go-delve/delve · error

unknown argument %q to 'target follow-exec'

Error message

unknown argument %q to 'target follow-exec'

What it means

The DAP 'target follow-exec' REPL command only accepts -on [regex], -off, or no argument (status). Any other first argument after 'follow-exec' produces this error. It is strict argument validation for the follow-exec (child process following) subcommand.

Source

Thrown at service/dap/command.go:304

				regex = argv[1]
			}
			if err := s.debugger.FollowExec(true, regex); err != nil {
				return "", err
			}
			if regex != "" {
				return fmt.Sprintf("Follow exec mode enabled with regex %q", regex), nil
			}
			return "Follow exec mode enabled", nil
		case "-off":
			if len(argv) > 1 {
				return "", errors.New("too many arguments")
			}
			if err := s.debugger.FollowExec(false, ""); err != nil {
				return "", err
			}
			return "Follow exec mode disabled", nil
		default:
			return "", fmt.Errorf("unknown argument %q to 'target follow-exec'", argv[0])
		}
	case "switch": // TODO: This may cause inconsistency between debugger and frontend.
		tgrp, unlock := s.debugger.LockTargetGroup()
		defer unlock()
		pid, err := strconv.Atoi(argv[1])
		if err != nil {
			return "", err
		}
		found := false
		for _, tgt := range tgrp.Targets() {
			if _, err = tgt.Valid(); err == nil && tgt.Pid() == pid {
				found = true
				tgrp.Selected = tgt
				tgt.SwitchThread(pid)
			}
		}
		if !found {
			return "", fmt.Errorf("could not find target %d", pid)

View on GitHub (pinned to a23773e6c3)

Solutions

1. Use exactly 'target follow-exec -on [regex]' to enable or 'target follow-exec -off' to disable.
2. Call 'target follow-exec' with no argument to see the current status instead of guessing flags.
3. Check the command string your frontend builds for misspelled or undashed flags.
4. Note extra arguments to -off also fail; pass none.

Example fix

// before
target follow-exec enable
// after
target follow-exec -on
// or with regex:
target follow-exec -on ^/path/to/child$

validArgs := map[string]bool{"-on": true, "-off": true}
if !validArgs[arg] {
    return fmt.Errorf("use 'target follow-exec -on [regex]' or '-off', got %q", arg)
}

When it happens

Trigger: Evaluating 'target follow-exec enable', 'target follow-exec -on extra args misparsed', or any misspelled flag like '-enable'/'-true' via the DAP evaluate/REPL command path.

Common situations: Users habituated to other debuggers typing 'on'/'off' without the dash; IDE extension frontends constructing the command string with wrong flag names; typos such as '-onn' or '--on'.

Related errors

• unknown target command
• follow exec not supported
• follow exec not implemented
• count/len must be a positive integer
• expected argument after -size

AI-assisted analysis of go-delve/delve@a23773e6c3 (2026-08-31). Data as JSON: /api/errors/10464a08c4fd8dae. Report an issue: GitHub.