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adroit



Joined: 21 Feb 2010
Posts: 252
adroit
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.

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meshnix
Post 21 Feb 2010, 21:42
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roboman



Joined: 03 Dec 2006
Posts: 122
Location: USA
roboman
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
Post 23 Feb 2010, 03:07
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adroit



Joined: 21 Feb 2010
Posts: 252
adroit
Thanks for the info. Very Happy

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.
Post 23 Feb 2010, 03:41
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DOS386



Joined: 08 Dec 2006
Posts: 1901
DOS386
> 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 Shocked

> 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 Sad
Post 18 Mar 2010, 07:18
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adroit



Joined: 21 Feb 2010
Posts: 252
adroit
Oh OK! Thanks!!
Post 18 Mar 2010, 11:55
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baldr



Joined: 19 Mar 2008
Posts: 1651
baldr
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. Wink
Post 18 Mar 2010, 15:31
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adroit



Joined: 21 Feb 2010
Posts: 252
adroit
That is similar to call, and ret, but instead, it closes and returns to the offset at which it was closed
Post 18 Mar 2010, 15:52
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baldr



Joined: 19 Mar 2008
Posts: 1651
baldr
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?
Post 18 Mar 2010, 16:56
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adroit



Joined: 21 Feb 2010
Posts: 252
adroit
Yes- I've designed some syntax for some instructions!
I not sure what to do after this.
Post 19 Mar 2010, 00:19
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baldr



Joined: 19 Mar 2008
Posts: 1651
baldr
MeshNix,

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

Can you present those design docs? To put it under scrutiny of some constructive critique.
Post 19 Mar 2010, 04:02
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adroit



Joined: 21 Feb 2010
Posts: 252
adroit
I have a draft document.
Post 19 Mar 2010, 04:32
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adroit



Joined: 21 Feb 2010
Posts: 252
adroit
Quote:
Now you need (at least) function to read one line from file.

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.
Post 19 Mar 2010, 23:39
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ManOfSteel



Joined: 02 Feb 2005
Posts: 1154
ManOfSteel
And why should that "variable" be limited to 256 bytes? Why not allocate as much as you need and load the entire script?
Post 19 Mar 2010, 23:53
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adroit



Joined: 21 Feb 2010
Posts: 252
adroit
I don't understand
Post 20 Mar 2010, 04:21
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 17279
Location: In your JS exploiting you and your system
revolution
Allocate a buffer of whatever size needed to store the entire file. No need to limit things to 256 bytes, is there?
Post 20 Mar 2010, 04:33
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adroit



Joined: 21 Feb 2010
Posts: 252
adroit
I guess not. Do i use rb instead of db?
Post 20 Mar 2010, 05:09
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revolution
When all else fails, read the source


Joined: 24 Aug 2004
Posts: 17279
Location: In your JS exploiting you and your system
revolution
Probably best to allocate it dynamically. At runtime, get the file size first and then allocate the needed amount.
Post 20 Mar 2010, 05:22
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DOS386



Joined: 08 Dec 2006
Posts: 1901
DOS386
MeshNix wrote:
I guess not. Do i use rb instead of db?


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

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 Idea
Post 20 Mar 2010, 09:35
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adroit



Joined: 21 Feb 2010
Posts: 252
adroit
CRLF it will be used for EOL.
In using DOS interrupts not Win32 APIs.
Post 20 Mar 2010, 15:33
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adroit



Joined: 21 Feb 2010
Posts: 252
adroit
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:
Code:
.start
FOR A = 1 TO 5:
 {
   PRINT "Repetition was successive " %A " times"
 }
.ENDFOR
.end
    


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


Last edited by adroit on 24 Mar 2010, 22:59; edited 3 times in total
Post 23 Mar 2010, 20:23
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