Is there a way to edit a symlink without deleting

问题:

This question already has an answer here:

• Can you change what a symlink points to after it is created? 7 answers

So I created a symlink:

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?

回答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.

回答2:

Try ln -sf new_destination linkname.

回答3:

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.

回答4:

Just change the symlink target:

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

This is an instant, atomic change.

回答5:

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

回答6:

On OSX, 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.

回答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.

回答8:

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.

回答9:

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.

回答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.