list all posix utility functions

[matu3ba]

I found the website for posix terrible to navigate and not very nice to read either.
Listing them allows to append the path with the command it just shows what the command does:
https://pubs.opengroup.org/onlinepubs/9699919799/utilities/ + diff.html =
https://pubs.opengroup.org/onlinepubs/9699919799/utilities/diff.html etc.

# See also utilities:
# https://pubs.opengroup.org/onlinepubs/9699919799/utilities/
# filter: grep, sed, cat, printf, tr, xargs
# action: test, cd, ls, mkdir, rm, vi, diff
# system: jobs, kill, fg, chmod
# well: alias, unalias, awk, echo, cut, sort, head, tail, more, pwd, df, du,
#       find, cp, mv, rmdir, dirname, basename
# few: tee, uniq, bc, c99, cksum, expr, read, sh, sleep, time, true, aflse, wc
#      csplit, dd, patch, expand, file, iconv, ln, mkfifo, nl, od, pax, touch
#      compress, uncompress,  zcat, at, date, bg, fuser, chgrp, chown, id, ps,
#      uname, type, nohup, wait, who