AWK(1) AWK(1)
NAME
awk - pattern scanning and processing language
SYNOPSIS
awk [ -Fc ] [ prog ] [ parameters ] [ files ]
DESCRIPTION
awk scans each input file for lines that match any of a set
of patterns specified in prog. With each pattern in prog
there can be an associated action that will be performed
when a line of a file matches the pattern. The set of
patterns may appear literally as prog, or in a file
specified as -f file. The prog string should be enclosed in
single quotes (') to protect it from the shell.
Parameters, in the form x=... y=... etc., may be passed to
awk.
Files are read in order; if there are no files, the standard
input is read. The file name - 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; see below). The
fields are denoted $1, $2, ...; $0 refers to the entire
line.
A pattern-action statement has the form:
pattern { action }
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
break
continue
{ [ statement ] ... }
variable = expression
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, new-lines, or right
braces. An empty expression-list stands for the whole line.
Expressions take on string or numeric values as appropriate,
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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
(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. String constants are quoted (").
The print statement prints its arguments on the standard
output (or on a file if >expr is present), separated by the
current output field separator, and terminated by the output
record separator. The printf statement formats its
expression list according to the format [see printf(3S) in
the Programmer's Reference Manual].
The built-in function length returns the length of its
argument taken as a string, or of the whole line if no
argument. There are also built-in functions exp, log, sqrt,
and int. The last truncates its argument to an integer;
substr(s, m, n) returns the n-character substring of s that
begins at position m. The function
sprintf(fmt, expr, expr, ...) formats the expressions
according to the printf(3S) format given by fmt and returns
the resulting string.
Patterns are arbitrary Boolean combinations ( !, ||, &&, and
parentheses) of regular expressions and relational
expressions. Regular expressions must be surrounded by
slashes and 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. 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, 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 must be the first pattern, END the last.
A single character c may be used to separate the fields by
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starting the program with:
BEGIN { FS = c }
or by using the -Fc option.
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 new-line);
and OFMT, the output format for numbers (default %.6g).
EXAMPLES
Print lines longer than 72 characters:
length > 72
Print first two fields in opposite order:
{ print $2, $1 }
Add up first column, print sum and average:
{ s += $1 }
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:
/start/, /stop/
Print all lines whose first field is different from previous
one:
$1 != prev { print; prev = $1 }
Print file, filling in page numbers starting at 5:
/Page/ { $2 = n++; }
{ print }
command line: awk -f program n=5 input
SEE ALSO
grep(1), sed(1).
lex(1), printf(3S) in the Programmer's Reference Manual.
BUGS
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Input white space is not preserved on output if fields are
involved.
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 the null string ("") to it.
ORIGIN
AT&T V.3
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