Unix softlinks and paths

I am somewhat confused how soft links work in unix. See the example.

% cd /usr/local/
% ls -la
total 6
drwxr-xr-x   2 root     r开发者_Python百科oot         512 Jan 19 15:03 .
drwxr-xr-x  41 root     sys         1024 Jan 20 16:24 ..
lrwxrwxrwx   1 root     root          38 Jan 19 15:03 java -> /otherDir/java/jdk1.6.0_17 **<- this is a soft link**

% cd java **<- move to the softlink**

% pwd
/usr/local/java **<- the current location, say LOCATION_A**

% cd /otherDir/java/jdk1.6.0_17/ **<-move to the location of the softlink**

% pwd
/otherDir/java/jdk1.6.0_17 **<- the new current location, say LOCATION_B**

Isn't this problematic that even though LOCATION_A is LOCATION_B, they have different paths?

Is there a command (other than pwd) that will give the real location of a file (not just how the user go there).

It seems to me like pwd is just the sum of a user's cd. NOT their current location.

Try pwd -P. It's not "other than pwd" but it does the trick, at least on my bash 4.0.35 on Fedora 12. YMMV.

Update: Even works with sh, so it seems to be portable.

This behaves like this with a purpose. If you cd to /a/b/c/d and then cd to .. then you realistically expect to be in /a/b/c. If c happens to be a symbolic link (or symlink in unix terms - but not soft link) that takes you to /f/g/h, with the behaviour you would like to have you would end up in /f/g and then you (or any program) would not understand how it got there.

You can use readlink on the current working directory to get the true directory name:

readlink `pwd`

Normally, pwd should return /usr/local/java in the last line, if i understand your example. But some shells have a build in pwd command that tries to be more "intelligent" handling symlinks in the current working directory.

Try /bin/pwd, do you get other results?

realpath does what you want.

It is not possible to absolutely get your path under all circumstances. This is a bit odd, but a variation of this (plus chroot and setuid) is sometimes used for locking down a process.

$ mkdir -p /tmp/a/b
$ cd /tmp/a/b
$ rmdir /tmp/a/b
$ chmod 0 /tmp/a
$ rmdir /tmp/a
$ ls ..
ls: cannot open directory ..: Permission denied
$ ls -al
total 0
$ pwd -P
pwd: error retrieving current directory: getcwd: cannot access parent directories: No such file or directory