perldoc perlipc

       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 d
+o the default
       thing.

       On most Unix platforms, the "CHLD" (sometimes also known as "CL
+D") signal
       has special behavior with respect to a value of 'IGNORE'.  Sett
+ing
       $SIG{CHLD} to 'IGNORE' on such a platform has the effect of not
+ creating
       zombie processes when the parent process fails to "wait()" on i
+ts child
       processes (i.e. child processes are automatically reaped).  Cal
+ling
       "wait()" with $SIG{CHLD} set to 'IGNORE' usually returns "-1" o
+n such platforms.
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