diff -r 764e41b09017 tools/libxl/xl.c
--- a/tools/libxl/xl.c	Thu Jun 17 08:53:12 2010 +0100
+++ b/tools/libxl/xl.c	Thu Jun 17 16:51:34 2010 +0100
@@ -37,8 +37,9 @@
 
 int main(int argc, char **argv)
 {
-    int opt = 0, i;
+    int opt = 0;
     char *cmd = 0;
+    struct cmd_spec *cspec;
 
     while ((opt = getopt(argc, argv, "+v")) >= 0) {
         switch (opt) {
@@ -69,18 +70,14 @@
 
     srand(time(0));
 
-    for (i = 0; i < cmdtable_len; i++) {
-        if (!strcmp(cmd, cmd_table[i].cmd_name))
-        	cmd_table[i].cmd_impl(argc, argv);
-    }
-
-    if (i >= cmdtable_len) {
-        if (!strcmp(cmd, "help")) {
-            help(argv[2]);
-            exit(0);
-        } else {
-            fprintf(stderr, "command not implemented\n");
-            exit(1);
-        }
+    cspec = cmdtable_lookup(cmd);
+    if (cspec)
+        return cspec->cmd_impl(argc, argv);
+    else if (!strcmp(cmd, "help")) {
+        help(argv[2]);
+        exit(0);
+    } else {
+        fprintf(stderr, "command not implemented\n");
+        exit(1);
     }
 }
diff -r 764e41b09017 tools/libxl/xl.h
--- a/tools/libxl/xl.h	Thu Jun 17 08:53:12 2010 +0100
+++ b/tools/libxl/xl.h	Thu Jun 17 16:51:34 2010 +0100
@@ -80,6 +80,8 @@
 
 extern struct cmd_spec cmd_table[];
 extern int cmdtable_len;
+/* Look up a command in the table, allowing unambiguous truncation */
+struct cmd_spec *cmdtable_lookup(const char *s);
 
 extern struct libxl_ctx ctx;
 extern xentoollog_logger_stdiostream *logger;
diff -r 764e41b09017 tools/libxl/xl_cmdimpl.c
--- a/tools/libxl/xl_cmdimpl.c	Thu Jun 17 08:53:12 2010 +0100
+++ b/tools/libxl/xl_cmdimpl.c	Thu Jun 17 16:51:34 2010 +0100
@@ -1282,6 +1282,7 @@
 void help(char *command)
 {
     int i;
+    struct cmd_spec *cmd;
 
     if (!command || !strcmp(command, "help")) {
         printf("Usage xl <subcommand> [args]\n\n");
@@ -1290,18 +1291,17 @@
             printf(" %-20s%s\n",
                    cmd_table[i].cmd_name, cmd_table[i].cmd_desc);
     } else {
-        for (i = 0; i < cmdtable_len; i++)
-            if (!strcmp(command, cmd_table[i].cmd_name))
-                break;
-        if (i == cmdtable_len) {
-            printf("command not implemented\n");
-        } else {
+        cmd = cmdtable_lookup(command);
+        if (cmd) {
             printf("Usage: xl %s %s\n\n%s.\n\n",
-                   cmd_table[i].cmd_name,
-                   cmd_table[i].cmd_usage,
-                   cmd_table[i].cmd_desc);
-            if (cmd_table[i].cmd_option)
-            printf("Options:\n\n%s\n", cmd_table[i].cmd_option);
+                   cmd->cmd_name,
+                   cmd->cmd_usage,
+                   cmd->cmd_desc);
+            if (cmd->cmd_option)
+                printf("Options:\n\n%s\n", cmd->cmd_option);
+        }
+        else {
+            printf("command \"%s\" not implemented\n", command);
         }
     }
 }
diff -r 764e41b09017 tools/libxl/xl_cmdtable.c
--- a/tools/libxl/xl_cmdtable.c	Thu Jun 17 08:53:12 2010 +0100
+++ b/tools/libxl/xl_cmdtable.c	Thu Jun 17 16:51:34 2010 +0100
@@ -11,6 +11,8 @@
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU Lesser General Public License for more details.
  */
+
+#include <string.h>
 
 #include "xl.h"
 
@@ -308,3 +310,24 @@
 };
 
 int cmdtable_len = sizeof(cmd_table)/sizeof(struct cmd_spec);
+
+/* Look up a command in the table, allowing unambiguous truncation */
+struct cmd_spec *cmdtable_lookup(const char *s)
+{
+    struct cmd_spec *cmd = NULL;
+    size_t len;
+    int i;
+
+    if (!s) 
+        return NULL;
+    len = strlen(s);
+    for (i = 0; i < cmdtable_len; i++) {
+        if (!strncmp(s, cmd_table[i].cmd_name, len)) {
+            if (cmd == NULL) 
+                cmd = &cmd_table[i];
+            else 
+                return NULL;
+        }
+    }
+    return cmd;
+}