Index: db.1
===================================================================
RCS file: /cvsroot/src/usr.bin/db/db.1,v
retrieving revision 1.27
diff -u -r1.27 db.1
--- db.1	17 Feb 2012 11:43:24 -0000	1.27
+++ db.1	6 Jan 2013 02:38:50 -0000
@@ -51,7 +51,7 @@
 .Op Fl T Ar visspec
 .Op Fl U Ar unvisitem
 .Op Fl X Ar extravis
-.Ar type
+.Op type
 .Ar dbfile
 .Op Ar key Op Ar \&.\&.\&.
 .
@@ -62,7 +62,7 @@
 .Op Fl f Ar infile
 .Op Fl T Ar visspec
 .Op Fl U Ar unvisitem
-.Ar type
+.Op type
 .Ar dbfile
 .Op Ar key Op Ar \&.\&.\&.
 .
@@ -76,7 +76,7 @@
 .Op Fl P Ar pagesize
 .Op Fl T Ar visspec
 .Op Fl U Ar unvisitem
-.Ar type
+.Op type
 .Ar dbfile
 .Op Ar key Ar value Op Ar \&.\&.\&.
 .
@@ -122,15 +122,19 @@
 .Ar insep ) .
 .El
 .Pp
-There are two mandatory arguments:
+There is one mandatory argument:
+.Ar dbfile
+is the database file to manipulate.
+The database type can be specified on the command line,
+by usint the
 .Ar type
-is the database type; either
+argument; either
 .Sq Sy btree
 or
 .Sq Sy hash ,
-and
-.Ar dbfile
-is the database file to manipulate.
+options are possible.
+If the database type is not specified, the type will be autodetected
+from the database file itself.
 .Pp
 Options valid for all modes are:
 .Bl -tag -width Fl -offset indent
Index: db.c
===================================================================
RCS file: /cvsroot/src/usr.bin/db/db.c,v
retrieving revision 1.26
diff -u -r1.26 db.c
--- db.c	17 Feb 2012 11:37:33 -0000	1.26
+++ db.c	6 Jan 2013 02:38:50 -0000
@@ -71,6 +71,14 @@
 	F_DECODE_VAL	= 1<<26,
 } flags_t;
 
+#ifndef __dead
+#define __dead	__dead2
+#endif
+
+#ifdef __FreeBSD__
+int  strsvisx(char *, const char *, size_t, int, const char *);
+#endif
+
 static void	db_print(DBT *, DBT *);
 static int	db_dump(void);
 static int	db_del(char *);
@@ -83,6 +91,7 @@
 static void	parse_encode_decode_arg(const char *, int);
 static int	parse_encode_option(char **);
 __dead static void	usage(void);
+static int	autodetect(char */*file*/, char */*type*/, size_t /*typesize*/);
 
 static flags_t	 	 flags = 0;
 static DB		*db;
@@ -106,6 +115,7 @@
 	HASHINFO	hashinfo;
 	FILE		*infp;
 	const char	*infile, *fieldsep;
+	char		 autotype[16];
 	char		*p, *key, *val;
 	int		ch, rv;
 	long		lval;
@@ -249,13 +259,21 @@
 	argc -= optind;
 	argv += optind;
 
-				/* validate arguments */
-	if (argc < 2)
-		usage();
-	oi.type = argv[0];
-	oi.file = argv[1];
-	argc -= 2;
-	argv += 2;
+	/* validate arguments */
+	if (argc < 2) {
+		/* auto-detect the type of database */
+		if (!autodetect(oi.file = argv[0], autotype, sizeof(autotype))) {
+			usage();
+		}
+		oi.type = autotype;
+		argc -= 1;
+		argv += 1;
+	} else {
+		oi.type = argv[0];
+		oi.file = argv[1];
+		argc -= 2;
+		argv += 2;
+	}
 
 	if (flags & F_WRITE) {
 		if (flags & (F_SHOW_KEY | F_SHOW_VALUE | F_DELETE))
@@ -752,3 +770,40 @@
 	    );
 	exit(1);
 }
+
+#include <arpa/inet.h>
+
+typedef struct dbtype_map_t {
+	uint32_t	 magic;
+	const char	*type;
+} dbtype_map_t;
+
+static dbtype_map_t	dbtypes[] = {
+	{	BTREEMAGIC,	"btree"	},
+	{	HASHMAGIC,	"hash"	},
+	{	0,		NULL	}
+};
+
+static int
+autodetect(char *file, char *type, size_t typesize)
+{
+	dbtype_map_t	*map;
+	uint32_t	 magic;
+	FILE		*fp;
+	int		 found;
+
+	if ((fp = fopen(file, "r")) == NULL) {
+		return 0;
+	}
+	found = 0;
+	if (read(fileno(fp), &magic, sizeof(magic)) == sizeof(magic)) {
+		for (map = dbtypes ; !found && map->type ; map++) {
+			if (magic == map->magic || magic == htonl(map->magic)) {
+				snprintf(type, typesize, map->type);
+				found = 1;
+			}
+		}
+	}
+	fclose(fp);
+	return found;
+}