Please stick to `$()` instead of using backticks - it's much more flexible and less error-prone.

Also, using `which` just to determine whether a command exists is also bad.  What if it doesn't exist as an actual binary, but is instead a bash builtin?  You'd still find it acceptable.  Instead, just use something like:
```bash
if command -v md5sum &> /dev/null; then
	md5sum "$DEST/docker-$VERSION" > "$DEST/docker-$VERSION.md5"
fi
```