Question

Using regex, write a linux expression to search up the following in a .txt file to match any IP address, the answer will show up in red:

Answer:
192.168.1.111
255.255.255.255
1.12.123.0
0.0.0.0

.txt file:
192.168.1.111
255.255.255.255
10.abc.1.13
192.168.1
1.12.123.0
18.19.20
255.255.255.
19211111111
.123.123.
...
0.0.0.0

Answer 1

Linux expression to search any IP address in a .txt file using regex is :

grep -o '[0-9]\{1,3\}\.[0-9]\{1,3\}\.[0-9]\{1,3\}\.[0-9]\{1,3\}' file.txt

In the above expression,

grep outputs the lines that contain the matching string

-o to only output the matching segment of the line

The squiggly brackets (e.g. { and }) indicate the number of instances of the match.

{1,3} requires that the previous character or character class must occur at least once, but no more than three times.

The character class [0-9] will successfully match against one or more numeric digits.

file.txt is the file that is to be searched for the pattern