xref: /freebsd/contrib/one-true-awk/awk.1 (revision f4b37ed0f8b307b1f3f0f630ca725d68f1dff30d) 
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awk

 AWK 1
.CT 1 files prog_other

 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 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:


.EX



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 \f(CW" ",
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 subscripts 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 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:
.TF length


 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
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 in
 egrep ;  see
 grep (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 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:
.TF FILENAME


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

 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


 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

.EX
length($0) > 72

Print lines longer than 72 characters.


.EX
{ print $2, $1 }

Print first two fields in opposite order.


.EX
BEGIN { FS = ",[ \et]*|[ \et]+" }
 { print $2, $1 }

.ns

Same, with input fields separated by comma and/or blanks and tabs.


.EX

 { s += $1 }
END { print "sum is", s, " average is", s/NR }



.ns

Add up first column, print sum and average.


.EX
/start/, /stop/

Print all lines between start/stop pairs.


.EX

BEGIN { # Simulate echo(1)
 for (i = 1; i < ARGC; i++) printf "%s ", ARGV[i]
 printf "\en"
 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
\f(CW"" to it.


The scope rules for variables in functions are a botch;
the syntax is worse.