git grep
git grep [-n] [-i] <pattern> [<rev>]
Risk: Safe
What it does
Searches the files Git tracks for a word or pattern.
When to use it
To find where something is used in your project.
Example
$ git grep -n footerShow every line with footer, with line numbers.
$ git grep TODO HEAD~2Search the files as they were two commits ago.
Learn it in: Search your history · Official docs