Here, placed side-by-side for comparison, are GNU's implementation of cat, Plan
9's implementation, Busybox's implementation, and NetBSD's implementation.

All cat.c files (renamed by prefixing the source) are presented, unaltered and
in their entirety.  Note how easy it is to read and understand plan9-cat.c (it
should take less than a couple of minutes possibly even for coders that don't
know C).  Other than that, I think the files speak for themselves.

Keep in mind while reading that the cat utility's purpose is to concatenate
files.

Lastly, here are the line counts, sorted:
35 plan9-cat.c
48 busybox-cat.c
316 netbsd-cat.c
782 gnu-cat.c
1181 total