require_relative in config.ru

config.ru

require_relative './mylib'

run ->(env){ [200, {}, ['']] }

mylib.rb

# I'm just required

running_rackup.txt

rackup
#=> /Users/tjsingleton/tmp/rack_relative/config.ru:1:in `require_relative': cannot infer basepath (LoadError)

This is because the rackup file is eval'd

ruby -e 'eval("require_relative %[./mylib]")'
-e:1:in `eval': cannot infer basepath (LoadError)
    from (eval):1:in `<main>'
    from -e:1:in `eval'
    from -e:1:in `<main>'

So, whats the solution for this?

Update your ruby version to 2.1.0. will be fixed.