shell script comparing two variables

Question

I have created a script for updating some ipaddress in iptables. Hereby I'm describing the issues which I'm facing with that.

Issues:

Comparison not happening between two variables within a script
At the end of script i need to execute a command ie; service restart/stop etc and output of the commands should be visible while executing the script.

1) Here am comparing two variable strings:

BASE=172.31.0.0
CMD=172.31.1.0

if [[ "$CMD" == "$BASE" ]]; then
   echo "ip are same"
else
   echo "not matched"
fi

but there is no response/output while executing the above script. Here its not comparison is not happening..Kindly suggest a best solution to resolve this issue.

2) after executing the script I need to restart the iptables:

BASE=172.31.0.0
CMD=172.31.1.0

if [[ "$CMD" == "$BASE" ]]; then
   echo "ip are same"
else
   echo "not matched"
fi

service iptables restart
iptables -nvL

A script should display the output of the last two lines (commands). Kindly suggest me the best solution and how to do this in a best way.

So ... exactly what shell are you using? bash, or sh? You know they're different, right? Because as-is, this script works in bash and produces an error in sh. Neither of which are what you're reporting. — ghoti
– ghoti, Commented Feb 13, 2013 at 12:45
Thanks for your reply, Am using bash script and I am trying to execute this script by ./script.sh. — suboss87
– suboss87, Commented Feb 13, 2013 at 14:37
You mean that you are getting no output and no error message? That sounds weird. — 244an
– 244an, Commented Feb 13, 2013 at 14:41
@user1565390 Add #!/bin/bash to the first line of your script, just to assert it will be executed with bash when you do ./script.sh. — Rubens
– Rubens, Commented Feb 13, 2013 at 16:14

darque · Accepted Answer · 2013-02-14 01:13:13Z

1

That's very odd. This should work, so if it's not working you forgot to mention something important.

How is this script being executed? Do you simply type ./script or is it executed by some service (like cron)?

Here are some of suggestions to debug:

Sanity check: see if bash works (perhaps your login shell isn't bash, so you didn't notice). Run this at the terminal:
```
/bin/bash -c 'echo hello world'
```

It prints hello world, right? How about this:

/bin/bash -c 'BASE=172.31.0.0; CMD=172.31.1.0; if [[ "$CMD" == "$BASE" ]]; then echo "ip are same"; else echo "not matched"; fi'

If any of the above doesn't work, you have a problem with your bash installation.

Instead of executing your script with ./script.sh, run it like this:
```
/bin/bash script.sh
```
Nothing? Run this:
```
file script.sh
```
If it ends with something like "with CRLF line terminators", then cdarke nailed it: the file was created on Windows with an improper tool. Recreate it on Linux or use dos2unix. But anyway, I doubt it because with a CRLF-ending file I get this printed:
```
bash: ./script.sh: /bin/bash^M: bad interpreter: No such file or directory
```
Instead of nothing at all.
Put those this line on the beginning of the file:
```
set -x
```
(below #!/bin/bash, if you have it). This ensures a debugging trace will be printed, showing each command as it is executed.
If still there is nothing shown.. put this at your script (below set -x if you put it):
```
touch /tmp/hi-this-is-strange
```
Then check if there is a /tmp/hi-this-is-strange file after you run the script.

answered Feb 14, 2013 at 1:13

darque

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3 Comments

suboss87 Over a year ago

Thanks for your timely reply...Can you please let me know how to remove "." within the ip-address... eg) 172.31.0.0 then by awk i need to get output as 1723100 how to do this by using "awk" tool.. Thanks in advance.

darque Over a year ago

I think sed is more appropriate for this task: echo 172.31.0.0 | sed 's/\.//g'

darque Over a year ago

@user1565390 Was any of of the points of my reply useful? I still don't understand what was your problem (and feel free to edit your question to add more info), but if my response solved it please accept it.

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