title: Perl, passing array into subroutine, dealing with undeclared variables
body: <p>I have a sub with some firmly variables and variables I declare and use within the sub, but when I call this sub I can't declare them.</p>
  
  <p>for example:</p>
  
  <pre><code>sub func{
  my ($firm1, $firm2, $possible) = @_;
  ...
  if($possible eq "smth"){ # in case i passed this scalar
  }
  elsif($possible eq ("smth else" or undef/i_don_t_know)){ # in case i didn't passed this var, but i need it as at least undef or smth like that
  }
  
  func(bla, bla, bla); # ok
  func(bla, bla); # not ok
  </code></pre>
  
  <p>When I tried that, I got an error </p>
  
  <blockquote>
    <p>"Use of uninitialized value $possible in string eq at test.pl line
    ..."</p>
  </blockquote>
  
  <p>How can I correct this?</p>