Here is the video version, if you prefer it:
The grep command is used to find text patterns within files. (Ward, 2014) Its usage is as follows:
grep pattern filename
grep outputs the lines which match the pattern. What is the pattern? The pattern is anything you want to match. You can use regular expressions here, but we are going to talk about that later. pattern, for our purposes right now, is a word or multiple words you want to find in a file. Say I had this file:
mislav@mislavovo-racunalo:~$ cat file.txt
Some line
Some other line
Here is what happens when I want to print out every line which contains the word (pattern) line:
mislav@mislavovo-racunalo:~$ grep line file.txt
Some line
Some other line
Here is the result if I want to print every line which contains the pattern other:
mislav@mislavovo-racunalo:~$ grep other file.txt
Some other line
If I wanted my pattern to be composed of multiple words, I would have to put them under single quotations, like this:
mislav@mislavovo-racunalo:~$ grep ‘other line’ file.txt
Some other line
If I wouldn’t I’d get an error. But you do know how to use Google for errors, do you?
Useful options are -i for case insensitive matches (no difference between capital letters and “small” letters) and -v for inverting matches (printing every line that does not contain a match).
Hope you found this helpful!
References
Ward, B. (2014). How Linux Works: What Every Superuser Should Know (2nd ed.). No Starch Press. Pages 18-19