SC2128

Expanding an array without an index only gives the element in the index 0.

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]} -- which is usually the first of multiple elements. This is also true for associative arrays. Therefore, if 0 (zero) is not a valid key, $myarray expands to an empty string.

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".

Bugs:

There is a known issue with this check's handling of local variables, causing ShellCheck to flag variables that were previously declared as arrays, even if they are in different scopes.

The easiest workaround is to simply use different variable names. Alternatively, you can ignore the check.

It is also possible to satisfy ShellCheck by declaring the local variable separately from assigning to it, e.g.:

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

bar () {
   local baz # ShellCheck gets confused if these lines are merged as local baz="qux"
   baz="qux"
   echo "$baz"
}