use strict;
use warnings;

my $cmd = 'ls nonexistent';
open( CMD, "$cmd 2>&1 |" ) or die "Could not execute $cmd: $!\n";
while ( <CMD> ) {
  chomp;
  print "<< $_ >>\n";
}
__END__
% perl 483558.pl
<< ls: nonexistent: No such file or directory >>