Ruby 'require' error: cannot load such file

Question

I just tried and it works with require "./tokenizer". Hope this helps.

Just do this:

require_relative 'tokenizer'

If you put this in a Ruby file that is in the same directory as tokenizer.rb, it will work fine no matter what your current working directory (CWD) is.

Explanation of why this is the best way

The other answers claim you should use require './tokenizer', but that is the wrong answer, because it will only work if you run your Ruby process in the same directory that tokenizer.rb is in. Pretty much the only reason to consider using require like that would be if you need to support Ruby 1.8, which doesn't have require_relative.

The require './tokenizer' answer might work for you today, but it unnecessarily limits the ways in which you can run your Ruby code. Tomorrow, if you want to move your files to a different directory, or just want to start your Ruby process from a different directory, you'll have to rethink all of those require statements.

Using require to access files that are on the load path is a fine thing and Ruby gems do it all the time. But you shouldn't start the argument to require with a . unless you are doing something very special and know what you are doing.

When you write code that makes assumptions about its environment, you should think carefully about what assumptions to make. In this case, there are up to three different ways to require the tokenizer file, and each makes a different assumption:

1. require_relative 'path/to/tokenizer': Assumes that the relative path between the two Ruby source files will stay the same.
2. require 'path/to/tokenizer': Assumes that path/to/tokenizer is inside one of the directories on the load path ($LOAD_PATH). This generally requires extra setup, since you have to add something to the load path.
3. require './path/to/tokenizer': Assumes that the relative path from the Ruby process's current working directory to tokenizer.rb is going to stay the same.

I think that for most people and most situations, the assumptions made in options #1 and #2 are more likely to hold true over time.

Ruby 1.9 has removed the current directory from the load path, and so you will need to do a relative require on this file, as David Grayson says:

require_relative 'tokenizer'

There's no need to suffix it with .rb, as Ruby's smart enough to know that's what you mean anyway.

require loads a file from the $LOAD_PATH. If you want to require a file relative to the currently executing file instead of from the $LOAD_PATH, use require_relative.

I would recommend,

load './tokenizer.rb'

Given, that you know the file is in the same working directory.

If you're trying to require it relative to the file, you can use

require_relative 'tokenizer'

I hope this helps.

Another nice little method is to include the current directory in your load path with

$:.unshift('.')

You could push it onto the $: ($LOAD_PATH) array but unshift will force it to load your current working directory before the rest of the load path.

Once you've added your current directory in your load path you don't need to keep specifying

 require './tokenizer' 

and can just go back to using

require 'tokenizer'

This will work nicely if it is in a gem lib directory and this is the tokenizer.rb

require_relative 'tokenizer/main'