MyOwnShell

mosh.c

#include<stdio.h>
#include<stdlib.h>
#include<unistd.h>
#include<string.h>

char *PATH="PATH=/bin:/usr/bin";  //System PATH variable.


void process(char *msg);           //function to execute a command without a pipe
void processWithPipe(char *msg);   //function to execute commands with a pipe
int numOfPipes(char msg[]);        //a simple funtion to count the number of pipes
void startup();                    //a simple function to display start up image
void info();                       //a simple function to display a brief description on MOSH

int main(){

    startup();
    int p = putenv(PATH);
    if(p !=0){
        printf("Error setting the path\n");
        exit(0);
    }
    
    int loop=1;
    while(loop == 1){            //will keep running the shell
        char cmd[100];             //char array used to store store the command.
        char *workingdir =getcwd(NULL,100);
        printf("%s ~ MOSH> ",workingdir);
        free(workingdir);        
        scanf ("%[^\n]%*c", cmd);
        if(cmd[strlen(cmd) -1] == '\n'){
            cmd[strlen(cmd) -1] = '\0';
        }
        if(cmd[0] == 'c' && cmd[1] == 'd' && cmd[2]==' '){
            if (chdir(&cmd[3]) == 0) {
                    } else {
                            printf("Invalid directory \n");
                       }    
        }else if(cmd[0] == 'i' && cmd[1] == 'n' && cmd[2] == 'f' && cmd[3] == 'o' ){
            info();
        }else if(cmd[0] == 'e' && cmd[1] == 'x' && cmd[2] == 'i' && cmd[3] == 't'){
            printf("Thank you for using MOSH.\n\n");
            exit(0);
        }else{
            int num = numOfPipes(cmd);
            if(num == 0){              //checks if not more than 1 pipe is used
                process(cmd);    
            }else if(num >1){
                printf("Version 1.0 supports only 1 pipe.\n");
            }else{
              processWithPipe(cmd);
            }
        }
    }
     return 0;
}

int numOfPipes(char msg[])
{
    int i,coun = 0;
    for( i = 0; i < strlen(msg)+1;i++){
        if(msg[i] == '|'){
            coun++;
        }
    }
    return coun;
}

void process(char *msg)
{
    char *buffer[25];             //
    char *tok;                    //
    char *msgCopy;                //
    msgCopy =msg;              //  preperation to torkaniz the command using spaces
    tok = strtok(msgCopy," ");    //
    buffer[0]= tok;               //
    int i=1;

    while((tok = strtok (NULL, " ")) != NULL ){
        buffer[i]= tok;
        i++;
    }
    buffer[i]=NULL;
    pid_t pid = fork();
    if(pid ==0){                             //child process
        if((execvp(buffer[0],buffer)) == 0){    //checks if the entered command is valid and excutes

        }else{
            printf("command not found :%s \n",buffer[0]);
            exit(0);
        }
    }else{                                 //parent process
        wait();
    }
}

void processWithPipe(char *msg)
{
    char *commands[2];            //
    char *cmd1args[25];           //
    char *cmd2args[25];           //up to first 2 loops, will break the two commands.
    char *temp;                   //
    char *msgCopy;                //

    msgCopy =msg;
    temp = strtok(msgCopy,"|");
    commands[0] = temp;
    temp = strtok(NULL, "|");
    commands[1]=temp;

    msgCopy = commands[0];
    temp = strtok(msgCopy, " ");
    cmd1args[0]= temp;
    int i=1;

    while((temp = strtok (NULL, " ")) != NULL ){   
        cmd1args[i]= temp;
        i++;
    }
        
    cmd1args[i]=NULL;
    msgCopy = commands[1];
    temp = strtok(msgCopy, " ");
    cmd2args[0]= temp;
    i=1;
    while((temp = strtok (NULL, " ")) != NULL ){  
        cmd2args[i]= temp;
        i++;
    }        
    cmd2args[i]=NULL;

        char temp1[100];
    strcpy(temp1,"which ");                          //
    strcat(temp1,cmd1args[0]);            //
    strcat(temp1," > /dev/null 2>&1");        //
    int ret = system(temp1);            //
    char temp2[100];                // Check wethr both commands are available.
    strcpy(temp2,"which ");                // if not, stop the execution and return back to caller funcion
    strcat(temp2,cmd2args[0]);            //
    strcat(temp2," > /dev/null 2>&1");        //
    int ret2 = system(temp2);
    
        if(ret != 0){
        printf("command not found : %s \n",cmd1args[0]);
        return;
    }else if(ret2 != 0){
        printf("command not found : %s \n",cmd2args[0]);
        return;
    }

        pid_t pid;
    if((pid=fork())){    // create a process tree for pipe
        wait(pid);                    
    }else{
        
        int fd[2];                    //file directory*(explain more?)
        pid_t process;
        pipe(fd);
            if((process = fork()) == -1){
            printf("Fork error \n");
        }else if(process == 0){      //child process
                dup2(fd[1],1);           //duplicates standard output so that the output is directed in to the pipe
            close(fd[0]);            //closes standard input
            if((execvp(cmd1args[0],cmd1args)==0)){  //checks if the entered command is valid and excutes
                
            }else{
                printf("Command not found: %s \n",cmd1args[0]);
            }
        }else{                      //parent process
                dup2(fd[0],0);          //duplicates standard input so that the input is directed out of the pipe
            close(fd[1]);           //closes standard output
            wait();
                    
                    if((execvp(cmd2args[0],cmd2args))==0){  //checks if the entered command is valid and excutes
                
            }else{
                printf("Command not found: %s \n",cmd2args[0]);
            }
        }
     }
}

void startup(){
    printf("*************************************************\n");
    printf("*************************************************\n");
    printf("**                                             **\n");
    printf("**                                             **\n");
    printf("**   ---     --- -------  -----  |     |       **\n");
    printf("**   |  \\   /  | |     |  |      |     |       **\n");
    printf("**   |   \\ /   | |     |  |      |     |       **\n");
    printf("**   |         | |     |   ----  |-----|       **\n");
    printf("**   |         | |     |      |  |     |       **\n");
    printf("**   |         | |     |      |  |     |       **\n");
    printf("**   |         | -------  -----  |     |       **\n");
    printf("**                                             **\n");
    printf("**                                      V 1.0  **\n");
    printf("**                                             **\n");
    printf("**                                             **\n");
    printf("*************************************************\n");
    printf("*************************************************\n");

    printf("\nUse command 'info' to get information about the shell.\nUse command 'exit' to exit from the shell.\n\n");
}

void info()
{ 
    printf("\n\n\n\n");
    printf("MOSH V1.0 was developed by CodeMasters\n");
    printf("Features :\n");
    printf(" * MOSH is a basic shell which can run basic commands \n");
    printf(" * It can handle a single pipe.\n");
    printf(" * If a particular command not found in the PATH, mosh will give error message.");
    
}

/*
*
*  References :
*
*    http://web.mst.edu/~ercal/284/PipeExamples/Examples.html
*    http://www.tldp.org/LDP/lpg/node11.html
*    http://www.cs.ecu.edu/karl/4630/sum01/example1.html
*    http://stackoverflow.com/questions/7851983/find-out-if-a-certain-application-command-is-available-on-linux
*
*
*
*
*/