while(<STDIN>){
  chomp();

# Oops, nope -- variable-length lookbehind:
#  s/(?!$shiftjis).(?<!$shiftjis)//ogx;

# This runs, but doesn't do the job:
#  s/(?!$shiftjis).//ogx;

# This should work:
  s/(?!$shiftjis).
    (?<![\x30-\x39\x41-\x59\x61-\x7A])
    (?<![\x82-\x83][\x3F-\xFE]
       |[\x88][\x9E-\xFE]
       |[\x89-\xE9][\x3F-\xFE]
       |[\xEA][\x3F-\x9F])
   //ogx;

  print $_."\n";
}