Shell Script (Bash) to Edit Output from a Command

Question

Shell Script (Bash) to Edit Output from a Command

I'm trying to make a shell script to determine the range of IP Addresses on my own personal wireless network. When I run this command:

ifconfig

I get this key information:

inet 192.168.1.228

broadcast 192.168.1.255

netmask 255.255.255.0

So now I know that the range is 192.168.1.0-255 (or 192.168.1.0/24). I tried to run this script I made:

#!/bin/bash

ifconfig | awk '/broadcast/ {print $6}'

This will output my max ip range:

192.168.1.255

How can I make this script find my max range like this but instead it writes it like this:

192.168.1.0-255

or

192.168.1.0/24

Any help is much appreciated!

`grep 'broadcast' | awk '{print $6}'` doesn't make much sense. `awk '/broadcast/ {print $6}'` — Hauke Laging, Aug 29 '17 at 20:56
You do not have enough information to verify your network is /24. Your network very well could be `192.168.1.224/27` based on the information you have provided. — jesse_b, Aug 29 '17 at 21:02
I'm trying to create the output in the form of a variable so I can perform an nmap scan that automatically finds the ip range to scan. That's why i mentioned 0/24 because thats what I used to scan the ip ranges for my network — iamr00t, Aug 29 '17 at 21:04
You cannot determine your "ip ranges" with an IP and broadcast. You need to have the subnet mask and either network ID or valid IP. — jesse_b, Aug 29 '17 at 21:07
Yes but now I'm extremely confused by what you are trying to do. Your question indicates that you want to calculate the ip range on the machine. Now it seems like you aren't interested in that and simply want to take action on 192.168.1.0/24. In which case just modify your script to take action on `192.168.1.{0..255}` — jesse_b, Aug 29 '17 at 21:11
It's really not that difficult...I'm making a script to perform a nmap scan for hosts on my network. I'm going to use the command (nmap -sP $iprange) where $iprange is the range of ip addresses on my network. My network isn't that complicated so all my devices have 192.168.1.x ip addresses. Sooo... i just need a script that will do what I metioned in the question so I can work on turning it into a variable and using it with nmap. — iamr00t, Aug 29 '17 at 21:18
So again you are asking for two different things. I understand that ultimately you want to run your nmap command against your range of IPs but it's unclear if you are still set on `calculating` your ip range. It seems as if you already figured it out as 192.168.1.0/24 and simply want to use that. In which case stop trying to calculate it and just set your iprange to `192.168.1.{0..255}`. — jesse_b, Aug 29 '17 at 21:31
I'm creating this tool to be usable for anyone, or at least function properly for anyone that uses it. I do know what my ip range is, but it's because I looked at the provided info from ifconfig...But my script doesn't know what the range is, which is what I'm trying to figure out. I just want to create a script that can take the numbers from 'inet, broadcast and netmask' and piece together a range to be used for future reference. Imagine this as a public tool and not just a personal script, otherwise, I would have just continued a scan a long time ago lol. — iamr00t, Aug 29 '17 at 21:40

Hauke Laging · Answer 1 · 2017-08-29T21:20:30.233

2

The simplest solution is to use ip address instead of ifconfig which you should do anyway.

And you can get the netmask from the ifconfig output and calculate the number of 1-bits with this:

echo 255.255.255.0 |
    awk -F. '{print "obase=2;" $1 "*2^24+" $2 "*2^16+" $3 "*2^8+" $4}' |
    bc |
    awk '{ sub("10*$","1", $0); print length($0); }'

edited Aug 29 '17 at 21:20

answered Aug 29 '17 at 20:59

Hauke Laging

88,146
18
125
174

Is this where the '24' comes from when I use 192.168.1.0/24? When I run this command I just get '24', that's why I am asking. – iamr00t Aug 29 '17 at 22:02
@iamr00t Yes. The /number is the number of 1-bits in the netmask (i.e. 32 minus the size of the local routing domain). 255 is eight 1-bits thus `255.255.255.0` is 24 1-bits. – Hauke Laging Aug 29 '17 at 22:21

Shell Script (Bash) to Edit Output from a Command

1 Answers1