grep
grep [-i] [-c] [-n] [-v] [-r] <word> <file>
Risk: Safe
What it does
Prints only the lines that contain a word.
When to use it
To pull answers out of logs and long files.
Example
$ grep -i unpaid orders.logEvery unpaid order, any spelling.
$ grep -c nasi-lemak orders.logCount the matching lines.
$ grep -r belacan ~/kedaiSearch every file in every folder.
Learn it in: Search inside files: grep · Official docs