Linux

If you are on Linux, the source code will be even shorter. Open your favorite source editor, whether it is nano, emacs, or vi, or whatever, and enter the following code:

 format ELF executable 3
 entry _start

 segment readable executable
 _start:
    mov eax, 4
    mov ebx, 1
    mov ecx, message
    mov edx, len
    int 0x80

    xor ebx, ebx
    mov eax, ebx
    inc eax
    int 0x80


 segment readable writeable
    message db 'Hello from FASM on Linux!', 0x0a
    len = $ - message

The code is much more compact than that on Windows, as we are not using any high-level API functions; we'd rather use Linux system calls directly (this could turn into a nightmare on Windows). Save the file as fasm1lin.asm (this is not GAS or GCC, so we are free to give the Assembly source file its usual extension) and go to the terminal emulator. Issue the following command (assuming the fasm executable is in the place mentioned in the PATH environment variable) in order to build the executable out of this code:

fasm fasm1lin.asm fasm1lin

Then, try to run the file with the following:

./fasm1lin

You should see something like this:

As simple as that.