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copied!<p>Let's assume you have a <code>script.rb</code>, which contains this:</p> <pre><code>$var = :value def get; A end load 'another_script.rb' get # Will it succeed? </code></pre> <p>When you run <code>ruby script.rb</code>, you spawn a Ruby process which will read the contents of <code>script.rb</code> and execute every line. The Ruby interpreter has an <em>execution state</em> which holds information such as object data, the variables that reference them, which scope they belong to, which method you're currently in and so much more.</p> <p>When the interpreter reads the <code>$var = :value</code> line, it modifies its own state. It stores a global variable which references the newly-created symbol object. Next, it defines a method which will return the value referenced by the <code>A</code> constant. Calling it at this point will raise a <code>NameError</code>, since the constant does not exist. When it reaches the <code>load 'another_script.rb'</code> line, it is analogous to running <code>ruby another_script.rb</code>, except no second process is started. The contents of the script are read and interpreted <em>within the same execution context</em>.</p> <p>Suppose <code>another_script.rb</code> contains the following:</p> <pre><code>$var = :changed class A; end </code></pre> <p>The <code>$var</code> variable, which previously referenced the <code>:value</code> symbol, will now reference the <code>:changed</code> symbol. Then, a <code>Class</code> object will be created and assigned to the new <code>A</code> constant.</p> <p><em>After</em> loading this script, the call to <code>get</code> will succeed. Another implication is that <em>order matters</em>. For example:</p> <pre><code>load 'another_script.rb' $var = :value </code></pre> <p>Whatever <code>another_script.rb</code> set <code>$var</code> to will be lost since it will be overridden immediately after it has finished executing.</p> <p>No matter how many scripts you <code>load</code>, <code>require</code> or <code>eval</code>, as long as they are running on the same process, they will <em>always</em> share the same data. <a href="http://www.ruby-doc.org/core-1.9.3/Kernel.html#method-i-load" rel="nofollow">Only local variables will not be shared between files</a>. Things get complicated when you want to share data between two <em>different</em> Ruby interpreters:</p> <pre><code>ruby script.rb & ruby another_script.rb & </code></pre> <p>In that case, you have to use <a href="http://en.wikipedia.org/wiki/Inter-process_communication" rel="nofollow">inter-process communication</a>.</p>

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