Can someone explain me what is happening here? What does the output means?
:$ echo $-3
:$ echo $-2
:$ echo $-1
$- is a variable that contains the currently active shell options.
(A hyphen.) Expands to the current option flags as specified upon invocation, by the set builtin command, or those set by the shell itself (such as the -i option).
Your command is evaluating to
the value of - then a number.