CODEWITHSUNDEEP
baship
user8536729
user8536729

Reputation: 11

+1 on IPv4 input string in a bash script

I'm trying to make a script in bash to ping to addresses at once. The adressess are always 1 over the one the user keyed in.

Example: What is the ip? 192.168.0.10

The program should ping 192.168.0.10 and 192.168.0.11. Finally it should give ping output.

I have problems incrementing on the last digit of the ip. My code:

#!/bin/bash
# Script for å pinge to lokasjoner samtidig.

read input
echo $input
ip1=$input

let "ip2=$input+1"

echo $ip1
echo $ip2

As you can see, I have a long way to go. But my first question is how to increment only the last digits of the input.

Upvotes: 0

Views: 1509

Answers (3)

Raman Sailopal
Raman Sailopal

Reputation: 12887

Awk alternative: 

ip="192.168.0.10"
ip2=$(awk -F\. '{ print $1"."$2"."$3"."$4+1 }' <<< $ip )
echo $ip2
192.168.0.11

Read the original ip address into awk and separate fields with "." Add 1 to the last field and then set this into the variable ip2

Upvotes: 0

RomanPerekhrest
RomanPerekhrest

Reputation: 92854

You need to process your ip1 octets separately:

part1=${ip1%.*}"."     # first 3 octets (with trailing separator `.`)
part2=${ip1##*.}       # last octet
ip2=$part1$[$part2+1]

printf "%s\n%s\n" $ip1 $ip2

The exemplary output:

192.168.0.10
192.168.0.11

Upvotes: 0

Nahuel Fouilleul
Nahuel Fouilleul

Reputation: 19315

using variable expansion and arithmetic expansion

ip2=${ip1%.*}.$((${ip1##*.}+1))
  • ${ip1%.*} removes the shortest suffix .* (last number)
  • ${ip1##*.} removes the largest prefix *. (all except last number)

Upvotes: 4

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