#!/bin/bash 

in=$1; out=$2; combos=$3

list=($(<"$1"));

function combos () {

    if (($1 < 1)) ; then echo "$2"
    
		else for x in "${list[@]}"; do echo "$(combos $(($1-1)) $x$2)"; done
		
    fi 
    
}

combos $3 > "$2"