Network ID calculator in a bash script

myegorov86 · 09-07-2011, 01:47 AM

Hello,
I need to create a script that receives 2 variables (ip address, subnet mask) and calculates a network id

can anyone help??

Thanks!

grail · 09-07-2011, 03:23 AM

What have you tried so far? What is your definition of a 'network id'?

sag47 · 09-07-2011, 03:26 AM

delete (replied to wrong post)

indeliblestamp · 09-07-2011, 03:34 AM

There are existing tools that can do this, e.g. sipcalc. You could try using that, unless your intention is to write the script yourself.

myegorov86 · 09-07-2011, 03:36 AM

http://www.techzoom.net/tools/networ...-calculator.en

You can see there a field named "Network ID", so this is basically what i need; receive 2 variables and based on them show the output of the so called "Network ID"

Thanks!

sag47 · 09-07-2011, 03:57 AM

Example: 192.168.10.10 with 255.255.255.0

The basic logic (not bash code) you'll need is...

(split IP into 4 components)
A=192
B=168
C=10
D=10

(split netmask into 4 components)
W=255
X=255
Y=255
Z=0

(calculate the result from each individual component where & is bitwise AND)
R1=$A & $W
R2=$B & $X
R3=$C & $Y
R4=$D & $Z

(Then compile and return the result)
echo "The network ID is $R1.$R2.$R3.$R4"

I'm just giving you that since this looks like homework.

myegorov86 · 09-07-2011, 04:15 AM

I'm writing a script that will help certain users to change some configuration in solaris without editing files.
The file i'm talking about is /etc/netmasks, which have the format of "network_id netmask".
I want the user to insert only the desired IP address and the subnet mask.
I'm not that strong in scripting, i can understand the logic of it but i don't know how to execute it.
So please, if you can just tell me how to it, i'll be very happy.

p.s
I wish it was a homework... unfortunately i need to write it as soon as possible, so i don't have much time to investigate it

Thanks!

jschiwal · 09-07-2011, 08:00 AM

Some tips that might help:

Code:

Use filename expansion:
${ipaddress}="192.168.1.100"

This extracts the 1st octet and assigns it to the first element of the octet[] array:
${octet[0]]=${ipaddress%%.*}

This strips of the 1st octet.  Repeated 3 times, you can extract each element using the code just above:
$ippart=${ipaddress#*.}

Either in a loop, or sequential lines of code, you can extract the first octet, and assign it to an element; strip off the first octet, and repeat.
${ippart}=${ipaddress}
${octet[0]]=${ippart%%.*}
$ippart=${ippart#*.}
${octet[1]]=${ippart%%.*}
...


You can use the '&' operator to calculate a bitwise AND.  You can use this to mask the IP address with the netmask, returning the network address part:
netpart[0]=$((${ipnum[0] & ${netmasknum[0]}))

To perform integer operations, enclose expressions in $(( .. )).  Otherwise, a value might be a string instead.