When filtering output with grep, the flag -o can be used to return only the
matched parts of a line. The flag -h can be used to suppress the filename for
each match.
To run eslint on a repo and find which typescript-eslint rules currently have
infractions, you can sort and then take uniques of the matches returned by
grep with the aforementioned flags:
$ npx eslint . | grep -oh "@typescript-eslint/.*" | sort | uniq