This little utility can be used to choose a random selection of files from a given directory and output the list to stdout. The invocation looks like this:

randfiles [options] [dir1, [dir2, [...]]]

If no directories are given, the current directory is used. The possible options are:

• -s, --size-limit [SIZE]: Set a size limit for the selected files. For example, randfiles --size-limit 400MB will select up to 400MB of files.
• -c --count [N]: Set the maximum number of files. randfiles --count 3 would only choose three random files.

To copy a random selection of music to a flash drive, limited to 3GB, you can do this:

randfiles --size-limit 3GB ~/music | xargs -i -d'\n' cp -v {} /mnt/usb

If you're unfamiliar with xargs:

• -i replaces all occurrences of {} with what's read as input
• -d'\n' ensures that the items are delimited by newlines (there may be spaces in the file names)

The project is available as a gem, so this should be enough:

gem install randfiles

• A -0 option for easier piping
• Filtering files by regex or glob