Unix Shell CprE 308 Project 1 Neh Batwara Contents 1 Summary 2 2 Code: 2 3 Included Files: 5 1 Summary In this project we created our own version of the UNIX shell. A UNIX shell is simply an interactive interface between the OS and the user. It repeatedly accepts input from the user and initiates processes on the OS based on that input. A challenging part of this project was string parsing since that was how the commands that the user inputs are executed by the shell.The shell uses fork( ) to call a program which creates a child process. To execute the command the child process calls the execvp( ) which exeutes the child process. I also used system calls to process the following process/commands: 1.chdir( ) to change the working directory with the string that gets passed in by the user inpu with cd 2.getcwd( ) to get the current working directory 3.getenv/setenv to retrieve and set environment variables. 4.waitpid( ) to wait for the child process to exit or to get exit status 2 Code: The following code is for the main Unix Shell. #include <s t d i o . h> #include <unistd . h> #include " p1 Unix Shell . h" #include <s t r i n g . h> #include <sys/types.h> #include <unistd . h> #include <sys / wait . h> #include <errno . h> #include <s t d l i b . h> /∗Maximum legnth of input allowed to the shell. ∗/ #define INPUT LENTH 100 /∗Maximum number of argument allowed to be passed to the shell. ∗/ #define ARGUMENT BUFFER 100 #define CHAR BUFFER 100 /∗ ∗ This function should parse the user input into an array. ∗/ int p a r s e i n p u t ( char ∗ cmd , char ∗ argv [ ] ) f int i = 1 ; argv[0] = strtok(cmd, " nn" ) ; while ( argv [ i −1] != NULL && i < (ARGUMENT BUFFER − 1 ) ) f argv[i] = strtok(NULL, " nn" ) ; i ++; g return i −1; g /∗ ∗ This function parses the arguments passed from the command line to the shell.. ∗/ char ∗ parse argument ( int argc , char ∗∗ argv ) f int arg ; o p t e r r = 0 ; char ∗ prompt = NULL; while ((arg = getopt(argc, argv, "p:")) != −1) f i f ( arg == ' p ' )f prompt = optarg; 2 g else f abort ( ) ; g g i f (prompt == NULL) f prompt = "308sh"; g return prompt ; g /∗ ∗ This is the main function with the while loop that executes the shell. ∗ It take the user imput from the command line and parses it to the shell program. ∗/ int main ( int argc , char ∗∗ argv ) f char ∗ prompt = parse argument(argc , argv); char input [INPUT LENTH ] ; while ( 1 ) f char ∗ argv [ARGUMENT BUFFER] ; p r i n t f ( ">>>%s> " , prompt ) ; fgets(input , INPUT LENTH, s t d i n ) ; int lastIndex = parse input(input, argv); i f (lastIndex != 0) f i f (!strcmp(argv[0] , "exit")) f break ; g else i f (!strcmp(argv[0] , "cd")) f cd ( argv ) ; g else i f (!strcmp(argv[0] , "cwd")) f p r i n t f ( " Current Working Directory : %s nn" , getcwd (NULL,CHAR BUFFER) ) ; g else i f (!strcmp(argv[0] , "pid")) f printf("PID = %i nn", getpid()); g else i f (!strcmp(argv[0] , "ppid")) f printf ("PPID = %i nn", getppid()); g else i f (!strcmp(argv[lastIndex −1] , "&" ) ) f argv[lastIndex −1] = NULL; execute(argv); g else f 3 e x e c u t e block(argv); g g int s t a t u s ; p i d t p r o c e s s child = waitpid(−1 , &status , WNOHANG) ; i f ( p r o c e s s c h i l d > 0) f printf("process %i e x i t e d nn" , p r o c e s s c h i l d ) ; processStatus(process child , status); g g return 0 ; g /∗ ∗ Fucntion when cd is called. ∗/ void cd ( char ∗ argv [ ] ) f i f (argv[1] == NULL) f p r i n t f ( "No paramaters s u p p l i e d to cdnn" ) ; g else f i f (chdir(argv[1]) == −1) f p r i n t f ( "Cd f a i l e d − %s nn", strerror(errno)); g g g /∗ ∗ This function prints the status so the user can see it. ∗/ void processStatus(pid t childPid , int s t a t u s ) f i f (WIFSIGNALED( s t a t u s ) ) f printf("Child %i e x i t e d with s i g n a l %dnn", childPid , WTERMSIG(status )); g else i f (WIFEXITED( s t a t u s ) ) f printf("Child %i e x i t e d with return code %dnn", childPid , WEXITSTATUS(status )); g g /∗ ∗ e x e c u t e block waits for the process to finish. ∗/ void e x e c u t e b l o c k ( char ∗ argv [ ] ) f p i d t pid = fork(); i f ( pid == 0) f printf("pid: %i nn", getpid()); execvp (∗ argv, argv); printf ("Unknown command . n n" ) ; 4 e x i t ( 0 ) ; g else f int s t a t u s ; waitpid(pid, &status , 0); processStatus(pid, status); g g /∗ ∗ Exceute does not block the main process and waits for the child process to finish. ∗/ void execute ( char ∗ argv [ ] ) f p i d t pid = fork(); i f ( pid == 0) f p r i n t f ( "nn PID : %i nn", getpid()); execvp (∗ argv, argv); printf("PID: %i f a i l e d − %s nn", getpid(), strerror(errno)); g g 3 Included Files: 1. makefile_cmake 2.p1 Unix Shell_c[MainC File] 3.p1 Unix Shellh_ [Header File] 4.p1 Unix Shell_o[Object File] 5.READMEtxt_ [text file for instructions] 5.