AWK(1)							      General Commands Manual							    AWK(1)

NAME

       awk - pattern-directed scanning and processing language

SYNOPSIS

       awk [ -Ffs ] [ -v var=value ] [ -mrn ] [ -mfn ] [ -f prog [ prog ] [ file ...  ]

DESCRIPTION

       Awk scans each input file for lines that match any of a set of patterns specified literally in prog or in one or more files specified as -f
       file.  With each pattern there can be an associated action that will be performed when a line of a file matches the pattern.  Each line	is
       matched	against  the  pattern portion of every pattern-action statement; the associated action is performed for each matched pattern.  The
       file name means the standard input.  Any file of the form var=value is treated as an assignment, not a file name, and is  executed  at  the
       time it would have been opened if it were a file name.  The option -v followed by var=value is an assignment to be done before prog is exe-
       cuted; any number of -v options may be present.

       An input line is normally made up of fields separated by white space, or by regular expression fs.  The fields are  denoted  $1,  $2,  ...,
       while $0 refers to the entire line.

       To  compensate for inadequate implementation of storage management, the -mr option can be used to set the maximum size of the input record,
       and the -mf option to set the maximum number of fields.

       A pattern-action statement has the form

	      pattern { action }

       A missing { action } means print the line; a missing pattern always matches.  Pattern-action statements are separated by newlines or  semi-
       colons.

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

       if( expression ) statement [ else statement ]
       while( expression ) statement
       for( expression ; expression ; expression ) statement
       for( var in array ) statement
       do statement while( expression )
       break
       continue
       { [ statement ... ] }
       expression	       # commonly var = expression
       print [ expression-list ] [ > expression ]
       printf format [ , expression-list ] [ > expression ]
       return [ expression ]
       next		       # skip remaining patterns on this input line
       delete array[ expression ]# delete an array element
       exit [ expression ]     # exit immediately; status is expression

       Statements  are	terminated  by semicolons, newlines or right braces.  An empty expression-list stands for $0.  String constants are quoted
       " ", with the usual C escapes recognized within.  Expressions take on string or numeric values as appropriate,  and  are  built	using  the
       operators + - * / % ^ (exponentiation), and concatenation (indicated by white space).  The operators ! ++ -- += -= *= /= %= ^= > >= < <= ==
       != ?: 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.  Multiple sub-
       scripts such as [i,j,k] are permitted; the constituents are concatenated, separated by the value of SUBSEP.

       The print statement prints its arguments on the standard output (or on a file if >file or >>file is  present  or  on  a	pipe  if  |cmd	is
       present),  separated  by  the  current  output field separator, and terminated by the output record separator.  file and cmd may be literal
       names or parenthesized expressions; identical string values in different statements denote the same open file.  The printf  statement  for-
       mats its expression list according to the format (see fprintf(2)).  The built-in function close(expr) closes the file or pipe expr.

       The mathematical functions exp, log, sqrt, sin, cos, and atan2 are built in.  Other built-in functions:

       length the length of its argument taken as a string, or of $0 if no argument.

       rand   random number on (0,1)

       srand  sets seed for rand and returns the previous seed.

       int    truncates to an integer value

       utf    converts its numerical argument, a character number, to a UTF string

       substr(s, m, n)
	      the n-character substring of s that begins at position m counted from 1.

       index(s, t)
	      the position in s where the string t occurs, or 0 if it does not.

       match(s, r)
	      the position in s where the regular expression r occurs, or 0 if it does not.  The variables RSTART and RLENGTH are set to the posi-
	      tion and length of the matched string.

       split(s, a, fs)
	      splits the string s into array elements a[1], a[2], ..., a[n], and returns n.  The separation is done with the regular expression fs
	      or with the field separator FS if fs is not given.

       sub(r, t, s)
	      substitutes t for the first occurrence of the regular expression r in the string s.  If s is not given, $0 is used.

       gsub   same as sub except that all occurrences of the regular expression are replaced; sub and gsub return the number of replacements.

       sprintf(fmt, expr, ...)
	      the string resulting from formatting expr ...  according to the printf format fmt

       system(cmd)
	      executes cmd and returns its exit status

       The  ``function'' getline sets $0 to the next input record from the current input file; getline <file sets $0 to the next record from file.
       getline x sets variable x instead.  Finally, cmd | getline pipes the output of cmd into getline; each call of getline returns the next line
       of output from cmd.  In all cases, getline returns 1 for a successful input, 0 for end of file, and -1 for an error.

       Patterns  are  arbitrary Boolean combinations (with ! || &&) of regular expressions and relational expressions.	Regular expressions are as
       in regexp(6).  Isolated regular expressions in a pattern apply to the entire line.   Regular  expressions  may  also  occur  in	relational
       expressions, using the operators ~ and !~.  /re/ is a constant regular expression; any string (constant or variable) may be used as a regu-
       lar expression, except in the position of an isolated regular expression in a pattern.

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

       A relational expression is one of the following:

	      expression matchop regular-expression
	      expression relop expression
	      expression in array-name
	      (expr,expr,...) in array-name

       where a relop is any of the six relational operators in C, and a matchop is either ~ (matches) or !~ (does not match).  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 and END do
       not combine with other patterns.

       Variable names with special meanings:

       FS     regular expression used to separate fields; also settable by option -Ffs.

       NF     number of fields in the current record

       NR     ordinal number of the current record

       FNR    ordinal number of the current record in the current file

       FILENAME
	      the name of the current input file

       RS     input record separator (default newline)

       OFS    output field separator (default blank)

       ORS    output record separator (default newline)

       OFMT   output format for numbers (default %.6g)

       SUBSEP separates multiple subscripts (default 034)

       ARGC   argument count, assignable

       ARGV   argument array, assignable; non-null members are taken as file names

       ENVIRON
	      array of environment variables; subscripts are names.

       Functions may be defined (at the position of a pattern-action statement) thus:

	      function foo(a, b, c) { ...; return x }

       Parameters  are passed by value if scalar and by reference if array name; functions may be called recursively.  Parameters are local to the
       function; all other variables are global.  Thus local variables may be created by providing excess parameters in the function definition.

EXAMPLES

       length > 72
	      Print lines longer than 72 characters.

       { print $2, $1 }
	      Print first two fields in opposite order.

       BEGIN { FS = ",[ 	]*|[ 	]+" }
	     { print $2, $1 }
	      Same, with input fields separated by comma and/or blanks and tabs.

	    { s += $1 }
       END  { print "sum is", s, " average is", s/NR }
	      Add up first column, print sum and average.

       /start/, /stop/
	      Print all lines between start/stop pairs.

       BEGIN	 {    # Simulate echo(1)
	    for (i = 1; i < ARGC; i++) printf "%s ", ARGV[i]
	    printf "
"
	    exit }

SOURCE

       /sys/src/cmd/awk

SEE ALSO

       sed(1), regexp(6),
       A. V. Aho, B. W. Kernighan, P. J. Weinberger, The AWK Programming Language, Addison-Wesley, 1988.

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.
       The scope rules for variables in functions are a botch; the syntax is worse.

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