$ cat bad.xml
<foo><bar></foo>

$ perl -MXML::LibXML::Reader -e'
   exit 1 if !eval {
      my $reader = XML::LibXML::Reader->new(
         location        => $ARGV[0],
         load_ext_dtd    => 0,
         expand_entities => 0,
      );
      1 while $reader->read;
      1
  };
' bad.xml

$ if [ $? -eq 0 ]; then echo "well-formed" ; else echo "error" ; fi
error