How can you use the grep command to perform a case-insensitive search?

When using the grep command for searching, if you need to perform a case-insensitive search, you can use the -i or --ignore-case option. This option causes grep to ignore the case of letters during the search.

Below is a simple example demonstrating how to use this option:

Suppose we have a file example.txt with the following content:

shell
Hello World
hello world
HELLO WORLD

If you want to search for lines containing the word "hello" in a case-insensitive manner, you can use the following command:

bash
grep -i "hello" example.txt

This command will return:

shell
Hello World
hello world
HELLO WORLD

As you can see, regardless of the case of "hello", all lines containing "hello" are correctly returned. This is the effect of the -i option.