Diff for "BashFAQ/004"

Anchor(faq4)

How can I check whether a directory is empty or not? How do I check for any *.mpg files?

• I just deleted three completely wrong answers from this question. Please, people, make sure that when you add to the FAQ, your answers

  • answer the question that was asked, and

  • actually work

  Thanks. -- GreyCat

In BASH, you can do this safely and easily with the nullglob and dotglob options (which change the behaviour of [:glob:globbing]), and arrays:

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

As you can see we unset the nullglob after using it, to prevent it affecting other globs in the script in unexpected ways. nullglob also simplifies various other operations:

    shopt -s nullglob
    for i in *.zip; do
        blah blah "$i"  # No need to check $i is a file.
    done
    shopt -u nullglob

Without the nullglob, that would have to be:

    for i in *.zip; do
        [[ -f $i ]] || continue  # If no .zip files, i becomes *.zip
        blah blah "$i"
    done

(You may want to use the latter anyway, if there's a possibility that the glob may match directories in addition to files.)

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 [:UsingFind:find-based examples] may be an appropriate solution:

   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

If your script needs to run with various shell implementations, you can try using an external program like python, perl, or find as indicated above, or you can try something like:

    cd foo
    if [ "$(printf '%s %s %s' .* *)" = '. .. *' ] && [ ! -f '*' ]
    then
        echo "directory is empty"
    fi

Yes, it's extremely ugly, but it should be more portable than anything depending on ls output. Even ls -A solutions can break (HPUX for one, if you are root).