save-load-export: clear cli-parsing default

...in order to silence Cobra's usually-helpful "(default xxx)"
message.

Initialization is now done in code, by testing for empty string
and setting that to /dev/std{in,out} as appropriate; make special
note of load.go where there's mild duplication between a local
variable and cliconfig.

Signed-off-by: Ed Santiago <santiago@redhat.com>

cmd/podman/export.go

@@ -36,7 +36,7 @@ func init() {
 	exportCommand.SetHelpTemplate(HelpTemplate())
 	exportCommand.SetUsageTemplate(UsageTemplate())
 	flags := exportCommand.Flags()
-	flags.StringVarP(&exportCommand.Output, "output", "o", "/dev/stdout", "Write to a file instead of terminal")
+	flags.StringVarP(&exportCommand.Output, "output", "o", "", "Write to a specified file (default: stdout, which must be redirected)")
 }
 
 // exportCmd saves a container to a tarball on disk
@@ -60,15 +60,16 @@ func exportCmd(c *cliconfig.ExportValues) error {
 	}
 
 	output := c.Output
-	if runtime.Remote && (output == "/dev/stdout" || len(output) == 0) {
+	if runtime.Remote && len(output) == 0 {
 		return errors.New("remote client usage must specify an output file (-o)")
 	}
 
-	if output == "/dev/stdout" {
+	if len(output) == 0 {
 		file := os.Stdout
 		if logrus.IsTerminal(file) {
 			return errors.Errorf("refusing to export to terminal. Use -o flag or redirect")
 		}
+		output = "/dev/stdout"
 	}
 
 	if err := parse.ValidateFileName(output); err != nil {

cmd/podman/load.go

@@ -34,7 +34,7 @@ func init() {
 	loadCommand.SetHelpTemplate(HelpTemplate())
 	loadCommand.SetUsageTemplate(UsageTemplate())
 	flags := loadCommand.Flags()
-	flags.StringVarP(&loadCommand.Input, "input", "i", "/dev/stdin", "Read from archive file instead of from terminal")
+	flags.StringVarP(&loadCommand.Input, "input", "i", "", "Read from specified archive file (default: stdin)")
 	flags.BoolVarP(&loadCommand.Quiet, "quiet", "q", false, "Suppress the output")
 	flags.StringVar(&loadCommand.SignaturePolicy, "signature-policy", "", "Pathname of signature policy file (not usually used)")
 
@@ -64,7 +64,10 @@ func loadCmd(c *cliconfig.LoadValues) error {
 	if runtime.Remote && len(input) == 0 {
 		return errors.New("the remote client requires you to load via -i and a tarball")
 	}
-	if input == "/dev/stdin" {
+	if len(input) == 0 {
+		input = "/dev/stdin"
+		c.Input = input
+
 		fi, err := os.Stdin.Stat()
 		if err != nil {
 			return err

cmd/podman/save.go

@@ -58,7 +58,7 @@ func init() {
 	flags := saveCommand.Flags()
 	flags.BoolVar(&saveCommand.Compress, "compress", false, "Compress tarball image layers when saving to a directory using the 'dir' transport. (default is same compression type as source)")
 	flags.StringVar(&saveCommand.Format, "format", v2s2Archive, "Save image to oci-archive, oci-dir (directory with oci manifest type), docker-archive, docker-dir (directory with v2s2 manifest type)")
-	flags.StringVarP(&saveCommand.Output, "output", "o", "/dev/stdout", "Write to a file instead of terminal")
+	flags.StringVarP(&saveCommand.Output, "output", "o", "", "Write to a specified file (default: stdout, which must be redirected)")
 	flags.BoolVarP(&saveCommand.Quiet, "quiet", "q", false, "Suppress the output")
 }
 
@@ -79,14 +79,14 @@ func saveCmd(c *cliconfig.SaveValues) error {
 		return errors.Errorf("--compress can only be set when --format is either 'oci-dir' or 'docker-dir'")
 	}
 
-	output := c.Output
-	if output == "/dev/stdout" {
+	if len(c.Output) == 0 {
 		fi := os.Stdout
 		if logrus.IsTerminal(fi) {
 			return errors.Errorf("refusing to save to terminal. Use -o flag or redirect")
 		}
+		c.Output = "/dev/stdout"
 	}
-	if err := parse.ValidateFileName(output); err != nil {
+	if err := parse.ValidateFileName(c.Output); err != nil {
 		return err
 	}
 	return runtime.SaveImage(getContext(), c)