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Old 02-11-2009
usfish usfish is offline
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problem about '..' in bash
There is an interview question about UNIX bash:

Some shells like bash try to make '..' always work propery, namely, from home directory, cd ../$USER will place you in your home directory. Does bash always get this behavior correct?

Anyway can provide any example that bash doesnt work well?

Thanks!
Last edited by usfish; 02-11-2009 at 02:34 AM..
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Old 02-11-2009
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cfajohnson cfajohnson is offline Forum Advisor  
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Quote:
Originally Posted by usfish View Post
There is an interview question about UNIX bash:

Some shells like bash try to make '..' always work propery, namely, cd ../$USER will place you in your home directory. Does bash always get this behavior correct?

Anyway can provide any example that bash doesnt work well?

"cd ../$USER" will not place you in your home directory unless you are in a directory on the same level as your home directory.

You may be thinking of:


Code:
cd ~user

That will not work with a variable unless you use eval:


Code:
eval "cd ~$USER"

To go to your home directory, use cd with no directory.
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Old 02-11-2009
usfish usfish is offline
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Quote:
Originally Posted by cfajohnson View Post

"cd ../$USER" will not place you in your home directory unless you are in a directory on the same level as your home directory.

You may be thinking of:


Code:
cd ~user

That will not work with a variable unless you use eval:


Code:
eval "cd ~$USER"

To go to your home directory, use cd with no directory.
Hi, thank you for your prompt response. I missed that condition. It is from the home directory and you type "..", and they meant to ask about ".." instead of $USER I guess.

I think there might be chance that bash fails on symbolic link?
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Old 02-11-2009
cfajohnson's Avatar
cfajohnson cfajohnson is offline Forum Advisor  
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Quote:
Originally Posted by usfish View Post
Hi, thank you for your prompt response. I missed that condition. It is from the home directory and you type "..", and they meant to ask about ".." instead of $USER I guess.

I think there might be chance that bash fails on symbolic link?

What do you mean by "fail"?

If you want to cd to the physical parent directory, use the -P option:


Code:
cd -P ..
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Old 02-11-2009
larryv larryv is offline
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hmmm
Quote:
Originally Posted by usfish View Post
There is an interview question about UNIX bash:
Funny, that looks an awful lot like one of the extra credit questions on my latest 6.033 (MIT Computer Systems Engineering) homework.

Let's clarify the problem.

Say we have some arbitrary directory at /some/long/path/name/, and say that our home directory is /home/me/.

Now, we do this:

Code:
ln -s /some/long/path/name /foo/bar
ln -s /home/me /foo/baz

So now, assuming that /foo does not contain two directories called bar and baz, we now have two symbolic links, /foo/bar and /foo/baz, that link to /some/long/path/name and /home/me, respectively. If we perform the following:

Code:
bash
cd /foo/bar
cd ../baz

we should end up in /foo/baz, which is really /home/me, because bash traced .. back up to /foo, not to /some/long/path/, as tcsh does (if I'm not mistaken; if not, it used to).

Ultimately, the question is, does bash always get this behavior correct? When cd-ing to another directory via a symlink, does cd .. always get you back to the directory that contains the symlink?
Last edited by larryv; 02-11-2009 at 06:50 PM.. Reason: clarify final sentence
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