Expanding an array without an index only gives the first element.

Problematic code:

myarray=(foo bar)
for f in $myarray
do
  cat "$f"
done

Correct code:

myarray=(foo bar)
for f in "${myarray[@]}"
do
  cat "$f"
done

Rationale:

When referencing arrays, $myarray is equivalent to ${myarray[0]} -- it results in only the first of multiple elements.

To get all elements as separate parameters, use the index @ (and make sure to double quote). In the example, echo "${myarray[@]}" is equivalent to echo "foo" "bar".

To get all elements as a single parameter, concatenated by the first character in IFS, use the index *. In the example, echo "${myarray[*]}" is equivalent to echo "foo bar".

Exceptions

ShellCheck can get confused by variable scope if the same variable name was used as an array previously, but is a string in the current context. You can ignore it in this case.

In the case of local variables, a workaround is to declare the local variable separately from assigning to it:

Problematic Code:

foo () {
   local -a baz
   baz+=("foo" "bar")
   echo "${baz[@]}"
}

bar () {
   local baz="qux"
   echo "$baz"
}

Correct Code:

foo () {
   local -a baz
   baz+=("foo" "bar")
   echo "${baz[@]}"
}

bar () {
   local baz
   baz="qux"
   echo "$baz"
}