$

Execute a command as a user

Print a variable

$ echo $[VARIABLE]

Print the exit status of the previous command

$ echo $?

Print a random number between 0 and 32767

$ echo $RANDOM

Print one of the prompt strings

$ echo $[PS0|PS1|PS2|PS3|PS4]

Expand with the output of command and run it. Same as enclosing command in backtics

$ $([command])

List how many arguments the current context has

$ echo $#

Print out a Bash array

$ echo ${array[@]}