Question

10

Why does cd ~k (& tab) expands to cd ~kernoops when I already have a folder named "~kernel-ppa" in pwd?

rated 0 times [ 10] [ 0] / answers: 1 / hits: 2023 / 3 Years ago, thu, may 13, 2021, 8:06:10

I have a folder named ~kernel-ppa inside ~/Downloads.

aditya@aditya-desktop:~$ cd Downloads/

aditya@aditya-desktop:~/Downloads$ ls

~kernel-ppa

Now when I type cd ~k and press Tab for automatic expansion, the shell expands it to cd ~kernoops/ instead of cd ~kernel-ppa/ although the folder with same starting characters is already present.

For automatic expansion to work, I need to escape it with . Thus using cd ~k and pressing Tab correctly expands it to cd ~kernel-ppa/. Even using cd and pressing Tab does the trick.

Why is it so and why do I need to escape? Moreover, what am I escaping since even ~ is not required for automatic expansion?

If I go with the flow and run cd ~kernoops/ and press Enter, the terminal status changes to //:

aditya@aditya-desktop:~/Downloads$ cd ~kernoops/

aditya@aditya-desktop://$ pwd

//

aditya@aditya-desktop://$ ls

bin   cdrom  etc   initrd.img  lost+found  mnt  proc  run   srv  tmp  var

boot  dev    home  lib         media       opt  root  sbin  sys  usr  vmlinuz

aditya@aditya-desktop://$

This looks like the / directory, but pwd says it is //. What exactly is it?

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answered 3 Years ago quivedge · Accepted Answer

As you know, ~ expands to your home directory. But what you seem to have missed is that ~john expands to the home directory of the user named "john".

Check your /etc/passwd file:

% grep ker /etc/passwd

kernoops:x:107:65534:Kernel Oops Tracking Daemon,,,:/:/bin/false

It has a "system user" named kernoops (for internal bug reporting reasons). So when you type cd ~kTab the shell gives preference(1) to user name expansion before local directories expansion, and you have cd ~kernoops. Now it results that user "kernoops" home dir is /, so it cds to it.

In my shell, zsh, I have no double slash(2):

[:/] % cd ~kernoops/ 

[:/] % pwd

/

[:/] % cd //

[:/] % pwd

/

As an aside, this directory name is not well thought. It will need triple care in scripts and whatever. The only worst idea I can think is embedding a tab in it...

Footnotes:

(1) In zsh, even if I have a directory named ~xdir and no user starting with x; doing cd ~xTab does not expand and not quoting the ~ gives error:

[:~/tmp/x] %  mkdir ~xdir

[:~/tmp/x] % ls

~xdir

[:~/tmp/x] % cd ~xdir  

zsh: no such user or named directory: xdir

[:~/tmp/x] 1 %

(2) I seem to remember that posix made an exception for the initial // in a path --- it should be maintained because some old unix variant (I used the apollos with Domain/OS that had that) used //machine-name/... to seamless access other machines' filesystem in the local network (security was not invented yet). So probably bash is right here. If you do cd /// you will have the normal / in both shell, though.

Yes, found on unix.se!