help w/pack 2

[bardley]

I still can't grasp how the pack function works.

I need to turn dotted ip addresses to decimal representations like so:

10.50.1.5 (the ip address)
0a.32.01.05 (change each octet to hex)
0a320105 (concatenate the octets)
171049221 (change that hex number back to decimal)

I just know there's a cool way to do this using pack, but I haven't been able to get it. It may even be in a module, I just haven't looked in the right place.

Brad Gunsalus
Cymtec Systems, Inc.
bgunsalus@cymtec.com

 

[toolkit]

Not using pack, but this gives you the steps you want:

$ip = "10.50.1.5";
$ip =~ s/(\d+)/sprintf("%02x",$1)/eg;
print "$ip\n";
$ip =~ s/\.//g;
print "$ip\n";
$ip = hex( $ip );
print "$ip\n";

Cheers, Neil

 

[scoon]

This is a little nasty but it works in one line:

my $out = hex(join('', map(sprintf("%02x", $_), split( /\./, $ip))));

The join uses two single quotes, not one double quote.

 

[MikeLacey]

nasty is right, neat though Mike
"Experience is the comb that Nature gives us after we are bald."

Is that a haiku?
I never could get the hang
of writing those things.

 

[toolkit]

And the same thing using pack:

$ip = unpack( "N", pack( "C4", ( split( /\./, $ip ) ) ) );

Reading from the inner brackets out:
[tt]split( /\./, $ip )[/tt] returns an array of 4 integers
[tt]pack( "C4", ... )[/tt] packs these as 4 signed chars
[tt]unpack( "N", ... )[/tt] unpacks the data as a single big-endian long (4 bytes).
Cheers, Neil

 

[bardley]

I knew if I threw it out there, I'd end up with at least one one-liner, and probably more.

Awesome, thanks guys! Brad Gunsalus
Cymtec Systems, Inc.
bgunsalus@cymtec.com

 

[toolkit]

A two-liner:

use Socket;
$ip = unpack( "N", inet_aton( $ip ) );

This will also accept an initial string like

"www.tek-tips.com"

. Try [tt]perldoc Socket[/tt] for more information on the functions that are available with this package.

Cheers, Neil

 

[MikeLacey]

Spot on Neil I'll use that. Mike
"Experience is the comb that Nature gives us after we are bald."

Is that a haiku?
I never could get the hang
of writing those things.