An /etc/hosts manager bash script (v1.1) -- Added import and export commands!

etchosts.sh

#!/bin/bash

HOSTSFILE="/etc/hosts"
BAKFILE="$HOSTSFILE.bak"
DOMAINREGEX="^[a-zA-Z0-9]{1}[a-zA-Z0-9\.\-]+$"
IPREGEX="^[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}$"
URLREGEX="^https?:\/\/[a-zA-Z0-9]{1}[a-zA-Z0-9\/\.\-]+$"

backup()
{
  echo "Backup created at $BAKFILE";
	cat $HOSTSFILE > $BAKFILE
}

usage()
{
	echo "Usage:"
	echo "$0 add [host] [ip]"
	echo "$0 remove [host]"
	echo "$0 update [host] [ip]"
	echo "$0 check [host]"
	echo "$0 rollback (reverts the last change)"
	echo "$0 import [file or url] [--append] (replaces or appends the host file with the new one)"
	echo
}

isroot()
{
	# Check for root user
	if [ $(whoami) != "root" ]; then
	  echo "$0 must be run as root... Aborting."; echo;
	  exit 192
	fi
}

# Check that we're in a BASH shell
if test -z "$BASH" ; then
  echo "update-hosts.sh must be run in the BASH shell... Aborting."; echo;
  exit 192
fi

case $1 in
add)
	isroot

	# Do we have enough arguments?
	if [ ! $# == 3 ]; then
		echo "Missing arguments: $0 add [host] [ip]"; echo;
		exit 192
	fi

	# Does the host look valid?
	if [[ ! $2 =~ $DOMAINREGEX ]]; then
		echo "Invalid hostname: $2"; echo;
		exit 192
	fi

	# Does the IP look valid?
	if [[ ! $3 =~ $IPREGEX ]]; then
		echo "Invalid IP address: $3"; echo;
		exit 192
	fi

	# Check to see if the host is already in the file
	REGEX="$2$"
	if [ $(cat $HOSTSFILE | grep '$REGEX' | wc -l | sed 's/^ *//g') != 0 ]; then
	  echo "The host $2 is already in the hosts file."; echo;
	  exit 192
	fi

	echo -e "$3\t$2" >> $HOSTSFILE
	echo "Added $2"; echo
	;;
check)
	# Do we have enough arguments?
	if [ ! $# == 2 ]; then
		echo "Missing arguments: $0 check [host]"; echo
		exit 192
	fi

	REGEX="${2}$"; 
	if [ $(cat $HOSTSFILE | grep $REGEX | wc -l | sed 's/^ *//g') != 0 ];
		then
	  		cat $HOSTSFILE | grep $2
		else
			echo "The host $2 was not found in the host file."; echo;
	fi

	;;
remove)
	# Do we have enough arguments?
	if [ ! $# == 2 ]; then
		echo "Missing arguments: $0 remove [host]"; echo
		exit 192
	fi

	isroot

	REGEX="$2$"
	if [ $(cat $HOSTSFILE | grep $REGEX | wc -l | sed 's/^ *//g') = 0 ]; then
		echo "The host $2 was not found in the host file."; echo;
		exit 0;
	fi

	backup

	cat $HOSTSFILE | sed -e "/$2$/ d" > tmp && mv tmp $HOSTSFILE
	echo "$2 entry removed."; echo
	;;
update)
	# Do we have enough arguments?
	if [ ! $# == 3 ]; then
		echo "Missing arguments: $0 update [host] [ip]"; echo
		exit 192
	fi

	isroot

	# Does the IP look valid?
	if [[ ! $3 =~ $IPREGEX ]]; then
		echo "Invalid IP address: $3"; echo;
		exit 192
	fi

	# Does the host look valid?
	if [[ ! $2 =~ $DOMAINREGEX ]]; then
		echo "Invalid hostname: $2"; echo;
		exit 192
	fi

	backup

	$0 remove $2

	$0 add $2 $3

	echo "$2 entry updated to $3"; echo
	;;
import)
	TEMPFILE="./hostsimport.$(date +%s).tmp"
	APPEND=0

	# Do we have enough arguments?
	if [ ! $# -gt 1 ]; then
		echo "Missing arguments: $0 import [file] {--append}"; echo
		exit 192
	fi

	isroot

	if [ ! -z $3 ]; then
		if [ $3 == "--append" ]; then
			APPEND=1
		fi
	fi

	# Check the file type and fetch it if needed.
	
	if [[ $2 =~ $URLREGEX ]]
		then
			echo "curl -s -o $TEMPFILE $2"
		else
			TEMPFILE=$2
	fi

	if [ -f $TEMPFILE ]; 
		then
			backup

			IMPORTPREFIX="\n\n## IMPORTED FROM: $2\n\n";

			if [ $APPEND == 0 ]
				then
					echo -e "$(head -n 11 $HOSTSFILE)$(echo $IMPORTPREFIX)$(cat $TEMPFILE)" > $HOSTSFILE
					echo "$2 has been imported in to $HOSTSFILE."; 
				else
					echo -e $IMPORTPREFIX >> $HOSTSFILE
					cat $TEMPFILE >> $HOSTSFILE
					echo "$2 has been appended on to $HOSTSFILE."; 
			fi
		else
			echo "Invalid import file."
	fi

	echo
	;;
export)
	# Do we have enough arguments?
	if [ ! $# == 2 ]; then
		echo "Missing arguments: $0 export [outfile]"; echo
		exit 192
	fi

	isroot

	cat $HOSTSFILE > $2

	echo "Current $HOSTFILE saved to $2"

	;;
rollback)
	isroot

	if [ -f $BAKFILE ]
		then
			cat $BAKFILE > $HOSTSFILE
			rm $BAKFILE
			echo "Rollback complete."; echo
		else
			echo "No backup file found!"; echo
	fi
	;;
-h)
	usage
	;;
*)
	echo "Missing command. Type $0 -h for usage."; echo
	;;
esac
exit 0

Thank you very much. This is really helpful.

Thank you. Just what I needed.
Apparently, there is a dependency on Bash 3.2. Had to upgrade bash 2.0 on the server :)

Hi Mike,

Just found an issue with the script.
I've scheduled your script in cron:
*/15 * * * * root /usr/local/bin/etchosts.sh update ecc606-b dig +short a hostname1.xyz.com

Despite using update command, after couple of days my /etc/hosts file is full of identical records like:

54.194.xxx.xxx  ecc606-b
54.194.xxx.xxx  ecc606-b
54.194.xxx.xxx  ecc606-b
54.194.xxx.xxx  ecc606-b
54.194.xxx.xxx  ecc606-b
54.194.xxx.xxx  ecc606-b
54.194.xxx.xxx  ecc606-b
54.171.yyy.yyy   ecc606-b
54.171.yyy.yyy   ecc606-b
54.171.yyy.yyy   ecc606-b
54.171.yyy.yyy   ecc606-b
54.171.yyy.yyy   ecc606-b
54.171.yyy.yyy   ecc606-b

I thought update should update the record, but not add a new one into the /etc/hosts file. Could you check please?

Dmitry

In playing around with this script I noticed that (at least for remove on OSX) the suffix of the hostname is matched. So, if you have bobworkstation and tomworkstation and remove tomworkstation, then you also lose the host entry for bobworkstation.

very useful, thank you!