Updates IP for changeip.com's DDNS service

UpdateChangeIP.sh

#!/bin/bash

###############################################################
## ChangeIP.com bash update script                             
###############################################################
## Written 3/18/09 by Tom Rinker, released to the Public Domain
## Re-write 09/15/2017 by Michael Bierman
## I replaced wget with curl so it can work on all macs. 
###############################################################
## This is a simple bash script to preform a dDNS update with  
## ChangeIP.com. It uses only bash and wget, and so should be  
## compatible with virtually any UNIX/Linux based system with  
## bash. It is intended to be executed as a cron job, and      
## will only execute an update of dDNS records when the IP     
## address changes. As ChangeIP.com dDNS records have a 5 min  
## Time-To-Live, it is basically pointless and wasteful to     
## execute it more often than every 5 minutes. This script     
## supports logging all activity, in 3 available log levels,   
## and supports simple management of log file size.            
###############################################################
## To use this script:                                         
## 1) set the variables in the script below                    
## 2) execute the script as a cron job                         
###############################################################
## WARNING: This script has two potential security holes.      
## First, the username and password are stored plaintext in    
## the script, so a system user who has read access to the     
## script could read them. This risk can be mitigated with     
## careful use of file permissions on the script.              
## Second, the username and password will show briefly to other
## users of the system via ps, w, or top. This risk can be     
## mitigated by moving the username and password to .wgetrc    
## This level of security is acceptable for some installations 
## including my own, but may be unacceptable for some users.
## 
## You can now pass username and passowrd as parameters instead
## of storing them them in the file. 
###############################################################

################ Script Variables #############################
BASE=$HOME/Downloads/changeip			# Where to store all the related files
LASTIP=$(cat $BASE/IP 2> /dev/null)					# IP address storage file
LOGPATH=$BASE/changeip.log				# Log file
CIPUSER=		# ChangeIP.com Username this can be passed via parm
CIPPASS=        # ChangeIP.com Password this can be passed via parm
CIPSET=1								# ChangeIP.com recordset
LOGLEVEL=2								# 0=off, 1=medium, 2=high this can be passed via parm
LOGMAX=500								# Max log lines, 0=unlimited
UA="Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/80.0.3987.163 Safari/537.36"
###############################################################

# Make sure the required directories are in place... 
if [ ! -d "$BASE" ]; then
	mkdir $BASE
fi


function cInputs () {
# Sort out what the user asked for
for i in "$@" ; do

	case $i in
	-log=* | --log=*)
		LOGLEVEL=$(echo $i | cut -f2 -d'=')
		;;
	-pass=* | --pass=*|-password=*)
		CIPPASS=$(echo $i | cut -f2 -d'=')
		;;
	-user=* | --user=*)
		CIPUSER=$(echo $i | cut -f2 -d'=')
		;;	
	*)
		echo -e "\n\n************************************************************\n        \""$i"\" not a recognized input. This will be ignored.\n\n Valid options are:\n   '-mode=silent (default is verbose)\n   '-user=username'\n   '-pass=password'\n************************************************************\n\n as in\n\n %$(basename $0) -user=fred -pass=hispassword -mode=silent\n\n\n"
		;;		
	esac
done
}

function setup {
	echo "--------------------------------" >> $LOGPATH
	date >> $LOGPATH
			}      

# See if there are any commandline options passwed to the script. 
cInputs "$@"

# get current IP from ip.changeip.com, and store in $CURRENTIP

CURRENTIP=$(curl --user-agent "$UA" --silent ip.changeip.com | grep IPADDR | cut -d= -s -f2 | cut -d- -s -f1)


# compare $LASTIP with $CURRENTPIP, and if different, execute update
if [ "$LASTIP" = "$CURRENTIP" ]
  then									# same IP, no update
	  if [ "$LOGLEVEL" -ge "1" ]
	  then							# if verbose, log no change
		  setup
		  echo "No Change" | tee -a $LOGPATH
		  echo "IP: " $LASTIP >> $LOGPATH
	  fi
  else									# different IP
	  RESULT=$(curl --user-agent "$UA" --silent -u $CIPUSER:$CIPPASS https://nic.changeip.com/nic/update?cmd=update&set=$CIPSET)
		  
	if [ $LOGLEVEL -ne 0 ]
	then							# if logging, log update
		setup
		echo "Updating IP" | tee -a $LOGPATH
		echo "NewIP: " $CURRENTIP >> $LOGPATH
	fi

	if [ $LOGLEVEL -ge 2 ] 
	then
		echo "OldIP: " $LASTIP >> $LOGPATH
		echo "Result: " $RESULT >> $LOGPATH
	fi

	echo $RESULT
	if [ "$RESULT" != "200 Successful Update" ]   # If there was an unsuccessful update (e.g. bad credentials), remove the last IP
	then
		rm $BASE/IP
	fi
fi


echo $CURRENTIP | tee $BASE/IP               # Store new IP


# if $LOGMAX not equal to 0 and we are logging, reduce log size to last $LOGMAX number of lines
if [ $LOGMAX -ne 0 -a $LOGLEVEL -ge 1 ]
  then
	  echo "$(tail -n $LOGMAX $LOGPATH)" > $LOGPATH
fi

• Rewrote this from wget to curl (because macOS doesn't have wget by default).
• Added command line args so you don't have to store username/password if you don't want to.
• Added command line arg for logging level.
• Got rid writing some temp files that were unnecessary.
• Improved handling of some corner cases.

#changeIP, #DDNS