title: Why some entries are missing in Perl ENV hash
body: <p>Perl is giving me an undef value when I access a variable that is supposed to be defined in the <strong>%ENV</strong> hash. How is this possible?</p>
  
  <pre><code>root@23cd5f45def7:~/bin$ perl -e 'warn $ENV{SHELL}'
  Warning: something's wrong at -e line 1.
  </code></pre>
  
  <p>I would expect perl to output <strong>/bin/bash</strong> instead. </p>
  
  <p>More info on the environment:</p>
  
  <pre><code>root@23cd5f45def7:~/bin$ echo $SHELL
  /bin/bash
  
  root@23cd5f45def7:~/bin$ $SHELL --version
  GNU bash, version 4.2.37(1)-release (x86_64-pc-linux-gnu)
  Copyright (C) 2011 Free Software Foundation, Inc.
  ...
  
  root@23cd5f45def7:~/bin$ perl -v
  
  This is perl 5, version 14, subversion 2 (v5.14.2) built for x86_64-linux-gnu-thread-multi
  (with 91 registered patches, see perl -V for more detail)
  ...
  </code></pre>
  
  <p>I am running this on Debian wheezy in a docker container.</p>
  
  <p>The image was created with </p>
  
  <pre><code>sudo debootstrap wheezy ../_build  http://ftp.us.debian.org/debian
  sudo tar -C ../_build -c . | docker import - wheezy/bootstrap
  </code></pre>
  
  <p>I get the same beheviour with perl-5.24.1 compiled manually from sources.</p>