[BUG] Error: No suitable shell found. Claude CLI requires a Posix shell environment. Please ensure you have a valid shell installed and the SHELL environment variable set.

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?

Issue: Claude CLI gives "No suitable shell found" error even though:

1. SHELL environment variable is correctly set (verified)
2. Git Bash is installed and functional (verified with independent tests)
3. All POSIX commands execute successfully (verified)

Potential Root Cause: Claude CLI's shell validation logic appears to only accept Unix-style
paths (starting with "/") and fails on valid Windows paths (starting with "C:\").

I was working in Claude code, locked my PC, and this morning I started to get this error "Error: No suitable shell found. Claude CLI requires a Posix shell environment. Please ensure you have a valid shell installed and the SHELL environment variable set.". Nothing has changed or updated. I checked the shell and its directed to the correct path. WSL is installed as well as cygwin and git bash. To make sure POSIX was working I ran some commands myself:

WSL (Windows Subsystem for Linux): All passed
wsl uname -a - Linux kernel 6.6.87.2
wsl ls -la - Directory listing successful
✅ wsl echo - Output working

Environment variable updated:

(I tried to see if the space between Program Files was causing an issue, still happened even when the length was shorted.) - All passed
$env:SHELL = C:\PROGRA~1\Git\bin\bash.exe
System SHELL = C:\PROGRA~1\Git\bin\bash.exe

All POSIX commands working:
uname -a → Linux DESKTOP-O065652 (WSL2)
pwd → /mnt/a/D/A
ls -la | head -5 → Directory listing with pipes working
grep → Pattern matching works
which bash → /usr/bin/bash found

Cant attach a pdf or run other things due to this error

What Should Happen?

Claude CLI should detect and use Git Bash on Windows when SHELL variable points to a valid bash executable.

Error Messages/Logs

Bash(echo "Testing POSIX shell detection")
  ⎿  Error: No suitable shell found. Claude CLI requires a Posix shell environment. Please ensure you have a valid shell installed and the SHELL environment variable set.

● Bash(uname -a)
  ⎿  Error: No suitable shell found. Claude CLI requires a Posix shell environment. Please ensure you have a valid shell installed and the SHELL environment variable set.

● Bash(pwd)
  ⎿  Error: No suitable shell found. Claude CLI requires a Posix shell environment. Please ensure you have a valid shell installed and the SHELL environment variable set.

Steps to Reproduce

1) Install claude
2) Run claude
3) Test POSIX

Claude Model

Sonnet (default)

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

v2.0.50

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Warp

Additional Information

_No response_