Compare ubuntu packages between two hosts

compare_hosts.sh

#!/bin/bash


# Reference: https://askubuntu.com/a/344396
function _compare_hosts () {
  echo "Usage: $ ./compare_pkgs.sh username@ip_address1 username@ip_address2 ~/.ssh/id_rsa1 ~/.ssh/id_rsa2"
  # 1: remote_host = user@ip_address
  # 2: ssh_key = ~/.ssh/id_rsa
  if [[ ! -z $1 ]]; then
    local remote_host1=$1
  else
    read -p "Enter remote host1 (ex: user@ip_address): " remote_host
  fi

  if [[ ! -z $2 ]]; then
    local remote_host2=$2
  else
    read -p "Enter remote host2 (ex: user@ip_address): " remote_host
  fi

  if [[ ! -z $3 ]]; then
    local ssh_key1="-i $3"
  else
    local ssh_key1=""
  fi

  if [[ ! -z $4 ]]; then
    local ssh_key2="-i $4"
  else
    local ssh_key2=""
  fi

  ssh $ssh_key1 $remote_host1 dpkg --get-selections | grep '\binstall$' | cut -f 1 > server-host1.txt
  ssh $ssh_key2 $remote_host2 dpkg --get-selections | grep '\binstall$' | cut -f 1 > server-host2.txt
  comm -12 <(sort server-host1.txt) <(sort server-local.txt) > server-host1-and-local.txt
  comm -23 <(sort server-host1.txt) <(sort server-local.txt) > only-server-host1.txt
  comm -13 <(sort server-host1.txt) <(sort server-local.txt) > only-server-local.txt
  echo $(wc -l *.txt)
}

_compare_hosts "${@}"