Is it possible to edit a symlink with a text editor?

问题

When we create a symlink, the number of bytes the symlink takes up is exactly the length of the origin it points to. For instance,

$ ln -s dest link1
$ ln -s longer_dest link2
$ ls -l
lrwxrwxrwx 1 username  4 Mar 26 20:21 link1 -> dest
lrwxrwxrwx 1 username 11 Mar 26 20:21 link2 -> longer_dest

where link1 takes up 4 bytes, which is the length of dest; link2 takes up 11 bytes, which is the length of longer_dest. Therefore, symlinks are in fact no more than the destination path stored in plain text. So I am wondering if it is possible to edit (the destination) of a symlink in text editors, preferably Emacs. I googled for a while and couldn't find anyone talking about this. Note that this question is purely out of curiosity; I know full well that I can overwrite a symlink by ln -f -s.

回答1:

Yes, in Emacs this is possible in dired-mode, specifically wdired (writable dired) mode.

Note, dired and wdired both are built-in packages.

Here's an example...

(BTW: I'm using Smex to give Emacs M-x command search & execute a more ergonomic UI + fuzzy matching)

回答2:

It's possible in principle, but the editor would need to specifically support it, since reading the destination of a symlink requires a special system call: readlink().

You're unlikely to find any editors that actually do this, since it's not very useful, and conflicts with what most users want the editor to do when asked to open a symlink: open the file that it points to.

回答3:

As per the Storage of symbolic links section in Wikipedia's article Symbolic Links, the symlinks are stored in an inode. This inode is a data structure containing several information about the file in question - as per this thread, the touch command can be used to change some of its values. So, it may not be possible to modify it by using a text editor, due to the problems that @Wyzard mentioned, but it might be modifiable by using some other command-line tools like touch.

I hope this helps!

回答4:

It's not possible directly, as others have already pointed out, but of course you can write a script for it. Here's one I came up with when I had to change lots of symlinks

#! /bin/bash

tmp=$(mktemp)
trap "rm $tmp" EXIT

while [ ! -z "$1" ]; do
    filename="$1"; shift
    if [ ! -h "$filename" ]; then
        echo "Not a symlink: $filename";
        continue
    fi
    stat -c "%N" "$filename" >> $tmp
done
emacs $tmp

while read filename linkname; do
    ln -sf "$linkname" "$filename"
done < <(sed "s/'\(.*\)' -> '\(.*\)'/\1 \2/" $tmp)

It worked for me, but it's certainly not perfect, so use at your own risk...

来源：https://stackoverflow.com/questions/22677707/is-it-possible-to-edit-a-symlink-with-a-text-editor

标签

Linux

shell

unix

symlink