AWK(1)							      General Commands Manual							    AWK(1)

NAME

       awk - pattern scanning and processing language

SYNOPSIS

       awk [ -Fc ] [ prog ] [ file ] ...

DESCRIPTION

       Awk scans each input file for lines that match any of a set of patterns specified in prog.  With each pattern in prog there can be an asso-
       ciated action that will be performed when a line of a file matches the pattern.	The set of patterns may appear literally as prog, or in  a
       file specified as -f file.

       Files  are  read  in  order;  if there are no files, the standard input is read.  The file name `-' means the standard input.  Each line is
       matched against the pattern portion of every pattern-action statement; the associated action is performed for each matched pattern.

       An input line is made up of fields separated by white space.  (This default can be changed by  using  FS,  vide	infra.)   The  fields  are
       denoted $1, $2, ... ; $0 refers to the entire line.

       A pattern-action statement has the form

	    pattern { action }

       A missing { action } means print the line; a missing pattern always matches.

       An action is a sequence of statements.  A statement can be one of the following:

	    if ( conditional ) statement [ else statement ]
	    while ( conditional ) statement
	    for ( expression ; conditional ; expression ) statement
	    break
	    continue
	    { [ statement ] ... }
	    variable = expression
	    print [ expression-list ] [ >expression ]
	    printf format [ , expression-list ] [ >expression ]
	    next # skip remaining patterns on this input line
	    exit # skip the rest of the input

       Statements  are	terminated by semicolons, newlines or right braces.  An empty expression-list stands for the whole line.  Expressions take
       on string or numeric values as appropriate, and are built using the operators +, -, *, /, %,  and concatenation	(indicated  by	a  blank).
       The  C operators ++, --, +=, -=, *=, /=, and %= are also available in expressions.  Variables may be scalars, array elements (denoted x[i])
       or fields.  Variables are initialized to the null string.  Array subscripts may be any string, not necessarily numeric; this allows  for  a
       form of associative memory.  String constants are quoted "...".

       The  print  statement prints its arguments on the standard output (or on a file if >file is present), separated by the current output field
       separator, and terminated by the output record separator.  The printf statement formats its expression list according to  the  format  (see
       printf(3S)).

       The  built-in  function	length	returns the length of its argument taken as a string, or of the whole line if no argument.  There are also
       built-in functions exp, log, sqrt, and int.  The last truncates its argument to an integer.  substr(s, m, n) returns the  n-character  sub-
       string  of  s  that  begins at position m.  The function sprintf(fmt, expr, expr, ...)  formats the expressions according to the printf(3S)
       format given by fmt and returns the resulting string.

       Patterns are arbitrary Boolean combinations (!, ||, &&, and parentheses)  of  regular  expressions  and	relational  expressions.   Regular
       expressions  must be surrounded by slashes and are as in egrep.	Isolated regular expressions in a pattern apply to the entire line.  Regu-
       lar expressions may also occur in relational expressions.

       A pattern may consist of two patterns separated by a comma; in this case, the action is performed for all lines between	an  occurrence	of
       the first pattern and the next occurrence of the second.

       A relational expression is one of the following:

	    expression matchop regular-expression
	    expression relop expression

       where a relop is any of the six relational operators in C, and a matchop is either ~ (for contains) or !~ (for does not contain).  A condi-
       tional is an arithmetic expression, a relational expression, or a Boolean combination of these.

       The special patterns BEGIN and END may be used to capture control before the first input line is read and after the last.   BEGIN  must	be
       the first pattern, END the last.

       A single character c may be used to separate the fields by starting the program with

	    BEGIN { FS = "c" }

       or by using the -Fc option.

       Other  variable	names  with special meanings include NF, the number of fields in the current record; NR, the ordinal number of the current
       record; FILENAME, the name of the current input file; OFS, the output field separator (default blank); ORS,  the  output  record  separator
       (default newline); and OFMT, the output format for numbers (default "%.6g").

EXAMPLES

       Print lines longer than 72 characters:

	    length > 72

       Print first two fields in opposite order:

	    { print $2, $1 }

       Add up first column, print sum and average:

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

       Print fields in reverse order:

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

       Print all lines between start/stop pairs:

	    /start/, /stop/

       Print all lines whose first field is different from previous one:

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

SEE ALSO

       lex(1), sed(1)
       A. V. Aho, B. W. Kernighan, P. J. Weinberger, Awk - a pattern scanning and processing language

BUGS

       There  are  no explicit conversions between numbers and strings.  To force an expression to be treated as a number add 0 to it; to force it
       to be treated as a string concatenate "" to it.

7th Edition							  April 29, 1985							    AWK(1)