CMSC 216 Exercise #5 Spring 2019
Shell Jr (”Shellito”) Due: Tue Apr 23, 2019, 11:30PM
1 Objectives
To practice fork() and exec by implementing a very simple shell.
2 Overview
The first thing you need to do is to copy the directory shelljr we have left in the grace cluster under the exercises
directory. Remember that you need that folder as it contains the .submit file that allows you to submit.
3 Specifications
For this exercise you will implement a very simpliflied shell. A shell is a C program that executes commands
by forking itself and using exec. We have been using tcsh, but there are other shells like ksh, sh, bash, etc. The
name of our shell is shell jr .
Unlike other assignments for this course, you can work together with other classmates, but you may NOT
exchange any code.
4 Shell Jr Functionality
Your shell will have a loop that reads command lines and process them. The prompt for your shell will be
”shell jr: ”. The commands your shell must handle are:
1. exit - When the user enters the exit command the shell will stop executing by calling exit(). Before
executing exit, the shell will print the message ”See you”.
2. hastalavista - Has the same functionality as exit.
3. cd - This command changes the current directory. You can assume the user will always provide a directory
as an argument.
4. A command with a maximum of one argument (e.g., wc location.txt). That means your shell should be
able to handle commands like pwd, date or wc location.txt .
5 Requirements

代做CMSC 216作业、代写Shellito留学生作业、C/C++语言作业代写
1. You must NOT use an exec* function to implement the functionality associated with the commands
exit, hastalavista, and cd. For other commands, you must create a child (via fork()) and use execvp() to
execute the command.
2. If the user provides an invalid command, the message ”Failed to execute ” followed by the command
name should be printed. In this case the child will exit returning the error code EX OSERR. Use printf
to display the message and flush the output buffer (e.g., fflush(stdout)). Note that the shell is not terminated
by executing an invalid command.
3. You don’t need to handle the case where the user just types enter (you can assume the user will always
provide a command).
4. Make sure you use printf to print the shell prompt and that you flush the buffer.
5. It is your responsibility to verify that your program generates the expected results in the submit server.
1
6. You must use execvp (and no other exec* system call).
7. Your code must be written in the file shell jr.c.
8. You may not use dup2, read, write, nor pipes.
9. You may not use system() in order to execute commands.
10. You can assume a line of input will have a maximum of 1024 characters.
11. Provide a makefile that builds an executable called shell jr. Name the target that builds the executable
shell jr . Feel free to add any other targets you need.
12. All your C programs in this course should be written using the compiler gcc, with the options defined
in the gcc aliases info.txt file. This file can be found in the info folder of the public grace account.
13. Your program should be written using good programming style as defined at
http://www.cs.umd.edu/~nelson/classes/resources/cstyleguide/
14. Common error: If you get the submit server message ”Execution error, exit code 126” execute ”make
clean” before submitting your code.
15. Common error: To forget to return the correct value (e.g., 0) in your code.
16. Your C program representing your shell does not take command line arguments. That is, the main
function is defined as:
int main() { }
17. When you see that execvp relies on argv that means it uses an array of strings (argv is not the parameter
associated with command line arguments). Just initialize argv with an array of strings and pass it to
execvp.
18. Your shell should exit when end of file is seen. This explains why public tests do not have exit nor
hastalvista as the last command.
19. ShellJr exercise relies on Standard I/O, NOT unix I/O.
20. ShellJr takes a maximum of two arguments (e.g., wc location.txt). You can ignore any other values
provided after the second argument. For example, if someone enters wc location.txt bla bla will be
ignored and the command will be processed successfully.
21. For exit and hastalavista you can ignore any values provided after the command (just exit the shell).
22. For cd you can ignore any values provided after the directory name. For example, cd /tmp bla will
change the current directory to /tmp.
23. If an invalid directory is provided to the cd command, your shell should print an error message similar
to:
"Cannot change to directory <DIRECTORY_HERE>"
24. Do not use signals.
2
6 How to Start
You should start by creating a loop that reads lines and displays them. Then you should begin to process
each command (starting with the exit and cd commands). You are free to process each line any way you
want, however, reading a whole line using fgets and then processing the line using sscanf could make things
simpler. Keep in mind that if sscanf cannot read a value into a string variable, it will not change the variable.
This could help you identify when a command has an argument or not.
7 Submitting your assignment
1. In the assignment directory execute the command submit.
2. Your assignment must be electronically submitted by the date and time above to avoid losing credit. See
the course syllabus for details.
8 Grading Criteria
Your assignment grade will be determined with the following weights:
Results of public tests 28%
Results of release tests 72%
9 Academic integrity statement
Please carefully read the academic honesty section of the course syllabus. Any evidence of impermissible
cooperation on assignments, use of disallowed materials or resources, or unauthorized use of computer accounts,
will be submitted to the Student Honor Council, which could result in an XF for the course, or suspension
or expulsion from the University. Be sure you understand what you are and what you are not permitted
to do in regards to academic integrity when it comes to assignments. These policies apply to all students, and
the Student Honor Council does not consider lack of knowledge of the policies to be a defense for violating
them. Full information is found in the course syllabus– please review it at this time.

因为专业,所以值得信赖。如有需要,请加QQ:99515681 或邮箱:99515681@qq.com

微信:codinghelp

CMSC 216 Exercise #5的更多相关文章

  1. Android Studio Error:CreateProcess error=216

    Error:CreateProcess error=216, This version of %1 is not compatible with the version of Windows you' ...

  2. MIT 6.828 JOS学习笔记12 Exercise 1.9

    Lab 1中Exercise 9的解答报告 Exercise 1.9: 判断一下操作系统内核是从哪条指令开始初始化它的堆栈空间的,以及这个堆栈坐落在内存的哪个地方?内核是如何给它的堆栈保留一块内存空间 ...

  3. MIT 6.828 JOS学习笔记13 Exercise 1.10

    Lab 1 Exercise 10 为了能够更好的了解在x86上的C程序调用过程的细节,我们首先找到在obj/kern/kern.asm中test_backtrace子程序的地址, 设置断点,并且探讨 ...

  4. MIT 6.828 JOS学习笔记11 Exercise 1.8

    Exercise 1.8       我们丢弃了一小部分代码---即当我们在printf中指定输出"%o"格式的字符串,即八进制格式的代码.尝试去完成这部分程序. 解答: 在这个练 ...

  5. MIT 6.828 JOS学习笔记8. Exercise 1.4

    Lab 1 Exercise 4 阅读关于C语言的指针部分的知识.最好的参考书自然是"The C Programming Language". 阅读5.1到5.5节.然后下载poi ...

  6. MIT 6.828 JOS学习笔记9. Exercise 1.5

    Lab 1 Exercise 5 再一次追踪一下boot loader的一开始的几句指令,找到第一条满足如下条件的指令处: 当我修改了boot loader的链接地址,这个指令就会出现错误. 找到这样 ...

  7. MIT 6.828 JOS学习笔记5. Exercise 1.3

    Lab 1 Exercise 3 设置一个断点在地址0x7c00处,这是boot sector被加载的位置.然后让程序继续运行直到这个断点.跟踪/boot/boot.S文件的每一条指令,同时使用boo ...

  8. MIT 6.828 JOS学习笔记3. Exercise 1.2

    这篇博文是对Lab 1中的Exercise 2的解答~ Lab 1 Exercise 2: 使用GDB的'si'命令,去追踪ROM BIOS几条指令,并且试图去猜测,它是在做什么.但是不需要把每个细节 ...

  9. Stanford coursera Andrew Ng 机器学习课程编程作业(Exercise 2)及总结

    Exercise 1:Linear Regression---实现一个线性回归 关于如何实现一个线性回归,请参考:http://www.cnblogs.com/hapjin/p/6079012.htm ...

随机推荐

  1. Redis学习之二 数据类型和相关命令

    原文:https://www.cnblogs.com/lonelyxmas/p/9073928.html 如果还不懂安装的,请看 Windows环境下安装Redis Redis一共支持五种数据类型 1 ...

  2. 【easy】100. Same Tree

    判断两棵二叉树是否相等 /** * Definition for a binary tree node. * struct TreeNode { * int val; * TreeNode *left ...

  3. Charles 抓包的简单使用

    1.准备工具: 软件 Charles 手机 随意哪个现代手机 2.基本配置 安装Charles的电脑和手机在同一个局域网下, 点击手机上的和电脑练得同一个局域网的名字进行配置,里面有个代理,选择手动, ...

  4. 【原创】大叔问题定位分享(27)spark中rdd.cache

    spark 2.1.1 spark应用中有一些task非常慢,持续10个小时,有一个task日志如下: 2019-01-24 21:38:56,024 [dispatcher-event-loop-2 ...

  5. Codeforces 1083C Max Mex [线段树]

    洛谷 Codeforces 思路 很容易发现答案满足单调性,可以二分答案. 接下来询问就转换成判断前缀点集是否能组成一条链. 我最初的想法:找到点集的直径,判断直径是否覆盖了所有点,需要用到树套树,复 ...

  6. 1.arm的linux系统搭建

    从裸板到系统 一般是CPU内部有启动代码,如nuvoton的nuc900系列的芯片内部就有ibr程序,来控制启动过程,在usb启动时负责加载usb驱动,这样在pc端就可以识别到usb设备了,然后通过t ...

  7. vue路由守卫(全局守卫)

    router.beforeEach((to,from,next)=>{}) 回调函数中的参数, to:进入到哪个路由去, from:从哪个路由离开, next:函数,决定是否展示你要看到的路由页 ...

  8. 03-django模型(1)

    一.内容回顾 1.路由层 a.简单使用 b.有名分组 c.路由分发 d.反向解析 2.视图层 a.HttpRequest对象 常用的属性 常用方法 b.HttpResponse对象 响应三剑客 3.模 ...

  9. centos/linux/ubuntu在局域网上网

    前言:对于服务器来说,一般不会安装windowns系统,都是会安装类unix系统,在局域网或者在内网中,上网还是走代理上网 1.知道代理服务器的ip及端口 2.就两条命令 export  http_p ...

  10. Python内置模块之configparse

    一.概述 1.1.处理的文件形式 configparse 主要是用来处理类似于windows的 ini文件,这个文件的特点是有多个节(section),每个节下会存储多个k=v的值 如下配置 [har ...