You may also choose to assign the strings 'IGNORE' or 'DEFAULT' as the
       handler, in which case Perl will try to discard the signal or do the default
       thing.

       On most Unix platforms, the "CHLD" (sometimes also known as "CLD") signal
       has special behavior with respect to a value of 'IGNORE'.  Setting
       $SIG{CHLD} to 'IGNORE' on such a platform has the effect of not creating
       zombie processes when the parent process fails to "wait()" on its child
       processes (i.e. child processes are automatically reaped).  Calling
       "wait()" with $SIG{CHLD} set to 'IGNORE' usually returns "-1" on such platforms.