title: invoking perl scripts
body: <p>I have perl scripts starting with <code>#!/usr/bin/perl</code> or <code>#!/usr/bin/env perl</code></p>
  
  <p>First, what does the second version mean?</p>
  
  <p>Second, I use Ubuntu. All the scripts are set as executables. When I try to run a script by simply invoking it's name (e.g. <code>./script.pl</code>) I get <code>: No such file or directory</code>. when I invoke by <code>perl ./script.pl</code> it runs fine.</p>
  
  <p>Why?</p>