# in perl 5.8.8:
perl -Mencoding=utf8 -e '$a="\x51";$b="\xE1"; printf( "a=%x b=%x\n",ord($a),ord($b))'
a=51 b=fffd

perl -Mencoding=utf8 -e '$a=chr(hex("51"));$b=chr(hex("E1")); printf( "a=%x b=%x\n",ord($a),ord($b))'
a=51 b=e1