AWK(1) GENIX Programmer's Manual AWK(1)
NAME
awk - pattern scanning and processing language
SYNOPSIS
awk [ -Fc ] [ prog ] [ file ] ...
DESCRIPTION
Awk scans each input file for lines that match any of a set of pat-
terns 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.
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 state-
ment; 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, vide infra.) 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, 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
(denoted x[i]) or fields. Variables are initialized to the null
string. Array subscripts may be any string, not necessarily
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AWK(1) GENIX Programmer's Manual AWK(1)
numeric; this allows for a form of associative memory. String con-
stants are quoted "...".
The print statement prints its arguments on the standard output (or
on a file if >file 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(3)).
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(3) 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. 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 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
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output field separator (default blank); ORS, the output record
separator (default newline); 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 }
SEE ALSO
lex(1), sed(1)
A. V. Aho, B. W. Kernighan, P. J. Weinberger, Awk - a pattern scan-
ning and processing language
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.
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