Homework 1: Basic Unix Shell Commands

This assignment focuses on using the bash shell to execute common Unix commands. Some of the questions are Unix commands you must figure out, and others are general questions about the particular Linux system you are using. Note: Unless otherwise specified, the answers to each question in Task 4 can be found entirely using commands shown in the lecture slides from the first week. You may use other commands if you like, but you should constrain yourself to those from lecture or from the Linux Pocket Guide textbook. Ask the instructor if you are unsure whether a particular command is allowed. For Task 3, there are reference cards posted on the course website but you are also allowed to google around. The goal of Task 3 is to become comfortable with using a command-line-based text editor by practicing, not to quiz you or challenge you to find the “answer.”

For Task 1 and Task 2 there is nothing to submit. For Tasks 3 and 4, you will fill out the provided task3.txt and task4.sh templates and submit your responses to Gradescope using the link on the course website.

Task 1: Log in to a Linux environment¶

First, log in to a Linux environment. You have several options to choose from here. Everyone should be able to install the CSE Virtual Machine (VM) Image. Other options include installing Linux on your machine, using one of the Linux computers in the CSE basement labs or using the CSE department’s attu Linux server using the ssh program. We refer you to the Working At Home link on our course home page for information on options available. If you aren’t able to successfully log in to a Linux environment, please contact us for help or ask a classmate.

If logged on to a Linux desktop environment (the CSE VM, a Linux machine in the basement), launch a Terminal window and a text editor from the Linux user interface, generally from the top left drop-down applications menu. You can usually find the terminal program under System Tools or Accessories. If logged on to attu, you can access editors like emacs or vim by typing them at the command line. You can also edit your text file on your own machine.

Task 2: Prepare a directory¶

We have set up a zip archive full of support files that you must download to your Linux environment. Do the following:

• Create a directory inside your home directory named 391.
• Download our file hw1.zip and save it into your new 391 directory. You can do this in one of two ways:
  1. By opening a web browser on your Linux environment, browsing to our course web site, clicking the Homework link, finding the link to hw1.zip, right-clicking it, choosing Save Link Target As…, and browsing to the hw1 folder;
  2. Or, by typing the following command into your terminal window, when the current directory is 391:

     wget https://courses.cs.washington.edu/courses/cse391/21sp/homework/hw1/hw1.zip
     

• Unzip the hw1.zip file’s contents into your hw1 folder. You can do this in one of two ways:
  1. By running a file browser/manager (in the CSE virtual machine you should have an icon that looks like a file cabinet that will open up a file manager) and browsing to the hw1 folder, then right or double-clicking on the hw1.zip file, and using the graphical unzipping program to extract the files;
  2. Or, by typing the following command into your terminal window, when the current directory is 391:

     unzip hw1.zip
     

If you did everything correctly, you should now have several files and directories within a hw1 directory, such as java/, website/, animals.txt, Burrot.java, numbers.txt, and song1.txt.

Task 3: Getting Comfortable with a Text Editor¶

The following are exercises and questions are meant to help you become more comfortable with a text editor that is built into the command line. You can choose either vim or emacs. It does not matter which editor you choose, but we recommend that you pick one and stick to learning it for the remainder of the quarter. While the answers to the questions themselves are relatively easy to find by simply looking them up, the real learning will come from you actually practicing these commands yourself. While we won’t be able to know whether you’ve really been practicing, this is not for our benefit, it’s for yours. We also recommend getting even more practice by writing the answers to your task3.txt and task4.sh files using this editor! 😊

Write your answers to the following questions on the indicated lines in the provided task3.txt file in the hw1 folder.

1. Which text editor are you choosing to use? emacs or vim?
2. From the hw1 directory, how do you open animals.txt in the text editor of your choice?
3. Practice moving your cursor around the file. Move your cursor up, down, left and right. Assuming your cursor is at the beginning of the first line of the file, what are the keystrokes to move your cursor to the end of the line and append the text “animal”?
4. Next, what are the keystrokes to move your cursor back to the front of the line and insert the word “animal”?
5. How do you save your changes to the file?
6. How do you exit the file and return back to your command line prompt in the shell?

Task 4: Linux Bash shell commands¶

For each of the numbered items below, determine a single bash shell statement that will perform the operation(s) requested. Each of your solutions must be a single one-line shell statement and should not use Linux’s multi-statement joining operators such as |, &&, ||, and ;. (We will learn about these next week.) Most of the questions below entirely use commands shown in the Lecture 1 and/or slides.

To test your commands, you should have unzipped hw1.zip into the current directory. You can assume you are in the hw1 directory when doing these problems.

In response to each question, you will provide the command that will perform the task described, not the output that the command produces. Write your commands on the indicated lines in the provided task4.sh file in the hw1 folder. For each of your answers, replace the line echo “not yet implemented” with your solution.

For example if a question asked you to list all the files in the current directory you would change:

function problem0 {
  # Type your answer to problem #1 below this line
  echo "Not yet implemented"
}

function problem0 {
  # Type your answer to problem #1 below this line
  ls
}

1. Copy the file MyProgram.java from the current directory to the java subdirectory.
2. List the files in the current directory, in “long listing format”.
3. List all files, including hidden files, in the /var directory, in reverse alphabetical order and long listing format. (Notice the slash in the directory!)

4. Rename the file Burrot.java to Borat.java.

   Hint: Renaming is done using the same command as moving.

5. Delete the files diff.html and diff.css. Note that your answer must be a single command and not multiple commands.

   Hint: Many commands can accept more than one parameter.

6. 🔍 Self Discovery: Set the file MyProgram.java to have a last-modified date of January 1, 2020, 4:15am.

   Hint: The man page for the proper command describes the timestamp 'STAMP' format to use. Look for this!

   Also note: Linux is case-sensitive when you are specifying file or directory names.

7. 🔍 Self Discovery: You can use a * (asterisk) as a “wild-card” character to specify a group of files. For example, *foo means all files whose names end with foo, and foo* means all files whose names begin with foo. You can use a wildcard in the middle of a file name, such as foo*bar for all files that start with foo and end with bar.

   List all web page files (files whose names end with the extension .html or .css) in the current directory. Note that the ls command can accept more than one parameter for what files you want it to list (e.g. ls website/ java/).

8. Copy all the text files (files whose names end with .txt) from the current folder to the java subdirectory.

9. The diff command outputs the differences between two files. Output the differences between lyrics.txt and lyrics2.txt. Notice the line differences from the first file argument begin with a left-pointing caret < and line differences from the second file argument begin with a right-pointing caret >. Gradescope will be picky about the order you provide lyrics.txt and lyrics2.txt to the diff command.

   Note: we use the diff command in the Gradescope autograder!

10. 🔍 Self Discovery: The cat command outputs the contents of a file to the terminal. The less command outputs the contents of a file to the terminal, page by page, pausing for you to press a key.

    Use whichever command is best suited to display the contents of the file lyrics.txt.

11. Display the contents of all files whose names begin with song and end with the extension .txt (e.g., song1.txt and song2.txt). Write a single command that displays all their contents concatenated.

12. 🔍 Self Discovery: The head and tail commands output only the first or last few lines (respectively) of a file to the terminal.

    Display only the first 7 lines of the file animals.txt from the current directory on the terminal.

Transferring files to your Local Machine from attu¶

If you are working in an ssh session connected to attu, you will likely want to transfer files from attu to your local machine so you can turn them into Gradescope. If you are working from the Linux VM, you have access to a browser within the VM. To transfer files, you can use the scp (secure copy) command which is like ssh + cp together! scp uses the following syntax:

scp <source-location> <destination-location>

For example, if you wanted to copy foo.txt from your home directory on attu to your current directory on your local machine, you would use the command:

scp <your_cse_id>@attu.cs.washington.edu:~/foo.txt .

If you wanted to copy the file foo.txt from your current directory on your local machine to your 391 folder in your home directory on attu, you would use the following command:

scp foo.txt <your_cse_id>@attu.cs.washington.edu:~/391

More information and tips on transferring files can be found at the top of the homework page on the course website.