.z.exit:f

Where f is a unary function, f is called with the exit parameter as the argument just before exiting the kdb+ session.

The exit parameter is the argument to the exit function, or 0 if manual exit with \\ quit

.z.exit can be unset with \x .z.exit, which restores the default behavior.

The default behavior is equivalent to setting .z.exit to {}, i.e. do nothing.

q).z.exit
'.z.exit
q).z.exit:{0N!x}
q)\\
0
os>..

q).z.exit:{0N!x}
q)exit 42
42
os>..

q).z.exit:{0N!x}
q)exit 0
0