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perl ipcalc oneliners

by mojobo (Initiate)
on Jun 09, 2005 at 23:21 UTC ( #465353=perlquestion: print w/ replies, xml ) Need Help??
mojobo has asked for the wisdom of the Perl Monks concerning the following question:

hi all, i'm building some fun perl one-liners for use with external programs and such.. i found a cool perl script that i converted to a single-liner that computes the network address of a unix machine:
this computes the network address..
perl -e '$ip="192.168.10.2"; $mask="255.255.254.0"; @maskbyte=split /\ +./,$mask; @ipbyte=split /\./, $ip; for($i=0;$i<4;$i++) { $b1=$maskbyt +e[$i]+0; $b2=$ipbyte[$i]+0;$NetByte=$b1&$b2; if($i != 0) {$NetAddr = +$NetAddr . "." . $NetByte; } else { $NetAddr=$NetByte ;}} print "$Net +Addr\n";'
now i'm trying to get the broadcast address, but i'm having some problems converting the 1's complement of the subnet mask back to something readable..
here's what i have so far:
perl -e '$ip="192.168.10.0"; $mask="255.255.254.0"; @maskbyte=split /\ +./,$mask; @ipbyte=split /\./, $ip; for($i=0;$i<4;$i++) { $b1=$maskbyt +e[$i]+0; $b2=$ipbyte[$i]+0; $NetByte=$b2 || ~$b1 ; if($i != 0) {$Ne +tAddr = $NetAddr . "." . $NetByte; }else { $NetAddr=$NetByte ;}} prin +t "$NetAddr\n";'
the one's complement of the subnet mask orred with the network address (formula for broadcast) gives a funky number..

192.168.10.4294967295

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Re: perl ipcalc oneliners
by monarch (Priest) on Jun 09, 2005 at 23:55 UTC
    Sometimes one can make these things more complicated than they are.

    The first one liner I would write as the following:

    # convert IP addresses to unsigned long integers my $addr="192.168.10.2"; my @addrb=split("[.]",$addr); my ( $addrval ) = unpack( "N", pack( "C4",@addrb ) ); my $mask="255.255.254.0"; my @maskb=split("[.]",$mask); my ( $maskval ) = unpack( "N", pack( "C4",@maskb ) ); # calculate network address my $netwval = ( $addrval & $maskval ); # convert network address to IP address my @netwb=unpack( "C4", pack( "N",$netwval ) ); my $netw=join(".",@netwb); # print print( $netw );

    What I'm doing is converting the dot notation into an integer. That way I can do bit manipulation on the address as a whole rather than trying to deal with individual bytes.

    To get the broadcast address should be just as easy. Although I haven't done bit inversions in Perl before..

    # calculate broadcast address my $brodval = ( $addrval & $maskval ) + ( ~ $maskval );

    So the whole file together looks like this:

    The output is:

    Network:192.168.10.0 Broadcast:192.168.11.255

    One lining this is left as an exercise for the reader.

    Update: on a more personal note I would caution against the byte-at-a-time approach because of the possible error whereby the third byte should be different to what you expect for the broadcast address.. using the netmask supplied (255.255.254.0) both the 3rd and 4th bytes are affected, not just the 4th.

    Update 2: Just making this more sexy, an alternative presentation of the code is as follows:

    Update 3: Just letting everyone know I added readmore tags to update 2. I have to put in lots of update notices cause I was told off by a Saint yesterday for not putting update notices in every single time I make an update, no matter how small, and no matter how frequently.

Re: perl ipcalc oneliners
by Fletch (Chancellor) on Jun 09, 2005 at 23:56 UTC

    You might want to look into Net::NetMask rather than trying to do the conversion yourself. And use <code></code> tags next time.

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