# open an euc-jp file:
open( $inp, "<:encoding(euc-jp)", "some_file.euc" ) or die "$!";

while (<$inp>) {  # data will be decoded on input
    ... # so $_ will have its utf8 flag "on" and 
        #   s///, ord(), etc will use character semantics
}

# open a utf8 file:
open( $inp, "<:utf8", "some_file.utf8" ) or die "$!";

while (<$inp>) {  # data will be interpreted as utf8 on input
    ... # so $_ will have its utf8 flag "on" and... (same as above)
}