How to find out Bluez version from command line?

If you have a rough idea (or are fine with covering the last 10 years), bluez provides tools in bluez-uils to request the version. Unfortunately, these tools changed between version 4 and 5, so you may have to check if one of both is installed.

For BlueZ 4.0:

bluetoothd --version

Since BlueZ 5.0, there is a new command-line tool bluetoothctl:

bluetoothctl --version

Bluez provides a shared library called libbluetooth.so. On x86_64 distros you should find this file in /usr/lib64/, so simply do a ls -la to find out

$ls -la /usr/lib64/libbluetooth.so
lrwxrwxrwx 1 root root 22 Jan 17 12:44 /usr/lib64/libbluetooth.so -> libbluetooth.so.3.17.0

In my case, I'm using version 3.17.0

readelf(1) can also provide some information as well.

On my distribution (Fedora 21), you can find it in /usr/share/doc/bluez/ChangeLog. You might try reading it with less or simliar.