I’ve used ls, cat, echo, cd, mkdir, mv, cp, rm, & ssh pretty much every day I’ve touched a computer since some time near the end of the twentieth century. Honorable mention to sudo, find, rename, ffmpeg, Gimp, & VLC. If you count ROMs for games, the list gets into the deeper past, though I don’t use them as often. I guess I still need to get around a few Windows/DOS machines, so DIR and CD are probably the absolute oldest when at the keyboard.