git get short hash from regular hash
The shortest SHA1 you can get has a length of 4. Rev parse will give you a SHA1 of 7 digits by default with the short option :
git rev-parse --short 921103db8259eb9de72f42db8b939895f5651489
921103d
You have to specify 4 to the short option to have the shortest unambiguous SHA1 :
git rev-parse --short=4 921103db8259eb9de72f42db8b939895f5651489
92110
You can also set it in the core.abbrev configuration variable.
$ git rev-parse --short 1a6f39665adf05810f70b37ef6470bbcf61fcd38
1a6f396