SC2198 – ShellCheck Wiki

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Arrays don't work as operands in [ ]. Use a loop (or concatenate with * instead of @).

Problematic code:

allowedExt=(jpg bmp png)
[ "$ext" = "${allowedExt[@]}" ] && echo "Extension is valid"

Correct code:

allowedExt=(jpg bmp png)
for value in "${allowedExt[@]}"
  [ "$ext" = "$value" ] && echo "Extension is valid"


Array expansions become a series of words in [ .. ]. Operators expect single words only.

The problematic code is equivalent to [ "$ext" = jpg bmp png ], which is invalid syntax. A typical error message is bash: [: too many arguments or dash: somefile: unexpected operator.

Instead, use a for loop to iterate over values, and apply your condition to each.

Alternatively, if you want to concatenate all the values in the array into a single string for your test, use "$*" or "${array[*]}".


If you are dynamically building an a test expression, make your array the only thing in the test expression. ShellCheck will not emit a warning for: set -- 1 -lt 2; [ "$@" ]

ShellCheck is a static analysis tool for shell scripts. This page is part of its documentation.