How to extract lines from txt file in Linux

Question

I have text file with 25 millions of lines (a list of domain names).

How can I extract domains that contain .co.uk to another txt file?

Answer 1

Given a file like:

foo.co.uk
bar.co.uk
baz.foo.bar

use the command:

grep "\.co\.uk$" file

Output:

foo.co.uk
bar.co.uk

Answer 2

Try this:

grep -F '.co.uk' file > filtered_file

-F lets grep search for a fixed string instead of a pattern which makes it a lot faster, especially given your 25 million lines. Then, you also don't need to escape the dots, which are special characters for a pattern.

Note, that this will also find lines like example.co.uk.com or example.co.uk/index.html. If you want the .co.uk always in the end, go with this answer.