PERL Beginners - Re: confusion with splitting columns using [-n, -n] (e.g; my ( $country, $bytes ) = (

Author

Re: confusion with splitting columns using [-n, -n] (e.g; my ( $country, $bytes ) = (

Andy Greenwood

2007-01-30, 6:59 pm

On 1/30/07, Michael Alipio <daem0nb0y@yahoo.com> wrote:
> Hi,
>
> I have a file that look like this:
>
> 1668 | 172.194.177.182 | US 12679172
> 10396 | 64.237.148.157 | PR 12679172
> 9318 | 211.187.212.242 | KR 1279172
> 22291 | 66.215.254.186 | US 1269172
> 22291 | 24.176.212.76 | US 1679172
> 30225 | 66.147.146.214 | US 2679172
> 17676 | 221.34.8.92 | JP 1267173
> 17858 | 125.180.111.187 | KR 12679172
> 6395 | 67.96.150.40 | US 12679172
> 17858 | 125.180.193.124 | KR 12679175
> 3462 | 218.168.176.39 | TW 12679472
> 9919 | 218.211.204.195 | TW 12666172
> 9318 | 222.235.22.225 | KR 12672272
> 9318 | 222.237.14.160 | KR 12679142
>
>
>
> Six columns including two colums with pipe symbols.
> The goal is to add up the values in the last column that belongs to the same country. That last column are the bytes received by a particular country. So I have to add all bytes received by US, KR, etc.
>
> Someone has given me this code:
>
> open WHOISWITHBYTES, '<', "whois.bytes" or die $!;
>
> my %data;
> while ( <WHOISWITHBYTES> ) {
> my ( $country, $bytes ) = ( split )[ -2, -1 ];
> $data{ $country } += $bytes;
> }
>
> print "Country Total Bytes\n";
> for my $country ( sort { $data{ $b } <=> $data{ $a } } keys %dat
> a ) {
> print "$country $data{ $country }\n";
> }
>
> It is working perfectly but now, I need to document this code. Can anyone help me out on understanding this code.
>
> I'm particularly

with the line:
> "my ($country, $bytes) = (split) [-2, -1];
>
> What does this tells? What does -2 and -1 tells? All I know is that split will output a list containing two values that will be assigned to $country and $bytes for every line of that whois.bytes file. But I'm not sure what those -2,-1 means and how it w
as able to extract column 5 and 6. I tried looking at perldoc -f split but cannot seem to find the explanation. Are those the LIMIT thing?

(split) gives you an array, and then you are referencing the last two
items. Negative array indecies mean to start that far from the end of
the list, similar to negative character offsets in substr.

>
>
> Thanks!
>
>
>
>
>
>
> ________________________________________
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>

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