Created SC2178 (markdown)

SC2178.md

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+## Variable was used as an array but is now assigned a string.
+
+### Problematic code:
+
+```sh
+flags[0]="-r"
+flags[1]="--delete-after"
+
+if [ "$dryrun" ]
+then
+   flags="--dry-run"
+fi
+
+```
+
+### Correct code:
+
+```sh
+flags[0]="-r"
+flags[1]="--delete-after"
+
+if [ "$dryrun" ]
+then
+   flags=( "--dry-run" )
+fi
+```
+### Rationale:
+
+ShellCheck noticed that you have used a variable as an array, but then assign it a string. `array=foo` is equivalent to `array[0]=foo`, and leaves the rest of the elements unaffected.
+
+In the incorrect code, `"${flags[@]}"` would contain `--dry-run` `--delete-after`.
+
+To set an array to only a single, given element, you should use `array=( foo )`.
+
+In the correct code, `"${flags[@]}"` will contain `--dry-run` only. 
+
+Another possible cause is accidentally missing the `$` on a previous assignment: `var=(my command); var=bar` instead of `var=$(my command); var=bar`. If the variable is not intended to be an array, ensure that it's never assigned as one.
+
+### 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.