a - variables variables are used to store and manipulate data Declaring variables → by assigning a value to them using = There should be no spaces around = my_variable="Hello, World!" → declares a variable Accessing variables → using $ with the variable name you can access its value echo $my_variable → prints the data stored in the variable You can use variables in shell scripts and in the Command line. You can unset a variable using unset
b - special variables Shell scripts have several special variables that are automatically set by the shell $0 → The name of the script. $1 to $9 → Positional parameters passed to the script. $# → Number of positional parameters. $* → All the positional parameters as a single word. $@ → All the positional parameters as separate words. $$ → Process ID of the current script. $? → Exit status of the last command executed.