Is there a way to edit a symbolic link without deleting it first? [duplicate]

Question

So I created a symbolic link:

ln -s /location/to/link linkname

Now I want to change the location that the symlink links to. How do I do that? Is there a way to do it without deleting it first?

Lief

I think you would get better response here: serverfault.com – Outshine

Answer 1

You could create the new link with a different name, then move it to replace the old link.

ln -s /location/to/link linkname

Later

ln -s /location/to/link2 newlink
mv newlink linkname

If newlink and linkname are on the same physical device the mv should be atomic.

Danford

@Lief - en.wikipedia.org/wiki/Atomic_operation – Danford

FYI, i'm sure this works on some os but this didn't work for me, the move operation just removed the 'new' link instead of replacing the old one. i still had to rm first. – Dotterel

@Dotterel You mean that mv newlink linkname caused the newlink file to be deleted, but didn't overwrite the linkname file? Did it do this silently? That seems extremely mysterious. – Affected

mv newlink linkname will move your newlink into linkname if they are directories. So this method is not 100% perfect. – Internee

@martinclayton @Internee Perhpas you should use mv -T instead of plain mv ? – Imputable

Answer 2

Try ln -sf new_destination linkname.

Seringapatam

This is non-atomic, though. See my answer for details. I'm not clear whether that's the poster's concern or not. – Diction

This also won't work with symlinks pointing to directories. It will just create a new symlink inside the old target directory. – Depressor

Use the -n (--no-dereference) switch to solve this. – Thromboplastin

It would be better to update the answer (but it may be too late now). – Kiel

Answer 3

Just change the symlink target:

# ln -sfT /path/to/new/target linkname

This is an instant, atomic change.

Norwood

what is a T option? I don't have in my MacOS – Vacancy

-T, --no-target-directory treat LINK_NAME as a normal file always you can brew install coreutils and access the GNU versions with a g prefix, like gln if you want the GNU versions on macOS. saves a lot of headache when there are subtle differences like this. – Philippic

What is implied here? As root? – Kiel

-n can also work, and has the benefit of existing both on GNU ln and MacOS's ln. – Uncrowned

Answer 4

If the symlink targets are directories, you need to add the -T flag to the mv command, otherwise it moves the new symlink in to the target directory of the old symlink.

Example of atomically switching a website to a new version:

Original setup - website is stored in www1 directory, vhost pointing at www symlink:

ln -s www1 www

Browse to website, see old version.

Put new website files in new www2 directory.

Set up new symlink to new website:

ln -s www_new www2

Move www symlink to directory of new website:

mv -T www_new www

Browse to website, see new version immediately.

Tarrsus

So apparently the version of mv on my NAS's microkernel doesn't support the -T argument. Any alternative suggestions for doing this atomically? – Hilburn

Try creating the symlink with the -f (force) flag. That seems to work. See the answer below: ln -sf new_destination linkname – Tarrsus

Answer 5

On OS X, the man page for ln says you can do it like this:

ln -shf /location/to/link link name

From the man page:

The options are as follows:

 -F    If the target file already exists and is a directory, then remove it so that the link may occur.  The -F
       option should be used with either -f or -i options.  If none is specified, -f is implied.  The -F option is
       a no-op unless -s option is specified.

 -h    If the target_file or target_dir is a symbolic link, do not follow it.  This is most useful with the -f
       option, to replace a symlink which may point to a directory.

 -f    If the target file already exists, then unlink it so that the link may occur.  (The -f option overrides any
       previous -i options.)

 -i    Cause ln to write a prompt to standard error if the target file exists.  If the response from the standard
       input begins with the character `y' or `Y', then unlink the target file so that the link may occur.  Other-
       wise, do not attempt the link.  (The -i option overrides any previous -f options.)

 -n    Same as -h, for compatibility with other ln implementations.

 -s    Create a symbolic link.

 -v    Cause ln to be verbose, showing files as they are processed.

Byrdie

What version of OS X? The default shell was changed to Z shell in macOS v10.15 (Catalina. 2019-10-07), if it matters. – Kiel

Answer 6

For directories, you want to do: ln -sfT /location/to/new/target old_linkname

Frohne

this is a much better solution than having to call a second command – Allayne

Isn't this already covered in previous answers? – Kiel

Answer 7

No. The symlink system call will return EEXIST if newpath already exists. You can only link from a new node in the filesystem. What's the requirement here? If you're worried about a race due to the non-atomicity of the unlink/symlink calls, then you might want to rethink the architecture a little to provide synchronization elsewhere. There have been some scary security bugs introduced by this kind of thing.

Diction

Answer 8

As others have mentioned, you basically have to delete the symlink first, either manually or by passing the -f flag to the ln utility.

Years ago, I had to make small edits to symlinks pretty frequently, so I wrote a simple readline-based utility (edln) to make this less annoying. In case anyone else finds it useful, I've put it online at https://github.com/jjlin/edln/.

edln will display the original symlink target; you can then use the arrow keys, or standard readline keystrokes (M-b, M-f, C-d, etc.) to move around and edit the target.

Archon

thank you! i could compile and run it on openbsd, the makefile misses install target though :-) – Windtight

Just a note that, at least with today's bash, you can use read built-in's readline support: read -e -p 'New: ' -i "$(readlink -- "$1")" lnk – Gonad

It would be quite nice to have a version of edln implemented as a bash script, but readline behavior doesn't appear to be as customizable via bash. I gave it a shot, but I haven't figured out how to avoid undesirable behavior like shell-escaped filename completions. – Archon

(touch 'a b'; IFS= read -e -p 'New: ' -i ./ lnk; echo ":$lnk:"; ls "$lnk") seems to work for me, read -e undoes the escapes; there's just a trailing whitespace after pressing <TAB> the user must delete – Gonad

Ah... the key is not passing -r to read -- with all its implications. Then tab-completion adds escapes, which are undone by read's default behavior – Gonad

Answer 9

Chain the commands like this:

rm currentlink && ln -s /path/to/link currentlink

The first command removes the existing one and the 2nd immediately creates it again.

Congregationalism

Answer 10

Just googled, found no good answer and had to solve myself:

ln -f -s -T `readlink SomeLibrary | sed 's/version.old/version.new/'` SomeLibrary

Editing by definition means not recreating from scratch but changing partly. Any answer requiring to memorize a path, maybe long or with weird symbols, is definitely bad.

Reconcile

What do you mean by "memorize a path"? Why would that be necessary? Can you provide an example of that? – Kiel