Diff for "BashFAQ/004"

How can I check whether a directory is empty or not? How do I check for any *.mpg files, or count how many there are?

In Bash, you can do this safely and easily with the nullglob and dotglob options (which change the behaviour of globbing), and an array:

    # Bash
    shopt -s nullglob dotglob
    files=(*)
    (( ${#files[*]} )) || echo directory is empty
    shopt -u nullglob dotglob

Or you can pour it into a SubShell to avoid having to reset (in fact, unset! - the code above assumes the shell options were unset before) the shell options again:

    # Bash
    if (shopt -s nullglob dotglob; f=(*); ((! ${#f[@]}))); then
        echo "The current directory is empty."
    fi

Of course, you can use any glob you like instead of *. E.g. *.mpg or /my/music/*.mpg works fine.

Both of these examples expand a glob and store the resulting filenames into an array, and then check whether the number of elements in the array is 0. If you actually want to see how many files there are, just print the array's size instead of checking whether it's 0:

    # Bash
    shopt -s nullglob dotglob
    f=(*)
    echo "The current directory contains ${#f[@]} things."

Some people dislike nullglob because having unmatched globs vanish altogether confuses programs like ls. Mistyping ls *.zip as ls *.zpi may cause every file to be displayed. Setting nullglob in a SubShell avoids accidentally changing its setting in the rest of the shell, at the price of an extra fork().

If your script needs to run with various non-Bash shell implementations, you can try using an external program like python, perl, or find; or you can try one of these:

    # POSIX
    # Clobbers the positional parameters, so make sure you don't need them.
    set -- *
    if test -e "$1" || test -L "$1"; then
        echo "directory is non-empty"
    fi

(The -L test is required because -e fails if the first file is a dangling symlink.)

    # Bourne
    # (Of course, the system must have printf(1).)
    if test "`printf '%s %s %s' .* *`" = '. .. *' && test ! -f '*'
    then
        echo "directory is empty"
    fi

Yes, they're quite ugly, but they should be more portable than anything depending on ls output. Even ls -A solutions can break (e.g. on HP-UX, if you are root, ls -A does the exact opposite of what it does if you're not root -- and no, I can't make up something that incredibly stupid).

In fact, you may wish to avoid the direct question altogether. Usually people want to know whether a directory is empty because they want to do something involving the files therein, etc. Look to the larger question. For example, one of these find-based examples may be an appropriate solution:

   # Bourne
   find "$somedir" -type f -exec echo Found unexpected file {} \;
   find "$somedir" -maxdepth 0 -empty -exec echo {} is empty. \;  # GNU/BSD
   find "$somedir" -type d -empty -exec cp /my/configfile {} \;   # GNU/BSD

Most commonly, all that's really needed is something like this:

    # Bourne
    for f in ./*.mpg; do
        test -f "$f" || continue
        mympgviewer "$f"
    done

In other words, the person asking the question may have thought an explicit empty-directory test was needed to avoid an error message like mympgviewer: ./*.mpg: No such file or directory when in fact no such test is required.

CategoryShell