Understanding boolean operators in bash script phone_missing=false echo "missing $phone_missing" if [ ! $phone_missing ] then echo "Lost phone at $readabletime" $phone_missing=true fi I just can't understand this. The line echo "missing $phone_missing" echos `missing false`, I would expect the statement if [ ! $phone_missing ] to be true and enter the `if` clause, but it doesn't? What am I missing here!?

The variable `$phone_missing` is a string that happens to contain `false`. And a non-empty string evaluates to `true`. See also <