A quick shell script that will automatically update a Linux HOSTS file to block domains (ads, malwares, ...). Support multiple hosts sources and initial host file.

update-hosts.sh

#!/bin/bash

# Filename: update-hosts.sh
#
# Author: George Lesica <george@lesica.com>
# Enhanced by Eliastik ( eliastiksofts.com/contact )
#
# Description: Replaces the HOSTS file with hosts lists from Internet,
# creating a backup of the old file. Can be used as an update script.
#
# Enhancement by Eliastik :
# Added the possibility to download multiple hosts files from multiple sources,
# added the possibility to use an initial host file to be appended at the top
# of the system host file, others fixes.
#
# Can be used as a cron script.

# Configuration variables:
# Add an host source by adding a space after the last entry of the variable HOSTS_URLS (before the ")"), then by adding your URL with quotes (ex: "http://www.example.com/hosts.txt")
HOSTS_URLS=( "http://someonewhocares.org/hosts/zero/hosts/" "https://pgl.yoyo.org/adservers/serverlist.php?showintro=0&mimetype=plaintext&useip=0.0.0.0" "http://winhelp2002.mvps.org/hosts.txt" )
INITIAL_HOSTS="/etc/hosts.initial"
NEW_HOSTS="hosts"
HOSTS_PATH="/etc/hosts"
NB_MAX_DOWNLOAD_RETRYING=10

# Check for root
if [ "$(id -u)" -ne "0" ]; then
    echo "This script must be run as root. Exiting..." 1>&2
    exit 1
fi

# Check curl
if ! [ -x "$(command -v curl)" ]; then
  echo 'Error: curl is not installed. Please install it to run this script.' >&2
  exit 1
fi

# create temporary directory
echo "Creating temporary directory..."
cd $(mktemp -d)
echo "Created temporary directory at $(pwd)"

# create new temp hosts
if [ -f "$INITIAL_HOSTS" ]
then
    cat $INITIAL_HOSTS>$NEW_HOSTS
else
    echo "The initial host file doesn't exist: $INITIAL_HOSTS"
    echo "">$NEW_HOSTS
fi

# Print the update time
DATE=`date '+%Y-%m-%d %H:%M:%S'`
echo "">>$NEW_HOSTS
echo "# HOSTS last updated: $DATE">>$NEW_HOSTS
echo "#">>$NEW_HOSTS

# Grab hosts file
for i in "${HOSTS_URLS[@]}"
do
   :
        nberror=0
        echo "Downloading hosts list from: $i"
        while true; do
            curl -s --fail "$i">>$NEW_HOSTS && break ||
            nberror=$((nberror + 1))
            echo "Download failed ! Retrying..."
            if [ $nberror -ge $NB_MAX_DOWNLOAD_RETRYING ]; then
                echo "Download failed $NB_MAX_DOWNLOAD_RETRYING time(s). Check your Internet connection and the host source then try again. Exiting..."
                exit 1;
            fi
        done
done

# Backup old hosts file
echo "Backup old hosts file..."
cp -v $HOSTS_PATH ${HOSTS_PATH}.bak
echo "Installing hosts list..."
cp -v $NEW_HOSTS $HOSTS_PATH

# Clean up old downloads
echo "Removing cache..."
rm $NEW_HOSTS*
echo "Done !"