Finds git commit that merged other commit into master

find-commit.rb

commit = ARGV[0]
master = ARGV[1] || 'origin/master'

unless commit
  puts "Usage: find-commit.rb commit [master-branch]"
  puts "Will show commit that merged <commit> into <master-branch>"
  exit 1
end

parents = `git rev-list #{commit}..#{master} --reverse --first-parent --merges`.split("\n")
ancestry = `git rev-list #{commit}..#{master} --reverse --ancestry-path --merges`.split("\n")
merge = (parents & ancestry)[0]

if merge
  system "git show #{merge}"
else
  puts "#{master} doesn't include #{commit}"
  exit 2
end