Why doesn't "cd" work in a shell script?

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)

When you run script in a Terminal, a child process runs. In this child program i.e. your script will change to whatever directory specified. But in the parent process, i.e. 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.

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.