git pre-receive hook to reject commits not matching a certain pattern

git pre-receive hook

#!/usr/bin/env ruby

# uncomment following if using update hook script
# $refname = ARGV[0]
# $oldrev  = ARGV[1]
# $newrev  = ARGV[2]

# pre-receive hook script get these values at STDIN
$input = STDIN.gets
inputs = $input.split(' ')

$refname = inputs[2]
$oldrev  = inputs[0]
$newrev  = inputs[1]

$user    = ENV['GL_USERNAME']
$protocol = ENV['GL_PROTOCOL']

if $user == "jenkins"
  puts "Ignoring update hook for jenkins"
  exit 0
end

if $newrev == "0000000000000000000000000000000000000000"
  puts "Ignoring policy check for branch deletion"
  exit 0
end

# if $protocol != "ssh"
#   puts "#############################################################"
#   puts "#                                                           #"
#   puts "# [POLICY] Only ssh protocol is allowed                     #"
#   puts "#                                                           #"
#   puts "#############################################################"
#   exit 1
# end

puts "Enforcing Policies..."
puts "(#{$refname}) (#{$oldrev}) (#{$newrev})"

# $regex = /\[ref: (\d+)\]/
$regex = /(ProjectA\-|Merge|Revert).*/

# enforced custom commit message format
def check_message_format
  # puts "#{Dir.pwd}"
  if "0000000000000000000000000000000000000000" == $oldrev
    # $oldrev = `git rev-list --boundary #{$newrev} --not --all | sed -n 's/^-//p'`.split("\n")[0]
    # missed_revs = `git rev-list #{$newrev} --not --branches=*`.split("\n")
    missed_revs = `git rev-list $(git for-each-ref --format='%(refname)' refs/heads/* | sed 's/^/\^/') "#{$newrev}"`.split("\n")
  else
    missed_revs = `git rev-list #{$oldrev}..#{$newrev}`.split("\n")
  end
  puts "Commits to check: #{missed_revs}"
  missed_revs.each do |rev|
    # puts "git cat-file commit #{rev} | sed '1,/^$/d'"
    message = `git cat-file commit #{rev} | sed '1,/^$/d'`
    if !$regex.match(message)
      puts "#############################################################"
      puts "#                                                           #"
      puts "# [POLICY] Your commit message doesn't have ticket number   #"
      puts "# Wrong message: #{message}                                 #"
      puts "#                                                           #"
      puts "#############################################################"
      exit 1
    end
  end
end

check_message_format