How to copy all files with extension/filetype in terminal? I want to copy all files in ~/Desktop with the extension .jpeg to my flash drive.

How can I do this in the terminal?
cp ~/Desktop/*.jpeg /Volumes/flashdrive/


will copy all of the files on the current user's desktop with extension ".jpeg" to the drive named "flashdrive".  

If the above command produces an Argument list too long error, then the safest most efficient way to handle it is to use a for loop like this:

for f in ~/Desktop/*.jpeg; do cp "$f" /Volumes/flashdrive/; done