How do I identify the file system of a drive in Mac OS?

Solution 1:

diskutil(8) with the info predicate will give you information about a disk or partition.

Solution 2:

Highlight the volume in finder (note, that it must be the root of the volume), and hit cmd + i. The info dialog that appears shows you the filesystem type against the Format label.

Solution 3:

Running mount in also works and has way less noise when compared to diskutil info -all.

Solution 4:

Unless you're wedded to doing it from the command line, use Disk Utility and it's "Info" button.