cd Command Linux and Mystery Flags

Question

Platform: CentOS 6.2 Shell:tcsh

I'm playing around with cd for a BASH script, and noticed the wondrous cd - option, but was left with many questions...

1. Why the cd -? Isn't this redundant with cd ..?
   
   EDIT
   [As FatalError points out, these two commands don't do the same things... so the answer is "no"]
   
   
2. Can you delve farther back into your history with - flag, a la in a browser?
   
   e.g. When I type cd -, it takes me to my previous directory, but then if I enter that command again, it takes me to the directory I just came from, creating a sort of loop.
   
   Is a shorthand for going back multiple levels supported?
   
   EDIT
   I realize I can go back with cd .., but was hoping this could be a gateway to a less verbose deep back, e.g. cd -3 vs. cd ../../../ ... hopefully that clarifies what I'm asking....
   
   EDIT2
   As to the current feedback, while .. is a special directory, I don't see a reason why the built-in cd to the terminal couldn't use a shorthand for ../../ ... ../ e.g. cd ..5 or why the built-in also couldn't have a history (a la auto pushd/popd) that could be turned on and used like cd -3. I get that this could be somewhat of security/privacy risk, but I don't see how it's any worst than storing a command history, which most shells/terminals do.
   
   
3. The manpage for cd, accessible via man cd and help cd (it's the same for either command), only lists -L and -P flags.
   
   However when I type in cd --help it outputs Usage: cd [-plvn][-|<dir>]..
   
   Am I right in assuming the other flags and the - (back) option are nonstandard?
   
   
4. What are the -n and -v flags for?
   
   Both seem to take me back to my home directory, that's all I've been able to figure out via experimentation.

A quick read on web resources [1][2] offered just the same sort of info that the man page did and didn't answer my questions.

Note: The second Linux-centric resource above claimed cd only had two options (obviously not true in current CentOS) hence my assumption that this functionality could be non-standard.

Answer 1

1. cd - is not the same as cd ... The cd - command goes to the previous directory you were in. For example, if you're in /home/bob and then you run cd /var/log, then running cd - will take you back to /home/bob. cd .. on the other hand, always goes to the parent directory.

2. If you want to keep a history like that, I suggest checking out pushd and popd which will let you use a "directory stack":

   user@host:/etc/init.d$ pushd /var/log
   /var/log /etc/init.d
   user@host:/var/log$ pushd /tmp
   /tmp /var/log /etc/init.d
   user@host:/tmp$ popd
   /var/log /etc/init.d
   user@host:/var/log$ popd
   /etc/init.d
   

   As for stepping back multiple levels in the directory tree, there's no common way that I know of. .. isn't a feature of the shell, it's actually a special directory link in *nix that refers to the parent dir.

3. cd is a built in command, so it's flags and usage may vary by shell. But, in general the options to cd in bash on one system ought to be the same as on another system.

4. My bash shell doesn't list either of these flags... are you experimenting using bash or tcsh? If you're using tcsh you're essentially using a totally different command, so you probably want to run bash and mess with cd there.

EDIT:

According to the tcsh man page:

With -p, prints the final directory stack, just like dirs. The -l, -n and -v flags have the same effect on cd as on dirs, and they imply -p.

(You can check the section about dirs if you want to read the specifics). Looks like it's basically making it print the directory stack after the command runs:

host:43> pushd /etc/init.d
/etc/init.d ~ 
host:44> pushd /var/log
/var/log /etc/init.d ~ 
host:45> pushd /tmp
/tmp /var/log /etc/init.d ~ 
host:46> cd -p
~ /var/log /etc/init.d ~ 
host:47> cd -v
0       ~
1       /var/log
2       /etc/init.d
3       ~
host:48> popd
/var/log /etc/init.d ~ 
host:49> cd -v
0       ~
1       /etc/init.d
2       ~

both show the directory stack, but -v seems a little easier to read. The top of the stack (element 0) is the current directory, and 1 is where you'd go if you execute popd once, and so on.