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I've got a command that is working when run as the current user but if I prefix sudo to the command, it gives me an error.

I'm trying to remove a file if it's a directory (but not if it's a symlink to a directory). This works great:

brad@ip-10-0-0-1:~$ [[ -d /path/to/my/place && ! -L /path/to/my/place ]] && rm -rf /path/to/my/place

But if I try to use sudo to do this as a super user I get an error because sudo seems to think [[ is a command:

brad@ip-10-0-0-1:~$ sudo [[ -d /path/to/my/place && ! -L /path/to/my/place ]] && rm -rf /path/to/my/place
sudo: [[: command not found

I had to add the double brackets to get the ! -L /path/to/my/place bit to work; sudo was working fine with single brackets before when I was running

brad@ip-10-0-0-1:~$ sudo [ -d /path/to/my/place ] && rm -rf /path/to/my/place

But now that I'm trying to check to ensure it's not a symlink I can't get it to work with sudo. How can I either:

  • Get the double bracket syntax to work with sudo or
  • Get the single bracket syntax to allow me to negate the -L portion?
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$ type -a [
[ is a shell builtin
[ is /usr/bin/[
$ type -a [[
[[ is a shell keyword
$ 

As you can see [ (beside being a shell builtin) is a regular command that sudo can use. [[ is not. You need bash to provide [[:

sudo bash -c '[[ -d /path/to/my/place && ! -L /path/to/my/place ]]' && …

Because [[ is a shell keyword, the parser recognizes it and changes the behavior of && between [[ and ]]. You cannot use && inside [ … ] because [ acts as a command and ] is in fact the last argument passed to it. Having && inside means there are two commands which is wrong.

However [ supports -a, so this may work:

sudo [ -d /path/to/my/place -a ! -L /path/to/my/place ] && …

You should avoid it though. From this article:

The binary -a and -o […] are XSI extensions to the POSIX standard. All are marked as obsolescent in POSIX-2008. They should not be used in new code. One of the practical problems with [ A = B -a C = D ] (or -o) is that POSIX does not specify the results of a test or [ command with more than 4 arguments. It probably works in most shells, but you can't count on it. If you have to write for POSIX shells, then you should use two test or [ commands separated by a && operator instead.

So this should be safer if you want to use [:

sudo [ -d /path/to/my/place ] && sudo [ ! -L /path/to/my/place ] && …
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  • Excellent! sudo bash -c ... Worked like a charm. Thanks. – Brad Dwyer Oct 12 '18 at 20:22

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