What are the paths that "require" looks up by default?

Question

In Ruby, I have been told that when doing

require "some_file"

Ruby will look for the file in certain places.

I know that it looks for some_file.rb, but where does it look for it by default?

Solution 1

It depends on your platform, and how Ruby was compiled, so there is no "the" answer to this. You can find out by running:

ruby -e 'puts $:'

Generally, though, you have the standard, site, and vendor Ruby library paths, including an arch, version, and general directory under each.

Solution 2

Ruby looks in all the paths specified in the $LOAD_PATH array.

You can also add a directory to search like so:

$LOAD_PATH.unshift File.expand_path('../path/from/this/file/to/another/directory', __FILE__)

Solution 3

additional paths can be specified by setting RUBYLIB environment variable

Solution 4

The $LOAD_PATH global variable (also named $:) contains the list of directories that are searched.

See: http://www.ruby-doc.org/core-1.9.3/Kernel.html#method-i-require

Solution 5

When calling ruby on command line, you can provide additional search paths using the -I argument. Compare the output of

$ ruby -e 'puts $:'

with the output of

$ ruby -I /tmp -e 'puts $:'

note how the second one lists /tmp as an option. You can use multiple -I to add multiple path.

You can also use it with the shebang:

#!/usr/bin/ruby -I /tmp -I /usr/local/lib/ruby

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Comments

[Perry]

There is a "the" answer. The $: or $LOAD_PATH variable does indeed give the full list of places that are searched. You yourself noted a simple and clean way to print that out...

[Daniel Pittman]

Ah. Depends how you read the question: there is "the" answer to where this Ruby looks, but it will change if you run a different Ruby or on a different platform. eg: MRI 1.8.7 and REE would use different paths, or Darwin and Linux MRI use subtly different paths. I wasn't sure which, so felt more comfortable with this answer.

[Perry]

That is true enough, though I'm guessing the questioner simply wanted to know how to find out what the load path was rather than assuming it was constant across platforms.

[Daniel Pittman]

You might well be right about that. It seemed more complex the first time I read it. :)