I don't make great use of all the gnu tools, but they sure come in handy some times.

Basic use is searching a file for a particular term, and grep spitting out each line that term occurs in.

grep [term] [file]

Search all files in current folder for a term.

grep -r -n -i [term] .

With the E flag you can use the usual regular expressions. So searching for either of two terms:

grep -E '[term1]|[term2]' [file]

Otherwise there's also a utility called egrep.

NB: [file]] doesn't even have to be a file, you can use wildcards and things there too.

There's probably a better way to do this, but to search for instances with all terms I use a pipe, like:

grep '[term1]' [file] | grep '[term2]'

• GNU Grep 3.4 on gnu.org
• Grep
• phiresky/ripgrep-all - Searches more file kinds.
• Multiline Grep
• Plaintext