"$*", "$@", "$#"

Two special variables contain all of the positional parameters (except positional parameter 0): * and @. The difference between them is subtle but important, and it's apparent only when they are within double quotes.

"$*" is a single string that consists of all of the positional parameters, separated by the first character in the value of the environment variable IFS (internal field separator), which is a space, TAB, and NEWLINE by default. On the other hand, "$@" is equal to "$1" "$2"... "$ N", where N is the number of positional parameters. That is, it's equal to N separate double-quoted strings, which are separated by spaces. If there are no positional parameters, "$@" expands to nothing. We'll explore the ramifications of this difference in a little while.

The variable # holds the number of positional parameters (as a character string). All of these variables are "read-only," meaning that you can't assign new values to them within scripts.