure  compatible behavior from different implementations. This is
       especially important in relational expressions since the	types  of  the
       operands	determine whether a string or numeric comparison is performed.
       From the	perspective of an application writer, it is usually sufficient
       to  expect  intuitive behavior and to force conversions (by adding zero
       or concatenating	a null string) when the	type of	an expression does not
       obviously match what is needed. The intent has been to specify histori-
       cal practice in almost all cases. The one exception is that, in histor-
       ical  implementations, variables	and constants maintain both string and
       numeric values after their original value is converted by any use. This
       means  that referencing a variable or constant can have unexpected side
       effects.	For example, with  historical  implementations	the  following
       program:

	      {
		  a = "+2"
		  b = 2
		  if (NR % 2)
		      c	= a + b
		  if (a	== b)
		      print "numeric comparison"
		  else
		      print "string comparison"
	      }

       would  perform a	numeric	comparison (and	output numeric comparison) for
       each odd-numbered line, but perform a  string  comparison  (and	output
       string  comparison)  for	 each even-numbered line. IEEE Std 1003.1-2001
       ensures that comparisons	will be	numeric	if necessary. With  historical
       implementations,	the following program:

	      BEGIN {
		  OFMT = "%e"
		  print	3.14
		  OFMT = "%f"
		  print	3.14
	      }

       would  output  "3.140000e+00" twice, because in the second print	state-
       ment the	constant "3.14"	would have a string value  from	 the  previous
       conversion. IEEE	Std 1003.1-2001	requires that the output of the	second
       print statement be "3.140000" . The behavior of historical  implementa-
       tions was seen as too unintuitive and unpredictable.

       It  was	pointed	out that with the rules	contained in early drafts, the
       following script	would print nothing:

	      BEGIN {
		  y[1.5] = 1
		  OFMT = "%e"
		  print	y[1.5]
	      }

       Therefore, a new	variable, CONVFMT, was introduced. The	OFMT  variable
       is now restricted to affecting output conversions of numbers to strings
       and CONVFMT is used for internal	conversions, such  as  comparisons  or
       array  indexing.	 The  default  value  is the same as that for OFMT, so
       unless a	program	changes	CONVFMT	(which	no  historical	program	 would
       do),  it	 will receive the historical behavior associated with internal
       string conversions.

       The POSIX awk lexical and syntactic conventions are specified more for-
       mally  than in other sources. Again the intent has been to specify his-
       torical practice. One convention	that may not be	obvious	from the  for-
       mal  grammar  as	 in  other verbal descriptions is where	<newline>s are
       acceptable. There are several obvious placements	such as	terminating  a
       statement, and a	backslash can be used to escape	<newline>s between any
       lexical tokens. In addition, <newline>s without backslashes can	follow
       a  comma,  an open brace, a logical AND operator	( "&&" ), a logical OR
       operator	( "||" ), the do keyword, the else keyword,  and  the  closing
       parenthesis of an if, for, or while statement. For example:

	      {	print $1,
		      $2 }

       The  requirement	that awk add a trailing	<newline> to the program argu-
       ment text is to simplify	the grammar, making it match a	text  file  in
       form.  There  is	 no  way for an	application or test suite to determine
       whether a literal <newline> is added or whether awk simply acts	as  if
       it did.

       IEEE Std	1003.1-2001 requires several changes from historical implemen-
       tations in order	to support  internationalization.  Probably  the  most
       subtle  of  these is the	use of the decimal-point character, defined by
       the LC_NUMERIC category of the locale, in representations of  floating-
       point  numbers.	 This locale-specific character	is used	in recognizing
       numeric input, in converting between strings and	numeric	values,	and in
       formatting  output. However, regardless of locale, the period character
       (the decimal-point character of the POSIX locale) is the	 decimal-point
       character  recognized in	processing awk programs	(including assignments
       in command line arguments). This	is essentially the same	convention  as
       the  one	 used in the ISO C standard. The difference is that the	C lan-
       guage includes the setlocale() function,	which permits  an  application
       to  modify  its	locale.	 Because  of  this capability, a C application
       begins executing	with its locale	set to the C locale, and only executes
       in  the	environment-specified  locale after an explicit	call to	setlo-
       cale(). However,	adding such an elaborate new feature to	the  awk  lan-
       guage  was seen as inappropriate	for IEEE Std 1003.1-2001. It is	possi-
       ble to execute an awk program explicitly	in any desired locale by  set-
       ting the	environment in the shell.

       The  undefined behavior resulting from NULs in extended regular expres-
       sions allows future extensions for the  GNU  gawk  program  to  process
       binary data.

       The  behavior  in  the case of invalid awk programs (including lexical,
       syntactic, and semantic errors) is undefined because it was  considered
       overly  limiting	 on  implementations  to  specify.  In most cases such
       errors can be expected to produce a diagnostic and a non-zero exit sta-
       tus. However, some implementations may choose to	extend the language in
       ways that make use of certain invalid constructs.  Other	 invalid  con-
       structs	might  be deemed worthy	of a warning, but otherwise cause some
       reasonable behavior.  Still other constructs may	be very	 difficult  to
       detect  in some implementations.	 Also, different implementations might
       detect a	given error during an initial parsing of the  program  (before
       reading	any  input  files) while others	might detect it	when executing
       the program after reading some input. Implementors should be aware that
       diagnosing errors as early as possible and producing useful diagnostics
       can ease	debugging of applications, and	thus  make  an	implementation
       more usable.

       The  unspecified	 behavior  from	 using multi-character RS values is to
       allow possible future extensions	based on extended regular  expressions
       used  for  record separators. Historical	implementations	take the first
       character of the	string and ignore the others.

       Unspecified behavior when split(	string,	array, <null>) is used	is  to
       allow  a	proposed future	extension that would split up a	string into an
       array of	individual characters.

       In the context of the getline function, equally good arguments for dif-
       ferent  precedences  of	the  | and < operators can be made. Historical
       practice	has been that:

	      getline <	"a" "b"

       is parsed as:

	      (	getline	< "a" )	"b"

       although	many would argue that the intent was that the file  ab	should
       be read.	However:

	      getline <	"x" + 1

       parses as:

	      getline <	( "x" +	1 )

       Similar	problems  occur	with the | version of getline, particularly in
       combination with	$. For example:

	      $"echo hi" | getline

       (This situation is particularly problematic when	used in	a print	state-
       ment, where the |getline	part might be a	redirection of the print.)

       Since in	most cases such	constructs are not (or at least	should not) be
       used (because they have a natural ambiguity for which there is no  con-
       ventional  parsing),  the  meaning  of  these  constructs has been made
       explicitly unspecified. (The effect is that  a  conforming  application
       that runs into the problem must parenthesize to resolve the ambiguity.)
       There appeared to be few	if any actual uses of such constructs.

       Grammars	can be written that would cause	an error under	these  circum-
       stances.	  Where	 backwards-compatibility is not	a large	consideration,
       implementors may	wish to	use such grammars.

       Some historical implementations have allowed some built-in functions to
       be called without an argument list, the result being a default argument
       list chosen in some "reasonable"	way. Use of length as  a  synonym  for
       length($0)  is the only one of these forms that is thought to be	widely
       known or	widely used; this particular form  is  documented  in  various
       places  (for example, most historical awk reference pages, although not
       in the referenced The AWK Programming Language) as legitimate practice.
       With  this  exception,  default argument	lists have always been undocu-
       mented and vaguely defined, and it is not at all	clear how (or if) they
       should  be  generalized	to user-defined	functions.  They add no	useful
       functionality and preclude possible future extensions that  might  need
       to  name	 functions without calling them.  Not standardizing them seems
       the simplest course. The	standard  developers  considered  that	length
       merited special treatment, however, since it has	been documented	in the
       past and	sees possibly substantial use in historical programs.  Accord-
       ingly,  this  usage  has	 been made legitimate, but Issue 5 removed the
       obsolescent marking for XSI-conforming implementations and many	other-
       wise conforming applications depend on this feature.

       In  sub	and  gsub,  if	repl  is  a  string literal (the lexical token
       STRING),	then two consecutive backslash characters should  be  used  in
       the string to ensure a single backslash will precede the	ampersand when
       the resultant string is passed to the function. (For example, to	 spec-
       ify  one	 literal  ampersand  in	the replacement	string,	use gsub( ERE,
       "\\&" ).)

       Historically the	only special character in the repl argument of sub and
       gsub string functions was the ampersand ( '&' ) character and preceding
       it with the backslash character was used	to turn	off its	special	 mean-
       ing.

       The  description	 in  the ISO POSIX-2:1993 standard introduced behavior
       such that the backslash character was another special character and  it
       was  unspecified	 whether there were any	other special characters. This
       description introduced several portability problems, some of which  are
       described  below,  and so it has	been replaced with the more historical
       description. Some of the	problems include:

	* Historically,	to create the replacement string, a script  could  use
	  gsub(	 ERE, "\\&" ), but with	the ISO	POSIX-2:1993 standard wording,
	  it was necessary to use gsub(	ERE, "\\\\&" ).	 Backslash  characters
	  are  doubled here because all	string literals	are subject to lexical
	  analysis, which would	reduce each pair of backslash characters to  a
	  single backslash before being	passed to gsub.

	* Since	 it was	unspecified what the special characters	were, for por-
	  table	scripts	to guarantee that characters  are  printed  literally,
	  each	character had to be preceded with a backslash. (For example, a
	  portable script had to use  gsub(  ERE,  "\\h\\i"  )	to  produce  a
	  replacement string of	"hi" .)

       The  description	 for  comparisons in the ISO POSIX-2:1993 standard did
       not properly describe historical	practice because of  the  way  numeric
       strings	are compared as	numbers. The current rules cause the following
       code:

	      if (0 == "000")
		  print	"strange, but true"
	      else
		  print	"not true"

       to do a numeric comparison, causing the if to  succeed.	It  should  be
       intuitively  obvious  that  this	 is incorrect behavior,	and indeed, no
       historical implementation of awk	actually behaves this way.

       To fix this problem, the	definition of numeric string was  enhanced  to
       include	only those values obtained from	specific circumstances (mostly
       external	sources) where it is not possible to  determine	 unambiguously
       whether the value is intended to	be a string or a numeric.

       Variables  that	are assigned to	a numeric string shall also be treated
       as a numeric string. (For example, the notion of	a numeric  string  can
       be propagated across assignments.) In comparisons, all variables	having
       the uninitialized value are to be treated as a numeric operand evaluat-
       ing to the numeric value	zero.

       Uninitialized  variables	 include  all  types  of  variables  including
       scalars,	array elements,	and fields. The	definition of an uninitialized
       value  in  Variables and	Special	Variables is necessary to describe the
       value placed on uninitialized variables and on fields  that  are	 valid
       (for example, < $NF) but	have no	characters in them and to describe how
       these variables are to be used in comparisons. A	valid field,  such  as
       $1,  that has no	characters in it can be	obtained from an input line of
       "\t\t" when FS= '\t' . Historically, the	comparison ( $1<10)  was  done
       numerically after evaluating $1 to the value zero.

       The  phrase  "...  also	shall  have  the  numeric value	of the numeric
       string" was removed from	several	sections of the	ISO POSIX-2:1993 stan-
       dard  because  is specifies an unnecessary implementation detail. It is
       not necessary for IEEE Std 1003.1-2001 to specify that these objects be
       assigned	 two  different	 values.  It is	only necessary to specify that
       these objects may evaluate to two different values  depending  on  con-
       text.

       The  description	 of numeric string processing is based on the behavior
       of the atof() function in  the  ISO C  standard.	 While	it  is	not  a
       requirement for an implementation to use	this function, many historical
       implementations of awk do. In the ISO C standard,  floating-point  con-
       stants  use  a  period  as  a  decimal point character for the language
       itself, independent of the current locale, but the atof() function  and
       the associated strtod() function	use the	decimal	point character	of the
       current locale when converting strings to numeric values. Similarly  in
       awk, floating-point constants in	an awk script use a period independent
       of the locale, but input	strings	use the	decimal	point character	of the
       locale.

FUTURE DIRECTIONS
       None.

SEE ALSO
       Grammar	Conventions,  grep,  lex, sed, the System Interfaces volume of
       IEEE Std	1003.1-2001, atof(), exec, popen(), setlocale(), strtod()

COPYRIGHT
       Portions	of this	text are reprinted and reproduced in  electronic  form
       from IEEE Std 1003.1, 2003 Edition, Standard for	Information Technology
       -- Portable Operating System Interface (POSIX),	The  Open  Group  Base
       Specifications  Issue  6,  Copyright  (C) 2001-2003 by the Institute of
       Electrical and Electronics Engineers, Inc and The Open  Group.  In  the
       event of	any discrepancy	between	this version and the original IEEE and
       The Open	Group Standard,	the original IEEE and The Open Group  Standard
       is  the	referee	document. The original Standard	can be obtained	online
       at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group		     2003			       AWK(1P)

PROLOG | NAME | SYNOPSIS | DESCRIPTION | OPTIONS | OPERANDS | STDIN | INPUT FILES | ENVIRONMENT VARIABLES | ASYNCHRONOUS EVENTS | STDOUT | STDERR | OUTPUT FILES | EXTENDED DESCRIPTION | EXIT STATUS | CONSEQUENCES OF ERRORS | APPLICATION USAGE | EXAMPLES | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

Want to link to this manual page? Use this URL:
<https://www.freebsd.org/cgi/man.cgi?query=awk&manpath=SuSE+Linux%2fi386+11.3>

home | help