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@@ -322,6 +322,44 @@ See `exercises/chapter-8.13`.
 
 ## Do problem 9 (What do the following commands do?) in Chapter 9.
 
+What do the following commands do?
+
+```bash
+$ cp -f sample sample.bak
+```
+
+```bash
+$ cp -fp sample sample.bak
+```
+
+```bash
+$ rm -i ∼/personal/memo*.doc
+```
+
+```bash
+$ rm -i ∼/unixbook/final/ch??.prn
+```
+
+```bash
+$ rm -f ∼/unixbook/final/*.o
+```
+
+```bash
+$ rm -f ∼/courses/ece446/lab[1-6].[cC]
+```
+
+```bash
+$ rm -r ∼/NotNeededDirectory
+```
+
+```bash
+$ rm -rf ∼/NotNeededDirectory
+```
+
+```bash
+$ rm -ri ∼/NotNeededDirectory
+```
+
 ## Enter a C program that reads a temperature in Celsius entered from a keyboard and displays the corresponding temperature in Fahrenheit and complete the steps below.
 (Hint: Look for such a program in the textbook or online.)