UNIX® Shells by Example Fourth Edition

Appendix A. Useful UNIX/Linux Utilities for Shell Programmers

apropos—searches the whatis database for strings

apropos keyword ...

apropos searches a set of database files (see directory /usr/man/whatis) containing short descriptions of system commands for keywords and displays the result on the standard output. Same as man -k.

Example A.1. 

1 $ apropos bash
  bash (1)                 - GNU Bourne-Again SHell

2 $ man -k tcsh
  tsh (1)               - C shell with filename completionand command-line editing

EXPLANATION

1. apropos searches for the keyword bash and prints a short description of what it is.

2. man -k behaves the same as apropos.

arch—prints the machine architecture (see uname -m)

arch

On current Linux systems, arch prints things such as i386, i486, i586, alpha, sparc, arm