netmask in a script

[thomas at redhat.com]

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Have you looked at ipcalc? It does some really cools stuff and can be
scripted.

On 10/27/2011 06:19 PM, Brian Cluff 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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> 
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Chief Architect, Canada and Central US
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