or download this
sub assemble{my($f,$s)=splice(@_,0,2);return$f unless$s;
$f=(sort{length($a)<=>length($b)}(c($f,$s),c($s,$f)))[0];
assemble($f,@_)}
sub c{($_,$b)=@_;return$_ if/$b/;my $r='';while($b and$r=chop($b).$r
and!(index($_,$b)>0)){}$_.$r.(length($b)==1?$b:'')}