16. grep

The grep command is quite possibly the most common text processing command you will use. It allows you to search files for characters that match a certain pattern. What if you wanted to know if a file existed in a certain directory or if you wanted to see if a string was found in a file? You certainly wouldn't dig through every line of text, you would use grep!

Let's use our sample.txt file as an example:

$ grep fox sample.txt

You should see that grep found fox in the sample.txt file.

You can also grep patterns that are case insensitive with the -i flag:

$ grep -i somepattern somefile

To get even more flexible with grep you can combine it with other commands with |.

$ env | grep -i User

As you can see grep is pretty versatile. You can even use regular expressions in your pattern:

$ ls /somedir | grep '.txt$'

Should return all files ending with .txt in somedir.