fatbase

awk.1 (17547B)

---

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 .Dd $Mdocdate: March 17 2014 $
 .Dt AWK 1
 .Os
 .Sh NAME
 .Nm awk
 .Nd pattern-directed scanning and processing language
 .Sh SYNOPSIS
 .Nm awk
 .Op Fl safe
 .Op Fl V
 .Op Fl d Ns Op Ar n
 .Op Fl F Ar fs
 .Op Fl v Ar var Ns = Ns Ar value
 .Op Ar prog | Fl f Ar progfile
 .Ar
 .Sh DESCRIPTION
 .Nm
 scans each input
 .Ar file
 for lines that match any of a set of patterns specified literally in
 .Ar prog
 or in one or more files specified as
 .Fl f Ar progfile .
 With each pattern there can be an associated action that will be performed
 when a line of a
 .Ar 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
 .Sq -
 means the standard input.
 Any
 .Ar file
 of the form
 .Ar var Ns = Ns Ar 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.
 .Pp
 The options are as follows:
 .Bl -tag -width "-safe "
 .It Fl d Ns Op Ar n
 Debug mode.
 Set debug level to
 .Ar n ,
 or 1 if
 .Ar n
 is not specified.
 A value greater than 1 causes
 .Nm
 to dump core on fatal errors.
 .It Fl F Ar fs
 Define the input field separator to be the regular expression
 .Ar fs .
 .It Fl f Ar progfile
 Read program code from the specified file
 .Ar progfile
 instead of from the command line.
 .It Fl safe
 Disable file output
 .Pf ( Ic print No > ,
 .Ic print No >> ) ,
 process creation
 .Po
 .Ar cmd | Ic getline ,
 .Ic print | ,
 .Ic system
 .Pc
 and access to the environment
 .Pf ( Va ENVIRON ;
 see the section on variables below).
 This is a first
 .Pq and not very reliable
 approximation to a
 .Dq safe
 version of
 .Nm .
 .It Fl V
 Print the version number of
 .Nm
 to standard output and exit.
 .It Fl v Ar var Ns = Ns Ar value
 Assign
 .Ar value
 to variable
 .Ar var
 before
 .Ar prog
 is executed;
 any number of
 .Fl v
 options may be present.
 .El
 .Pp
 The input is normally made up of input lines
 .Pq records
 separated by newlines, or by the value of
 .Va RS .
 If
 .Va RS
 is null, then any number of blank lines are used as the record separator,
 and newlines are used as field separators
 (in addition to the value of
 .Va FS ) .
 This is convenient when working with multi-line records.
 .Pp
 An input line is normally made up of fields separated by whitespace,
 or by the regular expression
 .Va FS .
 The fields are denoted
 .Va $1 , $2 , ... ,
 while
 .Va $0
 refers to the entire line.
 If
 .Va FS
 is null, the input line is split into one field per character.
 .Pp
 Normally, any number of blanks separate fields.
 In order to set the field separator to a single blank, use the
 .Fl F
 option with a value of
 .Sq [\ \&] .
 If a field separator of
 .Sq t
 is specified,
 .Nm
 treats it as if
 .Sq \et
 had been specified and uses
 .Aq TAB
 as the field separator.
 In order to use a literal
 .Sq t
 as the field separator, use the
 .Fl F
 option with a value of
 .Sq [t] .
 .Pp
 A pattern-action statement has the form
 .Pp
 .D1 Ar pattern Ic \&{ Ar action Ic \&}
 .Pp
 A missing
 .Ic \&{ Ar action Ic \&}
 means print the line;
 a missing pattern always matches.
 Pattern-action statements are separated by newlines or semicolons.
 .Pp
 Newlines are permitted after a terminating statement or following a comma
 .Pq Sq ,\& ,
 an open brace
 .Pq Sq { ,
 a logical AND
 .Pq Sq && ,
 a logical OR
 .Pq Sq || ,
 after the
 .Sq do
 or
 .Sq else
 keywords,
 or after the closing parenthesis of an
 .Sq if ,
 .Sq for ,
 or
 .Sq while
 statement.
 Additionally, a backslash
 .Pq Sq \e
 can be used to escape a newline between tokens.
 .Pp
 An action is a sequence of statements.
 A statement can be one of the following:
 .Pp
 .Bl -tag -width Ds -offset indent -compact
 .It Xo Ic if ( Ar expression ) Ar statement
 .Op Ic else Ar statement
 .Xc
 .It Ic while ( Ar expression ) Ar statement
 .It Xo Ic for
 .No ( Ar expression ; expression ; expression ) statement
 .Xc
 .It Xo Ic for
 .No ( Ar var Ic in Ar array ) statement
 .Xc
 .It Xo Ic do
 .Ar statement Ic while ( Ar expression )
 .Xc
 .It Ic break
 .It Ic continue
 .It Xo Ic {
 .Op Ar statement ...
 .Ic }
 .Xc
 .It Xo Ar expression
 .No # commonly
 .Ar var No = Ar expression
 .Xc
 .It Xo Ic print
 .Op Ar expression-list
 .Op > Ns Ar expression
 .Xc
 .It Xo Ic printf Ar format
 .Op Ar ... , expression-list
 .Op > Ns Ar expression
 .Xc
 .It Ic return Op Ar expression
 .It Xo Ic next
 .No # skip remaining patterns on this input line
 .Xc
 .It Xo Ic nextfile
 .No # skip rest of this file, open next, start at top
 .Xc
 .It Xo Ic delete
 .Sm off
 .Ar array Ic \&[ Ar expression Ic \&]
 .Sm on
 .No # delete an array element
 .Xc
 .It Xo Ic delete Ar array
 .No # delete all elements of array
 .Xc
 .It Xo Ic exit
 .Op Ar expression
 .No # exit immediately; status is Ar expression
 .Xc
 .El
 .Pp
 Statements are terminated by
 semicolons, newlines or right braces.
 An empty
 .Ar expression-list
 stands for
 .Ar $0 .
 String constants are quoted
 .Li \&"" ,
 with the usual C escapes recognized within
 (see
 .Xr printf 1
 for a complete list of these).
 Expressions take on string or numeric values as appropriate,
 and are built using the operators
 .Ic + \- * / % ^
 .Pq exponentiation ,
 and concatenation
 .Pq indicated by whitespace .
 The operators
 .Ic \&! ++ \-\- += \-= *= /= %= ^=
 .Ic > >= < <= == != ?:
 are also available in expressions.
 Variables may be scalars, array elements
 (denoted
 .Li 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
 .Li [i,j,k]
 are permitted; the constituents are concatenated,
 separated by the value of
 .Va SUBSEP
 .Pq see the section on variables below .
 .Pp
 The
 .Ic print
 statement prints its arguments on the standard output
 (or on a file if
 .Pf > Ns Ar file
 or
 .Pf >> Ns Ar file
 is present or on a pipe if
 .Pf |\ \& Ar cmd
 is present), separated by the current output field separator,
 and terminated by the output record separator.
 .Ar file
 and
 .Ar cmd
 may be literal names or parenthesized expressions;
 identical string values in different statements denote
 the same open file.
 The
 .Ic printf
 statement formats its expression list according to the format
 (see
 .Xr printf 1 ) .
 .Pp
 Patterns are arbitrary Boolean combinations
 (with
 .Ic "\&! || &&" )
 of regular expressions and
 relational expressions.
 .Nm
 supports extended regular expressions
 .Pq EREs .
 See
 .Xr re_format 7
 for more information on regular expressions.
 Isolated regular expressions
 in a pattern apply to the entire line.
 Regular expressions may also occur in
 relational expressions, using the operators
 .Ic ~
 and
 .Ic !~ .
 .Pf / Ns Ar re Ns /
 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.
 .Pp
 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
 through an occurrence of the second.
 .Pp
 A relational expression is one of the following:
 .Pp
 .Bl -tag -width Ds -offset indent -compact
 .It Ar expression matchop regular-expression
 .It Ar expression relop expression
 .It Ar expression Ic in Ar array-name
 .It Xo Ic \&( Ns
 .Ar expr , expr , \&... Ns Ic \&) in
 .Ar array-name
 .Xc
 .El
 .Pp
 where a
 .Ar relop
 is any of the six relational operators in C, and a
 .Ar matchop
 is either
 .Ic ~
 (matches)
 or
 .Ic !~
 (does not match).
 A conditional is an arithmetic expression,
 a relational expression,
 or a Boolean combination
 of these.
 .Pp
 The special patterns
 .Ic BEGIN
 and
 .Ic END
 may be used to capture control before the first input line is read
 and after the last.
 .Ic BEGIN
 and
 .Ic END
 do not combine with other patterns.
 .Pp
 Variable names with special meanings:
 .Pp
 .Bl -tag -width "FILENAME " -compact
 .It Va ARGC
 Argument count, assignable.
 .It Va ARGV
 Argument array, assignable;
 non-null members are taken as filenames.
 .It Va CONVFMT
 Conversion format when converting numbers
 (default
 .Qq Li %.6g ) .
 .It Va ENVIRON
 Array of environment variables; subscripts are names.
 .It Va FILENAME
 The name of the current input file.
 .It Va FNR
 Ordinal number of the current record in the current file.
 .It Va FS
 Regular expression used to separate fields; also settable
 by option
 .Fl F Ar fs .
 .It Va NF
 Number of fields in the current record.
 .Va $NF
 can be used to obtain the value of the last field in the current record.
 .It Va NR
 Ordinal number of the current record.
 .It Va OFMT
 Output format for numbers (default
 .Qq Li %.6g ) .
 .It Va OFS
 Output field separator (default blank).
 .It Va ORS
 Output record separator (default newline).
 .It Va RLENGTH
 The length of the string matched by the
 .Fn match
 function.
 .It Va RS
 Input record separator (default newline).
 .It Va RSTART
 The starting position of the string matched by the
 .Fn match
 function.
 .It Va SUBSEP
 Separates multiple subscripts (default 034).
 .El
 .Sh FUNCTIONS
 The awk language has a variety of built-in functions:
 arithmetic, string, input/output, general, and bit-operation.
 .Pp
 Functions may be defined (at the position of a pattern-action statement)
 thusly:
 .Pp
 .Dl function foo(a, b, c) { ...; return x }
 .Pp
 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.
 .Ss Arithmetic Functions
 .Bl -tag -width "atan2(y, x)"
 .It Fn atan2 y x
 Return the arctangent of
 .Fa y Ns / Ns Fa x
 in radians.
 .It Fn cos x
 Return the cosine of
 .Fa x ,
 where
 .Fa x
 is in radians.
 .It Fn exp x
 Return the exponential of
 .Fa x .
 .It Fn int x
 Return
 .Fa x
 truncated to an integer value.
 .It Fn log x
 Return the natural logarithm of
 .Fa x .
 .It Fn rand
 Return a random number,
 .Fa n ,
 such that
 .Sm off
 .Pf 0 \*(Le Fa n No \*(Lt 1 .
 .Sm on
 .It Fn sin x
 Return the sine of
 .Fa x ,
 where
 .Fa x
 is in radians.
 .It Fn sqrt x
 Return the square root of
 .Fa x .
 .It Fn srand expr
 Sets seed for
 .Fn rand
 to
 .Fa expr
 and returns the previous seed.
 If
 .Fa expr
 is omitted, the time of day is used instead.
 .El
 .Ss String Functions
 .Bl -tag -width "split(s, a, fs)"
 .It Fn gsub r t s
 The same as
 .Fn sub
 except that all occurrences of the regular expression are replaced.
 .Fn gsub
 returns the number of replacements.
 .It Fn index s t
 The position in
 .Fa s
 where the string
 .Fa t
 occurs, or 0 if it does not.
 .It Fn length s
 The length of
 .Fa s
 taken as a string,
 or of
 .Va $0
 if no argument is given.
 .It Fn match s r
 The position in
 .Fa s
 where the regular expression
 .Fa r
 occurs, or 0 if it does not.
 The variable
 .Va RSTART
 is set to the starting position of the matched string
 .Pq which is the same as the returned value
 or zero if no match is found.
 The variable
 .Va RLENGTH
 is set to the length of the matched string,
 or \-1 if no match is found.
 .It Fn split s a fs
 Splits the string
 .Fa s
 into array elements
 .Va a[1] , a[2] , ... , a[n]
 and returns
 .Va n .
 The separation is done with the regular expression
 .Ar fs
 or with the field separator
 .Va FS
 if
 .Ar fs
 is not given.
 An empty string as field separator splits the string
 into one array element per character.
 .It Fn sprintf fmt expr ...
 The string resulting from formatting
 .Fa expr , ...
 according to the
 .Xr printf 1
 format
 .Fa fmt .
 .It Fn sub r t s
 Substitutes
 .Fa t
 for the first occurrence of the regular expression
 .Fa r
 in the string
 .Fa s .
 If
 .Fa s
 is not given,
 .Va $0
 is used.
 An ampersand
 .Pq Sq &
 in
 .Fa t
 is replaced in string
 .Fa s
 with regular expression
 .Fa r .
 A literal ampersand can be specified by preceding it with two backslashes
 .Pq Sq \e\e .
 A literal backslash can be specified by preceding it with another backslash
 .Pq Sq \e\e .
 .Fn sub
 returns the number of replacements.
 .It Fn substr s m n
 Return at most the
 .Fa n Ns -character
 substring of
 .Fa s
 that begins at position
 .Fa m
 counted from 1.
 If
 .Fa n
 is omitted, or if
 .Fa n
 specifies more characters than are left in the string,
 the length of the substring is limited by the length of
 .Fa s .
 .It Fn tolower str
 Returns a copy of
 .Fa str
 with all upper-case characters translated to their
 corresponding lower-case equivalents.
 .It Fn toupper str
 Returns a copy of
 .Fa str
 with all lower-case characters translated to their
 corresponding upper-case equivalents.
 .El
 .Ss Input/Output and General Functions
 .Bl -tag -width "getline [var] < file"
 .It Fn close expr
 Closes the file or pipe
 .Fa expr .
 .Fa expr
 should match the string that was used to open the file or pipe.
 .It Ar cmd | Ic getline Op Va var
 Read a record of input from a stream piped from the output of
 .Ar cmd .
 If
 .Va var
 is omitted, the variables
 .Va $0
 and
 .Va NF
 are set.
 Otherwise
 .Va var
 is set.
 If the stream is not open, it is opened.
 As long as the stream remains open, subsequent calls
 will read subsequent records from the stream.
 The stream remains open until explicitly closed with a call to
 .Fn close .
 .Ic getline
 returns 1 for a successful input, 0 for end of file, and \-1 for an error.
 .It Fn fflush [expr]
 Flushes any buffered output for the file or pipe
 .Fa expr ,
 or all open files or pipes if
 .Fa expr
 is omitted.
 .Fa expr
 should match the string that was used to open the file or pipe.
 .It Ic getline
 Sets
 .Va $0
 to the next input record from the current input file.
 This form of
 .Ic getline
 sets the variables
 .Va NF ,
 .Va NR ,
 and
 .Va FNR .
 .Ic getline
 returns 1 for a successful input, 0 for end of file, and \-1 for an error.
 .It Ic getline Va var
 Sets
 .Va $0
 to variable
 .Va var .
 This form of
 .Ic getline
 sets the variables
 .Va NR
 and
 .Va FNR .
 .Ic getline
 returns 1 for a successful input, 0 for end of file, and \-1 for an error.
 .It Xo
 .Ic getline Op Va var
 .Pf \ \&< Ar file
 .Xc
 Sets
 .Va $0
 to the next record from
 .Ar file .
 If
 .Va var
 is omitted, the variables
 .Va $0
 and
 .Va NF
 are set.
 Otherwise
 .Va var
 is set.
 If
 .Ar file
 is not open, it is opened.
 As long as the stream remains open, subsequent calls will read subsequent
 records from
 .Ar file .
 .Ar file
 remains open until explicitly closed with a call to
 .Fn close .
 .It Fn system cmd
 Executes
 .Fa cmd
 and returns its exit status.
 .El
 .Ss Bit-Operation Functions
 .Bl -tag -width "lshift(a, b)"
 .It Fn compl x
 Returns the bitwise complement of integer argument x.
 .It Fn and x y
 Performs a bitwise AND on integer arguments x and y.
 .It Fn or x y
 Performs a bitwise OR on integer arguments x and y.
 .It Fn xor x y
 Performs a bitwise Exclusive-OR on integer arguments x and y.
 .It Fn lshift x n
 Returns integer argument x shifted by n bits to the left.
 .It Fn rshift x n
 Returns integer argument x shifted by n bits to the right.
 .El
 .Sh EXIT STATUS
 .Ex -std awk
 .Pp
 But note that the
 .Ic exit
 expression can modify the exit status.
 .Sh EXAMPLES
 Print lines longer than 72 characters:
 .Pp
 .Dl length($0) > 72
 .Pp
 Print first two fields in opposite order:
 .Pp
 .Dl { print $2, $1 }
 .Pp
 Same, with input fields separated by comma and/or blanks and tabs:
 .Bd -literal -offset indent
 BEGIN { FS = ",[ \et]*|[ \et]+" }
       { print $2, $1 }
 .Ed
 .Pp
 Add up first column, print sum and average:
 .Bd -literal -offset indent
 { s += $1 }
 END { print "sum is", s, " average is", s/NR }
 .Ed
 .Pp
 Print all lines between start/stop pairs:
 .Pp
 .Dl /start/, /stop/
 .Pp
 Simulate echo(1):
 .Bd -literal -offset indent
 BEGIN { # Simulate echo(1)
         for (i = 1; i < ARGC; i++) printf "%s ", ARGV[i]
         printf "\en"
         exit }
 .Ed
 .Pp
 Print an error message to standard error:
 .Bd -literal -offset indent
 { print "error!" > "/dev/stderr" }
 .Ed
 .Sh SEE ALSO
 .Xr lex 1 ,
 .Xr printf 1 ,
 .Xr sed 1 ,
 .Xr re_format 7 ,
 .Xr script 7
 .Rs
 .%A A. V. Aho
 .%A B. W. Kernighan
 .%A P. J. Weinberger
 .%T The AWK Programming Language
 .%I Addison-Wesley
 .%D 1988
 .%O ISBN 0-201-07981-X
 .Re
 .Sh STANDARDS
 The
 .Nm
 utility is compliant with the
 .St -p1003.1-2008
 specification,
 except
 .Nm
 does not support {n,m} pattern matching.
 .Pp
 The flags
 .Op Fl \&dV
 and
 .Op Fl safe ,
 as well as the commands
 .Cm fflush , compl , and , or ,
 .Cm xor , lshift , rshift ,
 are extensions to that specification.
 .Sh HISTORY
 An
 .Nm
 utility appeared in
 .At v7 .
 .Sh 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
 .Li \&""
 to it.
 .Pp
 The scope rules for variables in functions are a botch;
 the syntax is worse.