how to find out the parent branch in git code example

Example 1: find the parent branch of a git branch

git log --first-parent

Example 2: find out a branch a parent branch git

git show-branch -a | grep '\*' | grep -v `git rev-parse --abbrev-ref HEAD` | head -n1 | sed 's/.*\[\(.*\)\].*/\1/' | sed 's/[\^~].*//'