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Exercise 3-B

Learning Objectives

Part 1

To begin (if you have not already done so), log into the ugrad system using your ugrad account name and password. You can do so by logging in to ugradx.cs.jhu.edu, or any machine ugrad1.cs.jhu.edu, ugrad2.cs.jhu.edu, … ugrad24.cs.jhu.edu. On a Mac or Unix/Linux machine, you will log in to ugrad from the command line using ssh.

ssh USERNAME@ugrad5.cs.jhu.edu

If your machine is running Windows, you will use PuTTy or ssh using Windows Powershell to connect.

Part 2

First, create a copy (clone) of the public repository for the class by taking the following steps:

1. In your ugrad account, type cd ~ to make sure you are in your home directory.

2. If you have not already done so, use git to clone the class example repository by typing:

   git clone https://github.com/jhu-ip/cs220-sp24-public.git
   

3. Type:

   cd cs220-sp24-public
   

   to enter the newly created directory (that is, folder), and then type ls to list the files present in that directory. Review the filenames that it shows and confirm that the files README and the exercises folder are present.

If you did not successfully complete the above steps, ask of a member of the course staff and/or post on Piazza.

Part 3

Now that you have a local copy of the git repo in your ugrad account, we want to make a separate temporary directory structure in your account where you can do some work.

1. Change back to your home directory by typing either cd ~, or just cd. It’s important that you’re no longer in your local copy of the repo for the next step, so type pwd to check the name of your current directory; you should see that you’re in the folder named /home/your_username_, e.g. /home/ips22004 or similar. If you need help getting there, raise your hand (via Zoom) so we can help, or post on Piazza.

2. Create a subdirectory named temp by typing the command mkdir temp.

Part 4

Now, copy a file from your local copy of the class repo into the directory you just created in part 3, then compile and test it. Here is how:

1. Copy hello_world.c from your local copy of the class repository into your personal folder by navigating into ~/temp (the folder you just created) using cd temp and then typing (Hint: using tab-completion will help here!):

   cp ~/cs220-sp24-public/exercises/ex03b/hello_world.c .
   

   The command above ends with a period (“dot”), and there must be a space before the dot. The dot in Unix stands for the current directory; in this command you’re expressing that the current directory is the destination for the copy you’re making.

2. Type pwd to confirm that you are still working in the folder named ~/temp, and then type ls to see that it now contains a copy of hello_world.c

3. Now, compile the source file named hello_world.c and create an executable file by typing:

   gcc -std=c99 -Wall -Wextra -pedantic hello_world.c
   

   This command should create a new executable file named a.out. (Type ls again now to confirm that the new file has been created.)

4. Execute the file you just created by typing ./a.out and seeing what is printed. The ./ to start the command above indicates to Unix that this program resides in the current directory. Unix/Linux does not look in this directory for commands by default, so without this, the command will not be found.

5. Now, make a copy of the hello_world.c file in the same folder, and name it hello_me.c. Here is how: Type:

   cp hello_world.c hello_me.c
   

   Note that the cp (that is, copy) command uses two arguments; the first is the source, the second is the destination. Type ls once more to confirm that you now have a new copy of the file in your folder.

6. Using the emacs text editor (or vim if you prefer), modify the new file so that rather than displaying “Hello, world!” when it is executed, it instead displays “Hello, $your name$!” (e.g., “Hello, Anna!” or “Hello, Xin!”). To do this using emacs, first type emacs hello_me.c to open the file for editing. Once you’ve made the appropriate modifications in emacs, you can save the file using Ctrl-x Ctrl-s, and exit emacs using Ctrl-x Ctrl-c.

7. Next, compile your new file by typing

   gcc -std=c99 -Wall -Wextra -pedantic hello_me.c
   

   , then execute it by typing ./a.out. Confirm that it behaves as you planned. If it does not, go back and re-edit the file, re-compile it, and re-run it until you get it to work.

Part 5

Wrap up the exercise by cleaning up your files, and logging out of the ugrad system, as follows:

1. While you do not want to remove or even modify the cs220-sp24-public folder (that is, your copy of our public class repo), you will no longer need to keep the temporary directory named temp that we created today, or any of the files you put inside it. To remove the temp directory, first navigate to your home directory (that is, the top-level folder in your account) by typing cd ~ or simply cd.

2. Once you are sure you are in the right folder, type rm -r temp to remove the temp folder and all of its contents. Note that rm is the remove command, and the extra -r flag indicates that you wish the remove command to be applied recursively, meaning to all subfolders within temp. Be very careful when executing any rm command in Unix/Linux; there is no undo button if you make a mistake and delete important files! If you want to verify deletion before removing files, use the -i option with rm.
   Danger

   Be careful around the rm command from here on. Once you remove a file/folder, there will not be a (straightforward) way to recover it!

3. Finally, log out of the ugrad system by typing exit.