To extract attachments from the Terminal, you can use a couple of different methods. Probably the easiest is
perl -MMIME::Base64 -ne 'print decode_base64($_)' < file.eml > out
file.eml is the email file in question and
out is the name of the attachment.
The same thing can be accomplished by using the
base64 command, but you have to do some cleanup work on the original email file first -- namely strip everything out of the eml file before the base64 encoded attachment. The command would be something along these lines
base64 -D -i file.eml -o out
If you take the 2nd approach, recommend that you operate on a copy of the original file.
Of course for reading the eml files, you can probably use
cat or your favorite editor. Works in a pinch, but certainly not the easiest way to deal with email.