Average Price Script 0.0.1

So I made a small Perl script again. The script polls data from Google Finance and calculates the average price for a given symbol. The first parameter of the script is the Google Finance symbol that starts with the name of the exchange followed by a colon like 'NYSE:IBM'. The script expects an optional second parameter an integer number indicating the poll interval, 1 by default. Data is retrieved with curl. The response is in the JSON format. I get the current price with a regex from the response. All the prices are stored in an array and averaged. I also do some rudimentary logging.

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#!/usr/bin/perl
 
# This script polls data from Google Finance and calculates the average price for a given symbol.
#
# Parameters:
# symbol The Google Finance symbol like 'NYSE:IBM'.
# secondsSleep Integer number indicating the poll interval, 1 by default.
#
$symbol = $ARGV[0];
print "$symbol\n";
 
while(1) {
$data=`curl -s "http://finance.google.com/finance/inf...
$data =~ m/l_cur" : "(.*)"/;
$td=`date '%Y%m%d %H:%M - '`;
push(@prices, $1);
$num = scalar @prices;
$sum = 0;
 
for( $i = 0; $i < $num; $i ) {
$sum = $prices[$i];
}
 
$average = $sum / $num;
print "$num elements, average $average\n";
print "$1 $td";
sleep $ARGV[1];
}

Possible improvements

Here is a list of improvements I have been thinking about.

Use a proper JSON library.
Calculate standard deviation as well.
Calculate a time weighted average, where recent values have a higher weight.
Improve logging.

Random links of interest

List of freely available programming books
GTAC 2010
Irill days 2010