Perhaps in my sleep deprived state I'm overlooking something, but I believe that following work:

use strict;
use warnings;

my $text = "I love\tmy nation.";
$text =~ s/\t/,/g;
print "$text";
[download]

Output: I love,my nation.

However, if those are actually 8 spaces instead of an actual tab, the regex in my code won't work. In that case, you'd probably want to do something along the lines of what Nikhil Jain posted.