stderr
The channel on which a program writes its error messages. In hooks, what you write here reaches Claude as an explanation.
How it appears in the course
If the file name contains one of them, it writes a message on stderr (>&2) and exits with exit 2. That means “stop”. Claude gets the message and understands why it isn’t allowed.
Where you learn it
In module 07 · Hooks: automatic actions, in the Claude Code for Beginners course.
Related terms
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