# Knowledge Check: Files and Text

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**1. What's the difference between `>` and `>>`?**

*Answer:* `>` overwrites the target file's contents entirely; `>>` appends to the end of it,
preserving what was already there.

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**2. A command prints both normal output and an error message. What are these two streams
called?**

*Answer:* stdout (normal output) and stderr (error messages) — two separate streams that both
happen to print to your screen by default.

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**3. You want to watch a log file update live, as new lines are appended, without re-running a
command repeatedly.**

*Answer:* `tail -f <file>` — follows the file and prints new lines as they're written.

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**4. `cat app.log | grep ERROR`. What does the `|` actually do?**

*Answer:* It pipes `cat`'s output directly into `grep`'s input, so `grep` filters the file's
contents without needing a separate temporary file.

## Instructor Notes

**Facilitation:** Question 2 is worth a live show-of-hands check — many students haven't
consciously registered that stdout/stderr are separate until this module.

**Approximate timing:** 5 minutes.