SC2178 – ShellCheck Wiki

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Variable was used as an array but is now assigned a string.

Problematic code:

flags[0]="-r"
flags[1]="--delete-after"

if [ "$dryrun" ]
then
   flags="--dry-run"
fi

Correct code:

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.

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"
}

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