Environment Variables in Assembly Language

Assembly Language doesn’t have built-in functions for environment variables or string operations like the original Go code. However, we can demonstrate similar concepts using system calls and basic string operations. This example will use x86 assembly for Linux.

section .data
    foo db "FOO", 0
    foo_value db "1", 0
    bar db "BAR", 0
    newline db 10

section .bss
    env_var resb 100

section .text
    global _start

_start:
    ; Set environment variable FOO=1
    mov eax, 158         ; sys_setenv
    mov ebx, foo
    mov ecx, foo_value
    mov edx, 1           ; overwrite
    int 0x80

    ; Print FOO value
    mov eax, 4           ; sys_write
    mov ebx, 1           ; stdout
    mov ecx, foo
    mov edx, 3           ; length of "FOO"
    int 0x80

    mov eax, 4
    mov ebx, 1
    mov ecx, foo_value
    mov edx, 1           ; length of "1"
    int 0x80

    mov eax, 4
    mov ebx, 1
    mov ecx, newline
    mov edx, 1
    int 0x80

    ; Print BAR value (which is not set)
    mov eax, 4
    mov ebx, 1
    mov ecx, bar
    mov edx, 3           ; length of "BAR"
    int 0x80

    mov eax, 4
    mov ebx, 1
    mov ecx, newline
    mov edx, 1
    int 0x80

    ; Exit program
    mov eax, 1           ; sys_exit
    xor ebx, ebx         ; exit code 0
    int 0x80

This Assembly code demonstrates setting and getting environment variables using system calls. Here’s what it does:

1. We define the strings “FOO”, “1”, and “BAR” in the data section.

2. In the _start function:

   • We use the sys_setenv system call to set the environment variable FOO=1.
   • We then print “FOO” and its value using sys_write calls.
   • We attempt to print “BAR”, but since it’s not set, nothing will be printed after “BAR”.

3. Finally, we exit the program using sys_exit.

To run this program:

1. Save the code in a file, e.g., env_vars.asm
2. Assemble and link the code:

$ nasm -f elf env_vars.asm
$ ld -m elf_i386 -o env_vars env_vars.o

3. Run the program:

$ ./env_vars
FOO1
BAR

This example demonstrates basic environment variable operations in Assembly. However, it’s important to note that Assembly doesn’t have built-in functions for these operations, so we have to use system calls directly. Also, listing all environment variables would require more complex code to parse the environment block, which is beyond the scope of this basic example.