matthew@seymour:~$ rm -rf /home/matthewThis command deletes the /home directory of the user matthew. This is not
an uncommon command; after you have removed a user and backed up the
user’s data, you will probably want to issue something similar. However, if
you accidentally add a space between the / and the h in home, you get this:
Click here to view code image
matthew@seymour:~$ rm -rf / home/matthew
This time the command means “delete everything recursively from / and then
delete home/matthew”—quite a different result! You can stop this from
happening by using the —preserve-root parameter, which protects you
from catastrophe with this message:
Click here to view code image
rm: it is dangerous to operate recursively on '/'
rm: use --no-preserve-root to override this failsafe.
However, no one wants to keep typing —preserve-root each time when
running rm, so you could add this line to the .bashrc file in your /home
directory:
Click here to view code image
alias rm='rm --preserve-root'
This alias automatically adds —preserve-root to all calls to rm in future
bash sessions. Ubuntu (and Debian and perhaps other distributions now)
have done this by default—not by adding an alias in bashrc but by making
—preserve-root the default for the command.
Sorting the Contents of a File with sort
Say that you have a text file, and you want to sort its contents alphabetically.
That is easy. Assume that your text file is filled with one letter on each line,
upper- or lowercase. Here is what you get when you run the sort command
on this file:
Click here to view code image
matthew@seymour:~$ sort testfile.txt
a
A
b
B
This is useful. You can also sort in reverse order: