For instance, my code is :

my $infile = $ARGV[0];
open (IFILE, "<", $infile) || die "Cannot open : $!\n";
## read the input file
my @data;
my $COLUMNTOPARSE;
my $local;
while (<IFILE>) {
        chomp;
        my @local = split ('\t',$_);
        $COLUMNTOPARSE = $local[$ARGV[1]];
        push @data; $COLUMNTOPARSE;
}
close IFILE;
my $count = @data;
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Now I wanted to get a generalization of all the indices of 125 elements stored in the $COLUMNTOPARSE in order to calculate variance of those elements

my $variance;
my $var;
foreach my $data[$index] (@data) {
            $var = 1/($count-1);
            $variance = $var*(($data[$index]-$Average)**2);
}
print "$variance\n";
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But this $data$index way does not work.How should I proceed? Thanks..

It doesn't sound to me like you want the indices of the array, but the actual values. When you use foreach (or for) with a scalar followed by an array, that's what you get. So you can just go ahead and use the values in your formula:

foreach my $value (@data) {
    $var = 1/($count-1);
    $variance = $var*(($value-$Average)**2);
}
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If you actually need the indices, you can use a C-style for loop or the range operator, in both cases letting the scalar value of the array represent the number of elements in it:

for( my $i=0; $i < @data; $i++ ){
  # do something with $data[$i]
}

# or 

for my $i (0..(@data-1)){
  # do something with $data[$i]
}
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Hey, Thanks for the reply.I was actually confused if that way was right.In either of the three cases you have shown, it gives the same values. Thanks..