awk(1) UNIX System V(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
expressions. Variables may be scalars, array elements (denoted x[i]) or
fields. Variables are initialized to the null string. Array subscripts
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awk(1) UNIX System V(Directory and File Management Utilities) awk(1)
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 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(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) UNIX System V(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.
NOTES
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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