Agreed! Certainly more elegant than anything I might have done today.
Maybe back in the days when I made a living doing this stuff, but ...
Hmmm, I need to start saving some of these gems!
Thanks Dale.
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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--
Dazed_75 a.k.a. Larry
The spirit of resistance to government is so valuable on certain occasions,
that I wish it always to be kept alive.
- Thomas Jefferson
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