Bash – How to verify the target of a symbolic link points toward a particular path

bashshellsymlink

Within a bash script, I know I can check if a file is a symbolic link with the following syntax

if [ -L $path ]

Does any one know how I would test if that path was linked to a particular path? E.g. I want to check whether the target of $path is /some/where.

Best Answer

If you want to check whether $path is a symbolic link whose target is /some/where, you can use the readlink utility. It isn't POSIX, but it's available on many systems (GNU/Linux, BusyBox, *BSD, …).

if [ "$(readlink -- "$path")" = /some/where ]; then …

Note that this is an exact text comparison. If the target of the link is /some//where, or if it's where and the value of $path is /some/link, then the texts won't match.

Many versions of readlink support the option -f, which canonicalizes the path by expanding all symbolic links.

Many shells, including dash, ksh, bash and zsh, support the -ef operator in the test builtin to test whether two files are the same (hard links to the same file, after following symbolic links). This feature is also widely supported but not POSIX.

if [ "$path" -ef "/some/where" ]; then …

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Replace symbolic link which linked to directory target

You want the -T option:

$ mkdir v1
$ ln -s v1 foo
$ ls -FlA | grep foo
lrwxrwxrwx 1 phil phil     2 2011-09-05 01:58 foo -> v1/
$ mkdir v2
$ ln -s -T -f v2 foo
$ ls -FlA | grep foo
lrwxrwxrwx 1 phil phil     2 2011-09-05 01:59 foo -> v2/

Why change the owner of a symbolic link in linux

Suppose root is working in a directory that Eve can write to. There's a file foo in this directory that needs to be changed to belong to Eve. So root types chown eve foo. But just before root hits Enter, Eve runs ln -sf /etc/passwd foo. Now /etc/passwd belongs to Eve! If root can run chown -h eve foo to make sure not to follow symlinks, then the most harm that can be done is that some other file in the same directory has been changed to belong to Eve.

lchown is also convenient when you're changing the owner of a directory tree. You don't need to worry about accidentally affecting a file outside the tree because you called chown on a symbolic link.

Best Answer

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Replace symbolic link which linked to directory target

Why change the owner of a symbolic link in linux

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