41

I just want to write a script which changes my directory.

I put the below commands in the file /home/alex/pathABC

#!/bin/sh
cd /home/alex/Documents/A/B/C
echo HelloWorld

I did chmod +x pathABC.

In the terminal, while in /home/alex, I run ./pathABC, but the output is just HelloWorld and the current directory is not changed.

So what is wrong?

72

As others have explained, the directory is changed in the child process of your script, not in the terminal process from which the script is called. After the child process dies, you are back in the terminal which is left where it was.

Several alternatives:

1. Symbolic link

Put a symlink in your home to the long path you want to easily access

$ ln -s /home/alex/Documents/A/B/C ~/pathABC

then access the directory with:

$ cd ~/pathABC

2. Alias

Put an alias in your ~/.bashrc:

alias pathABC="cd /home/alex/Documents/A/B/C"

(from here)

3. Function

Create a function that changes the directory, the function runs in the process of your terminal and can then change its directory.

(from here)

4. Avoid running as child

Source your script instead of running it. Sourcing (done by . or source) causes the script to be executed in the same shell instead of running in its own subshell.

$ . ./pathABC

(from here and here)

5. cd-able vars

Set the cdable_vars option in your ~/.bashrc and create an environment variable to the directory:

shopt -s cdable_vars
export pathABC="/home/alex/Documents/A/B/C"

Then you can use cd pathABC

(from here)

  • 14
    Now I understand the usage of source! I always wondered why I do source .bashrc and not bash .bashrc – hytromo Jun 11 '14 at 12:05
  • Option 3 worked great. I just defined a function go_to_wherever() { cd my/directory } at the beginning of my script. Called it before running the operations in that directory. – i2097i Jan 28 '17 at 20:13
  • > 5. cd-able vars -- isn't it cd $pathABC ? – loxaxs Jul 2 '17 at 9:56
7

When you run script in a terminal, a child process runs. In this child program ie your script will change to whatever directory specified. But in the parent process ie where you run the script is still in the old path. OR simply we can say:

The scope of cd command is only for child process not parent

  • 2
    Adding to this, @alex to achieve the effect you are looking for, execute the script within the parent process by sourcing it: either . pathABC or source pathABC. – zwets Jun 11 '14 at 9:26
4

You are making a thinking error. While the current shell stays in the same directory, the script has moved to the new directory.

You could see that by creating another script in the new directory, and running it from your script, after it has changed directory:

#!/bin/sh
cd /home/alex/Documents/A/B/C && ./another_script.sh # (if it is executable)

The second script would run from the new directory.

HelloWorld 

is just the output of the script.

  • 3
    HelloWorld is not "returned" to the parent shell, it's output to the standard output – Mog Jun 11 '14 at 12:01
  • Might be clearer if you just run pwd in the new directory, instead of adding a whole new script to the situation. – wjandrea Jul 24 '18 at 21:17
0

Because hello world is just a trace statement, let's try this:

Create bash script file cd.sh containing:

#!/bin/bash
echo "/home/mike/Documents/A/B/C"
  • The .sh extension is an older convention of giving bash script filenames an extension. It's purely cosmetic and usually unnecessary. However in this case it's important to differentiate from the core cd command.

Mark the bash script file executable using:

chmod a+x cd.sh

Now run the file:

$ cd $(./cd.sh)
bash: cd: /home/alex/Documents/A/B/C: No such file or directory
  • cd we all know.
  • $(...) executes command inside parenthesis and returns output.
  • If cd.sh was in your path you don't need to specify where it is. We prefix with ./ to specify the command is in the current directory.
  • The echo output from the cd.sh script is sent back to the parent via the $(...). The parent (our shell prompt) uses this output and passes it to the Linux cd command.

As others have mentioned a child process can't change the parent's directory. This is one way the child can tell the parent where to go after the process ends.

  • @wjandrea That's what you get for coding on a phone! Just got home, I'll fix it up. Thanks. Um just checked and it works fine. Maybe it's your 14.04 version I read about an hour ago or so? – WinEunuuchs2Unix Jul 24 '18 at 22:51
  • Well, you totally changed the script. Previously it was just one command: cd /home/mike/Documents/A/B/C, which didn't produce any output. Now it's echo "/home/mike/Documents/A/B/C", which does produce output. – wjandrea Jul 25 '18 at 1:01
  • @wjandrea True, I also totally changed the way of calling the script too. Instead of a simple ./cd.sh it's now cd $(./cd.sh) but it accomplishes the goal of the child changing the parent's current directory. Yes it's unconventional but it's another way of doing it that I hope people find interesting. – WinEunuuchs2Unix Jul 25 '18 at 1:26

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