Unix, Solaris, Linux, AIX, HP-UX Commands

Linux Command Reference :

http://www.oracle.com/technology/pub/articles/calish_file_commands.html

http://www.oracle.com/technology/pub/articles/advanced-linux-commands/part1.html

http://www.oracle.com/technology/pub/articles/advanced-linux-commands/part2.html

Common Linux Commands Pocket Guide

HP-UX Command Reference : 

http://docs.hp.com/en/hpuxman_pages.html

AIX Command Reference :

http://www.ibm.com/developerworks/aix/library/au-dutta_cmds.html

Solaris Command Reference :

http://www.sun.com/bigadmin/shellme

Unix Command Reference :

Common UNIX Commands Pocket Guide

Command Reference for all Operating System :

http://www.tomshardware.com/ucg

Comparative Study of Commands in all Platforms :

http://www.unixguide.net/unixguide.shtml

Admittedly, a list such as this can be helpful in quickly answering some of your own questions. However,

it does not cover everything that you might need. You can extend the usefulness of such a list by adding

other commands that answer additional questions not addressed here.