scripting - 3 OR Conditions in Bash Statement

Question

I would think this would be simple, but I keep getting errors. I want 3 OR conditions in my if else statement. These are the variations I've tried. What syntax error am I making?

   if [[ $var == "a" ]] || [[ $var == "b" ]] || [[ $var == "c" ]]; then
#Do Stuff
    else
#Do Stuff
    fi

    if [ $var == "a" ] || [ $var == "b" ] || [ $var == "c" ]; then
#Do Stuff
    else
#Do Stuff
    fi

    if [[ $var == "a" ] || [ $var == "b" ]] || [ $var == "c" ]; then
#Do Stuff
    else
#Do Stuff
    fi

    if [[ $var == "a"  || $var == "b" || $var == "c" ]]; then
#Do Stuff
    else
#Do Stuff
    fi

question from:https://stackoverflow.com/questions/65832829/3-or-conditions-in-bash-statement

Answer 1

The first and last versions both look and act correctly for me. Are you sure you are using bash and not sh?

Note that [ and [[ are both "commands" (built-ins really, I think is the appropriate term) and are slightly different. Basically you want to use [[ unless you want legacy compatibility with old shells. If using [ there are additional considerations, for example it can cause problems with empty string comparisons.

Also as an aside, the 2nd version should generally work, but you get the problems mentioned above - and the 3rd version is not good.