Temporary Files and Directories in Assembly Language

Assembly language doesn’t have direct equivalents for many high-level concepts like temporary files and directories. However, we can demonstrate similar low-level operations using system calls. This example will focus on creating a file, writing to it, and then deleting it.

section .data
    filename db 'tempfile.txt', 0
    content db 'Hello, World!', 0
    content_len equ $ - content

section .text
    global _start

_start:
    ; Create a file
    mov eax, 8          ; sys_creat system call
    mov ebx, filename   ; filename
    mov ecx, 0644o      ; file permissions
    int 0x80            ; interrupt to invoke system call
    mov edi, eax        ; save the file descriptor

    ; Write to the file
    mov eax, 4          ; sys_write system call
    mov ebx, edi        ; file descriptor
    mov ecx, content    ; content to write
    mov edx, content_len ; content length
    int 0x80

    ; Close the file
    mov eax, 6          ; sys_close system call
    mov ebx, edi        ; file descriptor
    int 0x80

    ; Delete the file
    mov eax, 10         ; sys_unlink system call
    mov ebx, filename   ; filename
    int 0x80

    ; Exit the program
    mov eax, 1          ; sys_exit system call
    xor ebx, ebx        ; exit status 0
    int 0x80

This Assembly code demonstrates creating a temporary file, writing to it, and then deleting it. Here’s a breakdown of what’s happening:

1. We define the filename and content in the .data section.

2. In the _start section, we use the sys_creat system call to create a new file. The file descriptor is saved in the edi register.

3. We then use the sys_write system call to write our content to the file.

4. The sys_close system call is used to close the file.

5. Finally, we use the sys_unlink system call to delete the file.

6. The program exits using the sys_exit system call.

To assemble and run this program on a Linux system:

$ nasm -f elf tempfile.asm
$ ld -m elf_i386 -o tempfile tempfile.o
$ ./tempfile

Note that this program doesn’t print anything to the console. It creates a file, writes to it, and then immediately deletes it. You can modify the program to keep the file if you want to verify its contents.

Assembly language provides very low-level control, but it requires explicit management of system resources. Unlike high-level languages, there are no built-in functions for temporary file management, so we have to handle all aspects of file creation, writing, and deletion manually using system calls.