sayhello() {
  echo "Hello $1"
}
sayhello

./myscript World just prints "Hello " instead of "Hello World".

sayhello() {
  echo "Hello $1"
}
sayhello "$@"

./myscript World now prints "Hello World".

In a function, $1 and up refers to the function's parameters, not the script's parameters.

If you want to process your script's parameters in a function, you have to explicitly pass them. You can do this with myfunction "$@".

Note that "$@" refers to the current context's positional parameters, so if you call a function from a function, you have to pass in "$@" to both of them:

first() { second "$@"; }
second() { echo "The first script parameter is: $1"; }
first "$@"

If the parameters are optional and you currently just don't want to use them, you can ignore this message. In versions strictly greater than v0.6.0, ignoring SC2120 on a function will also disable SC2119 on each of the call sites.