I still create one liner batch files using copy con <batchfilename.bat>

alt+f6 <enter> to save

IIRC it's just F6, which is simply an alias for Ctrl+Z (ASCII code 26). That was the end-of-file marker on CP/M.

I stand corrected, you're right. You only need to press F6 <enter>.

On the PC you can enter pretty much any byte by holding Alt and typing the (decimal) value on the number pad. But here's a "Hello world" in plain ASCII, that works on two different CPU architectures (x86 and 8080):

x)y'!B:)),DM!G@))p,T]l%)),@@@Hello, world!$XP5]A%=!P[PZ^V!wV!wX5.<(GV(gX534,!(GWr!

My first version was shorter than 80 characters and "symmetrical" (same number of bytes before and after the string), but it didn't work on the 80486 and under DOSBox. The '486 needed an extra jump to clear the pipeline, and DOSBox didn't support the CP/M "CALL 5" interface.

I don't have the code handy, but I once was hanging out with a buddy in an OS/2 lab at uni and used copy con to write a reboot COM program. I meant it to be a soft reboot, but it ended up being a simulated hard boot.