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Plan 9 - man page for awk (plan9 section 1)

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 liter-
       ally 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 executed; 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 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
       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 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 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 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.

       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 expres-
       sion; 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:

       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 defini-
       tion.

EXAMPLES
       length > 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 }

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-Wes-
       ley, 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.

											   AWK(1)


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