On May 11, 2012, at 7:39 PM, Owen wrote:
> I found this on the internet to convert an IPv4 address (w.x.y.z) to
> a decimal number.
>
> w * 16,777,216 + x * 65,536 + y * 256 + z = decimalNumber
>
> I then found the subroutine, ip2dec in the script below.
>
> The script works, that's not my problem. The problem is "How does it
> work"?
>
> The "split /\./" I understand. I've looked at perldoc pack and sort of
> see it is taking the ip4 address, packing it up and then unpacking.
>
> But what's with these "=>" things? How is that routine meant to read?
>
>
> TIA
>
>
> Owen
>
> ========================================================
> #!/usr/bin/perl
>
> use strict;
> use warnings;
>
> my $Originator = '127.0.0.1';
>
> $Originator = ip2dec($Originator);
>
> my $stored = 'stored';
> $stored = "$stored$Originator";
>
> sub ip2dec {
> return unpack N => pack CCCC => split /\./ => shift;
> }
>
> print "$stored\n";
Perl will interpret the '=>' operator as a "fat comma", which also has the
side-effect of stringifying a word to its left.
Therefore, the return line will be interpreted as:
return unpack( 'N', pack( 'CCCC', split( /\./, shift)));
So the argument passed to the subroutine is split at '.' characters, yielding
four substrings ('127','0','0','1'). These are interpreted as four unsigned
char values and packed into a string, which is then interpreted as an unsigned
long 32-bit value and returned.
In my opinion, this is a case of someone being too clever and just trying to
show off. You shouldn't program like that.
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