[BUG] claude -p prints lines that cannot be redirected to stdout or stderr

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?

This is a cosmetic issue: Running "claude -p" prints unnecesarry blank lines. Below is the cause of the issue claude code detected about its own behaviour:

---
Found it! Look at this line near the end:
write(1, "It's currently 2026-01-10 (Janua"..., 208It's currently 2026-01-10 (January 10th, 2026).

The claude CLI is writing directly to file descriptor 1 (stdout) with write(1, ...) - this is a direct system call that bypasses shell redirections!
Before that write, there are likely write(1, "\n", 1) calls (writing newlines) that aren't shown in your filtered output.

To see the newline writes, run:
bashstrace -e write=1 claude -p --model=haiku "what time is it" 2>&1 | grep 'write(1'

The claude binary is using raw system calls to write directly to file descriptor 1, which means standard shell redirections won't work. You'd need to close/redirect FD 1 at the file descriptor level before launching the process, not just with shell redirections.

The only real solution: live with the empty lines - they appear on the terminal but won't be in your captured output variable.

What Should Happen?

claude -p --model=haiku "what time is it" 2>&1 > /dev/null
should have no output.

Error Messages/Logs

Steps to Reproduce

claude -p --model=haiku "what time is it" 2>&1 > /dev/null

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_