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
-fprogfile.
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
-Ffs
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:
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 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:
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.
getlinex
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:
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 = ",[ \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
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.
