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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 sepstring] [−v assignment]... program [argument...]

       awk [−F sepstring] −f progfile [−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> non-<new‐
       line> characters. This default <blank> and  <newline>  field  delimiter
       can  be	changed	 by using the FS built-in variable or the −F sepstring
       option. 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-evaluation of $0. Assign‐
       ing  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
       POSIX.1‐2008, Section 12.2, Utility Syntax Guidelines.

       The following options shall be supported:

       −F sepstring
		 Define the input field separator. This option shall be equiv‐
		 alent to:

		     -v FS=sepstring

		 except that if −F sepstring  and  −v  FS=sepstring  are  both
		 used,	it  is unspecified whether the FS assignment resulting
		 from −F sepstring is processed in command line	 order	or  is
		 processed  after  the last −v FS=sepstring.  See the descrip‐
		 tion of the FS built-in variable, and how it is used, in  the
		 EXTENDED DESCRIPTION section.

       −f progfile
		 Specify  the  pathname of the file progfile containing an awk
		 program. A pathname of '−' shall denote the  standard	input.
		 If  multiple instances of this option are specified, the con‐
		 catenation of the files specified as progfile	in  the	 order
		 specified  shall  be  the  awk	 program.  The awk program can
		 alternatively 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 speci‐
		 fied.

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	inter‐
		 mixed:

		 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 character from  the  portable  character
			   set	(see  the table in the Base Definitions volume
			   of POSIX.1‐2008, Section  6.1,  Portable  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 char‐
			   acters following the <equals-sign> shall be	inter‐
			   preted  as if they appeared in the awk program pre‐
			   ceded and followed by a double-quote ('"')  charac‐
			   ter,	 as  a STRING token (see Grammar), except that
			   if the last character is an unescaped  <backslash>,
			   it  shall  be  interpreted 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 assignment 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,
			   assignments 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 '−', or if a progfile option-argument  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	 vari‐
		 ables	that are unset or null. (See the Base Definitions vol‐
		 ume of POSIX.1‐2008, 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	 regu‐
		 lar 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 val‐
		 ues, 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 process‐
		 ing awk programs (including assignments in command line argu‐
		 ments).

       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 Def‐
		 initions volume of POSIX.1‐2008, Chapter 8, Environment Vari‐
		 ables.

       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 expres‐
       sions is given in Grammar.

	       Table 4-1: 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 ++		 │Post-increment	   │Numeric	    │N/A	   │
   │lvalue −−		 │Post-decrement	   │Numeric	    │N/A	   │
   ├─────────────────────┼─────────────────────────┼────────────────┼──────────────┤
   │++ lvalue		 │Pre-increment		   │Numeric	    │N/A	   │
   │−− lvalue		 │Pre-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 either by the equivalent of  the  following  calls	 to  functions
       defined by the ISO C standard:

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

       or  by converting the initial portion of the string to type double rep‐
       resentation as follows:

	      The input string is decomposed into two parts: an initial,  pos‐
	      sibly empty, sequence of white-space characters (as specified by
	      isspace()) and a subject sequence	 interpreted  as  a  floating-
	      point constant.

	      The  expected form of the subject sequence is an optional '+' or
	      '−' sign, then a non-empty sequence of  digits  optionally  con‐
	      taining  a <period>, then an optional exponent part. An exponent
	      part consists of 'e' or 'E', followed by an optional sign,  fol‐
	      lowed by one or more decimal digits.

	      The  sequence  starting  with  the  first	 digit or the <period>
	      (whichever occurs first) is interpreted as a  floating  constant
	      of  the  C  language,  and  if  neither  an  exponent part nor a
	      <period> appears, a <period> is assumed to follow the last digit
	      in the string. If the subject sequence begins with a minus-sign,
	      the value resulting from the conversion is negated.

       A numeric value that is exactly equal to the value of an	 integer  (see
       Section	1.1.2, Concepts Derived from the ISO C Standard) shall be con‐
       verted 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 POSIX.1‐2008 specifies no explicit conversions	 between  num‐
       bers  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 an implementation-dependent condition corresponding to either  case
       (a) or (b) below is met.

	a. After the equivalent of the following calls to functions defined by
	   the	 ISO C	 standard,   string_value_end	would	differ	  from
	   string_value,  and any characters before the terminating null char‐
	   acter in string_value_end would be <blank> characters:

	       char *string_value_end;
	       setlocale(LC_NUMERIC, "");
	       numeric_value = strtod (string_value, &string_value_end);

	b. 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> characters are discarded.

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

	   --  Each occurrence of the decimal point character from the current
	       locale is changed to a <period>.
       In  case (a) the numeric value of the numeric string shall be the value
       that would be returned by the strtod() call. In case (b) if  the	 first
       non-<blank>  is	'−',  the numeric value of the numeric string shall be
       the negation of the numeric value of the recognized NUMBER token;  oth‐
       erwise,	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 Section 1.1.2, 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 equivalent:

	   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.	Other‐
       wise,  operands	shall be converted to strings as required and a string
       comparison 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 unini‐
       tialized 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 standard 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 Inter‐
		 faces volume of POSIX.1‐2008. The indices of the array	 shall
		 be  strings  consisting of the names of the environment vari‐
		 ables, 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	 envi‐
		 ronment  variables (including the environment of any commands
		 that awk executes via the system  function  or	 via  pipeline
		 redirections  with the print statement, the printf statement,
		 or the getline function), the environment used shall  be  the
		 environment  at the time awk began executing; it is implemen‐
		 tation-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 with‐
		 out 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 processed.

       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  separator;  <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  con‐
		 tains	more  than one character, the results are unspecified.
		 If RS is null, then records are separated by  sequences  con‐
		 sisting  of a <newline> 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
		 function, 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 POSIX.1‐2008, 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
       POSIX.1‐2008,  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> characters  and	string
       constants  can  contain <newline> characters, 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 4-2: 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 is    │
 │	   │ by the longest sequence of one,	│ represented by the one, two, or    │
 │	   │ two, or three octal-digit charac‐	│ three-digit octal integer. Multi-  │
 │	   │ ters (01234567). If all of the	│ byte characters require multiple,  │
 │	   │ digits are 0 (that is, representa‐ │ concatenated escape sequences of   │
 │	   │ tion of the NUL character), the	│ this type, including the leading   │
 │	   │ behavior is undefined.		│ <backslash> for 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		│				     │
 │	   │ POSIX.1‐2008, Chapter 5, File For‐ │				     │
 │	   │ mat 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  POSIX.1‐2008,	 Section  9.1,
       Regular Expression Definitions, where a match occurs on any part of the
       string unless the regular expression is limited with  the  <circumflex>
       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
       assigning a string containing the expression to the  built-in  variable
       FS,  either  directly  or  as  a	 consequence of using the −F sepstring
       option.	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> and <new‐
	       line> characters; fields shall be delimited by sets of  one  or
	       more <blank> or <newline> characters.

	    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> charac‐
       ters embedded 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 appropri‐
       ate pattern shall match any character. However, in all awk  ERE	match‐
       ing,  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 curly braces. The application shall  ensure  that  statements	 in  a
       statement  list	are  separated by <newline> or <semicolon> characters.
       Statements in a statement 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 Section 1.1.2, Concepts Derived from
       the ISO C Standard), 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 POSIX.1‐2008 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 POSIX.1‐2008.

       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	POSIX.1‐2008 (see the Base Definitions volume of POSIX.1‐2008,
       Chapter 5, File Format Notation).  Output shall be produced  as	speci‐
       fied with the first expression argument as the string format and subse‐
       quent 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
	   lexically 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> characters not spec‐
	   ified 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 Section 1.1.2, 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	 indi‐
       cated  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 [−π,π].

       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  indicated  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	speci‐
		 fied.

       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 cre‐
		 ated and, if appropriate, the array element shall be  consid‐
		 ered  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  number  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 <back‐
		 slash> shall be interpreted as the literal <ampersand>	 char‐
		 acter.	 An  occurrence of two consecutive <backslash> charac‐
		 ters shall be interpreted as just  a  single  literal	<back‐
		 slash>	 character. Any other occurrence of a <backslash> (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 pro‐
		 cessing, including any	 lexical  <backslash>-escape  sequence
		 processing.  If  in is specified and it is not an lvalue (see
		 Expressions 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 speci‐
		 fies  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  map‐
		 ping  by the LC_CTYPE category of the current locale shall be
		 replaced in the returned string by the lowercase letter spec‐
		 ified	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 map‐
		 ping by the  LC_CTYPE	category  of  the  current  locale  is
		 replaced in the returned string by the uppercase letter spec‐
		 ified by the mapping. 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
		 implementation-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 cur‐
		 rently 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 evaluates to the same string value shall read sub‐
		 sequent records from the stream. The stream shall remain open
		 until	the  close  function 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  contain‐
		 ing  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 get‐
		 line shall set the FNR and NR variables.

       getline [var] < expression
		 Read the next record of input from a named file. The  expres‐
		 sion shall be evaluated to produce a string that is used as a
		 pathname.  If the file of that name is not currently open, it
		 shall	be  opened. As long as the stream remains open, subse‐
		 quent 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 con‐
		 taining  the  getline).  The result of evaluating such a con‐
		 struct is  unspecified,  and  conforming  applications	 shall
		 parenthesize properly all such usages.

       system(expression)
		 Execute  the  command given by expression in a manner equiva‐
		 lent to the system() function defined in  the	System	Inter‐
		 faces	volume	of  POSIX.1‐2008 and return the exit status of
		 the command.

       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>  characters,  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>  characters shall be optional
       before the opening brace and after the closing brace. Function  defini‐
       tions 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  Section
       1.3,  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 Ta‐
	   ble 4-1, 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.)

       Each  expression	 in an awk program shall conform to the precedence and
       associativity rules, even when this is not needed to resolve an ambigu‐
       ity.  For  example,  because  '$'  has higher precedence than '++', the
       string "$x++−−" is not a valid awk expression, even though it is	 unam‐
       biguously parsed by the grammar as "$(x++)−−".

       One  convention	that  might  not be obvious from the formal grammar is
       where <newline> characters are acceptable. There	 are  several  obvious
       placements  such	 as  terminating a statement, and a <backslash> can be
       used to escape <newline> characters  between  any  lexical  tokens.  In
       addition,  <newline> characters without <backslash> characters can fol‐
       low 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	 <num‐
	   ber-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 con‐
	   stant, a <backslash> character shall	 be  considered	 to  begin  an
	   escape  sequence  as specified in the table in the Base Definitions
	   volume of POSIX.1‐2008, Chapter  5,	File  Format  Notation	('\\',
	   '\a', '\b', '\f', '\n', '\r', '\t', '\v').  In addition, the escape
	   sequences in Table 4-2, Escape Sequences in	awk  shall  be	recog‐
	   nized.  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
	   constant. 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 Defini‐
	   tions volume of POSIX.1‐2008, Chapter 5, File Format Notation.   In
	   addition,  the  escape  sequences in Table 4-2, Escape Sequences in
	   awk shall be recognized. The application shall ensure that a	 <new‐
	   line>  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 either be equivalent to	the  decimal-floating-
	   constant token as specified by the ISO C standard, or it shall be a
	   sequence of decimal digits and shall be  evaluated  as  an  integer
	   constant  in	 decimal.  In  addition,  implementations  may	accept
	   numeric constants with the form and numeric value equivalent to the
	   hexadecimal-constant	 and  hexadecimal-floating-constant  tokens as
	   specified by the ISO C standard.

	   If the value is too large or too small  to  be  representable  (see
	   Section  1.1.2,  Concepts  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 POSIX.1‐2008,
	   Section 6.1, Portable Character Set),  beginning  with  an  <under‐
	   score> or alphabetic character, 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 con‐
	   sidered 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 con‐
       text where the token ERE could appear as the next token in a valid pro‐
       gram, 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, 'program') for applications using
       sh, because awk programs commonly contain characters that  are  special
       to  the	shell, including double-quotes. In the cases where an awk pro‐
       gram 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 character
	   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 lexi‐
	   cal processing of the string and once  in  processing  the  regular
	   expression:

	       $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
	   output:

	       {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> and <tab>
	   characters, 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 expres‐
       sions 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 POSIX.1‐2008 (see the Base Definitions vol‐
       ume of POSIX.1‐2008, Section 9.4, Extended Regular  Expressions).   The
       main  extensions are internationalization features and interval expres‐
       sions. Historical implementations of awk	 have  long  supported	<back‐
       slash>-escape  sequences	 as  an	 extension to extended regular expres‐
       sions, and this extension has been retained despite inconsistency  with
       other  utilities.  The  number  of  escape sequences recognized in both
       extended regular expressions and strings has varied (generally increas‐
       ing with time) among implementations. The set specified by POSIX.1‐2008
       includes most sequences known to be supported  by  popular  implementa‐
       tions  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-deterministic  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 lexi‐
       cal string concatenation. In the awk language, concatenation could also
       be a solution for strings, but not  for	extended  regular  expressions
       (either	lexical	 ERE  tokens  or  strings  used dynamically as regular
       expressions). Because of this limitation,  the  feature	has  not  been
       added to POSIX.1‐2008.

       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 <slash> characters.

       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 developer, it is usually suffi‐
       cient 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
       historical  practice in almost all cases. The one exception is that, in
       historical  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.	 POSIX.1‐2008  ensures
       that  comparisons  will be numeric if necessary. With historical imple‐
       mentations, 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. POSIX.1‐2008 requires that the output of the	 second	 print
       statement  be  "3.140000".   The behavior of historical implementations
       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>  charac‐
       ters  are acceptable. There are several obvious placements such as ter‐
       minating a statement, and a <backslash> can be used to escape <newline>
       characters  between  any lexical tokens. In addition, <newline> charac‐
       ters without <backslash> characters 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.

       POSIX.1‐2008  requires  several changes from historical implementations
       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 format‐
       ting output. However, regardless of locale, the <period> character (the
       decimal-point character of the POSIX locale) is the decimal-point char‐
       acter  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 language
       includes the setlocale() function, which permits an application to mod‐
       ify its locale. Because of this capability, a C application begins exe‐
       cuting with its locale set to the C locale, and only  executes  in  the
       environment-specified  locale  after  an	 explicit call to setlocale().
       However, adding such an elaborate new feature to the awk	 language  was
       seen  as	 inappropriate	for POSIX.1‐2008. It is possible to execute an
       awk program explicitly in any desired locale by setting 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
       specify	 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 pre‐
       ceding it with the <backslash> character was used to turn off its  spe‐
       cial meaning.

       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 histori‐
       cal 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, "\\\\&").	The <backslash>	 char‐
	   acters  are doubled here because all string literals are subject to
	   lexical analysis, which would reduce each pair of <backslash> char‐
	   acters 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 exam‐
	   ple, 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
       standard	 because is specifies an unnecessary implementation detail. It
       is not necessary for POSIX.1‐2008 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.

       Historical  implementations of awk did not parse hexadecimal integer or
       floating constants like "0xa" and "0xap0".  Due to  an  oversight,  the
       2001  through 2004 editions of this standard required support for hexa‐
       decimal floating constants. This was due to the	reference  to  atof().
       This  version  of  the standard allows but does not require implementa‐
       tions to use atof() and includes a description  of  how	floating-point
       numbers	are  recognized	 as an alternative to match historic behavior.
       The intent of this change is  to	 allow	implementations	 to  recognize
       floating-point  constants  according  to	 either	 the ISO/IEC 9899:1990
       standard or ISO/IEC 9899:1999 standard, and to allow (but not  require)
       implementations to recognize hexadecimal integer constants.

       Historical  implementations  of	awk  did  not  support	floating-point
       infinities and NaNs in numeric strings; e.g., "−INF" and	 "NaN".	  How‐
       ever,  implementations  that use the atof() or strtod() functions to do
       the conversion picked up support	 for  these  values  if	 they  used  a
       ISO/IEC 9899:1999  standard  version  of	 the  function	instead	 of  a
       ISO/IEC 9899:1990 standard version.  Due	 to  an	 oversight,  the  2001
       through	2004  editions	of  this  standard  did	 not allow support for
       infinities and NaNs, but in this revision support is allowed  (but  not
       required). This is a silent change to the behavior of awk programs; for
       example, in the POSIX locale the expression:

	   ("-INF" + 0 < 0)

       formerly had the value 0 because "−INF" converted to 0, but now it  may
       have the value 0 or 1.

FUTURE DIRECTIONS
       None.

SEE ALSO
       Section 1.3, Grammar Conventions, grep, lex, sed

       The  Base  Definitions  volume  of POSIX.1‐2008, Chapter 5, File Format
       Notation, Section 6.1, Portable Character Set, Chapter  8,  Environment
       Variables, Chapter 9, Regular Expressions, Section 12.2, Utility Syntax
       Guidelines

       The System Interfaces volume of POSIX.1‐2008, atof(), exec,  isspace(),
       popen(), setlocale(), strtod()

COPYRIGHT
       Portions	 of  this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       --  Portable  Operating	System	Interface (POSIX), The Open Group Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
       cal  and	 Electronics  Engineers,  Inc  and  The	 Open Group.  (This is
       POSIX.1-2008 with the 2013 Technical Corrigendum	 1  applied.)  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.unix.org/online.html .

       Any typographical or formatting errors that appear  in  this  page  are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors,	 see  https://www.ker‐
       nel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group		     2013			       AWK(1P)
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