awk(1) (Directory and File Management Utilities) 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, and are built using the
operators +, -, *, /, %, and concatenation (indicated by a blank).
The C operators ++, --, +=, -=, *=, /=, and %= are also available in
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awk(1) (Directory and File Management Utilities) awk(1)
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 (").
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awk(1) (Directory and File Management Utilities) awk(1)
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 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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awk(1) (Directory and File Management Utilities) awk(1)
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), nawk(1), sed(1).
lex(1), printf(3S) in the 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 concatenate the null string ("") to it.
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