... 
# Read the last 2 lines of a log file

 my $log = "log.log"; # if this file is still empty by the time the code runs.
 my $line = do {
      open my $line, '-|', tail => -2, $log
         or die "Can't spawn tail: $!\n";
         <$line>;
    };
    
 $line =~ s/[\r\n]+$//; my $show = ''; # <<<< happens here,  uninitialized value 

 if ($line =~ /(\bTest\b\s+.+\s+\baccount\b)?/) {  #<<<< happens here,  uninitialized value
   $show = $1 || '';
 }

 ...