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Append and prepend using sed

25 Aug 2012

Below is a small example that uses sed to create null routes based on the domain name. It can be useful when the domain name resolves to multiple IP addresses :

host facebook.com| awk {'print $4'} | sed -n '/^[1-9].*/p' | sed 's/^/ip route /;s/$/ 255.255.255.255 null0/'
The result:
ip route 69.171.234.21 255.255.255.255 null0
ip route 69.171.237.16 255.255.255.255 null0
ip route 69.171.247.21 255.255.255.255 null0
ip route 66.220.149.88 255.255.255.255 null0
ip route 66.220.152.16 255.255.255.255 null0
ip route 66.220.158.70 255.255.255.255 null0

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