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For example I have IP addresses list

192.168.20.5
192.168.20.12
192.168.20.141

How to remove all symbols after last dot and get this list (below) at the output

192.168.20.
192.168.20.
192.168.20.

I tried this:

LAN=$(nslookup localhost | awk '{print $2}' | head -1)
hosts=$(echo "${LAN::-1}"{1..254} | xargs -n1 -P0 ping -c 1 | grep "bytes from" | awk '{print $4}')

But ::-1 not suitable, because the number of digits may vary

Improve this question
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  • On SO we do encourage users to add their efforts which they have put in order to solve their own problems, please do add your efforts and let us know then.
    – RavinderSingh13
    Commented Dec 30, 2019 at 16:12
  • 1
    If you are using Awk anyway, use it to its full potential. Replace grep "bytes from" | awk '{print $4}' with awk '/bytes from/ { a=$4; gsub(/[.][^.]*$/, ".", a); print a}'; see also useless use of grep.
    – tripleee
    Commented Dec 30, 2019 at 16:18
  • 1
    Similarly, awk '{print $2}' | head -1 can be replaced with awk '{ print $2; exit }'
    – tripleee
    Commented Dec 30, 2019 at 16:19
  • With GNU awk: awk '{NF--} NF++' FS="." OFS="."
    – Cyrus
    Commented Dec 30, 2019 at 17:34
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