# Create an iterator...
my $reader;
if ( $opt{c} ) {
    open my $fh, '<', $MAILLOG
      or die "Can't open $MAILLOG: $!";
    $reader = sub { <$fh> }
}
else {
    my $tail = File::Tail->new( name => $MAILLOG, tail => -1 );
    $reader = sub { $tail->read };
}

# Use our iterator, however it works...
while ( my $line = $reader->() ) {
    ...
}