files compare

Hi,
I have 2 files like below;

File1

1010
1020
1050
1901
1905

File2

1010
1020
1050
1901
1905
1999
2001
2009

I want to write diff between 2 files to another file. I mean File3 will be

1999
2001
2009

thanks

Alice.

Have you looked at the following two commands?

comm
diff

diff file1 file2
5a6,8
> 1999
> 2001
> 2009

or 

grep -v -f file1 file2
1999
2001
2009

for more details:

man diff
man grep

thank you...