On Mon, Aug 06, 2018 at 04:14:49PM +0530, anant garg wrote: > $ mode=! > $ [ "$mode" != "ro" -a "$mode" != "rw" ] && echo OK > + '[' '!' '!=' ro -a '!' '!=' rw ']' > bash: [: too many arguments
The use of -a and -o as conjunctions inside a test or [ command is to be avoided. It's not POSIX compatible, and as you have now observed first-hand, even in bash, it is perilous. For this particular check, I would use case: case $mode in ro|rw) .... ;; *) .... ;; esac But if for some reason you've got an if-boner, you could either use two separate test commands: if [ "$mode" != ro ] && [ "$mode" != rw ] or use bash's [[ command: if [[ $mode != ro && $mode != rw ]] The former is POSIX comptaible. The latter is, of course, a bash extension.