These are some things I have learned and liked to know and/or have handy
For changing the mode (chmod) of files/directories
0 ---
1 --x
2 -w-
3 -wx
4 r--
5 r-x
6 rw-
7 rwx

tar program
-c create/add
-t list archive
-x extract
-v verbose (-vv very verbose)
-z gzip tarballs
-f filename

To switch video modes while in X windows through what you selected as options use
shift - alt - + (plus on keypad)

ctrl-L clears the screen in terminals
ctrl-d EOF
esc-d delete current word
esc-. last argument of previous command

${PATH} is colon (:) delimited
use 
#PATH=${PATH}:/home/jus/scripts
to add /home/jus/scripts to your path

#variable=vaule
sets the value of "variable"
#export variable
makes "variable" available to programs external to the shell
#export variable=value
exports and sets the value of "variable" in one command

special shell variables
$#	= number of arguments for the command
$0	= the command name
$1,$2,$3= the individual arguments of the command (use shift command for access beyond the 9th argument)
$*	= the entire list of arguments treated as a single word
$@	= the entire list of arguments treated as a series of words
$?	= the exit status of the previous command (0 = successful)
$$	= the pid of the current process