cmds: usage string based on binary name

Renaming binaries is sometimes preferrable or even necessary when
creating distribution packages. In order to reduce confusion for the
users, it's nice when the built in help text of the applications refers
to the actually used name of the binary.

By adapting the `Use` string, cobra also generates correct completion
scripts when using a changed name for the binary.

go/cs/cs.go

@@ -18,6 +18,7 @@ import (
 	"context"
 	"fmt"
 	"os"
+	"path/filepath"
 	"time"
 
 	"github.com/spf13/cobra"
@@ -74,10 +75,11 @@ func main() {
 	var flags struct {
 		config string
 	}
+	executable := filepath.Base(os.Args[0])
 	cmd := &cobra.Command{
-		Use:           "cs",
+		Use:           executable,
 		Short:         "SCION Control Service instance",
-		Example:       "  cs --config cs.toml",
+		Example:       "  " + executable + " --config cs.toml",
 		SilenceErrors: true,
 		SilenceUsage:  true,
 		Args:          cobra.NoArgs,

go/posix-gateway/main.go

@@ -22,6 +22,7 @@ import (
 	"net/http"
 	_ "net/http/pprof"
 	"os"
+	"path/filepath"
 
 	"github.com/spf13/cobra"
 	"github.com/syndtr/gocapability/capability"
@@ -46,10 +47,11 @@ func main() {
 	var flags struct {
 		config string
 	}
+	executable := filepath.Base(os.Args[0])
 	cmd := &cobra.Command{
-		Use:           "posix-gateway",
+		Use:           executable,
 		Short:         "SCION IP gateway",
-		Example:       "  posix-gateway --config gateway.toml",
+		Example:       "  " + executable + " --config gateway.toml",
 		SilenceErrors: true,
 		SilenceUsage:  true,
 		Args:          cobra.NoArgs,

go/posix-router/main.go

@@ -18,6 +18,7 @@ import (
 	"fmt"
 	"net/http"
 	"os"
+	"path/filepath"
 	"sync"
 
 	"github.com/spf13/cobra"
@@ -40,9 +41,11 @@ func main() {
 		config string
 	}
 	metrics := router.NewMetrics()
+	executable := filepath.Base(os.Args[0])
 	cmd := &cobra.Command{
-		Use:           "posix-router",
+		Use:           executable,
 		Short:         "SCION router",
+		Example:       "  " + executable + " --config br.toml",
 		SilenceErrors: true,
 		SilenceUsage:  true,
 		Args:          cobra.NoArgs,

go/scion-pki/BUILD.bazel

@@ -10,15 +10,13 @@ scion_go_binary(
 go_library(
     name = "go_default_library",
     srcs = [
-        "completion.go",
         "main.go",
         "version.go",
     ],
     importpath = "github.com/scionproto/scion/go/scion-pki",
     visibility = ["//visibility:private"],
     deps = [
         "//go/lib/env:go_default_library",
-        "//go/lib/serrors:go_default_library",
         "//go/pkg/command:go_default_library",
         "//go/scion-pki/certs:go_default_library",
         "//go/scion-pki/testcrypto:go_default_library",

go/scion-pki/main.go

@@ -17,6 +17,7 @@ package main
 import (
 	"fmt"
 	"os"
+	"path/filepath"
 
 	"github.com/spf13/cobra"
 
@@ -27,8 +28,9 @@ import (
 )
 
 func main() {
+	executable := filepath.Base(os.Args[0])
 	cmd := &cobra.Command{
-		Use:   "scion-pki",
+		Use:   executable,
 		Short: "SCION Control Plane PKI Management Tool",
 		Args:  cobra.NoArgs,
 		// Silence the errors, since we print them in main. Otherwise, cobra

go/scion/scion.go

@@ -17,6 +17,7 @@ package main
 import (
 	"fmt"
 	"os"
+	"path/filepath"
 
 	"github.com/spf13/cobra"
 
@@ -70,8 +71,9 @@ type CommandPather interface {
 }
 
 func main() {
+	executable := filepath.Base(os.Args[0])
 	cmd := &cobra.Command{
-		Use:   "scion",
+		Use:   executable,
 		Short: "A clean-slate Internet architecture",
 		Args:  cobra.NoArgs,
 		// Silence the errors, since we print them in main. Otherwise, cobra

go/sciond/main.go

@@ -20,6 +20,7 @@ import (
 	"net/http"
 	_ "net/http/pprof"
 	"os"
+	"path/filepath"
 	"time"
 
 	"github.com/spf13/cobra"
@@ -57,10 +58,11 @@ func main() {
 	var flags struct {
 		config string
 	}
+	executable := filepath.Base(os.Args[0])
 	cmd := &cobra.Command{
-		Use:           "sciond",
+		Use:           executable,
 		Short:         "SCION Daemon",
-		Example:       "  sciond --config sd.toml",
+		Example:       "  " + executable + " --config sd.toml",
 		SilenceErrors: true,
 		SilenceUsage:  true,
 		Args:          cobra.NoArgs,