I'd like to announce my idea of a command-line interpreter.
It would be similar to COMMAND.COM, but as a prototype it would have limited functionality.

The basic idea of the program would be, that it would be able to read data from its script (file).
It would read each line and execute the command on that line.

The problem I have with this idea is that, I don't know where, or how to start. I have a limited
knowledge of assembly. But I know enough to start this envision the project, and how I will create it.
I posted this topic to ask if anyone could assist in helping me with the project.


The basic algorithm would be something like:

Scan File
loop:
Get Line
Increment Stack
If Line = Any Command then
execute command
else
Highlight error
jump to: loop

That is how is picture the operation of the interpreter. I'd like to someone to
assist me with the basics of the project.

OpenDos / DR dos might be a good starting point to look at http://drdosprojects.de/

It's in asm open source and has a good batch processor (nearly the same as ms dos) Batch 'programs' are stored in a *.bat file. They were a left over thing from mainframes, where you would write a little script that would run a batch of programs over night or over the weekend. When desktops came around, IBM / Microsoft included the ability to run batch scripts and even expanded it a little. MS & DR dos will both run a batch file called autoex.bat when they start and a lot of programs for Dos were started with a bat file, to make sure the drivers and other things were setup right

Thanks for the info.

I checked out DR DOS and, but it's a bit complicated. I was thinking of designing my interpreter purely from assembly. Do you know any open sources like that where I can study the code.

> OpenDos / DR dos might be a good starting point to look at http://drdosprojects.de/
> It's in asm open source and has a good batch processor (nearly the same as ms dos)

Only the kernel is in (not-F)ASM, command thing is in C

> I'd like to announce my idea of a command-line interpreter.

DOS or Win32 ???

> Do you know any open sources like that where I can study the code.

NO. All known are in C

Oh OK! Thanks!!

MeshNix,

MS-DOS command.com had strange but useful feature: it closed the batch file after the line was parsed (remembering the offset at which the next line will be, to reopen and read later), so current command can modify .Bat and enjoy the possibility of self-modifying batch. 4DOS shell simulated this behavior and have separate .BTM (Batch-to-memory) files for immutable contract.

That is similar to call, and ret, but instead, it closes and returns to the offset at which it was closed

MeshNix,

Yes, but .Bat file can be changed in transit. Hell to debug, but fun to see one.

Do you have specs for syntax/semantics of your batch lang?

Yes- I've designed some syntax for some instructions!
I not sure what to do after this.

MeshNix,

Now you need (at least) function to read one line from file.

Can you present those design docs? To put it under scrutiny of some constructive critique.

I have a draft document.

What I was planning to do was to read the entire content of the file and store it into a variable, then parse each line until 0Dh (carriage return) is met, then that signifies the end of that line.
The problem is, what if the file contains more than 256 characters. Then it cannot store into the variable.

And why should that "variable" be limited to 256 bytes? Why not allocate as much as you need and load the entire script?

I don't understand

Allocate a buffer of whatever size needed to store the entire file. No need to limit things to 256 bytes, is there?

I guess not. Do i use rb instead of db?

Probably best to allocate it dynamically. At runtime, get the file size first and then allocate the needed amount.

You reasonably won't use db for this buffer or any buffer at all

Set some limit (maybe 4 KiB for the beginning), do GetFileSizeEx, check against your limit, reject if too bloated, if good hog the memory, and start processing, be aware of the CR vs LF vs CRLF mess, also don't forget to check for invlaid characters (ZERO) and handle them in a well defined way

CRLF it will be used for EOL.
In using DOS interrupts not Win32 APIs.

I'm seeking advice for my project (codename: Quantum-lite)

(1) My CLI supports loop statements like FOR loop, and WHILE loop.
These loops are mutli-line loops
example:


PRINT writes text to screen.
%A is a variable in the shell.

In that script, how would the shell do a repeat when it only processes line-by-line.
Please give some advices.

(2) What type of commands would you like into be implemented in my shell?
Please provide:
- Command/Statement name
- Syntax
- Description