my @lines;
{
    my $fh;
    open $fh, '<', '/path/to/file.txt' or die $!;
    @lines = <$fh>;
}
{
    my $fh;
    open $fh, '>' '/path/to/newfile.txt' or die $!;
    print $fh join $/, @lines[3,1,2];
    print $fh $/;
}