6.3 The NOT Operator

With logical NOT operators, there is only one argument:

##logical NOT

#if( !$foo )
  <strong>NOT that</strong>

Here, the if $foo is true, then !$foo evaluates to false, and there is no output. If $foo is false, then !$foo evaluates to true and NOT that will be output. Be careful not to confuse this with the quiet reference $!foo.