.bash_profile: Login shells. Calls for .bashrc
.bashrc: Interactive non-login shells
Note: Local variables won’t work with environmental variables
A=30
B=40
C=`expr $A + $B`
echo $C ## output=703 types of variables:
Local: A=20
Environmental: export A=20
System: Created by kernel
set: Show all variables OR show local variables (?) unset: delete a variable
env: Show environmental variables
local: Show local variables