The perl docs actually do have a good explanation of what the return value from system() is, but it's in "perldoc perlvar" instead of "perldoc -f system". system() returns the value of $? after the wait() is done. Here it is:

 $?      The status returned by the last pipe close, backtick
             (``) command, or system() operator.  Note that this
             is the status word returned by the wait() system
             call (or else is made up to look like it).  Thus,
             the exit value of the subprocess is actually ($? >>
             8), and $? & 127 gives which signal, if any, the
             process died from, and $? & 128 reports whether
             there was a core dump.  (Mnemonic: similar to sh and
             ksh.)

Just to clarify, $? >> 8 is bitshifting by 8, which is essentially dividing by 256. So, if you are getting a return val of 256 from system(), your spawned program did an exit(1).