Lab 06 - Dotfile Installer Script

• Lab Procedure
• Part 1 - bash aliases
• Part 2 - Dotfile Installer Script
• Part 3 - Retrospective
• Part 4 - Usage Guide
• Extra Credit - Improvements
• Submission
• Rubric
• getopts and Error Handling

Lab Procedure

Make sure to return to the AWS Learner Lab page (link in Pilot if you forgot to bookmark it) and hit “Start Lab” to turn on your sandbox / AWS instance.

Use ssh to connect to your AWS Ubuntu instance.

Go to the folder that contains your repository (likely named ceg2350-yourgithubusername).

Create a new directory, Lab06.

Create a file named README.md in the Lab06 folder. The Lab 06 Template can be copied from this link:

• https://raw.githubusercontent.com/pattonsgirl/CEG2350/refs/heads/main/docs/Labs/Lab06/LabTemplate.md

You may refer to additional resources outside of the recommended resources provided.

Any resource that you use that contributes to your understanding of exercises in this lab should be cited in the Citations section of your lab answers. To add citations, provide the site and a summary of what it assisted you with. If generative AI was used, include which generative AI system was used and what prompt(s) you fed it.

If you make mistakes with commands in the lab, note them! Writing down what went wrong and what the correction was will significantly help your learning journey. If you cannot find a correction, it will help the TAs or myself understand what point you reached and determine some potential solutions.

Part 1 - bash aliases

Craft an alias with a name of your choice that pipes a fortune to a cowsay cow of your choice (-f flag)

Craft an alias with a name of your choice to something “fun”. Checkout these as suggestions. You may need to install these programs first with apt.

• curl wttr.in
• have cat use lolcat instead
• asciiaquarium

Add the aliases to a file named .bash_aliases in your user’s home directory.

Read through the .bashrc file in your user’s home directory for a section that is relevant to “enabling” usage of the .bash_aliases file. Copy and paste the snippet into your lab template and describe what it does.

Confirm that your aliases continuously work as long as the conditions are met.

Copy your .bash_aliases file to your GitHub repository in your Lab06 folder.

You may delete the .bash_aliases file in your user’s home directory as needed through this lab.

Resources

• How to create bash aliases - linuxize

Part 2 - Dotfile Installer Script

Your tasking is to write a script that sets up your user account to use your .bash_aliases To accomplish this, you will create an “installation” script that accomplishes these taskings.

WARNING

You must have a minimum of 3 (THREE) COMMITS made for this script. Your commit messages must describe what’s currently working / tested. When (after which steps / testing) you make a commit is your choice. Your commits must demonstrate an incremental building process - a bulk dump and then making a spelling change or two will not get you out of the penalty in the rubric.

END WARNING

1. Create a script named dotinstall in your Lab06 folder.

2. Create a function called printHelp. printHelp should output the following:

Usage: dotinstall [-OPTION] [ARG]
  -s setup - attempts to create a symbolic link .bash_aliases file to user's home directory
  -d disconnect - removes symbolic link
  -a append - adds a new alias to .bash_aliases file
  -r remove - removes an alias from .bash_aliases file

1. Use getopts to read in options and save arguments that correlate with options. getopts should support the following options in the OPTSTRING

   • -h
     • call printHelp function and exit script
   • -s
     • calls function to attempt to create a symbolic link between the .bash_aliases in the Lab06 folder to a .bash_aliases in the user’s home directory
     • if .bash_aliases already exists, prompt the user to confirm the most appropriate action before overwriting the existing file
   • -d
     • calls function to remove symbolic link from user’s home directory
   • -a
     • is followed by an argument - a string containing an alias
     • calls a function to append the given alias to .bash_aliases
   • -r
     • is followed by an argument - a string containing an alias name
     • calls a function to search for and remove the alias of the name from .bash_aliases
     • user should be notified if no matching alias was found
   • \?
     • use as case when option is not part of OPTSTRING
     • call printHelp and exit script

# Sample runs of working script

$ bash dotinstall -h
Usage: dotinstall [-OPTION] [ARG]
  -s setup - attempts to create a symbolic link .bash_aliases file to user's home directory
  -d disconnect - removes symbolic link
  -a append - adds a new alias to .bash_aliases file
  -r remove - removes an alias from .bash_aliases file

$ bash dotinstall -s -a 'alias ls="ls -lah"'
No .bash_aliases file found in /home/ubuntu
Creating symbolic link in /home/ubuntu named .bash_alaises
Adding alias to .bash_alaises
User should the following to reload the shell:
   source ~/.bashrc

$ bash dotinstall -s -a "alias ls=\"ls -lah\""
No .bash_aliases file found in /home/ubuntu
Creating symbolic link in /home/ubuntu named .bash_alaises
Adding alias to .bash_alaises
User should the following to reload the shell:
   source ~/.bashrc

$ bash dotinstall -r ls
Found alias for ls in .bash_aliases
Alias for ls removed from .bash_aliases

$ bash dotinstall -d 
Removing symbolic link in /home/ubuntu named .bash_alaises
User should the following to reload the shell:
   source ~/.bashrc

$ bash dotinstall -z
Option not supported.
Usage: dotinstall [-OPTION] [ARG]
  -s setup - attempts to create a symbolic link .bash_aliases file to user's home directory
  -d disconnect - removes symbolic link
  -a append - adds a new alias to .bash_aliases file
  -r remove - removes an alias from .bash_aliases file

Resources Before panicking, keep in mind that getopts is mostly a while loop iterating through arguments with a switch statement to define what to do on finding certain options. Play with the demos linked below before diving all in. Plan plan plan!

• getopts-basics.sh
• cfgetopts.sh
• getopts tutorial - shellscript
• breaking down how getopts works - assertnotmagic
• parse Arguments In Bash Scripts Using getopts - ostechnix
• Passing Arguments to Bash Functions - linuxize
• ln Command in Linux - linuxize

Part 3 - Retrospective

1. How would you explain getopts to a friend?
2. What did you get stuck on while working on this script? How did you overcome it?
3. What feature would you add to this script?

Part 4 - Usage Guide

Fill out the Usage Guide section in your lab template. It should contain a minimum of the following:

1. Information on your script’s purpose
2. Information on what is in .bash_aliases
3. Examples of script usage and output

Resources

• GitHub markdown cheat sheet

Examples of bad README / Usage Guides:

• bash wordle
  • as discussed in class there was a hidden dependency of a word file, we needed to make it executable, and what if you didn’t know how to play wordle?

Examples of good README / Usage Guides:

• pokeget
  • this is far more thorough than what you are writing, but note here how much detail is included.

Extra Credit - Improvements

Add a feature to the dotinstall script. Ideas:

• If there is more than one alias name that could be deleted, output the options to the user - ask them to be more specific and exit or prompt the user to pick one in the moment
• Test the alias before adding it to .bash_aliases. If its use doesn’t error, then add it. If it does, output the error to the user and exit so that they can fix it before they run the script again or prompt them to provide an alternative
• If an alias or command already exists with the same name as the desired alias, prompt the user that the given alias already exists and exit.

Add notes to your documentation about your added feature and show examples of it in action.

Submission

1. Verify that your GitHub repo has a Lab06 folder with at minimum:

   • README.md
   • dotinstall
   • .bash_aliases

2. In the Pilot Dropbox, paste the URL to the Lab06 folder in your GitHub repo

   • URL should look like: https://github.com/WSU-kduncan/ceg2350-YOURGITHUBUSERNAME/tree/main/Lab06

Rubric

Your files should be cleanly presented in your GitHub repository. Citations should be included as needed. Include which generative AI system was used and what prompts were used if generative AI was used.

Rubric

getopts and error handling

I don’t not require any error handling outside of the sample program runs provided. However…

If you are reading this, you may have noted that getopts still doesn’t solve all user abuse cases by default.

For example, getopts can have a hard time “detecting” a missing argument after an option. bash dotinstall -s -d​ would not “count” as -r missing an argument, because OPTARG would read -d as the argument for -s. Fun right?

There are many ways to detangle this problem, some using getopts. You could play some quick games before running getopts, such as checking number of arguments passed… It isn’t failsafe, but it would help.

So let’s use what we have - stored values in variables. And we have an ability to check if those values contain anything… catch my drift? Check out the second answer in this post: https://unix.stackexchange.com/questions/50563/how-can-i-detect-that-no-options-were-passed-with-getopts

There are games you can play within the case statement to do this check, but it’s a little clunky. If you’re curious: https://stackoverflow.com/questions/43425556/getopts-behaves-not-as-expected-when-option-parameter-is-missing