Testing Whether $@ Is Empty Or Null

[Jessie Saenz]

bash version = 5.1.16(1)-release

I do not understand why the following statement returns 0 despite no 
arguments given to script:

    [ -n "$@" ] && echo true

However, the following statements return 1 when no arguments are given 
to script:

    [ "$@" ] && echo true

    var="$@"; [ -n "$var" ] && echo true

    [[ -n "$@" ]] && echo true

    (($#)) && echo true

Per bash Manual:

    "When there are no positional parameters, "$@" and $@ expand to 
nothing (i.e., they are removed)."

    "-n string
              True if the length of string is non-zero."

    "test expr or [ expr ]

              "...the expression is true if the unary test is true."