fix

cmd/link.go

@@ -14,39 +14,23 @@
 package cmd
 
 import (
-	"fmt"
-	"os"
-	"path/filepath"
-
 	"github.com/pingcap/tiup/pkg/environment"
 	"github.com/spf13/cobra"
 )
 
 func newLinkCmd() *cobra.Command {
 	cmd := &cobra.Command{
 		Use:   "link <component>[:version]",
-		Short: "Link component binary to $PATH",
-		Long: `[experimental feature]
-Link component binary to $PATH`,
+		Short: "Link component binary to $TIUP_HOME/bin/",
+		Long:  `[experimental] Link component binary to $TIUP_HOME/bin/`,
 		RunE: func(cmd *cobra.Command, args []string) error {
 			teleCommand = cmd.CommandPath()
 			env := environment.GlobalEnv()
 			if len(args) != 1 {
 				return cmd.Help()
 			}
 			component, version := environment.ParseCompVersion(args[0])
-			if version == "" {
-				var err error
-				version, err = env.SelectInstalledVersion(component, version)
-				if err != nil {
-					return err
-				}
-			}
-			binPath, _ := env.BinaryPath(component, version)
-			target := filepath.Join(env.LocalPath("bin"), filepath.Base(binPath))
-			fmt.Printf("package %s provides these executables: %s\n", component, filepath.Base(binPath))
-			_ = os.Remove(target)
-			return os.Symlink(binPath, target)
+			return env.Link(component, version)
 		},
 	}
 	return cmd

cmd/unlink.go

@@ -18,23 +18,34 @@ import (
 	"path/filepath"
 
 	"github.com/pingcap/tiup/pkg/environment"
+	"github.com/pingcap/tiup/pkg/tui"
 	"github.com/spf13/cobra"
 )
 
 func newUnlinkCmd() *cobra.Command {
 	cmd := &cobra.Command{
 		Use:   "unlink <component>",
-		Short: "Unlink component binary to $PATH",
-		Long: `[experimental feature]
-Unlink component binary in $PATH`,
+		Short: "Unlink component binary to $TIUP_HOME/bin/",
+		Long:  `[experimental] Unlink component binary in $TIUP_HOME/bin/`,
 		RunE: func(cmd *cobra.Command, args []string) error {
 			teleCommand = cmd.CommandPath()
 			env := environment.GlobalEnv()
 			if len(args) != 1 {
 				return cmd.Help()
 			}
-			component, _ := environment.ParseCompVersion(args[0])
-			target := filepath.Join(env.LocalPath("bin"), component)
+			component, version := environment.ParseCompVersion(args[0])
+			version, err := env.SelectInstalledVersion(component, version)
+			if err != nil {
+				return err
+			}
+			binPath, err := env.BinaryPath(component, version)
+			if err != nil {
+				return err
+			}
+			target := env.LocalPath("bin", filepath.Base(binPath))
+			if err := tui.PromptForConfirmOrAbortError("%s will be removed.\n Do you want to continue? [y/N]:", target); err != nil {
+				return err
+			}
 			return os.Remove(target)
 		},
 	}

pkg/environment/env.go

@@ -30,11 +30,6 @@ import (
 	"golang.org/x/mod/semver"
 )
 
-// Name of components
-const (
-	tiupName = "tiup"
-)
-
 var (
 	// ErrInstallFirst indicates that a component/version is not installed
 	ErrInstallFirst = errors.New("component not installed")
@@ -209,6 +204,9 @@ func (env *Environment) SelectInstalledVersion(component string, ver utils.Versi
 	})
 
 	errInstallFirst := errors.Annotatef(ErrInstallFirst, "use `tiup install %s` to install component `%s` first", component, component)
+	if !ver.IsEmpty() {
+		errInstallFirst = errors.Annotatef(ErrInstallFirst, "use `tiup install %s:%s` to install specified version", component, ver.String())
+	}
 
 	if ver.IsEmpty() || string(ver) == utils.NightlyVersionAlias {
 		var selected utils.Version
@@ -287,6 +285,45 @@ func (env *Environment) BinaryPath(component string, ver utils.Version) (string,
 	return env.v1Repo.BinaryPath(installPath, component, ver.String())
 }
 
+// Link add soft link to $TIUP_HOME/bin/
+func (env *Environment) Link(component string, version utils.Version) error {
+	version, err := env.SelectInstalledVersion(component, version)
+	if err != nil {
+		return err
+	}
+	binPath, err := env.BinaryPath(component, version)
+	if err != nil {
+		return err
+	}
+
+	target := env.LocalPath("bin", filepath.Base(binPath))
+	backup := target + ".old"
+	exist := true
+	_, err = os.Stat(target)
+	if err != nil {
+		if !os.IsNotExist(err) {
+			return err
+		}
+		exist = false
+	}
+	if exist {
+		if err := os.Rename(target, backup); err != nil {
+			fmt.Printf("Backup of `%s` to `%s` failed.\n", target, backup)
+			return err
+		}
+	}
+
+	fmt.Printf("package %s provides these executables: %s\n", component, filepath.Base(binPath))
+
+	err = os.Symlink(binPath, target)
+	if err != nil {
+		defer func() { _ = os.Rename(backup, target) }()
+	} else {
+		defer func() { _ = os.Remove(backup) }()
+	}
+	return err
+}
+
 // ParseCompVersion parses component part from <component>[:version] specification
 func ParseCompVersion(spec string) (string, utils.Version) {
 	if strings.Contains(spec, ":") {