nawk(1) UNIX System V(Directory and File Management Utilities) nawk(1)
NAME
nawk - pattern scanning and processing language
SYNOPSIS
nawk [-F re] [-v var=value] ['prog'] [file...]
nawk [-F re] [-v var=value] [-f progfile] [file...]
DESCRIPTION
nawk scans each input file for lines that match any of a set of patterns
specified in prog. The prog string must be enclosed in single quotes (')
to protect it from the shell. For each pattern in prog there may be an
associated action performed when a line of a file matches the pattern.
The set of pattern-action statements may appear literally as prog or in a
file specified with the -f progfile option. Input files are read in
order; if there are no files, the standard input is read. The file name
- means the standard input.
Each input line is matched against the pattern portion of every pattern-
action statement; the associated action is performed for each matched
pattern. Any file of the form var=value is treated as an assignment, not
a filename, and is executed at the time it would have been opened if it
were a filename, and is executed at the time it would have been opened if
it were a filename. The option -v followed by var=value is an assignment
to be done before prog is executed; any number of -v options may be
present.
An input line is normally made up of fields separated by white space.
(This default can be changed by using the FS built-in variable or the -F
re option.) The fields are denoted $1, $2, ...; $0 refers to the entire
line.
A pattern-action statement has the form:
pattern { action }
Either pattern or action may be omitted. If there is no action with a
pattern, the matching line is printed. If there is no pattern with an
action, the action is performed on every input line. Pattern-action
statements are separated by newlines or semicolons.
Patterns are arbitrary Boolean combinations ( !, ||, &&, and parentheses)
of relational expressions and regular expressions. A relational
expression is one of the following:
expression relop expression
expression matchop regular_expression
expression in array-name
(expression,expression, ... ) in array-name
where a relop is any of the six relational operators in C, and a matchop
is either ~ (contains) or !~ (does not contain). An expression is an
arithmetic expression, a relational expression, the special expression
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nawk(1) UNIX System V(Directory and File Management Utilities) nawk(1)
var in array
or a Boolean combination of these.
Regular expressions are as in egrep(1). In patterns they must be
surrounded by slashes. 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 pattern.
The special patterns BEGIN and END may be used to capture control before
the first input line has been read and after the last input line has been
read respectively. These keywords do not combine with any other
patterns.
A regular expression may be used to separate fields by using the -F re
option or by assigning the expression to the built-in variable FS. The
default is to ignore leading blanks and to separate fields by blanks
and/or tab characters. However, if FS is assigned a value, leading
blanks are no longer ignored.
Other built-in variables include:
ARGC command line argument count
ARGV command line argument array
ENVIRON array of environment variables; subscripts are names
FILENAME name of the current input file
FNR ordinal number of the current record in the current
file
FS input field separator regular expression (default
blank and tab)
NF number of fields in the current record
NR ordinal number of the current record
OFMT output format for numbers (default %.6g)
OFS output field separator (default blank)
ORS output record separator (default new-line)
RS input record separator (default new-line)
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nawk(1) UNIX System V(Directory and File Management Utilities) nawk(1)
SUBSEP separates multiple subscripts (default is 034)
An action is a sequence of statements. A statement may be one of the
following:
if ( expression ) statement [ else statement ]
while ( expression ) statement
do statement while ( expression )
for ( expression ; expression ; expression ) statement
for ( var in array ) statement
delete array[subscript] #delete an array element
break
continue
{ [ statement ] ... }
expression # commonly variable = expression
print [ expression-list ] [ >expression ]
printf format [ , expression-list ] [ >expression ]
next # skip remaining patterns on this input line
exit [expr] # skip the rest of the input; exit status is expr
return [expr]
Statements are terminated by semicolons, new-lines, or right braces. An
empty expression-list stands for the whole input line. Expressions take
on string or numeric values as appropriate, and are built using the
operators +, -, *, /, %, ^ and concatenation (indicated by a blank). The
operators ++ -- += -= *= /= %= ^= > >= < <= == != ?: are also available
in expressions. Variables may be scalars, array elements (denoted x[i]),
or fields. Variables are initialized to the null string or zero. Array
subscripts may be any string, not necessarily numeric; this allows for a
form of associative memory. Multiple subscripts such as [i,j,k] are
permitted; the constituents are concatenated, separated by the value of
SUBSEP. String constants are quoted (""), with the usual C escapes
recognized within.
The print statement prints its arguments on the standard output, or on a
file if >expression is present, or on a pipe if | cmd is present. The
arguments are 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 close(expr) closes
the file or pipe expr.
The mathematical functions: atan2, cos, exp, log, sin, sqrt, are built-
in.
Other built-in functions include:
gsub(for, repl, in)
behaves like sub (see below), except that it replaces
successive occurrences of the regular expression (like the ed
global substitute command).
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nawk(1) UNIX System V(Directory and File Management Utilities) nawk(1)
index(s, t)
returns the position in string s where string t first occurs,
or 0 if it does not occur at all.
int truncates to an integer value.
length(s) returns the length of its argument taken as a string, or of the
whole line if there is no argument.
match(s, re)
returns the position in string s where the regular expression
re occurs, or 0 if it does not occur at all. RSTART is set to
the starting position (which is the same as the returned
value), and RLENGTH is set to the length of the matched string.
rand random number on (0, 1).
split(s, a, fs)
splits the string s into array elements a[1], a[2], a[n], and
returns n. The separation is done with the regular expression
fs or with the field separator FS if fs is not given.
srand sets the seed for rand
sprintf(fmt, expr, expr,...)
formats the expressions according to the printf(3S) format
given by fmt and returns the resulting string.
sub(for, repl, in)
substitutes the string repl in place of the first instance of
the regular expression for in string in and returns the number
of substitutions. If in is omitted, nawk substitutes in the
current record ($0).
substr(s, m, n)
returns the n-character substring of s that begins at position
m.
The input/output built-in functions are:
close(filename)
closes the file or pipe named filename.
cmd | getline
pipes the output of cmd into getline; each successive call to
getline returns the next line of output from cmd.
getline sets $0 to the next input record from the current input file.
getline <file
sets $0 to the next record from file.
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nawk(1) UNIX System V(Directory and File Management Utilities) nawk(1)
getline x sets variable x instead.
getline x <file
sets x from the next record of file.
system(cmd)
executes cmd and returns its exit status.
All forms of getline return 1 for successful input, 0 for end of file,
and -1 for an error.
nawk also provides user-defined functions. Such functions may be defined
(in the pattern position of a pattern-action statement) as
function name(args,...) { stmts }
Function arguments are passed by value if scalar and by reference if
array name. Argument names are local to the function; all other variable
names are global. Function calls may be nested and functions may be
recursive. The return statement may be used to return a value.
EXAMPLES
Print lines longer than 72 characters:
length > 72
Print first two fields in opposite order:
{ print $2, $1 }
Same, with input fields separated by comma and/or blanks and tabs:
BEGIN { FS = ",[ \t]*|[ \t]+" }
{ 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:
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nawk(1) UNIX System V(Directory and File Management Utilities) nawk(1)
$1 != prev { print; prev = $1 }
Simulate echo(1):
BEGIN {
for (i = 1; i < ARGC; i++)
printf "%s", ARGV[i]
printf "\n"
exit
}
Print a file, filling in page numbers starting at 5:
/Page/ { $2 = n++; }
{ print }
Assuming this program is in a file named prog, the following command line
prints the file input numbering its pages starting at 5: nawk -f prog
n=5 input.
SEE ALSO
egrep(1), grep(1), sed(1).
lex(1), printf(3S) in the Programmer's Reference Manual.
The awk chapter in the User's Guide.
A. V. Aho, B. W. Kerninghan, P. J. Weinberger, The AWK Programming
Language Addison-Wesley, 1988.
NOTES
nawk is a new version of awk that provides capabilities unavailable in
previous versions. This version will become the default version of awk
in the next major UNIX system release.
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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