diff --git a/cmd/bug_report.go b/cmd/bug_report.go
index c15396e..201346d 100644
--- a/cmd/bug_report.go
+++ b/cmd/bug_report.go
@@ -10,10 +10,12 @@ import (
 
 func newBugReportCmd() *cobra.Command {
 	return &cobra.Command{
-		Use:     "bug-report",
-		Short:   "Submit a bug report at GitHub",
-		Long:    "bug-report opens the default browser to start a bug report which will include useful system information.",
-		Example: "   gup bug-report",
+		Use:               "bug-report",
+		Short:             "Submit a bug report at GitHub",
+		Long:              "bug-report opens the default browser to start a bug report which will include useful system information.",
+		Example:           "   gup bug-report",
+		Args:              cobra.NoArgs,
+		ValidArgsFunction: cobra.NoFileCompletions,
 		Run: func(cmd *cobra.Command, args []string) {
 			OsExit(bugReport(cmd, args, openBrowser))
 		},
diff --git a/cmd/check.go b/cmd/check.go
index fdfe1fc..d6303c7 100644
--- a/cmd/check.go
+++ b/cmd/check.go
@@ -22,12 +22,17 @@ func newCheckCmd() *cobra.Command {
 check subcommand checks if the binary is the latest version
 and displays the name of the binary that needs to be updated.
 However, do not update`,
+		Args:              cobra.NoArgs,
+		ValidArgsFunction: cobra.NoFileCompletions,
 		Run: func(cmd *cobra.Command, args []string) {
 			OsExit(check(cmd, args))
 		},
 	}
 
 	cmd.Flags().IntP("jobs", "j", runtime.NumCPU(), "Specify the number of CPU cores to use")
+	if err := cmd.RegisterFlagCompletionFunc("jobs", completeNCPUs); err != nil {
+		panic(err)
+	}
 
 	return cmd
 }
diff --git a/cmd/export.go b/cmd/export.go
index bfcb346..0e05749 100644
--- a/cmd/export.go
+++ b/cmd/export.go
@@ -23,6 +23,8 @@ exports the file to $XDG_CONFIG_HOME/.config/gup/gup.conf (e.g. $HOME/.config/gu
 After you have placed gup.conf in the same path hierarchy on
 another system, you execute import subcommand. gup start the
 installation according to the contents of gup.conf.`,
+		Args:              cobra.NoArgs,
+		ValidArgsFunction: cobra.NoFileCompletions,
 		Run: func(cmd *cobra.Command, args []string) {
 			OsExit(export(cmd, args))
 		},
diff --git a/cmd/import.go b/cmd/import.go
index eb5fcbd..c79e847 100644
--- a/cmd/import.go
+++ b/cmd/import.go
@@ -21,6 +21,8 @@ binaries across multiple systems. After you create gup.conf by
 import subcommand in another environment, you save conf-file in
 $XDG_CONFIG_HOME/.config/gup/gup.conf (e.g. $HOME/.config/gup/gup.conf.)
 Finally, you execute the export subcommand in this state.`,
+		Args:              cobra.NoArgs,
+		ValidArgsFunction: cobra.NoFileCompletions,
 		Run: func(cmd *cobra.Command, args []string) {
 			OsExit(runImport(cmd, args))
 		},
@@ -29,7 +31,13 @@ Finally, you execute the export subcommand in this state.`,
 	cmd.Flags().BoolP("dry-run", "n", false, "perform the trial update with no changes")
 	cmd.Flags().BoolP("notify", "N", false, "enable desktop notifications")
 	cmd.Flags().StringP("input", "i", config.FilePath(), "specify gup.conf file path to import")
+	if err := cmd.MarkFlagFilename("input", "conf"); err != nil {
+		panic(err)
+	}
 	cmd.Flags().IntP("jobs", "j", runtime.NumCPU(), "Specify the number of CPU cores to use")
+	if err := cmd.RegisterFlagCompletionFunc("jobs", completeNCPUs); err != nil {
+		panic(err)
+	}
 
 	return cmd
 }
diff --git a/cmd/list.go b/cmd/list.go
index eb96420..aef500a 100644
--- a/cmd/list.go
+++ b/cmd/list.go
@@ -12,9 +12,11 @@ import (
 
 func newListCmd() *cobra.Command {
 	return &cobra.Command{
-		Use:   "list",
-		Short: "List up command name with package path and version under $GOPATH/bin or $GOBIN",
-		Long:  `List up command name with package path and version under $GOPATH/bin or $GOBIN`,
+		Use:               "list",
+		Short:             "List up command name with package path and version under $GOPATH/bin or $GOBIN",
+		Long:              `List up command name with package path and version under $GOPATH/bin or $GOBIN`,
+		Args:              cobra.NoArgs,
+		ValidArgsFunction: cobra.NoFileCompletions,
 		Run: func(cmd *cobra.Command, args []string) {
 			OsExit(list(cmd, args))
 		},
diff --git a/cmd/man.go b/cmd/man.go
index e070b32..b6a02bd 100644
--- a/cmd/man.go
+++ b/cmd/man.go
@@ -16,10 +16,12 @@ import (
 
 func newManCmd() *cobra.Command {
 	cmd := &cobra.Command{
-		Use:     "man",
-		Short:   "Generate man-pages under /usr/share/man/man1 (need root privilege)",
-		Long:    `Generate man-pages under /usr/share/man/man1 (need root privilege)`,
-		Example: "  sudo gup man",
+		Use:               "man",
+		Short:             "Generate man-pages under /usr/share/man/man1 (need root privilege)",
+		Long:              `Generate man-pages under /usr/share/man/man1 (need root privilege)`,
+		Example:           "  sudo gup man",
+		Args:              cobra.NoArgs,
+		ValidArgsFunction: cobra.NoFileCompletions,
 		Run: func(cmd *cobra.Command, args []string) {
 			OsExit(man(cmd, args))
 		},
diff --git a/cmd/remove.go b/cmd/remove.go
index 256e317..75cb82e 100644
--- a/cmd/remove.go
+++ b/cmd/remove.go
@@ -21,6 +21,7 @@ func newRemoveCmd() *cobra.Command {
 		Long: `Remove command in $GOPATH/bin or $GOBIN.
 If you want to specify multiple binaries at once, separate them with space.
 [e.g.] gup remove a_cmd b_cmd c_cmd`,
+		Args: cobra.MinimumNArgs(1),
 		Run: func(cmd *cobra.Command, args []string) {
 			OsExit(remove(cmd, args))
 		},
diff --git a/cmd/root.go b/cmd/root.go
index 8473b6e..abd2d99 100644
--- a/cmd/root.go
+++ b/cmd/root.go
@@ -3,6 +3,8 @@ package cmd
 
 import (
 	"os"
+	"runtime"
+	"strconv"
 
 	"github.com/nao1215/gup/internal/assets"
 	"github.com/nao1215/gup/internal/completion"
@@ -55,3 +57,12 @@ func Execute() error {
 	rootCmd := newRootCmd()
 	return rootCmd.Execute()
 }
+
+func completeNCPUs(cmd *cobra.Command, args []string, toComplete string) ([]string, cobra.ShellCompDirective) {
+	n := runtime.NumCPU()
+	ret := make([]string, 0, n)
+	for i := 1; i <= n; i++ {
+		ret = append(ret, strconv.FormatInt(int64(i), 10))
+	}
+	return ret, cobra.ShellCompDirectiveNoFileComp
+}
diff --git a/cmd/update.go b/cmd/update.go
index 8f0c46e..a8dd2a3 100644
--- a/cmd/update.go
+++ b/cmd/update.go
@@ -34,9 +34,18 @@ under $GOPATH/bin and automatically updates commands to the latest version.`,
 	cmd.Flags().BoolP("dry-run", "n", false, "perform the trial update with no changes")
 	cmd.Flags().BoolP("notify", "N", false, "enable desktop notifications")
 	cmd.Flags().StringSliceP("exclude", "e", []string{}, "specify binaries which should not be updated (delimiter: ',')")
+	if err := cmd.RegisterFlagCompletionFunc("exclude", cobra.NoFileCompletions); err != nil {
+		panic(err)
+	}
 	cmd.Flags().StringSliceP("main", "m", []string{}, "specify binaries which update by @main or @master (delimiter: ',')")
+	if err := cmd.RegisterFlagCompletionFunc("main", cobra.NoFileCompletions); err != nil {
+		panic(err)
+	}
 	// cmd.Flags().BoolP("main-all", "M", false, "update all binaries by @main or @master (delimiter: ',')")
 	cmd.Flags().IntP("jobs", "j", runtime.NumCPU(), "Specify the number of CPU cores to use")
+	if err := cmd.RegisterFlagCompletionFunc("jobs", completeNCPUs); err != nil {
+		panic(err)
+	}
 
 	return cmd
 }
diff --git a/cmd/version.go b/cmd/version.go
index f44db2c..b7b40ed 100644
--- a/cmd/version.go
+++ b/cmd/version.go
@@ -9,8 +9,10 @@ import (
 
 func newVersionCmd() *cobra.Command {
 	return &cobra.Command{
-		Use:   "version",
-		Short: "Show " + cmdinfo.Name + " command version information",
+		Use:               "version",
+		Short:             "Show " + cmdinfo.Name + " command version information",
+		Args:              cobra.NoArgs,
+		ValidArgsFunction: cobra.NoFileCompletions,
 		Run: func(cmd *cobra.Command, args []string) {
 			fmt.Println(cmdinfo.GetVersion())
 		},