Of course being this is perlmonks, not catmonks . . .

open( OUT, ">xyzfile" ) or die "Can't create xyzfile: $!\n";
foreach( qw( xfile yfile zfile ) ){
  local( *IN );
  open( IN, $_ ) or die "Can't open $_: $!\n";
  print OUT while <IN>;
  close( IN );
}
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Originally posted as a Categorized Answer.