Why does cd in backticks never work

Question

Possible Duplicate:
Why doesn’t “cd” work in a bash shell script?

Why does cd command in backticks or $(..) never change to the new directory. Any idea how to do it in a single command, that is capture any error and change directory.

[root@linux ~]# pwd
/root
[root@linux ~]# cmdMsg=`cd /tmp 2>&1`
[root@linux ~]# pwd
/root

score 3 · Answer 1 · answered Oct 23 '12 at 15:28

3

Because the backticks spawn a separate process and run separately. So it does cd in that process but doesn't change your current process's working directory.

If you just need to see if the command succeeded and you want to change directory you can check it's exit code:

cd /tmp
retval = $?

if [ $retval -gt 0 ]; then
    echo "cd failed"
fi

answered Oct 23 '12 at 15:28

Cfreak

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actually you can just do it in one step, i.e. `if ! cd /tmp; then echo "cd failed"; fi` – doubleDown Oct 23 '12 at 15:48
@doubleDown - indeed. I just wanted to be verbose so it was clear what was going on. – Cfreak Oct 23 '12 at 15:50

score 0 · Answer 2 · answered Oct 23 '12 at 15:28

0

because it cd's within the context of the new shell that you opened up to run your cd, try for example:

cmdMsg=`cd /tmp; pwd`
echo $cmdMsg

it will show you that you were in /tmp

answered Oct 23 '12 at 15:28

hexist

5,151
26
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score 0 · Answer 3 · answered Oct 23 '12 at 15:29

0

Separate the commands with with ; if you want to run it all in a single command.

For example:

cd /; ls; cd ~; ls; cd /var; ls

But the problem in your case is that cd is run in a newly spawned shell, which doesn't affect your current shell.

answered Oct 23 '12 at 15:29

sampson-chen

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what does this have to do with backticks? – Cfreak Oct 23 '12 at 15:30

score 0 · Answer 4 · answered Oct 23 '12 at 15:35

A child process cannot change the environment of its parent process.

pwd
`cd /tmp 2>&1`
pwd

Print working directory in current process.
Create a new child process.
Change to directory /tmp inside the child process (while redirecting stderr to stdout).
Exit the child process.
Print working directory in current process.

Why does cd in backticks never work

4 Answers4