How do I see a value on register?

I read books on assembly language, a chapter about instructions. I understand what is doing the instruction mov, but i don't understand how do I check and see a result. I wrote a hello world.

.global _start
.data
some_var:
    .long 0x000721
.text
_start:
mov  $1, %rax         # system call 1 is write
mov  $1, %rdi         # file handle 1 is stdout
#  mov  $message, %rsi  # address of string to output
mov $0x1, %rsi
mov  $2, %rdx # number of bytes
syscall               # invoke operating system to do the write
                    # exit(0)
mov  $60, %rax        # system call 60 is exit
xor  %rdi, %rdi       # we want return code 0
syscall               # invoke operating system to exit
message:
.ascii  "Hello, Universe)\n"

But why it doesn't work. How do I see the value at memory and register?

os: linux (debian). intel 64-bit

Solution

You need an address in rsi, not a value. That's why it works with

mov  $message, %rsi

but not with

mov $0x1, %rsi

If you want to print numbers, you need a routine to convert numbers into ASCII strings first (basically you need to write a simple version of printf).