Check fstats instead of using isatty().

src/main.cpp

@@ -11,6 +11,7 @@
 #include <memory>
 #include <functional>
 #include <unistd.h>
+#include <sys/stat.h>
 #include <iterator>
 
 #define STRINGIZE_IMPL(s) #s
@@ -88,8 +89,19 @@ namespace {
 
 	std::string getCleanHtml (const std::string& parUrl, const po::variables_map& parVarMap) {
 		std::string tidyHtml;
+		struct stat stats;
 
-		if (isatty(fileno(stdin))) {
+		const int r = fstat(fileno(stdin), &stats);
+		bool interactive = true;
+		if (r < 0) {
+			//TODO: error
+			interactive = false;
+		}
+		else {
+			interactive = static_cast<bool>(S_ISCHR(stats.st_mode));
+		}
+
+		if (interactive) {
 			tidyHtml = duck::getCleanHtml(
 				parUrl,
 				false,