How do I detect plaintext in a MIME file?

Question

I have a large set of MIME files, which contain multiple parts. Many of the files contain parts labelled with the following headers:

Content-Type: application/octet stream

Content-Transfer-Encoding: Binary

However, sometimes the contents of these parts are some form of binary code, and sometimes they are plaintext.

Is there a clever way in either C++, Bash or Ruby to detect whether the contents of a MIME part labelled as application/octet stream is binary data or plaintext?

Thanks, Rik

Answer 1

The -I option of grep will treat binary files as files without a match. Combined with the -q option grep will return a nonzero exit status if a file is binary.

if grep -qI -e '' <file>
then
        # plaintext
else
        # binary
fi

Answer 2

The simplest method is to split the file into a set of multiple files each of which contains one of the component parts. We can then use grep and other functions to ascertain the text format.