catch command-not-found errors

Add a special handler to catch errors caused by specifying unknown
commands to Podman.  This allows printing a more helpful error message.

```
$ podman
Command "123123" not found.
See `podman --help`.

$ podman pod 123123
Command "123123" not found.
See `podman pod --help`.
```

Signed-off-by: Valentin Rothberg <vrothberg@suse.com>

Closes: #1379
Approved by: rhatdan

2 files changed, 5 insertions, 0 deletions

diff --git a/cmd/podman/common.go b/cmd/podman/common.go
index 3d0f1159f..93b16f4e3 100644
--- a/cmd/podman/common.go
+++ b/cmd/podman/common.go
@@ -51,6 +51,10 @@ func usageErrorHandler(context *cli.Context, err error, _ bool) error {
 	return fmt.Errorf("%s\nSee '%s --help'.", err, cmd)
 }
 
+func commandNotFoundHandler(context *cli.Context, command string) {
+	fmt.Fprintf(context.App.Writer, "Command %q not found.\nSee `%s --help`.\n", command, context.App.Name)
+}
+
 // validateFlags searches for StringFlags or StringSlice flags that never had
 // a value set.  This commonly occurs when the CLI mistakenly takes the next
 // option and uses it as a value.
diff --git a/cmd/podman/main.go b/cmd/podman/main.go
index 24d30fd0e..0e6a2e600 100644
--- a/cmd/podman/main.go
+++ b/cmd/podman/main.go
@@ -52,6 +52,7 @@ func main() {
 	app.Name = "podman"
 	app.Usage = "manage pods and images"
 	app.OnUsageError = usageErrorHandler
+	app.CommandNotFound = commandNotFoundHandler
 
 	app.Version = version.Version