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Perfect time for the rarely used sub shell.
A little bit smaller, faster and should handle files with special characters in the name.
I don't know if the --spider option works to execute a script, but it might be worth trying. Note that the Drupal project uses the following in a cron job.
wget -O - -q http://localhost/drupal/cron.php
The output is sent to standard out so it can be logged by cron.
This will calculate a running standard deviation in one pass and should never have the possibility for overflow that can happen with other implementations. I suppose there is a potential for underflow in the corner case where the deltas are small or the values themselves are small.
This is an on-line algorithm for calculating the mean value for numbers in a column. Also known as "running average" or "moving average".