With the help of user ikegami over at stackoverflow. The following solutions works.

[-
  use warnings;
  use strict;
  use IPC::Open3;
  use POSIX;

  $http_headers_out{'Content-Type'} = "text/plain";

  my $cmd = 'ls';

  open(my $fh, '>', '/dev/null') or die $!; 

  dup2(fileno($fh), 1) or die $! if fileno($fh) != 1;

  local *STDOUT;
  open(STDOUT, '>&=', 1) or die $!;

  my $pid = open3(*HIS_IN, *HIS_OUT, *HIS_ERR, $cmd);

  close(HIS_IN);  # give end of file to kid, or feed him

  my @outlines = <HIS_OUT>;              # read till EOF
  my @errlines = <HIS_ERR>;              # XXX: block potential if mas
+sive
  print OUT "STDOUT: ", @outlines, "\n";
  print OUT "STDERR: ", @errlines, "\n";

  waitpid( $pid, 0 );
  my $child_exit_status = $? >> 8;

  print OUT "child_exit_status: $child_exit_status\n";
-]
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