I think my favorite program in the entire linux/unix toolchain is "file". Did you even know about this program? It's on every system including MacOS and it's magic. You run it on any file and it just tells you what it is. Any file. I don't know who keeps this updated but it supports surprising things. Like it knows Windows file formats. If it's a executable it tells you if it's 32- or 64- bit. If it's an image it tells you the size and channels. If the file extension lies it just figures it out.
