$ perl -E '
    my $x = "PROMPT\t\tTO CHANGE";
    my $len = length $x;
    my $from_index = rindex($x, "\t") + 1;
    my $from_pos = $from_index + 1;
    say $x;
    say "$from_pos through $len";
    say substr $x, $from_index, $len - $from_index;
    say substr $x, $from_index;
'
PROMPT          TO CHANGE
9 through 17
TO CHANGE
TO CHANGE