Using grep

grep is a very common command used to search files for a certain word or phrase. This is the de-facto tool to use whenever you want to search for something in a text file; it’s so common that many programmers even say “grepping” instead of “searching”, even when they’re actually using a tool like Visual Studio Code which has its own search system.

Basic Usage

By default, grep prints out every line in its input that matches the “pattern” provided to it as an argument. For example, this searches a file for every line containing the word “hello”

cat input.txt | grep "hello"

We can also provide the file as a second argument to grep, like this:

grep "hello" input.txt

Regular Expressions

We often want to search for something more complicated than a fixed word or phrase. To do this, we can give grep a “regular expression”, a set of patterns to match against. We won’t go into the details of regular expressions here, but here’s an example:

grep -E "oo+" input.txt

searches for every line containing two or more o’s in a row.