NAWK(1) SysV NAWK(1)
NAME
nawk - pattern-directed scanning and processing language
SYNOPSIS
nawk [ -Ffs ] [ -v var=value ] [ prog ] [ file ... ]
DESCRIPTION
nawk is a new version of awk that provides capabilites unavailable in
previous versions. This version will become the default version of awk
in the next major UNIX system release.
nawk scans each input file for lines that match any of a set of patterns
specified literally in prog or in one or more files specified as -f file.
With each pattern there can be an associated action that will be
performed when a line of a file matches the pattern. Each line is
matched against the pattern portion of every pattern-action statement;
the associated action is performed for each matched pattern. The file
name means the standard input. 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 made up of fields separated by white space, or by
regular expression FS. The fields are denoted $1, $2, ..., while $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. Pattern-action statements are separated by newlines or
semicolons.
An action is a sequence of statements. A statement can be one of the
following:
if( expression ) statement [ else statement ]
while( expression ) statement
for( expression ; expression ; expression ) statement
for( var in array ) statement
do statement while( expression )
break
continue
{ [ statement ... ] }
expression # commonly var = expression
print [ expression-list ] [ > expression ]
printf format [ , expression-list ] [ > expression ]
return [ expression ]
next # skip remaining patterns on this input line
delete array[ expression ] # delete an array element
exit [ expression ] # exit immediately; status is expression
Statements are terminated by semicolons, newlines or right braces. An
empty expression-list stands for $0. String constants are quoted " ",
with the usual C escapes recognized within. Expressions take on string
or numeric values as appropriate, and are built using the operators +, -,
*, /, %, ^ (exponentiation), and concatenation (indicated by a blank).
The 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. Multiple
subscripts such as [i,j,k] are permitted; the constituents are
concatenated, separated by the value of SUBSEP.
The print statement prints its arguments on the standard output (or on a
file if >file or >>file is present or on a pipe if |cmd is present),
separated by the current output field separator, and terminated by the
output record separator. file and cmd may be literal names or
parenthesized expressions; identical string values in different
statements denote the same open file. The printf statement formats its
expression list according to the specified format (see printf(3S)). The
built-in function close(expr) closes the file or pipe expr.
The mathematical functions exp, log, sqrt, sin, cos, and atan2 are built
in. Other built-in functions:
length
the length of its argument taken as a string, or of $0 if no
argument.
rand random number on (0,1)
srand
sets seed for rand and returns the previous seed.
int truncates to an integer value
substr(s, m, n)
the n-character substring of s that begins at position m counted
from 1.
index(s, t)
the position in s where the string t occurs, or 0 if it does not.
match(s, r)
the position in s where the regular expression r occurs, or 0 if it
does not. The variables RSTART and RLENGTH are set to the position
and length of the matched string.
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.
sub(r, t, s)
substitutes t for the first occurrence of the regular expression r
in the string s. If s is not given, $0 is used.
gsub same as sub except that all occurrences of the regular expression
are replaced; sub and gsub return the number of replacements.
sprintf(fmt, expr, ... )
the string resulting from formatting expr ... according to the
printf(3) format fmt
system(cmd)
executes cmd and returns its exit status
The ``function'' 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. Finally, cmd | getline pipes the
output of cmd into getline; each call of getline returns the next line of
output from cmd. In all cases, getline returns 1 for a successful input,
0 for end of file, and -1 for an error.
Patterns are arbitrary Boolean combinations (with !, ||, and &&) of
regular expressions and relational expressions. Regular expressions 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, using the operators ~ and !~. /re/ is a constant
regular expression; any string (constant or variable) may be used as a
regular expression, except in the position of an isolated regular
expression in a pattern.
A pattern may consist of two patterns separated by a comma; in this case,
the action is performed for all lines from an occurrence of the first
pattern though an occurrence of the second.
A relational expression is one of the following:
expression matchop regular-expression
expression relop expression
expression in array-name
(expr,expr,...) in array-name
where a relop is any of the six relational operators in C, and a matchop
is either ~ (matches) or !~ (does not match). 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 and END do not
combine with other patterns.
Variable names with special meanings:
FS regular expression used to separate fields; also settable by option
-Ffs.
NF number of fields in the current record
NR ordinal number of the current record
FNR ordinal number of the current record in the current file
FILENAME
the name of the current input file
RS input record separator (default newline)
OFS output field separator (default blank)
ORS output record separator (default newline)
OFMT output format for numbers (default %.6g)
SUBSEP
separates multiple subscripts (default 034)
ARGC argument count, assignable
ARGV argument array, assignable; non-null members are taken as filenames
ENVIRON
array of environment variables; subscripts are names.
Functions may be defined (at the position of a pattern-action statement)
thus:
function foo(a, b, c) { ...; return x }
Parameters are passed by value if scalar and by reference if array name;
functions may be called recursively. Parameters are local to the
function; all other variables are global. Thus local variables may be
created by providing excess parameters in the function definition.
EXAMPLES
length > 72
Print lines longer than 72 characters.
{ print $2, $1 }
Print first two fields in opposite order.
BEGIN { FS = ",[ \t]*|[ \t]+" }
{ print $2, $1 }
Same, with input fields separated by comma and/or blanks and tabs.
{ s += $1 }
END { print "sum is", s, " average is", s/NR }
Add up first column, print sum and average.
/start/, /stop/
Print all lines between start/stop pairs.
BEGIN { # Simulate echo(1)
for (i = 1; i < ARGC; i++) printf "%s ", ARGV[i]
printf "\n"
exit }
SEE ALSO
grep(1), lex(1), sed(1).
printf(3S) in the SysV Programmer's Reference.
nawk in the SysV Programmer's Guide.
A. V. Aho, B. W. Kernighan, P. J. Weinberger, The AWK Programming
Language, Addison-Wesley, 1988.
BUGS
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 "" to it.
The scope rules for variables in functions are a botch; the syntax is
worse.