1. A shell-command returns '0' on success, and $? > 0 on failure.
This one-liner illustrates this (on unix):

perl -e 'print "true" if `/bin/true`, $?; print "false" if `/bin/false
+`, $?'
false
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2. Your code will state a succesful call if the command produced any output on STDOUT, check $? for the return-code instead of the output!

regards,
tomte