Best practices to prevent 'rm -rf /' in bash scripts

Question

It's well known fact that extra space in env.variable can lead to deletion of / directory in bash script.

#!/bin/bash
...
rm -rf /$MYPATH

if $MYPATH contains values like " dir" or "dir /" it will lead to "rm -rf / dir" or "rm -rf dir /". And will result into "rm -rf /"

Are there any best practices to prevent this situation?

Answer 1

alias rm='rm --preserve-root'

IIRC --preserve-root is the default in newer versions of coreutils.

Answer 2

Always quote your arguments. Even when you know they are sane, it almost never hurts to quote them in scripts.

rm -rf "/$FOO" will not delete / if $FOO has a leading space, instead you'll just not delete anything. This does require the quotes to be present on the line with rm -rf, of course, not something like:

TODEL="/$FOO"
rm -rf $TODEL

If you do that, you'll be back in a whole load of trouble.

Also, I tend to think a good ol':

if [ -d "/$FOO" ] ; then
    ...
fi

(Or -e if it's just a file) is always a good idea before deleting anything.

Answer 3

First things first: have backups. :-)

But while I hack up those potentially dangerous scripts, I always first echo the dangerous lines, so I can see what would happen.

You can also add a file named -i to important directories, so in some situations rm would prompt while trying to remove those. Of course, if you do the deletion via some other method, such as Perl script or even with different rm parameters, that would not help.

It's also possible to set immutable flag to important files and dirs with chattr +i, but be careful with that one. That can bite you if you actually should remove files from some directory or modify the files ...

Answer 4

One way to avoid the issue would be to use an OS that prevents such a command to succeed by design as it is arguably non POSIX compliant. It was initiated by Solaris 10 (2005), followed by BSD then Gnu rm in 2006.

Answer 5

Sanity check your code first. Seriously, anything anyone will tell you will just be something equivalent to the check you should have done inside your code to check the value of $MYPATH. If the script is running interactively, you could remove the -f.

Answer 6

You can trim the MYPATH variable before executing the rm command. Just use echo:

MYPATH=`echo $MYPATH`

Answer 7

After an embarrassing incident many years ago on an Ultrix box, where I did as root a userdel -r sccs (or Ultrix equivalent, it's been a long time) without checking what the sccs user's home directory was beforehand, and the sccs user's $HOME turned out to be /, and the file system went away, I've avoided putting rm -rf $ANYTHING in scripts. You can check the variable until you're blue in the face, but I tend instead to print out a message like "if you're happy with the idea, you should now run sudo rm -rf $ANYTHING".

Answer 8

You could pass MYPATH through sed and check that what you put in is that same as what you get out

MYPATH1=`echo "$MYPATH" | sed -e 's|[ \t]\/[ \t]| |' -e 's|^/[ \t]| |' -e 's|[ \t]/$| |' `
if [ "$MYPATH" != "$MYPATH1" ]
then
    dosomething 
fi

Answer 9

You're doing a really funny thing here by taking what looks like a relative path and turning it into an absolute one. Treating the given path as the given path is a good start towards accomplishing what you want, but take other commenters' advice and definitely quote everything.