Soft link pathname conversion for Linux and Unix

[Steven W. Orr]

On Saturday, Apr 28th 2007 at 19:42 +0100, quoth John Horne:

=>Hi,
=>
=>I have a shell problem that I am trying to easily resolve. If I have a
=>directory with a soft (symbolic) link in it such as:
=>
=>         fred -> ../bin/csh
=>
=>How can I convert the '../bin/csh' in to a full pathname? Is there a
=>command to do this that will work for Linux and Unices? I need it to
=>work for all circumstances, not just this one particular example. So
=>something like '../../abc/../def' should also work in being converted.
=>
=>Under Linux the 'readlink -f' command works fine, but NetBSD readlink
=>doesn't have the '-f' option, and Solaris doesn't have readlink. I do
=>not want to change directory at all, so changing to the link directory
=>and issuing 'pwd' isn't what I want to do.
=>
=>My only other thought is to process the link pathname bit-by-bit.
=>Preceed the pathname with the current working directory and then remove
=>any './' and jiggle (!) with any '../' to get the directory above. It's
=>messy and could get complicated. Better ideas welcome :-)

First you need to see if the symlink is pointing to a file or a directory. 
You can use -f or -d to see

if [[ -f fred ]]
then
    # do file stuff
elif [[ -d fred ]]
    # do dir stuff

In the file stuff section of your frozen food aisle, find out what fred 
points to.

symval=$(ls -l fred | awk '{print $11}')

Now, knowing that fred is a file, you can remove the file part of the 
symval, thus leaving you with the directory portion:

dirpart=${symval%/*}

Next you could cd there and do a pwd to see where you land:

cd $dirpart; pwd

But wait! How do I get pack and how do I get back knowing where I was on 
my little adventure?

abspath=$(cd $dirpart; pwd)

Use the force Luke!

-- 
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