Tukukkk

With Bash and Dash, you can check for an empty directory using just the shell
(ignore dotfiles to keep things simple):

set *

if [ -e "$1" ]

then

  echo 'not empty'

else

  echo 'empty'

fi

However I recently learned that Zsh fails spectacularly in this case:

% set *

zsh: no matches found: *



% echo "$? $#"

1 0

So not only does the set command fail, but it doesn't even set $@. I suppose
I could test if $# is 0, but it appears that Zsh even stops execution:

% { set *; echo 2; }

zsh: no matches found: *

Compare with Bash and Dash:

$ { set *; echo 2; }

2

Can this be done in a way that works in bash, dash and zsh?

While zsh's default behaviour is to give an error, this is controlled by the nomatch option. You can unset the option to leave the * in place the way that bash and dash do:

setopt -o nonomatch

While that command won't work in either of the others, you can just ignore that:

setopt -o nonomatch 2>/dev/null || true ; set *

This runs setopt on zsh, and suppresses the error output (2>/dev/null) and return code (|| true) of the failed command on the others.

As written it's problematic if there is a file, for example, -e: then you will run set -e and change the shell options to terminate whenever a command fails; there are worse outcomes if you're creative. set -- * will be safer and prevent the option changes.

Most portable way would be via set and globstar for all POSIX-compliant shells. This has been shown in Gilles's answer on a related question. I've adapted the method slightly into a function:

dir_empty(){ 

    # fully empty directory will only have

    # 3 parameters * . ..

    set -- * .*

    if [ $# -ne 3 ] || [ -e $1 ]; then

        echo "Directory not empty"

    else

        echo "Directory is empty"

    fi

}

The way it works is by using set to set items in current working directory as positional parameters ( $1, $2, and so on ). If glob doesn't expand to any existing files, there shall only be one, literal * as $1, . as $2 and $3, so we also account for hidden files here.

Of course, it's a possibility that * could be a real filename, which is why we also perform [ -e "$1" ] check. If you want to use the function silently, we could rewrite it to return a value:

dir_empty(){ 



    # fully empty directory will only have

    # 3 parameters * . ..

    set -- * .*

    if [ $# -ne 3 ] || [ -e $1 ]; then

        return 1

    else

        return 0

    fi

}

You can see it in action via this repl:

main.sh

rm -rf empty_dir

mkdir empty_dir

pwd

cd empty_dir

pwd

dir_empty(){ 

    # fully empty directory will only have

    # 3 parameters * . ..

    set -- * .*

    if [ $# -ne 3 ] || [ -e $1 ]; then

        echo "Directory not empty"

    else

        echo "Directory is empty"

    fi

}

dir_empty

touch  '*'

dir_empty

rm '*'

touch '.dot_file'

dir_empty

Output:

GNU bash, version 4.4.12(1)-release (x86_64-pc-linux-gnu)



/home/runner

/home/runner/empty_dir

Directory is empty

Directory not empty

Directory not empty