I feel almost embarassed for sharing some of these, but I either remember things the first time I'm exposed to them or am forever doomed to have to look them up.

    ln -s /the/target the_link (can never remember order)

    for f in *.mp4; do mv "$f" "$(echo "$f" | sed s/S1E/S01E/)"; done

    tar -theuniverse (insert xkcd here)

    grep -E 'foo|bar' file (can never remember the flag for regex)