Listing of special parameters in bash and it's expansion
| parameter | expansion |
| $* | all parameters. "$*" expands to "$1 $2 $3 ...." |
| $@ | same as $* with some differences "$@" expands to "$1" "$2" "$3" ..... |
| $# | number of parameters |
| $? | exit status of last executed command |
| $$ | processid |
| $! | processid of most recently executed background (asynchronous) command |
| $0 | name of the shellscript |
source: Bash Reference Manual