Question

How to get number of revision by using repo command?

Answer 1

The the revisions, mentioned by repo init is the name of a tag:

-b: specify a revision, i.e., a particular manifest-branch.

You can see those (tags) listed in projects like platform/development or platform/build.

However, as mentioned in “repo init a particular commit“, the -b option doesn’t take a SHA1:

So, the correct way of obtaining the sources of the repository for the particular build is to obtain it’s manifest.
I.e., manifest, that will contain SHA’s (or tags, which are practically the same, if they are present) instead of branch names