[BUG] Bash tool: stdout not captured, exit code 1 on Linux

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?

All Bash tool commands that produce stdout fail with exit code 1 and no output is returned. However, commands that redirect stdout to a file execute successfully — proving
the commands themselves work fine, but stdout capture is broken.

This applies to all commands: echo, whoami, pwd, cat, ls, etc. Commands like echo "hello" > file.txt succeed (exit 0), and reading the file confirms the output
was written correctly.

This happens regardless of shell: tested with fish, bash, and sh via CLAUDE_CODE_SHELL. Also persists with --dangerously-skip-permissions. No hooks are configured.

What Should Happen?

echo "hello world" should return exit code 0 with "hello world" on stdout, as it did in previous versions.

Error Messages/Logs

● Bash(echo "hello world")                                                                                                                                                 
    ⎿  Error: Exit code 1                                                                                                                                                      
                                                                                                                                                                               
  ● Bash(whoami)                                                                                                                                                               
    ⎿  Error: Exit code 1                                                                                                                                                      
                                                                                                                                                                               
  ● Bash(echo "hello" > /tmp/test.txt)  ← this works, exit 0                                                                                                                   
  ● Read(/tmp/test.txt) → "hello"       ← confirms command executed

Steps to Reproduce

1. Install Claude Code v2.1.63
2. Run claude (default shell: fish, but reproducible with any shell)
3. Ask Claude to run echo "hello world" via the Bash tool
4. Observe: exit code 1, no output
5. Ask Claude to run echo "hello world" > /tmp/test.txt
6. Observe: exit code 0, file contains "hello world"

Workarounds attempted (all still fail):

• CLAUDE_CODE_SHELL=/bin/bash claude
• CLAUDE_CODE_SHELL=/bin/sh claude
• CLAUDE_CODE_DISABLE_NONESSENTIAL_TRAFFIC=1 claude --dangerously-skip-permissions
• No hooks configured, settings.json is empty ({})

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.63

Platform

Anthropic API

Operating System

Other Linux

Terminal/Shell

Other

Additional Information

Possibly related to #26482 (same symptom on Cygwin) and #27623