CShell

What?

CShell is a very simple DOS shell for the Commodore 64. It allows running machine code programs directly from disk without needing to go through Basic, with command line parameter passsing and exit status codes. It's intended for scripting multiple commands together with the SUBMIT command; I wanted to use it for running my Cowgol compiler, but it turned out that there's not enough memory on a stock C64 to do that.

How?

Build it with 64tass, and then copy CSHELL and all the .COM files onto a Commodore 64 disk (I use Vice with an emulated drive for testing). Then do:

LOAD "CSHELL",8
RUN

...to start the environment.

Now, typing 'echo' will try to load and run the file 'ECHO.COM'. Command line parameters work.

Typing '#9' will change drive to device 9.

Look at echo.asm for a minimal example of how to write a CShell program. In essence:

• Programs are simple .PRG files which are loaded at 0x0801. The entry point is 0x080d, making them compatible with the normal Basic machine code stub. A program can detect whether it's being run under CShell by looking for 'C', 'S' and 'H' in A, X and Y respectively on startup. See hybrid.asm for an example.
• Zero page address 0x0002 contains a pointer back to CShell. Call this when you're finished (or do a rts). Doing brk will set the exit status and restart the shell.
• Zero page address 0x0004 contains a pointer to the Program Parameter Block, which is where you can find the current drive, exit status of the last program, top of memory, command line arguments etc.

Where?

• Check out the GitHub repository and build from source.

• Ask a question by creating a GitHub issue, or just email me directly at dg@cowlark.com. (But I'd prefer you opened an issue, so other people can see them.)

Who?

Cowgol was written mostly by me, David Given. Feel free to contact me by email at dg@cowlark.com. You may also like to visit my website; there may or may not be something interesting there.

License?

CShell is open source software available under the 2-clause BSD license. Simplified summary: do what you like with it, just don't claim you wrote it.