not(1)

NAME
not -- negate the exit status of a job

  Synopsis

not COMMAND [OPTIONS...]

  Description
not negates the exit status of another command. If the exit status is zero, not returns 1. Otherwise, not returns 0.

  Example
The following code reports an error and exits if no file named spoon can be found.

if not test -f spoon
    echo There is no spoon
    exit 1
end