Why Doesn't the Cd Command Work in My Shell Program

Why can't I change directories using cd in a script?

Shell scripts are run inside a subshell, and each subshell has its own concept of what the current directory is. The cd succeeds, but as soon as the subshell exits, you're back in the interactive shell and nothing ever changed there.

One way to get around this is to use an alias instead:

alias proj="cd /home/tree/projects/java"

LINUX CD command does not work in shell script

Use an absolute path or, even better, an environment variable.

cd ~/Desktop

cd command doesn't work as desired inside a shell script

I think there is one escape to much, change:

cd \""$d"\"

to:

cd "$d"

How come cd doesn't work in my shell script?

In order to make a script runnable you need to modify the permissions on the script so that it is executable.

The command to change permissions on Linux or UNIX is chmod.

chmod +x ./name_of_your_script

Will grant the current user permission to execute the script.

The #! at the start of your script indicates to the interactive shell that the script is to be interpreted by /bin/bash so you do not really need add an extention to the file name. However, it is a common convention to append .sh to shell scripts.

Student Shell - cd not working

It's true that you need to avoid forking, but you also need to avoid executing. There is no /bin/cd that programs call to change directories.

Instead of executing something, call the chdir system call with your path. If the user types cd /tmp, call chdir("/tmp")

The current directory is a property of each process (as the open files or the umask value) You cannot call a program to change your current dir, as a program is a different process and will change effectively its directory (not yours). That's the reason of not existing a cd external command and to have to make a system call to change it.

Why 'which -a cd' command doesn't give any output in linux?

Think about how shells and changing directories work: For each command you enter it will start a new process for the command. Changing directory only applies to the currently running process. If the cd command was executed as an external command, then it would run it its own process, change its process directory, and then the process would exit and the parent process (the shell) would not know anything at all what the child process did.

Therefore the cd command can only be internal to the shell. It has to be parsed and executed completely by the shell and its own process.