REBOL [
    Title:   "Find Invalid Chars"
    Date:    4-June-1998
    Author:  "Carl Sassenrath"
    File:    %findchars.r
    Purpose: "Finds odd unprintable ASCII characters in a file"
    Category: [file text 2]
]

bad-chars: complement charset ["^I^J^M" #" " - #"~"]

file: to-file ask "Filename? "

data: read/binary file

forall data [
    if find bad-chars first data [
        print ["Bad char at" index? data]
        print mold to-string copy/part data 10
    ]
]