[Solved] Lab 5 UNIX Shell

Purpose and rationaleThe purpose of this lab is to allow students to learn a user interface aspect (shell), how to interface to process management and some basic system calls. Please read the document closely.Lab 5 UNIX ShellA simple shell is a basic shell program that supports commands with I/O re-direction. Once, a user enters a command string (ended with a return key), your program should parse the command line and determines whether it has a regular command or contains I/O redirection signified by for output to a file or < for input from a file. The program has also 3 built-in commands: cd (change directory), pwd (print working directory), and exit (exit shell). The built-in functions are not executed by forking and executing an executable. Instead, the shell process executes them itself. All other command must be executed in a child process. Your shell is basically an interactive loop: it repeatedly prints a prompt csc60msh , parses the input, executes the command specified on that line of input, and waits for the command to finish. You should structure your shell such that it creates a new process for each new command (except for cd, pwd, and exit). Running commands in a new process protects the main shell process from any errors that occur in the new command.Please follow these steps: On athena, copy all source files from /tmp/nguyendh/hw5/ directory to your hw5 directory. Review the source codes, compile, and execute the programs. Examine the output texts to understand the behavior of each program. I have provided you with a simple shell template (csc60mshell.c) that you can choose to work from. Read the template closely to identify the key components and understand its execution flow. You can compile the shell using the following command: gcc csc60mshell.c Input processing, fork, execute: work on the basic core functions by completing the code labeled as step 1 in csc60mshell.c. Here, with a new shell, we want to establish the basic functions by executing simple command like ls, cat, etc. The commands are parsed by a provided function called parseline. Handling built-in Commands: There are three special cases where your shell should execute a command directly itself instead of running a separate process. First, if the user enters exit as a command, the shell should terminate. Second, if the user enters cd dir, you should change the current directory to dir by using the chdir system call. Users can run programs with paths relative to the working directory without specifying an absolute path. For example, instead of typing /a/b/c/myprog, a user could type two commands: cd /a/b/c followed by cd myprog. If the user simply types cd (no dir specified), change to the users home directory. The $HOME environment stores the desired path; use getenv(HOME) to obtain this. Third, if the user enters pwd, print the current working directory. This can be obtained with getcwd(). Handling input, output redirection: complete the code for section labeled as step 2. Please also review the sample code for redir.c. You should be able to reuse part of the code here. Below are the high level steps:Implementing < and : Open the file Eg. newfd=open(..) Assign newfd to 0(if <) or 1(if ) using dup2 Eg. dup2(newfd,0); Close your file Eg. close(newfd); Execute the command using execvp system call The command reads from 0 which is your file nowNote: Pipe function will be handled in the next assignment. Handling input errors: Be very careful to check for error conditions at all stages of command line parsing. Since the shell is controlled by a user, it is possible to receive bizarre input. For example, your shell should be able to handle all these errors:csc60mshell /bin/cat < foo < gubERROR Cant have two input redirects on one line.csc60mshell /bin/cat <ERROR No redirection file specified.csc60mshell out.txtERROR No command. Make sure file out.txt is not overwritten.csc60mshell cat test.cERROR No redirection file specified. Handling test cases: Your program should be able to handle the following examples of commands. However, your program will be tested with more than these commands (including error handling cases).csc60mshell ls ls.out # redirect lss stdout to file ls.outcsc60mshell cat foo.txtcsc60mshell wc < ls.outcsc60mshell cd /usr/bincsc60mshell lscsc60mshell cd ../csc60mshell pwdcsc60mshell /usr/bin/pscsc60mshell cdcsc60mshell find . -name foo1.txtcsc60mshell wc foo1.txtcsc60mshell exitcsc60mshell pwdcsc60mshell cd hw5csc60mshell cat foo1.txt ls.out out.txcsc60mshell gcc o test test.c gcsc60mshell <carriage-returncsc60mshellMarks DistributionYour documented c program: csc60mshell.c with core functions no I/O redirection, no build-in function10 pointsYour full documented c program: csc60mshell.c build-in function3 pointsYour full documented c program: csc60mshell.c I/O redirection4 pointsYour full documented c program: csc60mshell.c with error checks3 pointsTOTAL20 pointsResourcesUseful Unix System Calls:getenv/setenv: get/setenv the value of an environment variablepath = getenv(PATH);cwd = getenv(PWD);setenv(PWD, tempbuf,1);getcwd: get current working directory.chdir: change the current working directory (use this to implement cd)fork-join: create a new child process and wait for it to exit:if (fork() == 0) { // the child process.} else { // the parent processpid = wait(&status);}execv: overlay a new process image on calling processexecvp( full_path_name, command_argv_list, 0);open, close, dup2: for I/O Redirection:int fid = open(foo, O_WRONLY|O_CREAT);close(1);dup2(fid,1);close(fid);Exit shell:_exit(); exit without flushing stdioexit(); exit with flushing stdioC Library functions: #include <string.h String compare: int strcmp(const char *s1, const char *s2);strcmp(.,cd)strcmp(.,exit)strcmp(.,pwd)strcmp(.,)strcmp(.,<)print a system error message:perror(Shell Program error);input of characters and strings:fgets(cmdline, MAXLINE, stdin);Compilation & Building your programTo compile and build your executable program, please reuse the makefile, for assignment 2, for this new assignment. Please make appropriate changes where they are applicable. The makefile for assignment 2 is located in the directory /tmp/nguyendh/hw2 .PartnershipStudents may form a group of 2 students (maximum) to work on this project. As usual, please always contact your instructor for question or clarification.DeliverablesYour source file(s): csc60mshell.c, your programs output text (with various test cases please use the UNIX script command to capture your programs output), and your makefile. Please submit your assignment via SacCT.Hints Writing your shell in a simple manner is a matter of finding the relevant library routines and calling them properly. Please see the resources section above. Remember to get the basic functionality of your program working before worrying about all of the error conditions and corner cases. For example, for your shell, first get a single command running (probably first a command with no arguments, such as ls). Then try adding more arguments. Next, try working on multiple commands. Make sure that you are correctly handling all of the cases where there is miscellaneous white space around commands or missing commands. Finally, support for built-in commands, redirection, and pipes (for next assignment). I strongly recommend that you check the return codes of all system calls from the very beginning of your work. This will often catch errors in how you are invoking these new system calls. And, its good programming practice. Keep versions of your code. This is in case you need to go back to your older version due to an unforeseen bug/issue.

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