[BUG] Bash tool: all commands fail with Bad file descriptor on Windows (Git Bash stdout broken)

Found 3 possible duplicate issues:

1. https://github.com/anthropics/claude-code/issues/18748
2. https://github.com/anthropics/claude-code/issues/18469
3. https://github.com/anthropics/claude-code/issues/19057

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🤖 Generated with Claude Code

Confirmed regression in 2.1.45, pin versions and the difference is in 45.

This is not a duplicate of those issues. Here's why:

| | #18469 / #18748 / #19057 (fixed v2.1.27) | This issue (#26413) |
|---|---|---|
| Symptom | Silent empty stdout, exit code 0 | echo: write error: Bad file descriptor, exit code 1 |
| Root cause | .bashrc -> set -o onecmd in shell snapshot | stdout fd itself is broken |
| .bashrc involved? | Yes - removing it was the workaround | No - tested by removing .bashrc, still broken |
| Version | v2.1.0-v2.1.26 | v2.1.45 (includes the v2.1.27 fix) |

Likely regression: v2.1.45 changed bash stdio from pipes to file descriptors (stdio: [pipe, fd, fd] where fd = openSync(path, a)). MSYS2/Git Bash cannot inherit a Windows file HANDLE opened via Node.js openSync() as a valid POSIX file descriptor - its crt0 initialization doesn't translate the HANDLE, so fd 1 is invalid from bash's perspective. This is why echo (a bash builtin writing to fd 1) fails with Bad file descriptor.

The previous pipe-based stdio worked because Node.js pipes use proper Windows named pipes that MSYS2 can handle. The file-based approach works for native Windows programs (PowerShell) but not for MSYS2 programs.

Repro: Any bash command on Windows with v2.1.45:

Having this as well, noticed SSH commands breaking, rolling back to 2.1.44 fixes it for now.

See: #26418

Downgrade (pwsh): & ([scriptblock]::Create((irm https://claude.ai/install.ps1))) 2.1.44

Can confirm this on Windows 10 Pro (10.0.19045) + Git Bash + Claude Code.

Additional diagnostic finding that narrows down the root cause:

Standalone .exe binaries work through the Bash tool, but builtins and pipes don't:

| Command | Result |
|---|---|
| node -e "console.log('test')" | Works |
| git --version | Works |
| git -C /path ls-files | Works (returned 683 files) |
| echo hello | Exit code 1, no output |
| whoami | Exit code 1, no output |
| ls | Exit code 2, no output |
| echo hello \| wc -l | Exit code 1, no output |
| printf "hello" | Exit code 1, no output |

Key proof that bash itself is fine: Running bash commands through Node's execSync with the Git Bash shell explicitly specified works perfectly:

// This works — proves bash is healthy, only Claude Code's pipe is broken
execSync('echo hello | wc -l', {
  encoding: 'utf8',
  shell: 'C:/Program Files/Git/usr/bin/bash.exe'
});
// Returns: "1"

Also confirmed: no ~/.bashrc, ~/.bash_profile, or ~/.profile exists — the issue is purely in how the Bash tool spawns the process, not shell init.

Workaround: route anything that needs shell features through node -e instead of running bash commands directly.

Having this as well, noticed SSH commands breaking, rolling back to 2.1.44 fixes it for now. See: #26418 Downgrade (pwsh): & ([scriptblock]::Create((irm https://claude.ai/install.ps1))) 2.1.44

Problem is that claude self-updates to .45. I went for 2.1.37 and used /config within claude to set the Auto-update channel policy to stable (which is 2.1.37 currently).

Confirming this on Windows 11 with WSL bash (not just Git Bash)

Adding a data point — this also affects WSL bash (C:\Windows\System32\bash.exe), not only Git Bash/MSYS2. Same symptoms:
all commands producing stdout return exit code 1 with no output. Commands with no output succeed.

Environment:

• Claude Code v2.1.45 (native install, auto-updated 2026-02-18)
• Windows 11, WSL bash (C:\Windows\System32\bash.exe)
• Git Bash also installed (C:\Program Files\Git\bin\bash.exe, git 2.50.1) but not in PATH
• Both WSL and Git Bash work fine from PowerShell — only broken inside Claude Code

What I tried (none helped):

• Setting $env:SHELL to Git Bash path
• Adding Git Bash to PATH ahead of System32
• Both together
• Windows Defender — no blocks detected

What fixed it: Rolling back to v2.1.37 via winget.

Note for others rolling back: The native install auto-updater is aggressive — it reverted my first rollback (to 2.1.44)
back to 2.1.45 immediately. To make the rollback stick, set "autoUpdatesChannel": "stable" in ~\.claude\settings.json
before reinstalling the older version:

1. Edit ~\.claude\settings.json — set autoUpdatesChannel to "stable"
2. Then:

winget install Anthropic.ClaudeCode --version 2.1.37 --force

Has anyone confirmed if this is still an issue in 2.1.47?

Confirmed fixed in v2.1.47.

CHANGELOG (v2.1.47)

Fixed an issue where bash tool output was silently discarded on Windows when using MSYS2 or Cygwin shells.

Local verification (Windows 11 + Git Bash)

• echo, date, printf — all return output correctly
• Shell scripts using set -euo pipefail — no longer fail silently

The issue reported here is resolved.

Sorry about this. This issue was fixed in Claude Code v2.1.47.

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