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TheDev100 wrote:Hey guys. I am trying to compare a string. I am wanting to make a shell with commands.
For example, if I type clear, it will clear the screen.

I've tried INT 16 and cmp but it hasn't worked.
How would I make it so if I type a command and press enter, it would do something.

Thanks
John

cmp eax, 'clear'
je clearscreen

TheDev100 wrote:Thanks man but is it possible for this to be 16-bit and also give me an example of how to do the other part?
I mean the part when you type in clear and press enter then it clears the screen.

TheDev100 wrote:Hey guys. I am trying to compare a string. I am wanting to make a shell with commands.
For example, if I type clear, it will clear the screen.

I've tried INT 16 and cmp but it hasn't worked.
How would I make it so if I type a command and press enter, it would do something.

DixiumOS wrote:Let's assume what the user typed is in EAX, and we're using intel syntax (destination, source).

Code: Select all

cmp eax, 'clear'
je clearscreen

This code compares eax (assuming it contains something like 'clear') and if equal/succesful, it jumps to the label clearscreen where you can later clear the screen and reinitialize the shell.

Hope this works,

Dixium

DixiumOS wrote:

TheDev100 wrote:Hey guys. I am trying to compare a string.

Code: Select all

cmp eax, 'clear'
je clearscreen

Hope this works

glauxosdever wrote:The string "clear" takes 5 bytes (or 6, if NUL terminator is accounted for), while eax can hold only 4 bytes.
You need a string comparison function that takes two pointers as input and traverses the strings pointed to.
I suggest you first learn before giving advice.

Gigasoft wrote:What is this I don't even

  mov esi, buffer
  xor eax, eax
  mov esi, buffer
  mov edi, esi
  stosd ; clear buffer to all zeros
; get user input and limit to 4 ascii characters
  lodsd ; esi points to user input string
  or eax, 0x20202020 ; convert to lower case
; and pad less than 4 character input with spaces for comparison
  cmp eax, 'clea' ; r screen
  je clear_screen
  cmp eax, 'time'
  je get_time
  cmp eax, 'xxx '
  je show_pomography
; ... and so on

DixiumOS wrote:Let's assume what the user typed is in EAX, and we're using intel syntax (destination, source).

Code: Select all

cmp eax, 'clear'
je clearscreen

This code compares eax (assuming it contains something like 'clear') and if equal/succesful, it jumps to the label clearscreen where you can later clear the screen and reinitialize the shell.

onlyonemac wrote: That is literally THE worst string comparison function that I have ever seen. Note that character literals are not the same as string literals and that strings are arrays of integer values with each element containing the ASCII code of the respective character in the string. It is standard practice to pass a pointer to (i.e. the memory address of) these arrays around in registers. This is not the same as storing the string itself in a register. Once you understand that registers are fixed sizes and that strings can have any number of characters in them, it should be fairly to understand why we don't store strings themselves in registers.

onlyonemac wrote:

DixiumOS wrote:Let's assume what the user typed is in EAX, and we're using intel syntax (destination, source).

Code: Select all

cmp eax, 'clear'
je clearscreen

This code compares eax (assuming it contains something like 'clear') and if equal/succesful, it jumps to the label clearscreen where
you can later clear the screen and reinitialize the shell.

That is literally THE worst string comparison function that I have ever seen. Note that character literals are not the same as string
literals and that strings are arrays of integer values with each element containing the ASCII code of the respective character in the
string. It is standard practice to pass a pointer to (i.e. the memory address of) these arrays around in registers. This is not the same
as storing the string itself in a register. Once you understand that registers are fixed sizes and that strings can have any number of
characters in them, it should be fairly to understand why we don't store strings themselves in registers.

MichaelFarthing wrote:Slightly unfair (though the code being discussed has one or two little difficulties like trying to use stos with esi instead of edi).