OK, so you say it's SUID. Be sure to clean up some environment variables:

  $ENV{PATH}='';
  $ENV{IFS}='';
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With no PATH you have to explicitly give the entire path to system calls and so forth, but you're doing that anyway.

Now I can suggest the way I normally play with STDOUT:

open LS, qq(/bin/ls -al|) ||
   die qq(cannot execute /bin/ls: $!);
while (<LS>) {
  # Do whatever you want to do with STDOUT from
  # the ls call here
}
close LS;
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This is basically straight out of perlipc.