special_system_variables.txt

 Special Variables in Shell Scripting:


1. $0 - This variable will be provide the filename of the current script.

2. $n - These variables correspond to the arguments with which a script was invoked. Here n is a positive decimal number corresponding to the position of an argument (the first argument is $1, the second argument is $2, and so on).

3. $? - The exit status of the last command executed.

4. $$ - The process number of the current shell. For shell scripts, this is the process ID under which they are executing.

5. $* - All the arguments are double quoted. If a script receives two arguments, $* is equivalent to $1 $2.

6. $@ - All the arguments are individually double quoted. If a script receives two arguments, $@ is equivalent to $1 $2.
$@ and $* returns the same output but "$@" took only double quoted argument as single argument and "$*" took entire arguments as single argument

7. $! - The process number of the last background command.