bash-4.2$ t=something

bash-4.2$ [ $t=="hi" ] ; echo $?
0

bash-4.2$ [ $t == "hi" ] ; echo $?
1

bash-4.2$ [ "foo"=="bar" ] ; echo $?
0

bash-4.2$ [ "foo" == "bar" ] ; echo $?
1

bash-4.2$ (($t=="hi")) ; echo $?
0

bash-4.2$ (("foo"=="bar")) ; echo $?
0

bash-4.2$ ((3==4)) ; echo $?
1