Fix Windows startup hook failure caused by inherited SHELLOPTS

[danshapiro]

Problem

On Windows with Git Bash, the superpowers SessionStart hook fails with:

SessionStart:startup hook error

This happens because Claude Code's shell environment exports SHELLOPTS with the onecmd option enabled:

SHELLOPTS=braceexpand:hashall:igncr:interactive-comments:monitor:onecmd

When bash inherits this exported variable and runs session-start.sh, the onecmd option causes bash to exit after processing one compound command. Combined with set -euo pipefail in the script, this causes the script to exit before producing any output.

Root Cause Analysis

1. Claude Code on Windows runs in an environment where SHELLOPTS is exported with onecmd
2. When the hook runs bash session-start.sh, bash inherits SHELLOPTS and enables all those options
3. The onecmd option (equivalent to set -t) causes bash to "exit after reading and executing one command"
4. When set -euo pipefail runs, the script exits immediately
5. No JSON output is produced, so Claude Code reports a hook error

Reproduction

# With SHELLOPTS containing onecmd:
$ bash session-start.sh
# (no output, exits silently)

# Without SHELLOPTS:
$ env -u SHELLOPTS bash session-start.sh
{
  "hookSpecificOutput": {
    "hookEventName": "SessionStart",
    ...
  }
}

Solution

Use env -u SHELLOPTS to unset the problematic environment variable before invoking bash. This ensures the script runs in a clean environment regardless of what shell options are inherited.

Testing

Tested on Windows 11 with Git Bash 5.1.16 and Claude Code 2.1.x. After applying this fix, the startup hook works correctly and the "SessionStart:startup hook error" message no longer appears.

---

🤖 Generated with Claude Code

Summary by CodeRabbit

Release Notes

• Bug Fixes
  • Improved session initialization hook environment handling to ensure consistent shell configuration during startup.

_{✏️ Tip: You can customize this high-level summary in your review settings.}

[coderabbitai]

📝 Walkthrough

Walkthrough

The session-start hook command is modified to execute the bash script with an unmodified shell environment by wrapping it with env -u SHELLOPTS bash, preventing inherited SHELLOPTS from affecting script execution.

Changes

Cohort / File(s)	Summary
Session-start hook configuration hooks/hooks.json	Modified hook invocation to wrap bash script execution with env -u SHELLOPTS, removing inherited shell options from the environment

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

Possibly related issues

• SessionStart hook produces no output on Windows (Git Bash shebang issue) #354 — Both changes modify the session-start hook invocation mechanism in the hooks configuration.

Possibly related PRs

• Add Windows support for plugin hooks #134 — Both PRs modify the session-start hook command invocation in hooks/hooks.json.

Poem

🐰 A hop through the shell, so clean and so bright,
We strip away options that cloud up the night,
With env and SHELLOPTS gone from the way,
Our hooks now start fresh, hip-hip-hooray! ✨

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title directly and specifically describes the main change: fixing a Windows startup hook failure caused by inherited SHELLOPTS environment variable.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

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[pedropaulovc]

I tested this fix and it did not work on my setup. bash.exe intercepted the hook arguments and did not recognize env as a valid command.

• CC 2.1.27
• Windows Terminal
• pwsh 7.2.1

2026-01-30T23:50:22.653Z [DEBUG] Getting matching hook commands for SessionStart with query: startup
2026-01-30T23:50:22.653Z [DEBUG] Found 1 hook matchers in settings
2026-01-30T23:50:22.653Z [DEBUG] Matched 1 unique hooks for query "startup" (1 before deduplication)
2026-01-30T23:50:22.660Z [DEBUG] [API:auth] OAuth token check complete
2026-01-30T23:50:22.701Z [DEBUG] Total LSP servers loaded: 0
2026-01-30T23:50:22.701Z [DEBUG] [LSP SERVER MANAGER] getAllLspServers returned 0 server(s)
2026-01-30T23:50:22.702Z [DEBUG] LSP manager initialized with 0 servers
2026-01-30T23:50:22.702Z [DEBUG] LSP server manager initialized successfully
2026-01-30T23:50:22.702Z [DEBUG] LSP notification handlers registered successfully for all 0 server(s)
2026-01-30T23:50:22.785Z [DEBUG] Hook output does not start with {, treating as plain text
2026-01-30T23:50:22.785Z [DEBUG] Hook SessionStart:startup (SessionStart) error:
/usr/bin/env: /usr/bin/env: cannot execute binary file

[pedropaulovc]

In my case the best I could come up with was to use Git Bash's full path instead of /bin/bash. It seems to be some conflict between Git Bash and WSL bash (I am not running CC on WSL though). Obviously this won't work for Linux.

Final working config:

  {
    "hooks": {
      "SessionStart": [
        {
          "matcher": "startup|resume|clear|compact",
          "hooks": [
            {
              "type": "command",
              "command":  "\"C:\\Program Files\\Git\\bin\\bash.exe\" -c \"source \\\"$(cygpath \\\"$CLAUDE_PLUGIN_ROOT\\\")/hooks/session-start.sh\\\"\""
            }
          ]
        }
      ]
    }
  }