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BSD 2.11 - man page for awk (bsd section 1)

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AWK(1)											   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 associated 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 appropri-
       ate, 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 initial-
       ized  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  for-
       mat (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
       substring 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.
       Regular 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 conditional  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  sepa-
       rator (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 lan-
       guage

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)
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