I found this lovely snippet of code while fixing* a broken script. I especially love how as a side effect it removes the spaces from $_.
sub Commify { s/ //g; my $delimiter = ','; my($n,$d) = split /\./,shift,2; my @a = (); while($n =~ /\d\d\d\d/) { $n =~ s/(\d\d\d)$//; unshift @a,$1; } unshift @a,$n; $n = join $delimiter,@a; $n = "$n\.$d" if $d =~ /\d/; return $n; }
*The sort of fixing that is done with rm.