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awk getline 8 times and if $3 = 8 when subtracted from 1st line,print


 
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# 1  
Old 08-16-2013
awk getline 8 times and if $3 = 8 when subtracted from 1st line,print

I have kind of a strange one here. I have a file of consecutive /24 ip blocks. If there are 8 consecutive ip blocks which represent a /20 then I need to print the first line. I played around and did not get the results I need, especially when considering that the highest $3 will be is 255 and then start over to 0.

Here is a sample file
Code:
10.71.192.0
10.71.193.0
10.71.194.0
10.71.195.0
10.71.196.0
10.71.197.0
10.71.198.0
10.71.199.0
10.78.176.0
10.78.177.0
10.78.178.0
10.78.179.0
10.90.25.0
10.90.26.0
10.122.232.0
10.122.233.0
10.122.234.0
10.122.235.0
10.122.236.0
10.122.237.0
10.122.238.0
10.122.239.0
10.144.251.0
10.144.252.0
10.144.253.0
10.144.254.0
10.144.255.0
10.145.0.0
10.145.1.0
10.145.2.0

What I need to see output is:
Code:
10.71.192.0
10.122.232.0
10.144.251.0

I tried something like this but did not get good results
Code:
nawk -F"." '{p=$0; v=$3; getline;getline;getline;getline;getline;getline;getline;getline; d=$3 - v} d = 8 {print p}' myfile

# 2  
Old 08-17-2013
First things first: 8 consecutive /24 blocks do not represent a /20 block but a /21 block and only if the lowest third number of the consecutive /24 ranges is divisible by 8.
# 3  
Old 08-17-2013
Typo, sorry that is correct a /21.

Last edited by numele; 08-17-2013 at 10:12 AM..
# 4  
Old 08-17-2013
Your sample output is not correct!

Try
Code:
awk  '{if (++C[$1$2($3-$3%8)] == 8) print $1,$2,($3-$3%8),$4}' FS="." OFS="." file
10.71.192.0
10.122.232.0

These 3 Users Gave Thanks to RudiC For This Post:
# 5  
Old 08-17-2013
Nice solution RudiC !

I think it would be better to separate the fields in the index to avoid overflow between ranges.
I made an adaptation to your solution so that the CIDR prefix becomes variable:
Code:
awk -F. -v cp=21 'BEGIN{s=2^(24-cp)}{r=$1 FS $2 FS $3-$3%s FS $4} ++C[r]==s{print r}' file


Last edited by Scrutinizer; 08-17-2013 at 03:06 PM..
These 2 Users Gave Thanks to Scrutinizer For This Post:
# 6  
Old 08-17-2013
Above was a "sketch", a "draft", and I was thinking about making it a bit more flexible myself. Thank for your proposals; separating the index fields is a good one, as is the variable bit depth for the netmask... Although the requestor asked for 8; we just infer he wants to see if that subnet is "full".

Last edited by RudiC; 08-17-2013 at 03:15 PM..
# 7  
Old 08-17-2013
Thank you both, worked very well.

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