s/(.)/ord($1)>127 or ord($1)<=32 ? sprintf("%%%02x",ord($1)) : $1/se;

##</code><code>##

for my $ofs (0..length($str)-1) {
  my $c=substr($str,$ofs,1);
  substr($str,$ofs,1)=sprintf("%%%02x",ord($c)) if ord($c)>127 or ord($c)<=32;
}