.TH AWK 1 "18 January 1983"
awk \- pattern scanning and processing language
for lines that match any of a set of patterns specified in
there can be an associated action that will be performed
The set of patterns may appear literally as
if there are no files, the standard input is read.
means the standard input.
Each line is matched against the
pattern portion of every pattern-action statement;
the associated action is performed for each matched pattern.
An input line is made up of fields separated by white space.
(This default can be changed by using FS,
The fields are denoted $1, $2, ... ;
$0 refers to the entire line.
A pattern-action statement has the form
A missing { action } means print the line;
a missing pattern always matches.
An action is a sequence of statements.
A statement can be one of the following:
if ( conditional ) statement [ else statement ]
while ( conditional ) statement
for ( expression ; conditional ; expression ) statement
print [ expression-list ] [ >expression ]
printf format [ , expression-list ] [ >expression ]
next # skip remaining patterns on this input line
exit # skip the rest of the input
Statements are terminated by
semicolons, newlines or right braces.
An empty expression-list stands for the whole line.
Expressions take on string or numeric values as appropriate,
and are built using the operators
+, \-, *, /, %, and concatenation (indicated by a blank).
The C operators ++, \-\-, +=, \-=, *=, /=, and %=
are also available in expressions.
Variables may be scalars, array elements
Variables are initialized to the null string.
Array subscripts may be any string,
this allows for a form of associative memory.
String constants are quoted "...".
statement prints its arguments on the standard output
is present), separated by the current output field separator,
and terminated by the output record separator.
statement formats its expression list according to the format
returns the length of its argument
or of the whole line if no argument.
There are also built-in functions
The last truncates its argument to an integer.
.IR sprintf(fmt,\ expr,\ expr,\ ...)
and returns the resulting string.
Patterns are arbitrary Boolean combinations
(!, \(or\(or, &&, and parentheses) of
Regular expressions must be surrounded
Isolated regular expressions
in a pattern apply to the entire line.
Regular expressions may also occur in
A pattern may consist of two patterns separated by a comma;
in this case, the action is performed for all lines
between an occurrence of the first pattern
and the next occurrence of the second.
A relational expression is one of the following:
expression matchop regular-expression
expression relop expression
where a relop is any of the six relational operators in C,
and a matchop is either ~ (for contains)
or !~ (for does not contain).
A conditional is an arithmetic expression,
may be used to capture control before the first input line is read
BEGIN must be the first pattern, END the last.
may be used to separate the fields by starting
Other variable names with special meanings
include NF, the number of fields in the current record;
NR, the ordinal number of the current record;
FILENAME, the name of the current input file;
OFS, the output field separator (default blank);
ORS, the output record separator (default newline);
OFMT, the output format for numbers (default "%.6g").
Print lines longer than 72 characters:
Print first two fields in opposite order:
Add up first column, print sum and average:
END { print "sum is", s, " average is", s/NR }
Print fields in reverse order:
{ for (i = NF; i > 0; \-\-i) print $i }
Print all lines between start/stop pairs:
Print all lines whose first field is different from previous one:
$1 != prev { print; prev = $1 }
A. V. Aho, B. W. Kernighan, P. J. Weinberger,
Awk \- a pattern scanning and processing language
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 ""