https://stackoverflow.com/questions/13617843/unary-operator-expected
If you know you're always going to use bash, it's much easier to always use the double bracket conditional compound command [[ ... ]], instead of the Posix-compatible single bracket version [ ... ]. Inside a [[ ... ]] compound, word-splitting and pathname expansion are not applied to words, so you can rely on
if [[ $aug1 == "and" ]];
to compare the value of $aug1 with the string and.
If you use [ ... ], you always need to remember to double quote variables like this:
if [ "$aug1" = "and" ];
If you don't quote the variable expansion and the variable is undefined or empty, it vanishes from the scene of the crime, leaving only
if [ = "and" ];
which is not a valid syntax. (It would also fail with a different error message if $aug1 included white space or shell metacharacters.)
The modern [[ operator has lots of other nice features, including regular expression matching.