Ruby require 'file' doesn't work but require './file' does. Why?

Question

I have a folder full of ruby files, and when I try and require one file in another that is in the same directory using require \'file\' I get a LoadError

Answer 1

Though it is very old post I think some extra information will be very useful to beginner.

The best way to think of require is in relation to the UNIX $PATH variable. Just by way of a refresher, the $PATH variable in UNIX is a list of directories where executables can be found. So when you type the name of a program on any UNIX terminal, your computer is looking through the executable files in the directories specified in your $PATH variable. require does something very similar. When, for example, you write require 'set' at the top of your Ruby file, you are telling Ruby to look through a bunch of directories for a library called set.rb (Ruby's set library).

So where does Ruby look for set.rb? Well, once again, Ruby has something very similar to UNIX's $PATH variable. It is the global variable $LOAD_PATH also sometimes known by it's ugly and undescriptive alias $: (which I don't suggest using by the way--short though it may be). It is an array of directory names where Ruby looks when it comes across a require.

There is nice informative post here where you can get more information about require, load and require_relative