For OS X and other platforms where you don't have GNU sort, but want a quick way to shuffle lines. This has been done many times before, but most implementations I've seen don't deal equally with filename arguments and stdin.

unsort.sh

#!/bin/bash
# Licensed under any of GPLv2, MIT, and BSD 2-clause licenses

(
  if [[ $1 ]]; then
		while [[ $1 ]]; do
			cat $1
			shift
		done
	else cat
	fi
) |\
while read line; do
	echo "${RANDOM}~$line";
done | sort | sed -E 's/^[0-9]+~//'