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

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

Answer 5

when you open a binary file you would see unreadable characters, the reason is that ascii encoding uses 7 bits , therefore all the characters that have a code point from 128 to 255 won't be recognized by the editor and therefore you see unknown characters.
if you want to see all the contents of a binary file , you could use programs like hexdump,objdump and readelf, for example lets say we want to dissect /bin/bash as a binary file in linux(elf) into its bytes in hexadecimal representation, so we say:
hexdump /bin/bash
but the best tool for these kind of files is: readelf
if we want to see all the contents of a binary file in a more human-readable format than the hexdump output we could just say:
readelf -a /bin/bash
and we would see all different sections of the binary file (elf header, program header , sections header and data).
also using other flags we could see only one header at a time, or we could just disassemble the .text sections in the file and so on.