Cat/grep just the lines with single ip

Question

I have a file something like this

Script http://127.0.0.1/ blabla
127.0.0.1
Script 127.0.0.2/index.html bla bla
127.0.0.2
Script 127.0.0.3/contact bla bla
Script 127.0.0.4/settings bla bla
127.0.0.4

I want to get only the lines that contain just a single ip not all the ips from all the lines.

How can i do this?

the results should be

127.0.0.1
127.0.0.2
127.0.0.4

Answer 1

The cat utility just concatenates the data given to it, so it would not be of much use here.

Assuming it's ok to be somewhat sloppy with what constitutes a valid IP address:

grep -Ex '([0-9]{1,3}\.){3}[0-9]{1,3}' file

This would match and print any lines matching the given regular expression (and discard the others).

An even sloppier solution would be to discard lines that contains anything but dots and digits:

grep -v '[^0-9.]' file

Depending on your requirements, one of these would be enough.

For a completely correct regular expression (does not match invalid IP addresses), you could use

grep -Ex '((25[0-5]|2[0-4][0-9]|1[0-9][0-9]|[1-9]?[0-9])\.){3}(25[0-5]|2[0-4][0-9]|1[0-9][0-9]|[1-9]?[0-9])' file