Dump9660 (and mk9660). Until we either do something

intelligent with symlinks or put in a switch for things
like dump9660, this is of rather limited utility under Unix.

src/cmd/9660/uid.c

@@ -0,0 +1,41 @@
+#include <u.h>
+#include <libc.h>
+
+/*
+ * /adm/users is
+ *	id:user/group:head member:other members
+ *
+ * /etc/{passwd,group}
+ *	name:x:nn:other stuff
+ */
+
+static int isnumber(char *s);
+
+sniff(Biobuf *b)
+{
+	read first line of file into p;
+
+	nf = getfields(p, f, nelem(f), ":");
+	if(nf < 4)
+		return nil;
+
+	if(isnumber(f[0]) && !isnumber(f[2]))
+		return _plan9;
+
+	if(!isnumber(f[0]) && isnumber(f[2]))
+		return _unix;
+
+	return nil;
+}
+
+
+int
+isnumber(char *s)
+{
+	char *q;
+
+	strtol(s, &q, 10);
+	return *q == '\0';
+}
+
+/* EOF */