title: Execute Unix command in a Perl script
body: <p>How I can make the following external command within ticks work with variables instead?</p>
  
  <p>Or something similar?</p>
  
  <p><code>sed -i.bak -e '10,16d;17d' $docname</code>;   (this works)</p>
  
  <p>I.e., <code>sed -i.bak -e '$line_number,$line_end_number;$last_line' $docname</code>;</p>