New files.

Python/dup2.c

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+/*
+ * Public domain dup2() lookalike
+ * by Curtis Jackson @ AT&T Technologies, Burlington, NC
+ * electronic address:  burl!rcj
+ *
+ * dup2 performs the following functions:
+ *
+ * Check to make sure that fd1 is a valid open file descriptor.
+ * Check to see if fd2 is already open; if so, close it.
+ * Duplicate fd1 onto fd2; checking to make sure fd2 is a valid fd.
+ * Return fd2 if all went well; return BADEXIT otherwise.
+ */
+
+#include <fcntl.h>
+
+#define BADEXIT -1
+
+int
+dup2(fd1, fd2)
+int fd1, fd2;
+{
+	if (fd1 != fd2) {
+		if (fcntl(fd1, F_GETFL) < 0)
+			return BADEXIT;
+		if (fcntl(fd2, F_GETFL) >= 0)
+			close(fd2);
+		if (fcntl(fd1, F_DUPFD, fd2) < 0)
+			return BADEXIT;
+	}
+	return fd2;
+}