Calculate subnet in Solaris shell

I need to calculate the subnet, having a IP address and net mask in a Solaris machine shell (bash, but could be other).

Some examples:

IP=192.168.100.6, MASK=255.255.255.0 => SUBNET=192.168.100.0
IP=11.95.189.33, MASK=255.255.0.0 => SUBNET=11.95.0.0
IP=66.25.144.216, MASK=255.255.255.192 => SUBNET=66.25.144.192

I have two ways to calculate this:

SUBNET=$((`echo $IP | awk 'BEGIN { FS = "." } ; {print $1}'`&`echo $MASK | awk 'BEGIN { FS = "." } ; {print $1}'`)).\
$((`echo $IP | awk 'BEGIN { FS = "." } ; {print $2}'`&`echo $MASK | awk 'BEGIN { FS = "." } ; {print $2}'`)).\
$((`echo $IP | awk 'BEGIN { FS = "." } ; {print $3}'`&`echo $MASK | awk 'BEGIN { FS = "." } ; {print $3}'`)).\
$((`echo $IP | awk 'BEGIN { FS = "." } ; {print $4}'`&`echo $MASK | awk 'BEGIN { FS = "." } ; {print $4}'`))

and

l="${IP%.*}";r="${IP#*.}";n="${MASK%.*}";m="${MASK#*.}"
subnet=$((${IP%%.*}&${NM%%.*})).$((${r%%.*}&${m%%.*})).$((${l##*.}&${n##*.})).$((${IP##*.}&${NM##*.}))

But I think both of them are a little "dirty". I would like a "cleaner" way to calculate the subnet, easy to understand by other people in my project.

I prefer not to use perl or python, but could be considered.

Solution

Assume that you store your ip and mask into two shell variables: $ip and $mask:

 awk -vip="$ip" -vmask="$mask" 'BEGIN{
split(ip,a, "."); 
split(mask,b,".");
for(i=1;i<=4;i++)a[i]=b[i]==255?a[i]:b[i]; 
printf"SUBNET=";for(i=1;i<=3;i++)printf a[i]".";printf a[4]}'

will give you result in format: SUBNET=xxx.xxx.xxx.xxx

take one example:

kent$  ip="192.168.100.6"                                                                                                                                                   

kent$  mask="255.255.255.192"                                                                                                                                               

kent$  awk -vip="$ip" -vmask="$mask" 'BEGIN{split(ip,a, "."); split(mask,b,".");for(i=1;i<=4;i++)a[i]=b[i]==255?a[i]:b[i]; printf"SUBNET=";for(i=1;i<=3;i++)printf a[i]".";printf a[4]}'
SUBNET=192.168.100.192