Ruby, which exception is best to handle unset environment variables?

Question

The script I wrote runs at start up and requires that an environment variable be set, but which of Ruby's Exceptions, is best? I used LoadError, I just want to be as descriptive as possible and follow the proper conventions.

Secondly, I can't find another way to see if an environment variable is set besides checking it's length, but that doesn't seem so elegant.

begin
  raise LoadError if ENV['FOO'].to_s.length == 0
  system "open http://example.com/" + ENV['FOO']
rescue Exception => e
  puts "=> #{e} FOO environment variable not set"
end

Translucent

any reason to not just write your own exception? – Phlebotomy

Because I'd rather follow a convention that is more popular if it's available to me. – Translucent

Answer 1

Could use ENV.fetch('FOO') which then raises a KeyError if not found.

Wilser

This is the most simple and straight forward, since 2012 things have changed and this seems to have emerged as a popular design pattern. – Translucent

Answer 2

You can do something like:

ENV['SECRET_KEY_XXYY'] || raise('no SECRET_KEY_XXYY provided')

Nonpayment

Answer 3

According to the documentation for LoadError that is supposed to be used for when a 'require' has an issue. I think the more proper method would be to subclass StandardError and make one that fits your use. If that seems a bit much I would just go with StandardError with a descriptive message.

Android

Answer 4

Making your own exceptions is easy:

MyError = Class.new(StandardError)
raise MyError, "FOO environment variable not set" unless ENV['FOO']
system "open http://example.com/" + ENV['FOO']

Catching the exception in that code block may not be appropriate in this case, since it seems you are just printing a message with it. As a rule, never raise an exception unless you are prepared for it to terminate the program. In other words, avoid using exceptions for expected conditions. If the program can continue without FOO being set, it would be better to simply make execution of the system statement conditional:

system("open http://example.com/" + ENV['FOO']) if ENV['FOO']

or

ENV['FOO'] && system("open http://example.com/" + ENV['FOO'])

Sigismond

Answer 5

There's a list of exception types at http://bugs.ruby-lang.org/projects/ruby/wiki/ExceptionClassesDoc

I'd probably choose ArgumentError , as you're saying that the value of ENV['FOO'] isn't what you expected it to be.

Delphiadelphic

Answer 6

You could use fetch with a block to raise specific error

ENV.fetch('FOO') { raise 'FOO environment variable is not set' }

Ess