[BUG] Bash tool produces no output when executing scripts on Windows/MSYS2

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

## Summary

When using Claude Code's Bash tool on Windows (MSYS2/Git Bash), executing shell scripts directly produces zero output. The
same scripts work correctly when run via source or in a clean environment with env -i.

## Environment

• Platform: Windows 10/11 with MSYS2 (Git Bash)
• Shell: /usr/bin/bash (MSYS2)
• Claude Code version: (current as of 2026-01-20)

What Should Happen?

All execution methods should produce output:

Error Messages/Logs

Steps to Reproduce

## Reproduction Steps

1. Create a simple test script:

``bash
cat > /tmp/test-script.sh << 'EOF'
#!/usr/bin/env bash
echo "stdout from script"
echo "stderr from script" >&2
EOF
chmod +x /tmp/test-script.sh
``

1. Execute via different methods:

```bash
# These produce NO OUTPUT:
/tmp/test-script.sh
./tmp/test-script.sh
bash /tmp/test-script.sh
/usr/bin/bash /tmp/test-script.sh
cat /tmp/test-script.sh | bash

# These WORK correctly:
source /tmp/test-script.sh # Output: both lines
eval "$(cat /tmp/test-script.sh)" # Output: both lines
env -i PATH="..." bash /tmp/test-script.sh # Output: both lines
```

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.12 (Claude Code)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Windows Terminal

Additional Information

Seems like the output is not being harvested from sub-processes. I think I have ruled out any issues with my script.