Install MongoDB 4.0 on Ubuntu 18.04 - http://jasonwatmore.com/post/2018/09/26/setup-nodejs-mongodb-production-server-on-ubuntu-1804

install-mongodb-40-on-ubuntu-1804.sh

#!/usr/bin/env bash

echo "
----------------------
  MONGODB
----------------------
"

# import mongodb 4.0 public gpg key
sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv 9DA31620334BD75D9DCB49F368818C72E52529D4

# create the /etc/apt/sources.list.d/mongodb-org-4.0.list file for mongodb
echo "deb [ arch=amd64 ] https://repo.mongodb.org/apt/ubuntu bionic/mongodb-org/4.0 multiverse" | sudo tee /etc/apt/sources.list.d/mongodb-org-4.0.list

# reload local package database
sudo apt-get update

# install the latest version of mongodb
sudo apt-get install -y mongodb-org

# start mongodb
sudo systemctl start mongod

# set mongodb to start automatically on system startup
sudo systemctl enable mongod

bash: line 1: 404:: command not found error occurs

bash: line 1: 404:: command not found error occurs

it's related to file permission.
sudo chmod -R 755 install-mongodb-40-on-ubuntu-1804.sh
Then run it again.