COMP2211 Creating a small shell interface

Chapter 5 Week 4: Creating a small shell interface You must submit your work to the appropriate submission point in Gradescope, which will be automatically marked. You should submit a single file called my_shell.c. Any other files you submit will not be marked. Although you do not need to include any additional supporting documentation or report, we do expect that your code is well written, tested and commented. Deadline: Week 6 of teaching. Thursday. 7th of Novem ber, 2024. 14:00. Extensions of up to 7 days are available. Weighting: 40% of the final module mark. In this coursework you will demonstrate: • An understanding of how processes are created by the operating system. • An understanding of file descriptors and their relationship to pipes and redirection. • The ability to program components of an operating system. Exercise In this coursework you will implement a simple shell for the xv6 operating system. This new shell will be implemented as a user space program. Before you attempt this coursework, make sure you have gone through most of the formative assessment exercises in the preceding weeks and convinced yourself that you know how various parts work. Where you have doubts, read relevant parts again and redo the coursework, which will make you spot new things and gain a deeper understanding of the material. You should provide your implementation in a new file called my_shell.c. You may use any helper functions provided by the xv6 kernel or user libraries. For each of the following items implement the feature into your shell, as you progress the features to implement become harder. This exercise should not require you to modify any file other than my_shell.c and the Makefile. To start with clone the repository containing the starting code and copy my_shell.c from it into your xv6 user/ directory: 29 $git clone https://github.com/mmikaitis/COMP2211-shell-template.git Modify the Makefile accordingly and rebuild xv6. It will not compile because my_shell.c is not finalised yet. However, it also contains some comments that should help in finishing the intended structure. Your task is to finish writing methods getcmd, run_command, and main, by inserting code 代写COMP2211 Creating a small shell interface in the indicated locations. No other methods should be developed. You are allowed to look at a default xv6 shell source code as well as learn about implementing shells using external resources. However, you are required to follow the unique structure outlined in the tem plate and are not allowed to supply any code which was not developed solely by yourself, starting from design stage. If you depend highly on some online tutorials then you need to declare the sources in the comments, which includes large language models. If you discuss early ideas with someone in the lab you should make sure that you don’t end up with similar code structure; you should not code together. Gradescope will run a similarity check of your submission and if the logic of the new code is reported to be similar to someone else’s, the submission will be carefully checked manually and reported as academic integrity violation if required. See this website for some detail. The similarity check is resilient to changing variables names or adding comments and new lines. Going through academic integrity interviews is a daunting process and may result in severe delays to your degree progression. It is better to submit nothing than submit the code that was partially developed by others. If you are behind, speak to the lab demonstrators and the module lead for guidance on best ways forward. Part 1: Execute simple commands (5 Marks) Implement the execution of simple commands. Your shell should be able to: • Prompt the user for a command by printing “>>>” as a command prompt. • Execute a command inputted to the command prompt. • Loop indefinitely until the shell is exited. • Handle the “cd” command—you will notice that this command will need to be treated as a special case. Do not forget to stress-test your simple shell before moving on to advanced features. The automatic marking will be testing it on various cases and marks will be deducted if it does not work when the same command is provided in a different format, such as with extra 30 spacing. For example, consider (note the amount and location of space characters which may impact the shell if they are not detected):$ echo hello world $echo hello world Once you are comfortable that you have tested your shell with any possible command that could reveal bugs, move on to implement the following advanced features. Part 2: Input/Output redirection (6 Marks) Implement Input/Output redirection. Your shell should be able to handle two element redirections. For example,$ echo "Hello world" > temp $cat < temp Part 3: Pipes (6 Marks) Implement pipes. Your shell should be able to handle two element pipelines. For example,$ cat README | grep github Part 4: Additional features (8 Marks) Implement the following advanced features:

1. Implement multi-element pipelines. For example, $ ls | grep test | cat
2. Implement non-trivial combinations of pipes and redirection. For example, $ ls | grep test | cat > myoutput
3. Implement the “;” operator that allows a list of shell commands to be given and executed sequentially. $ls | grep test | cat > myoutput; cat myoutput Marking Gradescope will run 26 test commands and award a mark out of 25. The commands that will be run are not disclosed and you are required to use creativity to think of various scenarios which may break your shell and test it thoroughly before submitting. 3 out of 25 marks 31 will be awarded to those who spot three especially tricky cases of specifying commands and implement their shells to get around them. There are many ways to type commands, some straightforward as shown above, and some not, such as when people type commands without using any spaces or with arbitrary number of spaces in various places. Your shell should be resilient to this ambiguity in specifying commands. Those students who spent more time in thinking about various test cases and check them will get more marks than those who only try a few straightforward commands listed above. Here are a few example commands running in the new completed shell to get you started: xv6 kernel is booting hart 2 starting hart 1 starting init: starting sh$ my_shell

mkdir tempdir ls . 1 1 1024 .. 1 1 1024 README 2 2 2292 cat 2 3 35080 echo 2 4 33960 forktest 2 5 16080 grep 2 6 38512 init 2 7 34424 kill 2 8 33888 ln 2 9 33712 ls 2 10 37016 mkdir 2 11 33952 rm 2 12 33936 sh 2 13 56504 stressfs 2 14 34816 usertests 2 15 179160 grind 2 16 49736 wc 2 17 36024 zombie 2 18 33288 my_shell 2 19 40032 console 3 20 0 tempdir 1 21 32 cd tempdir ../ls . 1 21 32 32 .. 1 1 1024 cd .. ls . 1 1 1024 .. 1 1 1024 README 2 2 2292 cat 2 3 35080 echo 2 4 33960 forktest 2 5 16080 grep 2 6 38512 init 2 7 34424 kill 2 8 33888 ln 2 9 33712 ls 2 10 37016 mkdir 2 11 33952 rm 2 12 33936 sh 2 13 56504 stressfs 2 14 34816 usertests 2 15 179160 grind 2 16 49736 wc 2 17 36024 zombie 2 18 33288 my_shell 2 19 40032 console 3 20 0 tempdir 1 21 32 echo hello hello echo hello hello cat README | grep xv6 xv6 is a re-implementation of Dennis Ritchie’s and Ken Thompson’s Unix Version 6 (v6). xv6 loosely follows the structure and style of v6, xv6 is inspired by John Lions’s Commentary on UNIX 6th Edition (Peer (kaashoek,rtm@mit.edu). The main purpose of xv6 is as a teaching cat README| grep xv6 xv6 is a re-implementation of Dennis Ritchie’s and Ken Thompson’s Unix Version 6 (v6). xv6 loosely follows the structure and style of v6, xv6 is inspired by John Lions’s Commentary on UNIX 6th Edition (Peer (kaashoek,rtm@mit.edu). The main purpose of xv6 is as a teaching

It is worth to note that the default xv6 does not pass all of our expected tests. For example: 33 xv6 kernel is booting hart 2 starting hart 1 starting init: starting sh $cd .$ cd . cannot cd . $mkdir temp$ cd temp $cd ..$ cd temp cannot cd temp $ Submission You are required to submit only my_shell.c. See Minerva.

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