This little script essentially spits out a nicely formatted report from running git branch --contains <branch> on your local repository. You might use this script if you wanted to see which branches have been merged into master already.

git-branch-report

#!/usr/bin/env ruby

require 'optparse'

options = {}

OptionParser.new do |opts|
  opts.banner = "Usage: git-branch-report [options]"

  opts.on("--porcelain", "Output machine-readable output") do |v|
    options[:porcelain] = v
  end

  opts.on_tail("-h", "--help", "Show this message") do
    puts opts
    exit
  end
end.parse!

branches = `git branch | sed -e "s/[\* ]*//"`.split("\n")

containing_branches = branches.inject({}) do |ret, branch|
  ret[branch] = `git branch --contains "#{branch}" | sed -e "s/[\* ]*//"`.split("\n")
  ret
end

if options[:porcelain]
  containing_branches.each do |branch, branches|
    puts "#{branch}: #{branches.join(" ")}"
  end
else
  puts "Branch Report"
  containing_branches.each do |branch, branches|
    puts <<-EOM

#{branch}:
  -- #{branches.join("\n  -- ")}
EOM
  end
end