Bash script to report whether a user is logged in or not

Code:

#!/bin/bash

function checkUser
{
    for u in $(who | awk '{print $1}' | sort | uniq)
    do 
        if [ "$u"="$user" ]; then
            echo "User $u is logged in."
            echo "Exit status: $?"
            exit $?
        else
            "User $u is not logged in."
            echo "Exit status: $?"
            exit $?
        fi
    done
}

if [ -z $1 ]; then
    echo "User to check:"
    read user
else
    "$user"="$1"
fi
checkUser $1

Code:

$ ./checkuser henrix
.checkuser: line23: =henrix: command not found
User adam is logged in.
Exit status 0.

Code:

$ ./checkuser
User to check: henrix
User adam is logged in.
Exit status 0.

Code:

$ who | awk '{print $1}' | sort | uniq
adam
henrix