Value comparison in bash shell script

linuxmantra · 02-26-2015, 03:13 PM

I need to compare a value with different fixed value. Below is the code concept I implemented in my bash script but its giving me error.
Here "a' is the nameserver value that I extract using command line from /etc/resolv.conf. I did not put command here.

#! /bin/bash
a=1.2.3.4

if [ $a == 1.2.3.4 || 5.6.7.8 || 8.9.1.4]
then
echo " You have correct ntpserver"
else
echo"wrong ntpserver"

fi

Am I comparing the value correctly or any suggestion?

Thank you

Didier Spaier · 02-26-2015, 06:58 PM

There is no "==" in bash and the || (or) should separate conditions, not values[1].

Also, you forgot a space between echo and "wrong ntpserver"

Try this:

Code:

#! /bin/bash
a="1.2.3.4"
if [ "$a" = "1.2.3.4" ] || [ "$a" = "5.6.7.8" ] || [ "$a" = "8.9.1.4" ]; then
 echo " You have correct ntpserver"
else
  echo "wrong ntpserver"
fi

[1]Edited, see post #5.

Tadaen · 02-26-2015, 07:46 PM

Don't know where you get that idea. You must be running some crazy version of bash. I have several scripts that rely on "==" or "!=".

Most typically to run the script one way if root, another if regular user

Code:

if [[ "$USER" == root ]] ; then
  do root stuff here
else
  do user stuff here
fi

works great.

metaschima · 02-26-2015, 09:01 PM

A slightly more compact option:

Code:

#!/bin/bash

a="1.2.3.4"

case "$a" in
	1.2.3.4|5.6.7.8|8.9.1.4)
		echo " You have correct ntpserver"
	;;
	*)
		echo "wrong ntpserver"
	;;
esac

exit 0

Didier Spaier · 02-27-2015, 12:38 AM

Quote:

Originally Posted by Tadaen

Don't know where you get that idea. You must be running some crazy version of bash. I have several scripts that rely on "==" or "!=".

Yes, I stand corrected.

However, to keep the script portable I recommend avoiding bashisms, i.e. write the scripts using only the syntax defined in the POSIX specification of the Shell Command Language whenever possible and in this case it is easy.