The Perl Cookbook claims (in the Discussion 16.1) that there is overhead associated with the backticks that does not exist with the system call. I imagine perl does the openpipe/fork combination to get the STDOUT from the backticks; if you don't need the output (as in the tar example above), it is thus more efficient to use system.

-Ton
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Be bloody, bold, and resolute; laugh to scorn
The power of man...