checking if an IP is valid.

echo $IP | egrep '^(([0-9]{1,2}|1[0-9][0-9]|2[0-4][0-9]|25[0-5])\.){3}([0-9]{1,2}|1[0-9][0-9]|2[0-4][0-9]|25[0-5])$'

0
By: andregyn62
2015-10-19 18:06:32
echo egrep validate ip check ip
1
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What Others Think

At first I thought this was a little hackish, but the other example has more problems. Sometimes keeping it simple and a a little bit longer works better. This works and is simple assuming you don't care about actually matching usable IPs because that will depend on the subnet mask. The first and last IP specified in a given network can't be used and might not be considered, "valid" they might still be valid but still not usable depending on how you want to define what a valid IP is. The first IP is used as the network ID and the last IP is used as the broadcast address. Those numbers are often going to be 0 and 255 for the last number in the last octet but it depends on the subnet mask. It's actually good practice to just not use 0 or 255 in the last octet even though using sometimes 0 can be valid and I know admins who intentionally use it for things like their DHCP server or a DNS server. There's plenty of talk about this online of course.
sonic · 523 weeks and 4 days ago

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Any thoughts on this command? Does it work on your machine? Can you do the same thing with only 14 characters?

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