Array variable is being reassigned as a string

Problem

Once a variable has been declared or used as an array (`declare -a arr`, or `arr=(...)`), assigning to it with plain `arr=value` (no parentheses) does not add an element — it replaces the entire array with a single-element scalar assignment to index 0, discarding every other element and effectively demoting the variable back to string-like use. ShellCheck flags this because it is very often unintentional: the author wanted to either add an item to the array or reset it to a fresh single value, but wrote the assignment in a way that quietly destroys the existing array structure.

Bad

declare -a files=(a.txt b.txt c.txt)
files="d.txt"        # destroys the array, files is now just files[0]="d.txt"

Good

declare -a files=(a.txt b.txt c.txt)
files=("d.txt")      # replace with a new array
# or, to append:
files+=("d.txt")

Explanation

Use `arr=(...)` to reassign an array wholesale and `arr+=(...)` to append elements while preserving the existing ones. If you truly intend to convert the variable into a scalar going forward, do so deliberately and make sure nothing downstream still expects array semantics.

Related

SC2124

SC2128

SC2206

When It Matters

Assigning a plain string to a name that was declared as an array replaces element zero and leaves the rest of the array in place. The variable is then half array and half scalar, and later code reading "${arr[@]}" gets a mixture of the new value and stale elements. It usually happens when a variable is reused for a different purpose halfway down a script, and the resulting bug is very hard to read back from the symptoms.

Second Example

Exceptions

None. Reusing a name for two types is a readability problem even when the mechanics happen to work; give the second use its own name.

Faq