Comparing two IP Addresses in Bash

Question

I am trying to find if two ip addresses are the same or not. I admit that I am new with bash, but I see no reason this would not work:

if [[ "$IPAddress" != "$OLDIPAddress" ]]
then
  echo "IP Not the Same"
else
  echo "IP Same"
fi

For testing purposes, I have even hard coded the values for the two variables, and they still don't show up as the same. I know you don't always see your own typos, but I do not see why this would not work. Any ideas?

Answer 1

Quick demo script for comparing differently formated ip addresses, "normal" vs. DHCP always 3 digit octets for instance. Hopefully a couple of useful tricks you can use for parsing and validation in addition to compares, and a catalyst for some more from the community. (This is my first post with code so hopefully it comes through ok - as always YMMV.)

#!/bin/bash
# demo.sh - parse, validate, compare ip addresses
# usage: demo.sh {ipaddress1} {ipaddress2}

#--- IP ADDRESS 1
#---   Is there anything besides digits and three dots?
#---   Parse out the octets
#---   There should be exactly 4 populated octets
#---   All 4 octets must not be > 255
[ "${1//[0-9]/}" != '...' ] && echo "invalid" && exit 1
O1=(${1//./ })
[ -z "${O1[3]}" -o -n "${O1[4]}" ] && echo "invalid" && exit 1
[ ${O1[0]} -gt 255 -o ${O1[1]} -gt 255 -o ${O1[2]} -gt 255 -o ${O1[3]} -gt 255 ] && echo "invalid" && exit 1
#--- IP ADDRESS 2
[ "${2//[0-9]/}" != '...' ] && echo "invalid" && exit 1
O2=(${2//./ })
[ -z "${O2[3]}" -o -n "${O2[4]}" ] && echo "invalid" && exit 1
[ ${O2[0]} -gt 255 -o ${O2[1]} -gt 255 -o ${O2[2]} -gt 255 -o ${O2[3]} -gt 255 ] && echo "invalid" && exit 1

#--- Numeric compares of each octet
echo "Comparing each octect"
if [ ${O1[0]} -eq ${O2[0]} ]
  then
    echo "  ${O1[0]} == ${O2[0]}"
  else
    echo "  ${O1[0]} != ${O2[0]}"
  fi
if [ ${O1[1]} -eq ${O2[1]} ]
  then
    echo "  ${O1[1]} == ${O2[1]}"
  else
    echo "  ${O1[1]} != ${O2[1]}"
  fi
if [ ${O1[2]} -eq ${O2[2]} ]
  then
    echo "  ${O1[2]} == ${O2[2]}"
  else
    echo "  ${O1[2]} != ${O2[2]}"
  fi
if [ ${O1[3]} -eq ${O2[3]} ]
  then
    echo "  ${O1[3]} == ${O2[3]}"
  else
    echo "  ${O1[3]} != ${O2[3]}"
  fi

#--- Numeric IP address compare
echo "Compare via long if"
if [ ${O1[0]} -eq ${O2[0]} -a ${O1[1]} -eq ${O2[1]} -a ${O1[2]} -eq ${O2[2]} -a ${O1[3]} -eq ${O2[3]} ]
  then
    echo "  ${1} == ${2}"
  else
    echo "  ${1} != ${2}"
  fi

#--- Loop for numeric compare
echo "Compare via loop"
SAME="Y"
for I in 0 1 2 3
  do
   echo "  loop ${I} compare ${O1[$I]} ${O2[$I]}"
   [ ${O1[$I]} -ne ${O2[$I]} ] && SAME="" && break
  done
echo "  result"
if [ -n "${SAME}" ]
  then
    echo "  ${1} == ${2}"
  else
    echo "  ${1} != ${2}"
  fi

exit


$ ./demo.sh 1.2.3.4 1.2.3
invalid
$ ./demo.sh 1.2.3.4 1.2.q.4
invalid
$ ./demo.sh 1.2.3.4 1.2.3.4.
invalid
$ ./demo.sh 1.2.3.4 1.2.3.4.5
invalid
$ ./demo.sh 1.2.3.4 1.2.300.4
invalid
$ ./demo.sh 1.02.3.004 01.2.003.4
Comparing each octect
  1 == 01
  02 == 2
  3 == 003
  004 == 4
Compare via long if
  1.02.3.004 == 01.2.003.4
Compare via loop
  loop 0 compare 1 01
  loop 1 compare 02 2
  loop 2 compare 3 003
  loop 3 compare 004 4
  result
  1.02.3.004 == 01.2.003.4
$ ./demo.sh 1.02.3.004 01.2.030.4
Comparing each octect
  1 == 01
  02 == 2
  3 != 030
  004 == 4
Compare via long if
  1.02.3.004 != 01.2.030.4
Compare via loop
  loop 0 compare 1 01
  loop 1 compare 02 2
  loop 2 compare 3 030
  result
  1.02.3.004 != 01.2.030.4
$

Answer 2

While your command should work, you can use the simple test operator (just a single bracket). The advantage is that it will work with any (POSIX) shell. However, the [[ operator should work too.

Can you reproduce this little example? (Should output 'yes'):

IPAddress="127.0.0.1"
OLDIPAddress="127.0.0.1"

if [ "$IPAddress" != "$OLDIPAddress" ] ; then 
    echo "no"
else
    echo "yes"
fi