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open (my $FH, "<", $file) or die ...
# reads the whole file, assigns first line to $headline
...
# since the whole file is already read, there's nothing
# more to be read, so the while block will never be executed
while( my $line = <$FH> ) {

sub xxx {
  # error, must be my ($firstParam) = @_; if you don't want
  # to get the number of parameters but the first param
  my $firstParam = @_; 
...

my $x = reverse('abcdef');
my ($y) = reverse('abcdef');
print "x=$x\ny=$y\n";