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NetBSD 6.1.5 - man page for awk (netbsd section 1)

AWK(1)				   BSD General Commands Manual				   AWK(1)

NAME
     awk -- pattern-directed scanning and processing language

SYNOPSIS
     awk [-F fs] [-v var=value] [-safe] [-d[N]] [prog | -f filename] file ...
     awk -version

DESCRIPTION
     awk is the Bell Labs' implementation of the AWK programming language as described in the The
     AWK Programming Language by A. V. Aho, B. W. Kernighan, and P. J. Weinberger.

     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 filename.	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 associ-
     ated 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 options are as follows:

     -d[N]   Set debug level to specified number N.  If the number is omitted, debug level is set
	     to 1.

     -f filename
	     Read the AWK program source from specified file filename, instead of the first com-
	     mand line argument.  Multiple -f options may be specified.

     -F fs   Set the input field separator FS to the regular expression fs.

     -mr NNN, -mf NNN
	     Obsolete, no longer needed options.  Set limit on maximum record or fields number.

     -safe   Potentially unsafe functions such as system() make the program abort (with a warning
	     message).

     -v var=value
	     Assign the value value to the variable var before prog is executed.  Any number of
	     -v options may be present.

     -version
	     Print awk version on standard output and exit.

     An input line is normally made up of fields separated by white space, or by regular expres-
     sion 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.  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 (see next subsection).  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 SUBSEP.

   Operators
     awk operators, in order of decreasing precedence, are:

     (...)  Grouping
     $	    Field reference
     ++ --  Increment and decrement, can be used either as postfix or prefix.
     ^	    Exponentiation (the ** form is also supported, and **= for the assignment operator).
     + - !  Unary plus, unary minus and logical negation.
     * / %  Multiplication, division and modulus.
     + -    Addition and subtraction.
     space  String concatenation.
     < >
     <= >=
     != ==  Regular relational operators
     ~ !~   Regular expression match and not match
     in     Array membership
     &&     Logical AND
     ||     Logical OR
     ?:     C conditional expression.  This is used as expr1 ? expr2 : expr3 .	If expr1 is true,
	    the result value is expr2, otherwise it is expr3.  Only one of expr2 and expr3 is
	    evaluated.
     = += -=
     *= /= %= ^=
	    Assignment and Operator-Assignment

   Control Statements
     The control statements are as follows:

	   if ( expression ) statement [else statement]
	   while ( expression ) statement
	   for ( expression ; expression ; expression ) statement
	   for ( var in array ) statement
	   do statement while ( expression )
	   break
	   continue
	   delete array [expression]
	   delete array
	   exit [expression] expression
	   return [expression]
	   { [statement ...] }

   I/O Statements
     The input/output statements are as follows:

     close(expr)
	     Closes the file or pipe expr.  Returns zero on success; otherwise nonzero.

     fflush(expr)
	     Flushes any buffered output for the file or pipe expr.  Returns zero on success;
	     otherwise nonzero.

     getline [var]
	     Set var (or $0 if var is not specified) to the next input record from the current
	     input file.  getline returns 1 for a successful input, 0 for end of file, and -1 for
	     an error.

     getline [var] < file
	     Set var (or $0 if var is not specified) to the next input record from the specified
	     file file.

     expr | getline
	     Pipes the output of expr into getline; each call of getline returns the next line of
	     output from expr.

     next    Skip remaining patterns on this input line.

     nextfile
	     Skip rest of this file, open next, start at top.

     print [expr-list] [> file]
	     The print statement prints its arguments on the standard output (or to a file if >
	     file or to a pipe if | expr is present), separated by the current output field sepa-
	     rator OFS, and terminated by the output record separator ORS.  Both file and expr
	     may be literal names or parenthesized expressions; identical string values in dif-
	     ferent statements denote the same open file.

     printf format [, expr-list] [> file]
	     Format and print its expression list according to format.	See printf(3) for list of
	     supported formats and their meaning.

   Mathematical and Numeric Functions
     AWK has the following mathematical and numerical functions built-in:

     atan2(x, y)
	     Returns the arctangent of x / y in radians.  See also atan2(3).

     cos(expr)
	     Computes the cosine of expr, measured in radians.	See also cos(3).

     exp(expr)
	     Computes the exponential value of the given argument expr.  See also exp(3).

     int(expr)
	     Truncates expr to integer.

     log(expr)
	     Computes the value of the natural logarithm of argument expr.  See also log(3).

     rand()  Returns random number between 0 and 1.

     sin(expr)
	     Computes the sine of expr, measured in radians.  See also sin(3).

     sqrt(expr)
	     Computes the non-negative square root of expr.  See also sqrt(3).

     srand([expr])
	     Sets seed for random number generator ( rand()) and returns the previous seed.

   String Functions
     AWK has the following string functions built-in:

     gensub(r, s, h, [t])
	     Search the target string t for matches of the regular expression r.  If h is a
	     string beginning with g or G, then replace all matches of r with s.  Otherwise, h is
	     a number indicating which match of r to replace.  If no t is supplied, $0 is used
	     instead.  Unlike sub() and gsub(), the modified string is returned as the result of
	     the function, and the original target is not changed.  Note that the \n sequences
	     within replacement string s supported by GNU awk are not supported at this moment.

     gsub(r, t, [s])
	     same as sub() except that all occurrences of the regular expression are replaced;
	     sub() and gsub() return the number of replacements.

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

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

     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.

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

     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.

     substr(s, m, [n])
	     Returns the at most n-character substring of s starting at position m, counted from
	     1.  If n is omitted, the rest of s is returned.

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

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

   Time Functions
     This awk provides the following two functions for obtaining time stamps and formatting them:

     systime()
	     Returns the value of time in seconds since the start of Unix Epoch (Midnight, Janu-
	     ary 1, 1970, Coordinated Universal Time).	See also time(3).

     strftime([format [, timestamp]])
	     Formats the time timestamp according to the string format.  timestamp should be in
	     same form as value returned by systime().	If timestamp is missing, current time is
	     used.  If format is missing, a default format equivalent to the output of date(1)
	     would be used.  See the specification of ANSI C strftime(3) for the format conver-
	     sions which are supported.

   Other built-in functions
     system(cmd)
	     executes cmd and returns its exit status

   Patterns
     Patterns are arbitrary Boolean combinations (with ! || &&) of regular expressions and rela-
     tional expressions.  Regular expressions are as in egrep(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 per-
     formed 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.

   Built-in Variables
     Variable names with special meanings:

     ARGC	argument count, assignable

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

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

     ENVIRON	array of environment variables; subscripts are names.

     FILENAME	the name of the current input file

     FNR	ordinal number of the current record in the current file

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

     NF 	number of fields in the current record

     NR 	ordinal number of the current record

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

     OFS	output field separator (default blank)

     ORS	output record separator (default newline)

     RS 	input record separator (default newline)

     RSTART	Position of the first character matched by match(); 0 if not match.

     RLENGTH	Length of the string matched by match(); -1 if no match.

     SUBSEP	separates multiple subscripts (default 034)

   Functions
     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
     egrep(1), lex(1), sed(1), atan2(3), cos(3), exp(3), log(3), sin(3), sqrt(3), strftime(3),
     time(3)

     A. V. Aho, B. W. Kernighan, P. J. Weinberger, The AWK Programming Language, Addison-Wesley,
     1988.  ISBN 0-201-07981-X

     AWK Language Programming, Edition 1.0, published by the Free Software Foundation, 1995

HISTORY
     nawk has been the default system awk since NetBSD 2.0, replacing the previously used GNU
     awk.

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.

BSD					   May 25, 2008 				      BSD


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