title: Why does OpenSSL return 0 even though there's an error?
body: <p>I performed</p>
  <pre><code>openssl rsa -check -in foo.key
  </code></pre>
  <p>and received</p>
  <blockquote>
  <p>RSA key error: dmq1 not congruent to d</p>
  </blockquote>
  <p>Nevertheless,</p>
  <blockquote>
  <p>shell&gt; echo $?</p>
  <p>0</p>
  </blockquote>
  <p>Why should I receive a return code of 0 even though there's an error?</p>