Question 20

export PATH=/new/dir:$PATH

Using the command `export PATH=/new/dir:$PATH` correctly adds the directory `/new/dir` to the existing PATH environment variable, ensuring that it is recognized in the current session and any child processes.

A) $PATH=/new/dir:$PATH

This option is incorrect because it attempts to assign a new value to the PATH variable without using the `export` command. As a result, the change will not be applied to the current shell environment or its child processes.

B) PATH=/new/dir:$PATH

While this option modifies the PATH variable, it does so without exporting it. Therefore, the change will only take effect in the current shell session and will not be available to any subprocesses created after this command is executed.

C) export PATH=/new/dir:$PATH

This option is correct as it not only modifies the PATH variable to include `/new/dir` but also exports this new value, making it accessible to the current shell and any subprocesses. This is the proper way to permanently add directories to the PATH in a session.

D) export $PATH=/new/dir:$PATH

This option is incorrect because it incorrectly uses the `$` sign when attempting to export the PATH variable. The `$` sign is used to reference the value of a variable, not to define or export it, leading to a syntax error.

E) export PATH=/new/dir; $PATH

This option is incorrect as it tries to export the PATH variable but then uses `$PATH` without any assignment or purpose. The command does not effectively add `/new/dir` to the PATH environment variable in a usable format.

Conclusion

The command `export PATH=/new/dir:$PATH` is the only option that correctly modifies the PATH variable and exports it for use in the current session and its child processes. All other options either fail to export the variable or contain syntax errors that prevent them from functioning as intended. Hence, option C is definitively the right choice.