Grep is one of the key Unix/Linux utilities for any user, whether you are a systems administrator, developer or general desktop user using grep can save you a ton of time. Below is an example of counting the number of lines that match the search string. This can be extremely useful if you are looking through large log files or sometimes even the passwd file.
[[email protected] ~]$ grep -c root /etc/passwd 2
In the above example you can see there are 2 lines with the word root. The next example will show you the number of lines that do not have the search string of root in them.
[[email protected] ~]$ grep -vc root /etc/passwd 35