$s = "The\tquick\tbrown\tfox\njumps\tover\tthe\tlazy\tdog";;

print $s;;
The     quick   brown   fox
jumps   over    the     lazy    dog

($t=$s); 
$t =~ s[([^\n]+\n?)]{ my$l=$1; 1 while $l=~s[(\t)]{ '.'x(8-($-[0] % 8))}e; $l}ge; 
print $t;;
The.....quick...brown...fox
jumps...over....the.....lazy....dog