Deleting a file named -f and other Linux tricks.

How to delete a file with a strange filename

This can be an annoying trick to play on someone. Create a file named -f with this command: >-f and then ask them to delete it with the command line only. This can be frustrating exercise; you try to use rm \-f and that does not work; then you try something else like rm "-f" and the file is still there. The trick I discovered is to use this command.

john@deusexmachina:~/Desktop$ rm -- -f

This will delete that file easily. This is another command I saw on the web that someone was wanting people to run.

john@deusexmachina:~/Desktop$ chmod -x $(which chmod)

This will remove the executable permissions on the chmod command and then you will be unable to run it again to fix this. Not a good idea to run this command at all though as fixing it would be fun. But the best way would be to run this C program on it and it will set the executable flag back onto the file.

#include <stdlib.h>
 
int main(void) {
 
	chmod("/bin/chmod", 0755);
	return 0;
}

I would not actually do this, but this is an interesting exercise anyway. Getting back to the file deletion; deleting a file named -e is the same as -f and you just use the same fix as above for that. Below I am using the ed UNIX line editor to add a line of text to a text file. This editor is not too hard to use; editing a file one line at a time. Just load the ed editor and then press the “a” key to start appending text and then type away.

john@deusexmachina:~/Desktop$ ed hello
7
a
This is another line I am adding to a text file.
^C
?
w
56
q
john@deusexmachina:~/Desktop$ cat hello 
Hello.
This is another line I am adding to a text file.
john@deusexmachina:~/Desktop$

A command that looks like this is one you should never run.

`echo "c3VkbyBybSAtcmYgLwo=" | base64 -d`

Or this.

echo cm0gLXJmICo7IGNkIC4uOyBybSAtcmYgKjsgY2QgLi47IHJtIC1yZiAqCg== | base64 -d | sh -s

Run the command like this instead and you may see what it really does…

┌──[jason@11000000.10101000.00000001.00000011]─[~]
└──╼  ╼ $ echo cm0gLXJmICo7IGNkIC4uOyBybSAtcmYgKjsgY2QgLi47IHJtIC1yZiAqCg== | base64 -d
rm -rf *; cd ..; rm -rf *; cd ..; rm -rf *

Very destructive command indeed.