var==value

Assignment:

var=value

Comparison:

[ "$var" = value ]

ShellCheck has noticed that you're using == in an unexpected way. The two most common reasons for this is:

• You wanted to assign a value but accidentally used == instead of =.

• You wanted to compare two values, but neglected to use [ .. ] or [[ .. ]].

If you wanted to assign a literal equals sign, use quotes to make this clear:

var="=sum(A1:A10)"