[BUG] Claude Code CLI hangs with whitespace-only prompt and empty stdin

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?

Claude Code print mode appears to hang when given a whitespace-only prompt with an empty stdin. Instead of rejecting the input or exiting cleanly, the process stays running until killed by a timeout.

Reproducer:

1. Create an empty file: /tmp/empty
2. Run Claude Code in print mode with a whitespace-only prompt and redirect stdin from the empty file.
3. Wrap the command with a 20-second timeout.
4. The process exits with timeout status 124, showing it did not terminate on its own.

or use these commands

/usr/bin/time -v timeout 20s claude -p " " < /tmp/empty
or claude -p " "
and claude -p " " < empty file
The CLI hangs until externally killed. This works also with -c -p " space"

Impact:
This is a low-severity local DoS / reliability issue that may affect scripts, so not a major issue.

What Should Happen?

Should Claude not hang, I guess? Maybe a better parser?

Error Messages/Logs

N/A

Steps to Reproduce

Reproducer:

1. Create an empty file: /tmp/empty
2. Run Claude Code in print mode with a whitespace-only prompt and redirect stdin from the empty file.
3. Wrap the command with a 20-second timeout.
4. The process exits with timeout status 124, showing it did not terminate on its own.

or use these commands

/usr/bin/time -v timeout 20s claude -p " " < /tmp/empty
or claude -p " "
and claude -p " " < empty file
The CLI hangs until externally killed. This works also with -c -p " space"

Claude Model

Not sure / Multiple models

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.140 (Claude Code)

Platform

Other

Operating System

Ubuntu/Debian Linux

Terminal/Shell

Non-interactive/CI environment

Additional Information

Best

• Kenan Alghythee