How to mkdir only if a directory does not already exist?
Try mkdir -p:
mkdir -p fooNote that this will also create any intermediate directories that don't exist; for instance,
mkdir -p foo/bar/bazwill create directories foo, foo/bar, and foo/bar/baz if they don't exist.
Some implementation like GNU mkdir include mkdir --parents as a more readable alias, but this is not specified in POSIX/Single Unix Specification and not available on many common platforms like macOS, various BSDs, and various commercial Unixes, so it should be avoided.
If you want an error when parent directories don't exist, and want to create the directory if it doesn't exist, then you can test for the existence of the directory first:
[ -d foo ] || mkdir foo
This should work:
$ mkdir -p diror:
if [[ ! -e $dir ]]; then mkdir $direlif [[ ! -d $dir ]]; then echo "$dir already exists but is not a directory" 1>&2fiwhich will create the directory if it doesn't exist, but warn you if the name of the directory you're trying to create is already in use by something other than a directory.