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OpenDarwin 7.2.1 - man page for awk (opendarwin section 1)

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AWK(1)											   AWK(1)

awk

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 liter-
       ally 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 pat-
       tern.  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 filename.  The
       option -v followed by var=value is an assignment to be done before prog is  executed;  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 semicolons.

       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

       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 expres-
       sions.  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  subscripts  such  as
       [i,j,k]	are  permitted; the constituents are concatenated, separated by the value of SUB-
       SEP.

       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 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 expression 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 expression are replaced; sub
	      and gsub return the number of replacements.

       sprintf(fmt, expr, ... )
	      the string resulting from formatting expr ...  according to  the	printf(3)  format
	      fmt

       system(cmd)
	      executes cmd and returns its exit status

       tolower(str)
	      returns  a  copy	of  str with all upper-case characters translated to their corre-
	      sponding lower-case equivalents.

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

       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 egrep; see grep(1).  Isolated regu-
       lar 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 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:

       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

       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 filenames

       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 defini-
       tion.

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  Language,  Addison-Wes-
       ley, 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.

											   AWK(1)
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