How to check if a parent directory is a symbolic link

compnovice · 10-05-2005, 04:15 PM

How can I check if a parent directory is a symbolic link.

Suppose I create a symbolic link like say,

ln -s /abc/xyz abc_xyz

now Suppose I am in another directory say /abc_xyz/tom/install/

how can I check by running a script in the install directory that abc_xyz is a symbolic link. I know by using

if [ -h /abc_xyz ] we can test if abc_xyz is a symbolic link. But by sitting in a subdirectory of this directory, how can we check if the parent is a symbolic link.

Thanks in advance

anomie · 10-05-2005, 05:32 PM

How about:

Code:

if [[ -h . ]] ; then something ; fi

That's if all you want to evaluate is the parent directory.

Or:

Code:

while [[ $( cd ..; pwd; ) != '/' ]] ; do cd .. ; done
if [[ -h . ]] ; then something ; fi

The while loop will get you to the subdirectory that is an immediate child of /. Then it will perform the symlink test.

You might want to launch a child shell to perform that test if you're not keen on leaving the current directory.

compnovice · 10-05-2005, 07:05 PM

I want to check for the symbolic link in the middle of a complex shell script. I should not change the current directory. All I have is a variable with the complete path say /home/harry/abc_xyz/tom/install/ . I initially thought of tokenizing the string with "/", but I am not sure how we can tokenize strings in linux scripts.

Anomie, How can I launch a child shell to do that? Thanks for your reply.

anomie · 10-05-2005, 09:09 PM

Here is one script called symlink-test

Code:

#!/bin/sh

while [[ $( cd ..; pwd; ) != '/' ]]
  do cd .. 
done

if [[ -h . ]] 
  then exit 1
fi

exit 0

And here is your main script:

Code:

#!/bin/sh

doing stuff....
doing stuff....

# Test if top-level parent directory is symlink
sh symlink-test

# Evaluate exit code from symlink-test
if [[ $? -eq 1 ]]
  ISSYMLINK=yes
else
  ISSYMLINK=no
end-if

doing stuff....
doing stuff....

exit 0

Does that answer your question? Even though symlink-test will be cd-ing up to the parent directories, your main script should stay put and never leave its directory.

compnovice · 10-06-2005, 08:32 AM

The problem I am having is suppose I have a symbolic link say

ln -s /abc/xyz abc_xyz

now I have a variable set to say /home/tom/abc_xyz/install/config/

now from the main script if I echo the 'pwd', it shows /abc/xyz/install/config/ and not the whole path. And by using "cd .." I am not able to get to the symbolic link.

Thanks

anomie · 10-06-2005, 10:52 AM

Is there any constant information you know about the directory you want to test as a symlink? You either need to know the name of the directory you want to test, or you need a way to know where it will fall in the folder/subfolder hierarchy.

Without that there isn't a good way to test for it.

compnovice · 10-06-2005, 11:58 AM

I have a varibale say $completePath = /home/tom/abc_xyz/tom/install/. From this I need a way to find out that the dir /home/tom/abc_xys is a symbolic link. I was just wondering if there is a way to parse the string.

anomie · 10-06-2005, 12:25 PM

I am still not clear what information you know going into this. Do you always know that abc_xyz is the directory you want to test as a symlink?

If so, try

Code:

PATHTOTEST=`echo $COMPLETEPATH | sed 's/abc_xyz.*/abc_xyz/'`

That will truncate everything after the 'abc_xyz' and assign it to PATHTOTEST. Then you can evaluate that.

compnovice · 10-06-2005, 05:36 PM

I see what you are saying. Sorry for not making myself clear before. I dont know where exactly the symbolic link "abc_xyz" will be present in the complete path. So, I need to check each parent directory in the variable.

I wonder if there is a way, to parse the string with "/" delimiter, that would make my job easier.

anomie · 10-06-2005, 05:42 PM

Well, as long as you know that the directory will always be called abc_xyz, then my previous post should work for you.

After assigning that value to PATHTOTEST, it is a simple test of

Code:

if [[ -h $PATHTOTEST ]]

compnovice · 10-06-2005, 05:44 PM

Oops, "abc_xyz" is not a constant, it changes. I just gave an example

anomie · 10-06-2005, 05:59 PM

So would you like to check each level of the parent directories along the way? If so, here's a rewrite of symlink-test:

Code:

#!/bin/sh

while [[ $( cd ..; pwd; ) != '/' ]]
  do cd .. 

  if [[ -h . ]] 
    then exit 1
  fi
done

exit 0

Now it will check each directory as it goes up. And if it hits a symlink it will exit with a code of 1.

I am sure you could write something to parse $COMPLETEPATH using cut or awk as well. Lots of ways to accomplish the same task in *nix.