How can I select random files from a directory in bash?

Here's a script that uses GNU sort's random option:

ls |sort -R |tail -$N |while read file; do
    # Something involving $file, or you can leave
    # off the while to just get the filenames
done

You can use shuf (from the GNU coreutils package) for that. Just feed it a list of file names and ask it to return the first line from a random permutation:

ls dirname | shuf -n 1
# probably faster and more flexible:
find dirname -type f | shuf -n 1
# etc..

Adjust the -n, --head-count=COUNT value to return the number of wanted lines. For example to return 5 random filenames you would use:

find dirname -type f | shuf -n 5