IP address calculator script - bash

Question

I need to write a Bash script that converts IP address from CIDR format to quad-style.
I must enter the IP address in the following style:
10.10.10.10/24
If I entered it in this style:
10.10.10.10 255.255.255.0
an error message should appear.
I tried this script:
#!/bin/bash
echo "enter you ip"
read ip
case $ip in
*.*.*.*/*)
b=`echo $ip | cut -d/ -f1`
a=`echo $ip | cut -d/ -f2`
if [ $a -eq 24 ];then
echo "$b 255.255.255.0"
elif [ $a -eq 25 ];then
echo "$b 255.255.255.128"
elif [ $a -eq 26 ];then
echo "$b 255.255.255.192"
elif [ $a -eq 27 ];then
echo "$b 255.255.255.224"
elif [ $a -eq 28 ];then
echo "$b 255.255.255.240"
elif [ $a -eq 29 ];then
echo "$b 255.255.255.248"
elif [ $a -eq 30 ];then
echo "$b 255.255.255.252"
elif [ $a -eq 31 ];then
echo "$b 255.255.255.254"
elif [ $a -eq 32 ];then
echo "$b 255.255.255.255"
fi
case $ip in
*.*.*.* *.*.*.*)
echo "enter a valid address"
esac
but I get an error
./ipcalculater2.sh: line 32: syntax error near unexpected token `...'
./ipcalculater2.sh: line 32: ` ... ...)'
What is wrong with my script?

Answer 1

Here's an example of four ways one might convert from CIDR to netmask notation in bash.
#!/usr/bin/env bash
if [[ "$1" != *.*.*.*/* ]]; then
echo "Usage: ${0##*/} ip.ad.dr.ess/bits" >&2
exit 1
fi
# separate our input into network and mask using IFS
IFS=/ read network bits <<<"$1"
# build a temporary variable $s that we'll use to build $bitmask
# for the first three variants...
read zeros <<< $(printf '%032s' 0)
s=${zeros//0/1}${zeros}
# convert the mask into a 32-digit binary number
bitmask=${s:$((32-bits)):32}
# Four different methods for generating the netmask...
# The first two use `bc` and `dc`. One is likely installed on your system.
read mask1 <<<$( dc -e "2i $(fold -w8 <<<"$bitmask " | paste -sdp -)" | paste -sd. - )
read mask2 <<<$( fold -w8 <<<"$bitmask" | paste - | bc -e 'ibase=2' | paste -sd. - )
# And if dc and bc are unavailable, or you prefer not to spawn subshells, or
# risk missed dependencies, you can do this in pure bash with a few more lines.
unset mask3
for ((i=0;i<4;i++)); do
mask3+="${mask3:+.}$((2#${bitmask:$((8*i)):8}))"
done
# And finally, instead of a loop, you can do the same thing with fancy math:
# This variant avoides the need for $bitmask, set above.
mask4="$(( 2**32 - (1 << (32-$bits)) ))"
mask4=$(( mask4/2**24 )).$(( mask4/2**16 %256 )).$(( mask4/2**8 % 256 )).$(( mask4 % 256 ))
# Print the results, obviously.
echo "network=$network"
echo "netlength=$bits"
echo "netmask via 'dc': $mask1"
echo "netmask via 'bc': $mask2"
echo "netmask via loop: $mask3"
echo "netmask via math: $mask4"
I've included code that works in each of dc and bc, since I can't predict which calculator will be available on your system. These calculators are used for base conversion. If you don't mind your script being a little longer, you can avoid spawning external tools (like fold and paste and the calculator) using the method that generates $netmask3.
Note that in the third case, this usage of bc depends on availability of a -e option which exists in *BSD. Use another variant if you're using GNU bc (i.e. you're in Linux.)
You can of course adjust the output so that it meets your needs, as well as trim the parts of the script you're not using.

Answer 2

Please check for this corrections:
#!/bin/bash
echo "enter you ip"
read ip
case $ip in
*.*.*.*/*)
b=`echo $ip | cut -d/ -f1`
a=`echo $ip | cut -d/ -f2`
if [ $a -eq 24 ];then
echo "$b 255.255.255.0"
elif [ $a -eq 25 ];then
echo "$b 255.255.255.128"
elif [ $a -eq 26 ];then
echo "$b 255.255.255.192"
elif [ $a -eq 27 ];then
echo "$b 255.255.255.224"
elif [ $a -eq 28 ];then
echo "$b 255.255.255.240"
elif [ $a -eq 29 ];then
echo "$b 255.255.255.248"
elif [ $a -eq 30 ];then
echo "$b 255.255.255.252"
elif [ $a -eq 31 ];then
echo "$b 255.255.255.254"
elif [ $a -eq 32 ];then
echo "$b 255.255.255.255"
fi
;;
*.*.*.*\ *.*.*.*)
echo "enter a valid address"
;;
esac