AWK(1) USER COMMANDS AWK(1)
NAME
awk - pattern scanning and processing language
SYNOPSIS
awk [ -f program-file ] [ -Fc ] [ program ] [ variable=value
... ] [ filename...]
DESCRIPTION
awk scans each of its input filenames for lines that match
any of a set of patterns specified in program. The input
filenames are read in order; the standard input is read if
there are no filenames. The filename `-' means the standard
input.
The set of patterns may either appear literally on the com-
mand line as program, or, by using the `-f program-file'
option, the set of patterns may be in a program-file; a
program-file of `-' means the standard input. If the pro-
gram is specified on the command line, it should be enclosed
in single quotes (') to protect it from the shell.
awk variables may be set on the command line using arguments
of the form variable=value. This sets the awk variable
variable to value before the first record of the next
filename argument is read.
With each pattern in program there can be an associated
action that will be performed when a line of a filename
matches the pattern. See the discussion below for the for-
mat of input lines and the awk language. Each line in each
input filename is matched against the pattern portion of
every pattern-action statement; the associated action is
performed for each matched pattern.
OPTIONS
-f program-file
Use the contents of program-file as the source for the
program.
-Fc Use the character c as the field separator (FS) charac-
ter. See the discussion of FS below.
USAGE
Input Lines
An input line is made up of fields separated by white space.
The field separator can be changed by using FS - see Special
Variable Names below. Fields are denoted $1, $2, and so
forth. $0 refers to the entire line.
Pattern-action Statements
A pattern-action statement has the form
pattern { action }
A missing action means copy the line to the output; a miss-
ing pattern always matches.
Action Statements
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 ]
Sprintf format [ , expression-list ] [ > expression ]
next skip remaining patterns on this
input line
exit skip the rest of the input
Format of the awk Language
statements are terminated by semicolons, NEWLINE characters
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 con-
catenation (indicated by a blank). The C operators ++ , --
, += , -= , *= , /= , and %= are also available in expres-
sions.
variable 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,
providing a form of associative memory. String constants
are quoted "... ".
The print statement prints its arguments on the standard
output (or on a file if >filename 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 template format (see
printf(3V) for a description of the formatting control char-
acters).
Built In Functions
The built-in function length returns the length of its argu-
ment taken as a string, or of the whole line if no argument.
There are also built-in functions exp, log, sqrt, and int,
where int truncates its argument to an integer. `substr( s,
m, n )' returns the n-character substring of s that begins
at position m. `sprintf (format, expression, expression,
...)' formats the expressions according to the printf format
given by format, and returns the resulting string.
Patterns
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(1V)), 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 a relop is any of the six relational operators in C,
and a matchop is either ~ (contains) or !~ (does not con-
tain). A conditional is an arithmetic expression, a rela-
tional expression, or a Boolean combination of these.
The special pattern BEGIN may be used to capture control
before the first input line is read, in which case BEGIN
must be the first pattern. The special pattern END may be
used to capture control after the last input line is read,
in which case END must be the last pattern.
Special Variable Names
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
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
grep(1V), lex(1), sed(1V), printf(3V)
Editing Text Files
A. V. Aho, B. W. Kerninghan, P. J. Weinberger, The AWK Pro-
gramming Language Addison-Wesley, 1988.
NOTES
The awk command is not changed to support 8-bit symbol
names, as this would produce awk source code that is not
portable between systems.
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 concaten-
ate the null string ("") to it.
There is no escape sequence that prints a double-quote. A
workaround is to use the sprintf (see printf(3V)) function
to store the character into a variable by its ASCII
sequence.
dq = sprintf("%c", 34)
Syntax errors result in the cryptic message `awk: bailing
out near line 1'.
Sun Release 4.1 Last change: 24 September 1987
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