as @0x00pf explained in his ELF injection tutorial, you can extract the .text (actualy code) from an ELF (binary) file to get the payload.
There are many ways to do this and picoflamingo showed us one way.
Today I will share a shell script I wrote that does the same thing and prints it in ascii on your terminal, or wherever you redirect / pipe it.
#!/bin/bash
xxd -g 1 -s `h2d $(objdump -h $1 | grep .text | awk -e '{print $6}')` $1
That’s all, it’s pretty short, but can be very functional for shellcode development.
You can check man xxd for more options to change it’s output format.
Hope it’s of any use to you !
I forgot to include h2d, it’s a C program I wrote 
#include <stdio.h>
#include <string.h>
int main(int argc, char *argv[])
{
int indx = strlen(argv[1]) - 1;
int i,j=1, sum = 0;
for(i=indx;i>=0;i--,j*=16) {
if(argv[1][i] >= '0' && argv[1][i] <= '9')
sum += ((argv[1][i] - '0') * j);
else
sum += ((argv[1][i] - 'a' + 10) * j);
}
printf("%d\n", sum);
return 0;
}
After compiling you need to put it in your path, you can do this by moving it to /usr/bin, or make your own path folder, put the program in there and then update your PATH variable.
The best way to do this, is to add the addition in ~/.bashrc
export PATH="$PATH:$HOME/.rvm/bin:$HOME/.path/" # Add RVM to PATH for scripting
You will find this liine in your .bashrc probably if you have RVM installed. As you can see I added the folder .path to it
Else put in the line:
export PATH="$PATH:$HOME/.path (if your folder is at ~/.path.)
After doing that, either restart your terminal or use:
source ~/.bashrc
