Updated SC2024 (markdown)

SC2024.md

@@ -1,9 +1,32 @@
-# SC2024 sudo doesn't affect redirects. Use ..| sudo tee file
+## sudo doesn't affect redirects. Use ..| sudo tee file
 
-## Problematic Code:
+### Problematic code:
 
-    sudo echo 'export FOO=bar' > /etc/profile
+    sudo echo 'export FOO=bar' >> /etc/profile
 
-## Correct Code:
+### Correct code:
 
-    echo 'export FOO=bar' | sudo tee /etc/profile > /dev/null
+    echo 'export FOO=bar' | sudo tee -a /etc/profile > /dev/null
+
+### Rationale:
+
+Redirections are performed by the current shell before `sudo` is started. This means that it will use the current shell's user and permissions to open and write to the file.
+
+`tee` is a simple command that opens and writes to files without help from the shell, which means that it will use the permissions that `sudo` grants it.
+
+There is nothing special about `tee`. It's just the simplest command that can both truncate and append to files without help from the shell. Here are equivalent alternatives:
+
+Truncating:
+
+    echo 'data' | sudo dd of=file
+    echo 'data' | sudo sed 'w file'
+
+Appending: 
+
+    echo 'data' | sudo awk '{ print $0 >> "file" }'
+    echo 'data' | sudo sh -c 'cat >> file'
+    
+
+### Contraindications
+
+If you want to run a command as root but redirect as the normal user, you can ignore this message.