awk(1)
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awk Command
pattern scanning and processing language
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SYNTAX
awk [ -Fc ] [ -f file ] [ prog ] [ parameters ] [ files ]
DESCRIPTION
Awk scans each input file for lines that match any of a set of
patterns specified in prog. Each pattern in prog can have 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.
The -Fc option specifies c as a field separator.
Parameters, in the form x=... y=... etc., may be passed to awk.
The parameters cannot be array elements.
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 the -Fc option or 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 ]
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awk(1)
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 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 enquoted (").
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)).
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
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.
You can use the special patterns BEGIN and END to capture control
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awk(1)
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 blank); ORS, the output
record separator (default new-line); and OFMT, the output format
for numbers (default %.6g).
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EXAMPLES
$ awk "length > 72" infile
This form of the command will print only those lines in the file
"infile" that are longer that 72 characters.
$ awk '{ s += $3 }
> END { print "sum is", s, " average is", s/NR }' salesreport
This form of the command will add up the third column of the
file, "sales_report", and print the sum and average of that sum.
$ awk '{ for (i = NF; i > 0; --i) print $i }' infile
This form of the command will print each of the fields in reverse
order.
$ cat cmdfile
/page/ { $2 = n++; }
{ print }
$ awk -f cmdfile n=1 report > numreport
Using the commands in the file "cmd_file", this form of the
command will print file "report", filling in page numbers and
outputting file "num_report" which will be the original report
with page numbers.
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SEE ALSO
grep(1), lex(1), sed(1), malloc(3X). Programmer's Guide to the
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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, concatenate the null string
("") to it.
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