GDB oneliners

Recently I wanted to print disassembled main funciton of the program to the file so I can read it in my Emacs, but it turned out I can't simply redirect the GDB output to the file with `disassemble main > main.asm` command in gdb command line.

But there is `-ex` option exists in gdb command so we can execute some gdb commands right after gdb is initialized.

Looks like this: