Determine "parent" of the active git branch (Ubuntu)

git_branch_parent.sh

#!/usr/bin/env bash

# via http://stackoverflow.com/a/17843908/773209
#
# Ubuntu variant
#
# if ack-grep isn't found:
#   $ sudo apt-get install ack-grep

branch=`git rev-parse --abbrev-ref HEAD`

git show-branch 2>&1 | ack-grep '\*' | ack-grep -v "$branch" | head -n1 | sed 's/.*\[\(.*\)\].*/\1/' | sed 's/[\^~].*//' | grep -v 'more than 25'

# How it works:
#  1| Get a textual history of all commits.
# 1A| Redirect git's STDERR to STDOUT.
#  2| Ancestors of the current commit are indicated
#     by a star. Filter out everything else.
#  3| Ignore all the commits in the current branch.
#  4| The first result will be the nearest ancestor branch.
#     Ignore the other results.
#  5| Branch names are displayed [in brackets]. Ignore 
#     everything outside the brackets, and the brackets.
#  6| Sometimes the branch name will include a ~2 or ^1 to
#     indicate how many commits are between the referenced
#     commit and the branch tip. We don't care. Ignore them.
#  7| Strip excessive refs warnings (originally sent to
#     STDERR) before rendering the output.

Note: If you need this script, it's worth reading the StackOverflow thread ;)