Rails: difference between ENV.fetch() and ENV[]
The ENV hash-like object is plain Ruby, not part of Rails. From the fine ENV#[] manual:
Retrieves the value for environment variable
nameas a String. Returnsnilif the named variable does not exist.
and the fine ENV#fetch manual:
Retrieves the environment variable
name.If the given name does not exist and neither
defaultnor a block a provided an IndexError is raised. If a block is given it is called with the missing name to provide a value. If a default value is given it will be returned when no block is given.
So just like Hash#[] and Hash#fetch, the only difference is that fetch allows you to specify the behavior if a key is not found (use a default value passed to fetch, default block passed to fetch, or raise an exception) whereas [] just silently gives you nil if the key isn't found.
In the specific case of:
ENV.fetch("MY_VAR")ENV['MY_VAR']the difference is that ENV['MY_VAR'] will give you nil if there is no MY_VAR environment variable but ENV.fetch('MY_VAR') will raise an exception.