Hi,
I hope you'll guys can help me with this one
I need a function to convert an IP Number to IP Address
eg
IP Number = A x (256*256*256) + B x (256*256) + C x 256 + D

I have been reading a couple of shell scripting tutorials, but have not been able to figure it out...

I think I know the answer to your question

you have an IP number , for example 130.194.166.33

and you want to find out the name that is given to the ip number, eg fred.pizza.overthere.com

If this is the case you just use the command `nslookup`

do a man on it.

nope, i dont want the hostname

like for the IP - 130.194.166.33

i want to return the computed value of

(130*256*256*256)+(194*256*256)+(166*256)+(33)

anybody ?

The nice thing about UNIX is there's tons of tools around. The not-so-nice thing is that you have to know what they are to use them. This is a job for "awk", which is good at both splitting your IP address into its four components, and doing the arithmetic. Here's a function that does it:

function IPtoNum()
{
echo "$1" | awk -F. '{printf("%ld\n", ($1 * 256 * 256 * 256) + ($2 * 256 * 256) + ($3 * 256) + ($4))}'
}

It's a bit more complicated to go the other way:

function NumtoIP()
{
echo "$1" | awk '{
a = int($1 / (256 * 256 * 256));
b = int(($1 / (256 * 256)) - (a * 256));
c = int(($1 / 256) - (a * 256 * 256) - (b * 256));
d = int($1 - (a * 256 * 256 * 256) - (b * 256 * 256) - (c * 256));
printf("%d.%d.%d.%d\n", a, b, c, d)}'
}

Not all of the parentheses are necessary, I just put them in for clarity. I hope this helps!

For jobs like that, you should be using PERL.

Why perl for something so simple? Anyways, here is how I would do it: Someday I really have to learn awk, but I always seem to find away around it :-)

#!/bin/bash
# For clarity, assign first argument to ip
ip=$1
#initialize
i=1
m=1
sum=0
#loop
while [ $i -lt 5 ]
do
part=`echo $ip|cut -d. -f$((5-$i))`
let sum+=$(($m*$part))
let i+=1
let m*=256
done
#print sum
echo $sum
exit

Yeah, PERL is serious overkill for this. I used awk because I'm an old-timer who still writes shell scripts so that they work in Bourne shell. If you want a bash-only script, you can do it entirely in the shell, without executing any external program, which is nice and fast. Here's the equivalent functions in bash:

function IPtoNum() {
echo "$1" | (IFS='.' read a b c d; \
echo $(((($a*256+$b)*256+$c)*256+$d)) )
}

function NumtoIP() {
a=$(($1/256/256/256))
b=$(($1/256/256-$a*256))
c=$(($1/256-($a*256+$b)*256))
d=$(($1-(($a*256+$b)*256+$c)*256))
echo $a.$b.$c.$d
}

Nice and simple, no? Faster than, but not as portable as, the awk scripts.