Debugging Git Errors Using Environment Variables

One of the frustrating things I've found with Git is that it can be difficult to work out why errors have occurred:

error: gpg failed to sign the data
fatal: failed to write commit object

This is especially frustrating as some commands have a --verbose flag, but do not tell us anything useful (which is made clear on the man pages, once you read about it).

I've found today that the official Git documentation has a section on "Environment Variables", and gives us information about various environment variables we can use to debug.

For instance, GIT_TRACE gives us information about what's happening under the hood:

$ GIT_TRACE=1 git commit -m "Add page that always requires a logged-in user"
20:52:58.902766 git.c:328               trace: built-in: git 'commit' '-vvv' '-m' 'Add page that always requires a logged-in user'
20:52:58.918467 run-command.c:626       trace: run_command: 'gpg' '--status-fd=2' '-bsau' '23810377252EF4C2'
error: gpg failed to sign the data
fatal: failed to write commit object