Confusing option parser

Help & Support
1

The first one is quite normal, works as expected.

OptionParser.parse do |parser|
  parser.on("-h", "--help", "Show config help") do
    puts "config --help"
    exit
  end
  parser.on("-v", "--version", "Print the version") do
    puts "config --version"
    exit
  end
end

The second will exit directly, which indicates the program doesn’t execute in sequence but following a nested order.

OptionParser.parse do |parser|
  parser.on("-h", "--help", "Show config help") do
    puts "config --help"
  end
  parser.on("-v", "--version", "Print the version") do
    puts "config --version"
  end
  exit
end
2

The block passed to OptionParser.parse is meant to configure the option parser instance. The actual parsing starts after the entire block has completed.

Your code is equivalent to this:

parser = OptionParser.new
parser.on("-h", "--help", "Show config help") do
  puts "config --help"
end
parser.on("-v", "--version", "Print the version") do
  puts "config --version"
end
exit
parser.parse

Note that parse is called after exit, so it never happens.

OptionParser#on registers the block as a handler which is used when the option name matches while executing parse.

1 Like