AWK(1) INTERACTIVE UNIX System AWK(1)
NAME
awk - pattern scanning and processing language
SYNOPSIS
awk [ -Fc ] [ prog ] [ parameters ] [ files ]
DESCRIPTION
The awk language scans each input file for lines that match
any of a set of patterns specified in prog. With each pat-
tern 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,
and are built using the operators +, -, *, /, %, and
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concatenation (indicated by a blank). The C operators ++,
--, +=, -=, *=, /=, and %= are also available in expres-
sions. 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 (").
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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 expres-
sion list according to the format [see printf(3S) in the
INTERACTIVE SDS Guide and Programmer's Reference Manual].
The built-in function length returns the length of its argu-
ment taken as a string, or of the whole line if no argument
is present. 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 expres-
sions. Regular expressions must be surrounded by slashes
and are as in egrep [see grep(1)]. Isolated regular expres-
sions 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 relop is any of the six relational operators in C, and
matchop is either ~ (for contains) or !~ (for does not con-
tain). A conditional is an arithmetic expression, a rela-
tional 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
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
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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 INTERACTIVE SDS Guide and
Programmer's Reference Manual.
BUGS
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, con-
catenate the null string ("") to it.
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