Why don't backticks work as they do in shells?

    Several reason.  One is because backticks do not interpolate within
    double quotes in Perl as they do in shells.  
    
    Let's look at two common mistakes:

         $foo = "$bar is `wc $file`";  # WRONG

    This should have been:

         $foo = "$bar is " . `wc $file`;

    But you'll have an extra newline you might not expect.  This
    does not work as expected:

      $back = `pwd`; chdir($somewhere); chdir($back); # WRONG

    Because backticks do not automatically eat trailing or embedded
    newlines.  The chop() function will remove the last character from
    a string.  This should have been:

          chop($back = `pwd`); chdir($somewhere); chdir($back);

    You should also be aware that while in the shells, embedding
    single quotes will protect variables, in Perl, you'll need 
    to escape the dollar signs.

        Shell: foo=`cmd 'safe $dollar'`
        Perl:  $foo=`cmd 'safe \$dollar'`;