thanks for your reply. I have checked "perldoc -v '$@' " at my RHE4 with perl v5.8.5, but it shows "No documents found for '$@' ". I then checked the link you provided (Error Variables) to find an explanation as this:
$@ is set if the string to be eval-ed did not compile (this may happen if open or close were imported with bad prototypes), or if Perl code executed during evaluation die()d. In these cases the value of $@ is the compile error, or the argument to die (which will interpolate $! and $? ).
Is this mean $@ is only used to contain reasons why perl failed? Thanks.