Most members of this command were quite young. I believe this man belonged to Perrin's Co. "D", which included recruits from Greene, Tuscaloosa and Pickens Counties. Early records show it as Co. "B" of Major Hatch's Battalion before the command was turned over to Confederate service.
The name "Perrin" may look like "Price" in script. Capt. George G. Perrin of the University of Alabama class of 1863 was killed at Pine Barren Creek, Florida, December 17, 1864.

With regard to your question about unit identification, it helps to know the following about each company:

1. Official designation as assigned by the War Department
2. Names of each company captain
3. Home county of most members
4. Previous and subsequent designations
5. Unit service history

Sometime you can read a veteran's testimony about when and where he served along with one or two others clues and place him in a unit. Sometimes it's just a captain's name and a place of recruitment. For instance, someone asked about a soldier who was assigned to the 21st Alabama as a conscript, was discharged and later enrolled in Captain Moore's Cavalry. Since he was from Cedar Grove (modern-day Leeds), that places him in Co. "D", Livingston's 8th Alabama Cavalry, Capt. John G. Moor, which organized at Cedar Grove on Sept. 25, 1863, and served for a time as an independent company before joining Livingston's command.

With regard to units like Hatch's and Livingston's, I reviewed pay receipts and requisitions for each officer to determine what their companies were called and where they were prior to joining a regiment. These documents provide important clues on company histories that are not found elsewhere.