Pattern: Array expansion in [[ ]]
Issue: -
Array expansions in [[ .. ]] will implicitly concatenate into a single string, much like in assignments.
Example of incorrect code:
ext=png
allowedExt=(jpg bmp png)
[[ "$ext" = "${allowedExt[@]}" ]] && echo "Extension is valid"This is equivalent to [ "$ext" = "jpg bmp png" ].
Instead, use a for loop to iterate over values, and apply your condition to each.
Alternatively, if you do want to concatenate all the values in the array into a single string for your test, use "$*" or "${array[*]}" to make this explicit.
Example of correct code:
ext=png
allowedExt=(jpg bmp png)
for value in "${allowedExt[@]}"
do
[[ "$ext" = "$value" ]] && echo "Extension is valid"
done