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 make a small file to search. Type or paste this line and press Enter:

$ echo 'The quick brown; fox jumps over the lazy dog' > sample.txt

Check it worked with cat sample.txt. We will reuse this file in a couple of later lessons.

Now search it:

$ 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. Note the backslash before the dot. In a regular expression a plain . means "any character", so grep '.txt$' would also match a file called atxt. Escaping it with . asks for a literal dot.