On Thu, Oct 27, 2011 at 4:19 PM, Brian Cluff <brian@snaptek.com> wrote:

I've never had a need to do any bit twiddling in bash... thanks for this solution, It was very educational.

Brian Cluff

On 10/27/2011 11:43 AM, Dale Farnsworth wrote:

Larry wrote:

I would like to apply a netmask to an arbitrary IP in a bash/dash script
(e.g. apply 255.255.255.0 to 173.10.3.155 to get 173.10.3.0). Is there any
easy way to do that without taking the IP apart, doing 4 operations and
reassembling the results?

I know you said without disassembly/reassembly, but here are some
bash functions that apply the mask using disassembly/reassembly.

===================== begin =======================
to_int()
{
# Convert from dotted-quad to integer
local i=$1
local OIFS="$IFS"
IFS=.
i=($i)
IFS="$OIFS"
echo $(((${i[0]}<< 24) + (${i[1]}<< 16) + (${i[2]}<< 8) + ${i[3]}))
}

to_ip()
{
# Covert from integer to dotted-quad
local d=$1
echo $(($d>> 24)).$(($d>> 16& 255)).$(($d>> 8& 255)).$(($d&255))

}

and_ip()
{
# And two ip addresses in dotted-quad format
local ip1=$1
local ip2=$2
echo $(to_ip $(($(to_int $ip1)& $(to_int $ip2))))

}
===================== end =======================

Just pass the ip and netmask to and_ip:
Example:

$ and_ip 11.22.33.44 255.255.255.0
11.22.33.0

-Dale
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