A crystal git command that prints the shasum of your last commit. Just `crystal build git-sum.cr --release` and put the resulting `git-sha` executable in your PATH, then `git sha`.

git-sha.cr

require "colorize"
require "option_parser"

##
# Use color by default if stdout is a terminal.
color = STDOUT.tty?

OptionParser.parse! do |opts|
  opts.banner = "usage: git sum [-h --help] [--no-color]"

  # Git redirects --help to the manpage.
  opts.on "-h", "print this help menu" do
    puts opts
    exit
  end

  opts.on "--no-color", "omit color" do
    color = false
  end
end

checksum = IO::Memory.new
git_error = IO::Memory.new
checksum_command = Process.run "git", {"rev-parse", "HEAD"}, output: checksum, error: git_error

abort git_error.to_s.chomp, checksum_command.exit_code unless checksum_command.success?

if color
  abbrev = IO::Memory.new
  abbrev_command = Process.run "git", {"config", "--get", "core.abbrev"}, output: abbrev
  short = abbrev_command.success? ? abbrev.to_s.to_i : 9

  print checksum.to_s[0..short.to_s.to_i.pred].colorize(:green).mode(:bold)
  print checksum.to_s[short.to_s.to_i..-1].colorize(:magenta).mode(:bold)
else
  print checksum
end