AWK(1) AWK(1)
awk
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 separa-
tor 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 pat-
tern always matches. Pattern-action statements are sepa-
rated 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 recog-
nized within. Expressions take on string or numeric val-
ues as appropriate, and are built using the operators + -
* / % ^ (exponentiation), and concatenation (indicated by
white space). The operators ! ++ -- += -= *= /= %= ^= >
>= < <= == != ?: are also available in expressions. Vari-
ables 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 sepa-
rator. file and cmd may be literal names or parenthesized
expressions; identical string values in different state-
ments 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 posi-
tion 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 regu-
lar expression r in the string s. If s is not
given, $0 is used.
gsub same as sub except that all occurrences of the reg-
ular 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 charac-
ters translated to their corresponding lower-case
equivalents.
toupper(str)
returns a copy of str with all lower-case charac-
ters 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 get-
line; each call of getline returns the next line of output
from cmd. In all cases, getline returns 1 for a success-
ful input, 0 for end of file, and -1 for an error.
Patterns are arbitrary Boolean combinations (with ! || &&)
of regular expressions and relational expressions. Regu-
lar 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 expres-
sions, 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 occur-
rence 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 pro-
viding 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 Pro-
gramming 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 con-
catenate "" to it.
The scope rules for variables in functions are a botch;
the syntax is worse.
AWK(1)