wwctl image completions and arguments

Signed-off-by: Jonathon Anderson <janderson@ciq.com>

internal/app/wwctl/image/shell/main.go

@@ -11,36 +11,39 @@ import (
 	"github.com/spf13/cobra"
 	cntexec "github.com/warewulf/warewulf/internal/app/wwctl/image/exec"
 	"github.com/warewulf/warewulf/internal/pkg/image"
+	"github.com/warewulf/warewulf/internal/pkg/util"
 	"github.com/warewulf/warewulf/internal/pkg/wwlog"
 )
 
 func CobraRunE(cmd *cobra.Command, args []string) error {
-
 	imageName := args[0]
-	var allargs []string
 
 	if !image.ValidSource(imageName) {
 		return fmt.Errorf("unknown Warewulf image: %s", imageName)
 	}
-	shellName := os.Getenv("SHELL")
 	if !image.ValidSource(imageName) {
 		return fmt.Errorf("unknown Warewulf image: %s", imageName)
 	}
+
 	var shells []string
-	if shellName == "" {
-		shells = append(shells, "/bin/bash")
-	} else {
-		shells = append(shells, shellName, "/bin/bash")
+	if os.Getenv("SHELL") != "" {
+		shells = append(shells, os.Getenv("SHELL"))
 	}
+	shells = append(shells, "/bin/bash", "/bin/sh")
+
+	shellName := ""
 	for _, s := range shells {
-		if _, err := os.Stat(path.Join(image.RootFsDir(imageName), s)); err == nil {
+		if util.IsFile(path.Join(image.RootFsDir(imageName), s)) {
 			shellName = s
 			break
 		}
 	}
+	if shellName == "" {
+		return fmt.Errorf("no shell found in image: %s", imageName)
+	}
+
 	args = append(args, shellName)
-	allargs = append(allargs, args...)
-	wwlog.Debug("Calling exec with args: %s", allargs)
+	wwlog.Debug("%s: exec with args: %v", imageName, args)
 	cntexec.SetBinds(binds)
 	cntexec.SetNode(nodeName)
 	cntexec.SyncUser = syncUser
@@ -48,5 +51,5 @@ func CobraRunE(cmd *cobra.Command, args []string) error {
 	if cntexec.Build {
 		wwlog.Info("Image build will be skipped if the shell ends with a non-zero exit code.")
 	}
-	return cntexec.CobraRunE(cmd, allargs)
+	return cntexec.CobraRunE(cmd, args)
 }