Script to whitelist hosts in hosts.allow using the feed of a gmail account

whitelistFeed.sh

#!/bin/bash
# Script to whitelist hosts for remote access using gmail's https atom feed.
# Update the vars defined below and chmod 700 root:root, since the password is in clear text.
# Use cron to run it periodically.
#
# To add a host to the whitelist send an email to the GMAILUSER account with a subject like: "allow 13.13.13.13" (whithout quotes) using any of the accounts in ALLOWED
# To remove a host from whitelist read or delete the corresponding email. Note the feed shows only unread mail.
#
# The script works by updating hosts.allow. It checks the feed for mails like those described above. 
# The whitelist stored in hosts.allow, between 2 markers (START FEEDSCRIPT, END FEEDSCRIPT), which should not be removed
# Other entries in hosts.allow will not be affected.
#
# Acknowledgement: This script is heavily based on the one posted by silvik in:
# https://bbs.archlinux.org/viewtopic.php?id=114828

#The account used to administrate the list 
GMAILUSER=""
GMAILPASSWD=""
#Accounts that are allowed to change the file using this script, separated by "|".
ALLOWED="$GMAILUSER@gmail.com|anotherUser@gmail.com"
#Token of the daemon to be allowed (e.g., sshd or ALL)
ALLOWTOKEN="ALL"
#pattern matching valid IPs (only IPv4 here)
IPPATTERN="(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)"
#path to the hosts.allow file
FILE="/etc/hosts.allow"

#remove old whitelist
perl -ni -e 'print unless(/START FEEDSCRIPT/../END FEEDSCRIPT/)' $FILE

echo "#START FEEDSCRIPT" >> $FILE
echo "#IPs allowed by the gmail feed script" >> $FILE
echo "#Do not remove these markers" >> $FILE

curl -u $GMAILUSER:$GMAILPASSWD --silent "https://mail.google.com/mail/feed/atom" | tr -d '\n' | \
awk -F '<entry>' '{for (i=2; i<=NF; i++) {print $i}}' | sed -n "s/<title>\(.*\)<\/title.*email>\(.*\)<\/email>.*/\2 - \1/p" | \
grep -Ei "^($ALLOWED) - allow $IPPATTERN$" | cut -d- -f2 | sed "s/ allow/$ALLOWTOKEN :/g"  >> $FILE

echo "#END FEEDSCRIPT" >> $FILE