Linux - Bash - Replace a digit with another digit

[spbr]

Hi,

#! /bin/bash
ip="172.16.0.1"
networkconf="filetext.txt"
dhcpd="filetext.txt"
netmask30="2"
netmask29="6"
netmask28="14"
echo "How many raspberry pi's are on your premises?"
        read norpi
if [[ "$norpi" -le "$netmask30" ]]; then
        sed -i "30s/.*/netmask 255.255.255.252/" "$networkconf"
        sed -i.bak "10s/$/ 255.255.255.252{/" "$dhcpd"
elif [[ "$norpi" -ge 3 && "$norpi" -le "$netmask29" ]]; then
        sed -i "30s/.*/netmask 255.255.255.248/" "$networkconf"
        sed -i.bak "10s/$/ 255.255.255.248{/" "$dhcpd"
elif [[ "$norpi" -ge 7 && "$norpi" -le "$netmask28" ]]; then
        sed -i "30s/.*/netmask 255.255.255.240/" "$networkconf"
        sed -i.bak "10s/$/ 255.255.255.240{/" "$dhcpd"
else
        echo "unable"
fi

lastoct=${ip: -1}
range="$(($lastoct + $norpi))"
echo "$range"

So at the moment I'm able to take the last digit of the ip and add the amount of raspberry pi's, but what I want to do know is to place the new digit, from variable 'range' and replace the last digit of 'ip' with 'range'.

 

Any Suggestions?

Thank you

[SCHISCHKA]

Its a bit tricky with different subnet ranges, so i dont know how much you want to get into that but here is a start:

a=(${ip//./ })

will give to an array with all the numbers between the dots

you can access each number with

${a[0]}

${a[1]}

etc.

Then you can do what you want to do with the range. If I take my interpretation of your question it would be:

a=(${ip//./ })

range="$(($lastoct + $norpi))"

newRange=$(($range+${a[3]}))

echo "${a[0]}.${a[1]}.${a[2]}.$newRange"

 

EDIT corrected wrong bracket type

[Fetzie]

23 hours ago, SCHISCHKA said:

a={${ip//./ })

Shouldn't this be

 

a=(${ip///./})

 

to make an array out of it?

[SCHISCHKA]

16 minutes ago, Fetzie said:

Shouldn't this be

 

a=(${ip///./})

 

to make an array out of it?

I did incorrectly use a { instead of a (

You can try a=(${ip//./})

but that just results in
echo ${a[0]}
1721601

Any other symbol i try other than a space "/ " doesn't work. I dont know why this is the case. Its just something iv always done and never thought about questioning it.