AWK(1)							      General Commands Manual							    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 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 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 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

       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 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 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.  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 corresponding lower-case equivalents.

       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 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
       defined	in re_format(7).  Isolated regular expressions in a pattern apply to the entire line.  Regular expressions may also occur in rela-
       tional 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 definition.

EXAMPLES

       length($0) > 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 }

SEE ALSO

       lex(1), sed(1)
       A. V. Aho, B. W. Kernighan, P. J. Weinberger, The AWK Programming Language, 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.

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