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Bash moves in mysterious ways

Posted 12-04-2011 at 01:52 PM by druuna
Updated 12-23-2011 at 03:35 PM by druuna

Playing with the mv command I ran into this:

From a safe location create 2 Directories, create some files in one of the directories and enter that directory:

Code:

$ mkdir Temp_0{1,2}
$ ls -la
total 40
drwxr-x---  4 druuna internet  4096 Dec  4 20:16 .
drwxr-x--- 38 druuna internet 28672 Dec  4 20:16 ..
drwxr-x---  2 druuna internet  4096 Dec  4 20:16 Temp_01
drwxr-x---  2 druuna internet  4096 Dec  4 20:16 Temp_02

$ touch Temp_01/{foo,bar}
$ ls -la *
Temp_01:
total 8
drwxr-x--- 2 druuna internet 4096 Dec  4 20:17 .
drwxr-x--- 4 druuna internet 4096 Dec  4 20:16 ..
-rw-r----- 1 druuna internet    0 Dec  4 20:17 bar
-rw-r----- 1 druuna internet    0 Dec  4 20:17 foo

Temp_02:
total 8
drwxr-x--- 2 druuna internet 4096 Dec  4 20:16 .
drwxr-x--- 4 druuna internet 4096 Dec  4 20:16 ..

$ cd Temp_01/
$ pwd ; /bin/pwd
/home/druuna/Temp/Temp_01
/home/druuna/Temp/Temp_01

~/Temp/Temp_01 $ ls -la
total 8
drwxr-x--- 2 druuna internet 4096 Dec  4 20:17 .
drwxr-x--- 4 druuna internet 4096 Dec  4 20:16 ..
-rw-r----- 1 druuna internet    0 Dec  4 20:17 bar
-rw-r----- 1 druuna internet    0 Dec  4 20:17 foo

Nothing special this far all is where you expect it to be. Now the fun part.

Move the directory you are standing in to the other directory:

Code:

$ pwd ; /bin/pwd
/home/druuna/Temp/Temp_01
/home/druuna/Temp/Temp_01

$ mv ../Temp_01 ../Temp_02

No errors. But which directory are you presently in?

Code:

 $ pwd ; /bin/pwd
/home/druuna/Temp/Temp_01
/home/druuna/Temp/Temp_02/Temp_01

The build-in places you at /home/druuna/Temp/Temp_01. Sounds reasonable, that is where you cd-ed into.
But the binary version places you in home/druuna/Temp/Temp_02/Temp_01. Also sounds reasonable, that is where you moved yourself to.... Hmmmm.

You are actually standing in /home/druuna/Temp/Temp_02/Temp_01:

Code:

$ cd ..
$ pwd ; /bin/pwd
/home/druuna/Temp/Temp_02
/home/druuna/Temp/Temp_02

$ ls -la
total 12
drwxr-x--- 3 druuna internet 4096 Dec  4 20:19 .
drwxr-x--- 3 druuna internet 4096 Dec  4 20:19 ..
drwxr-x--- 2 druuna internet 4096 Dec  4 20:17 Temp_01

$ ls -l Temp_01/
total 0
-rw-r----- 1 druuna internet 0 Dec  4 20:17 bar
-rw-r----- 1 druuna internet 0 Dec  4 20:17 foo

Like I said: Bash moves in mysterious ways

Here's another example where pwd (the build-in) is "wrong":

Code:

$ mkdir Temp
$ cd Temp/
$ touch foo
$ ls -l
total 0
-rw-r----- 1 druuna internet 0 Dec  4 20:49 foo

$ rm -rf ../Temp/

$ pwd
/home/druuna/Temp/Temp

$ /bin/pwd
/bin/pwd: couldn't find directory entry in `..' with matching i-node

$ ls -l
total 0

$ cd ..
$ ls -la
total 32
drwxr-x---  2 druuna internet  4096 Dec  4 20:49 .
drwxr-x--- 38 druuna internet 28672 Dec  4 20:16 ..

The build-in pwd can be wrong and I would advise you to use /bin/pwd instead.

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