FreeBSD Man Pages

awk(1)

NAME

       awk - pattern-directed scanning and processing language

SYNOPSIS

       awk [ -F fs ] [ -v var=value ] [ 'prog' | -f progfile ] [ 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
       progfile.   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 state-
       ment; 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 filename, and  is  executed  at  the
       time  it  would	have been opened if it were a filename.  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.  The -F fs option
       defines the input field separator to be the regular expression fs.

       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.  If FS is null, the input line  is  split
       into one field per character.

       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
	      nextfile		      # skip rest of this file, open next, start at top
	      delete array[ expression ]# delete an array element
	      delete array	      # delete all elements of array
	      exit [ expression ]     # exit immediately; status is expression
       (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 subscripts 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	paren-
       thesized  expressions;  identical string values in different statements
       denote the same open file.  The printf statement formats its expression
       list  according	to  the format (see printf(3)).  The built-in function
       close(expr) closes the  file  or  pipe  expr.   The  built-in  function
       fflush(expr) flushes any buffered output for 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

       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
	      position 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  expres-
	      sion  fs	or with the field separator FS if fs is not given.  An
	      empty string as field separator splits the string into one array
	      element per character.

       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  expres-
	      sion  are  replaced;  sub and gsub return the number of replace-
	      ments.

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

       toupper(str)
	      returns a copy of str with all lower-case characters  translated
	      to their corresponding upper-case equivalents.

       The ``function'' getline sets $0 to the next input record from the cur-
       rent 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
       egrep; see grep(1).  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 regular
       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 combi-
       nation 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:

       CONVFMT
	      conversion format used when converting numbers (default %.6g)

       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

       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	state-
       ment) 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($0) > 72
	      Print lines longer than 72 characters.

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

       BEGIN { FS = ",[ \t]*|[ \t]+" }
	     { 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 "\n"
	    exit }

SEE ALSO

       lex(1), sed(1)
       A.  V. Aho, B. W. Kernighan, P. J. Weinberger, The AWK Programming Lan-
       guage, Addison-Wesley, 1988.  ISBN 0-201-07981-X

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.

SPONSORED LINKS