# Special Variables

> Source: https://learn-bash.net/special-variables/
> Part of Learn Bash, free to read.

In last tutorial about shell function, you use “$1” represent the first argument passed to function_A. Moreover, here are some special variables in shell:

  - `$0` - The filename of the current script.

  - `$n` - The Nth argument passed to script was invoked or function was called.

  - `$#` - The number of argument passed to script or function.

  - `$@` - All arguments passed to script or function.

  - `$*` - All arguments passed to script or function.

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

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

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

### Example:

```bash
#!/bin/bash
echo "Script Name: $0"
function func {
    for var in $*
    do
        let i=i+1
        echo "The \$${i} argument is: ${var}"
    done
    echo "Total count of arguments: $#"
}
func We are argument
```

`$@` and `$*` have different behavior when they were enclosed in double quotes.

```bash
#!/bin/bash
function func {
    echo "--- \"\$*\""
    for ARG in "$*"
    do
        echo $ARG
    done

    echo "--- \"\$@\""
    for ARG in "$@"
    do
        echo $ARG
    done
}
func We are argument
```