nawk(1) DG/UX 5.4.2 nawk(1)
NAME
nawk, awk - 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. 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 regularexpression
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
var in array
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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)
SUBSEP separates multiple subscripts (default is 034)
An action is a sequence of statements. A statement may be one of the
following:
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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
excapes 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)]. 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).
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.
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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.
getline x sets variable x instead.
getline x <file
sets x from the next record of file.
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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:
$1 != prev { print; prev = $1 }
Simulate echo(1):
BEGIN {
for (i = 1; i < ARGC; i++)
printf "%s", ARGV[i]
printf "\n"
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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), oawk(1), sed(1), lex(1), printf(3S).
The awk chapter in the Using the DG/UX Software Development Tools.
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 eventually become the
default version of awk.
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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