How can I see the 0s and 1s / machine code from a executable file / object file?

Question

I already tried this, I opened a a.out file with a text editor but I get only a bunch of characters with some instructions in it like:

üÙ

Answer 1

Try hexdump. Something like:

$ hexdump -X a.out

It will give you just that: an hexadecimal dump of the file.

Having said that, another possibility might include using GDB's disassemble command.

Answer 2

Lookup your local friendly Hex Editor.

Answer 3

To see the disassembly (with opcode bytes) of the code only, not including any file headers:

objdump -d a.aot

Answer 4

Executable files come in several formats. For Unix/Linux it's ELF: http://en.wikipedia.org/wiki/Executable_and_Linkable_Format

For Windows it's PE: http://en.wikipedia.org/wiki/Portable_Executable

Use the objdump tools to see the opcodes as others have pointed out