### 5.7 Exclamation mark as not operator

The exclamation mark ‘`!`’ (aka “Bang!”) is a negation operator, just like the tilde ‘`~`’:

         octave:1> if ! strcmp (program_name, "octave"),
         >   "It's an error"
         > else
         >   "It works!"
         > end
         ans = It works!

Note however that Matlab uses the ‘`!`’ operator for shell escapes, for which Octave requires using the `system` command.