Why cd // goes to /

netpumber · 12-27-2016, 07:20 AM

Accidentally i typed cd // and it went me to / dir and bash line changed to

[username@linux-pc //]$ <-- double slashes

Tried the same with cd /// , cd //// but then it went back to normal

[username@linux-pc /]$ <-- one slash

Is this happening to everyone ?

bbuske · 12-27-2016, 07:46 AM

Have tried it myself on openSUSE 42.2 and it does exactly the same. Running ls on it shows that it is the same as / though.

Interesting finding.

rknichols · 12-27-2016, 09:14 AM

In all cases, the directory you are actually in is "/". See the output from "/bin/pwd".

Your shell keeps track internally of the path to your CWD, and "//" is mostly equivalent to "/". This internal path can be significant when symbolic links are involved. Try running the following 4 commands:

Code:

ln -s /etc /tmp/myetc
cd /tmp/myetc
pwd
/bin/pwd

Now try "cd ..". Your shell will move up on its internal path and put you in "/tmp", while the actual parent of "/etc" is "/".

Contrast this with:

Code:

cd /tmp/myetc
cd -P ..

The "-P" tells cd to follow the physical path, and it will put you in "/".

dlb101010 · 12-27-2016, 09:45 AM

Nice explanation. I've done that typo myself, ending up in '//' that was actually '/' and wondered what was going on. Thanks, now I know.

(BTW, if I'm following things right, shouldn't the fourth line in your first code example should be '/tmp/myetc'?)

Dave

bbuske · 12-27-2016, 09:47 AM

Yeah nicely explained indeed!
Rep for you.

rknichols · 12-27-2016, 09:49 AM

Quote:

Originally Posted by dlb101010

(BTW, if I'm following things right, shouldn't the fourth line in your first code example should be '/tmp/myetc'?)

No, "/bin/pwd" is a system command that will show your current working directory independent of what your shell has stored. That's in contrast with just "pwd", which is a shell built-in.

pan64 · 12-27-2016, 09:58 AM

Code:

user@host:/tmp/bash-4.4$ cd //
user@host://$ echo $PWD
//
user@host://$ cd ///
user@host:/$ echo $PWD
/

it is implemented that way in bash, but I don't know why.
what is more interesting:

Code:

user@host:/$ cd //
user@host://$ zsh
user@host // % echo $PWD
//
user@host // % cd //
user@host / % echo $PWD
/

hydrurga · 12-27-2016, 11:09 AM

// can be interpreted by a POSIX implementation in an implementation-defined manner.

See here for a couple of links to the relevant POSIX sections: https://askubuntu.com/questions/2745...-a-path/274517

Bash maintains the double forward slashes in case the particular implementation using Bash actually treats these as different from a single forward slash.