Do you need this in perl? From command line, it would just be:

top -b -n 1 | grep ^CPU
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if you want it in perl, probably (other ways of course) want a loop something like:

while(<PIPE>){
  next unless /^CPU.*? ([0-9.]+)% idle, ([0-9.]+)% user/;
  my ( $idle, $user ) = ( $1, $2 );
  ...
  last;
}
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