OSDev.org

Posted: **Thu Feb 19, 2009 11:33 am**

Hi, all.
i'm about to implement the command line interface for my os, but something confused me.
As i know, the prototype of a shell is :

Code: Select all

oid shell_init()
{
        while(1) {
                puts("$ ");
                
                /* type the command first */

                /*(1)*/then reading it from console buffer;
                
                parsing the command buffer;

                run the command;
                
        }
}

but the problem is :
How can i stop (1) be happened before the command totally be entered?

if not solve this, as you can see from the above code, it'll puts "$ " at all the time.

Have any body have ideas?
and i would appreciate it very much if some one give me some useful information about CLI.
Thanks!
negcit.K

Posted: **Thu Feb 19, 2009 11:44 am**

Hmmm... isn't that obvious?

When you type into the shell of your OS of choice. You can type, backspace, copy, paste, and only when you press return is the line passed to the shell process.

Posted: **Thu Feb 19, 2009 11:51 am**

Solar wrote:Hmmm... isn't that obvious?

When you type into the shell of your OS of choice. You can type, backspace, copy, paste, and only when you press return is the line passed to the shell process.

Yeah, that's what i think. but how can i stop the kernel from running just waiting your keyboard press?
like this?

Code: Select all

while( get_char() != '\n' )
        ;

in this way , while i pressed a key, the kernel hangs(is this my kernel's problem?).

Posted: **Thu Feb 19, 2009 12:20 pm**

you can have the shell program block while there are no keystrokes, and have keystrokes wake it up and then it processes the keystroke, be it either echo the character, or go back a space or whatever, and if the keystroke is enter, process the line. The whole time the shell internally is building a modifying a string consisting of keystrokes

Posted: **Thu Feb 19, 2009 4:36 pm**

The basic command loop behind Socks is as follows (pseudocode):

Code: Select all

while(1)
{
  key = getKey(); // Waits for keypress
  if(key == '\b')
     removeCharFromBuffer(cmdBuffer);
  else if(key == '\n')
  {
    parseBuffer(cmdBuffer);
    findFile(cmd);
    runPrgm(foundFile, args);
    resetBuffer(cmdBuffer);
  }
  else if(' ' <= key && key <= '~')
    addCharToBuffer(cmdBuffer)
  setCursor(0, promptLine);
  print(prompt);
  print(cmdBuffer);
}

Of course, this is just a basic overview of what's going on, and isn't entirely accurate, but it's close enough. There are also probably better ways of handling it, too.

Posted: **Thu Feb 19, 2009 5:36 pm**

More psuedocode, but more C-ish:

Code: Select all

void shell()
{
    char cmd_buffer[256];
    char cmd_help[] = "help";
    char cmd_hello[] = "hello";

    while(1)
    {
        puts("$ ");
        get_string(cmd_buffer,255);
        if (string_compare(cmd_buffer,cmd_help);)
        {
            puts("help file\n\n");
        }
        else if (string_compare(cmd_buffer,cmd_hello);)
        {
            puts("hello world!\n\n");
        }
        else
        {
            puts("bad command entered.\n\n");
        }
    }
}

Posted: **Thu Feb 19, 2009 5:39 pm**

Solar wrote:Hmmm... isn't that obvious?

When you type into the shell of your OS of choice. You can type, backspace, copy, paste, and only when you press return is the line passed to the shell process.

Urrmmm, no. Most shells accept characters one-at-a-time, and have the terminal in Raw mode, so no echo, and use backspace/space characters to move the cursor left/right. Curses apps can use cleverer stuff if they have a terminfo/termcap file.

The answer is to use a grammar to parse the input. The grammar should terminate when a fully-fledged command has been entered - not just when the user presses enter. Why?

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$ echo "my 
> shell is cool and has newline
> breaks"

So that you can handle the above.

James

Posted: **Thu Feb 19, 2009 8:12 pm**

JamesM wrote:
Solar wrote:Hmmm... isn't that obvious?

When you type into the shell of your OS of choice. You can type, backspace, copy, paste, and only when you press return is the line passed to the shell process.
Urrmmm, no. Most shells accept characters one-at-a-time, and have the terminal in Raw mode, so no echo, and use backspace/space characters to move the cursor left/right. Curses apps can use cleverer stuff if they have a terminfo/termcap file.

I think that's what Solar meant. The bottom line is the shell never actually runs anything until you tell it to (most of the time by pressing enter). To me it seems like the OP was under the impression that shells would spontaneously run their input.

Posted: **Thu Feb 19, 2009 11:30 pm**

Thanks all.

but i think the most key problem is how to sleep the kernel before a key pressed.
or in another word, how to implement:

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wait_for_keypress();

and why the following code doesn't work for me?

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while ( (c=get_char()) != '\n')
        ;

Posted: **Fri Feb 20, 2009 3:53 am**

negcit.K wrote:but i think the most key problem is how to sleep the kernel

I think the most 'key problem' is that you do not only understand at all how an OS works, but you also do not know how to program. Please, learn some programming first, then learn some OS stuff (like interrupt handling, scheduling, multi-tasking, blocking, critical sections, etc.), then come back. See you in 3 years (yeah, I'm an optimist)...

JAL

Posted: **Fri Feb 20, 2009 4:21 am**

jal wrote:
negcit.K wrote:but i think the most key problem is how to sleep the kernel
I think the most 'key problem' is that you do not only understand at all how an OS works, . Please, learn some programming first, then learn some OS stuff (like interrupt handling, scheduling, multi-tasking, blocking, critical sections, etc.), then come back. See you in 3 years (yeah, I'm an optimist)...

JAL

Thank you first, just for some unknown reason.!

But, can you give me more details on what you saying?
especially

but you also do not know how to program

this sentence.

Thanks again!

Posted: **Fri Feb 20, 2009 6:04 am**

negcit.K wrote:But, can you give me more details on what you saying?
especially
but you also do not know how to program
this sentence.

It seems obvious from the problems you seem to be having. Alternatively, you just really do not know how to ask questions. Otherwise you would have asked straight away how to implement reading characters without a busy loop and/or blocking the kernel. That would still be a question revealing your ignorance about OS design, but at least I wouldn't have had expected you not being able to program.

JAL

Posted: **Fri Feb 20, 2009 6:34 am**

Alternatively, you just really do not know how to ask questions

I'm sorry for my bad english 'cause english isn't my mother language.
and , at first i just wanna collect some useful information about CLI since i haven't seen any things about CLI implementation on various OSDEV websites.

and after some thinking , i found the key problem is how to block the kernel before a key pressed.
something like:

Code: Select all

void shell_init()
{
        while(1) {
                puts("$ ");
               
               [color=#FF0000] **** STOP kernel running until return pressed *****[/color]
               
                parsing the command buffer;

                run the command;
               
        }
}

but, unfortunately, i make my shell work in another way.
in the ker_interrupt_handle(), i allocated a comand buffer char array com_buffer; if'\n' met, send the com_buffer to command parse routine, or store it in com_buffer.
what an ugly implementation, but it works

Posted: **Fri Feb 20, 2009 6:55 am**

negcit.K wrote:I'm sorry for my bad english 'cause english isn't my mother language.

It isn't for about half of the people here. But we would forgive you your language problems allright.

at first i just wanna collect some useful information about CLI since i haven't seen any things about CLI implementation on various OSDEV websites.

That is because the CLI is a user-space thing, unless we're talking about a "toy" kernel. That means you don't implement it until most of your kernel work is already done.

i found the key problem is how to block the kernel before a key pressed.

No it isn't. The problem is that you don't implement the CLI within the kernel.

in the ker_interrupt_handle(), i allocated a comand buffer char array com_buffer; if'\n' met, send the com_buffer to command parse routine, or store it in com_buffer.
what an ugly implementation, but it works

There is nothing ugly about it, it's how I would expect it to be.

Posted: **Fri Feb 20, 2009 9:15 am**

in the ker_interrupt_handle(), i allocated a comand buffer char array com_buffer; if'\n' met, send the com_buffer to command parse routine, or store it in com_buffer.
what an ugly implementation, but it works

Again, use a grammar! This is a language problem. So solve it with a parser for a language.

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