Shell - $@ and $*

In Bash (and all POSIX-like shells), $@ or ${@} is a "special parameter" that expands to a list of all positional parameters (= command-line arguments). It is in that respect similar to $*, but with the addition that it can be double-quoted to expand to a list of individual tokens rather than one string containing all positional parameters separated by spaces⁽¹⁾.

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⁽¹⁾ Actually, the arguments are not joined explicitly by "space", but rather by the first character of $IFS, the input field-separator variable, which however defaults to "space" in many shells. In the further text I will still use "space" for simplicity and assume that either you left $IFS at its default or changed it to your needs but know what you do.

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So,

• "$*" is equivalent to "$1 $2 $3 ... " and would be treated as "one word" whereas
• "$@" is equivalent to "$1" "$2" "$3" ...  and would be treated as "several individual words".

Without quotes, both would simply be a space-separated list of words. The difference becomes important when the command-line arguments themselves are strings with spaces, as in

./my_script.sh parameter1 parameter2 "a whole sentence as parameter"

• $* or $@ without quotes would expand to a list of seven individual tokens. This is rarely what you want.
• "$*" would expand to one token consisting of seven space-separated words (parameter1 parameter2 a whole sentence as parameter). This is in most cases not what you want.
• "$@" would expand to a list of 3 tokens, the first two being parameter1 and parameter2, and the last being the string a whole sentence as parameter including its spaces. This is what you will want in most cases, in particular when you want to use it as a list of tokens (to iterate over, to assign to an array, or to pass to a self-defined function).