the mac equivalent is apple shift 3 for the whole screen
or apple shift 4 for a selectable marqueee snapshot.
both have a nice camera snapshot sound in the os so u know it worked.
it automatically saves it as a pict to your hard drive.
and keeps a copy in memory if required.
f9 will fail in a compiled executable so u need to add some code if u want it to work in your game on another users console.
rem 1
rem screenshot export code
if inkey$()="s" then save bitmap "screenshot.bmp"
rem 2
rem numerical acsending screenshot export code
if inkey$()="s" then i=i+1 : save bitmap "screenshot_"+str$(i)+".bmp"
rem 3
rem using f9 as the button
if scancode() = 67 then i=i+1 : save bitmap "screenshot_"+str$(i)+".bmp"
rem 4
rem using f9 as the button
if keystate(67) then inc i : save bitmap "screenshot_"+str$(i)+".bmp"