s/\s*$//;       # means substitute zero or more spaces
                # before end-of-line with NOTHING (get rid of them)

##</code><code>##

$jo = "Mary had a little lamb     ";
print $jo . "blah\n";

$jo =~ s/\s*$//;               # get rid of the spaces
print $jo . "blah\n";

##</code><code>##

Mary had a little lamb     blah         # spaces at end of $jo
Mary had a little lambblah              # spaces be gone!

##</code><code>##

s/\s*$//gm;