Compare 2 branches by number of commits behind/ahead metric

.gitconfig

[alias]
        ba = "!f() { \
                LEFT=${1-master}; \
                RIGHT=${2-HEAD}; \
                OUTPUT=$(echo $(git rev-list --left-right --count $LEFT...$RIGHT) "$LEFT $RIGHT" | awk '{print $4\" is \"$1\" behind and \"$2\" ahead of \"$3}');\
                echo $OUTPUT; \
              }; f"
              
# Example:
# $  git ba develop feature/shiny-new-feature
# // feature/shiny-new-feature is 0 behind and 12 ahead of develop

# This git alias takes 2 branch names as arguments and will show how many
# commits branch 2 is behind and/or ahead branch 1.
#
# GitHub and Bitbucket have this feature but only compare branches with
# the default or main branch.

# This allows you to compare any 2 branches - including remote ones (don't forget to fetch first) - so you
# can make use of it even with your weird branching strategy.
#
# If no arguments are passed when using the alias, it will default to
# comparing HEAD with master (change the $LEFT variable to set an
# alternative main branch (e.g. develop)).

# Credit goes to this answer on stack overflow for the actual git command:
# https://stackoverflow.com/a/27940027
#
# I just turned it into an alias and formatted the output in a human-friendly way.