Oh oh. Here's the same non-buggy version that does invoke the shell. To fix the bug in your code, you'll need to follow symlinks and whenever considering entering a directory, decide whether you've been there before. Symlinks will cause your existing code to enter infinite loops and to run the command on some things more than once.

#!perl -w
use strict;
use File::Find;

my ( $start_dir, $command ) = @ARGV;
find( sub { system $command if -d }, $start_dir );
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See? Thanks to PM, I know have my whole 2 months back. Awesome, diotalevi, and also kudos to those who've pointed out how to use *NIX find! :D