I want to take down data in /path/to/data/folder/month/date/hour/minute/file and symlink it to /path/to/recent/file and do this automatically every time a file is created.
Assuming I will not know ahead of time if /path/to/recent/file exists, how can I go about creating it (if it doesn't exist) or replacing it (if it does exist)? I am sure I can just check if it exists and then do a delete, symlink, but I'm wondering if there is a simple command which will do what I want in one step.
This is the purpose of ln's -f option: it removes existing destination files, if any, before creating the link.
ln -sf /path/to/data/folder/month/date/hour/minute/file /path/to/recent/file
will create the symlink /path/to/recent/file pointing to /path/to/data/folder/month/date/hour/minute/file, replacing any existing file or symlink to a file if necessary (and working fine if nothing exists there already).
If a directory, or symlink to a directory, already exists with the target name, the symlink will be created inside it (so you'd end up with /path/to/recent/file/file in the example above). The -n option, available in some versions of ln, will take care of symlinks to directories for you, replacing them as necessary:
ln -sfn /path/to/data/folder/month/date/hour/minute/file /path/to/recent/file
POSIX ln doesn’t specify -n so you can’t rely on it generally. Much of ln’s behaviour is implementation-defined so you really need to check the specifics of the system you’re using. If you’re using GNU ln, you can use the -t and -T options too, to make its behaviour fully predictable in the presence of directories (i.e. fail instead of creating the link inside the existing directory with the same name).
ln replaces the file atomically: it creates the new symlink using a random name, then renames it to the desired name, overwriting the existing file instead of deleting it.
Commented
Nov 13, 2022 at 7:10
Please read the manual.
ln -sfn /new/target /path/to/symlink
$ man ln
-n, --no-dereference
treat LINK_NAME as a normal file if it is a symbolic link to a directory
/path/to/symlink is already a symlink to a directory, without the -n flag, you'll get the symlink created in /path/to/symlink/target instead of replacing /path/to/symlink
/path/to/symlink exists and is a directory, and but not a symlink. I think the only way to work around it is to run rm -rf first.
--force/-f does replace existing files or symlinks, but not entire directory trees, and nor should it. Try it for yourself: ln -snf path/to/any/target some-existing-dir. You'll find your symlink is created inside some-existing-dir rather than replacing it. If it deleted recursively, the simple, common error case of transposing target & destination arguments would regularly cause data loss.