tsh.c

/*
 * tsh - A tiny shell program with job control
 *
 * Kayo Yin kayo.yin
 * Shrey Aryan shrey.aryan
 */
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <ctype.h>
#include <signal.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <errno.h>

/* Misc manifest constants */
#define MAXLINE    1024   /* max line size */
#define MAXARGS     128   /* max args on a command line */
#define MAXJOBS      16   /* max jobs at any point in time */
#define MAXJID    1<<16   /* max job ID */

/* Job states */
#define UNDEF 0 /* undefined */
#define FG 1    /* running in foreground */
#define BG 2    /* running in background */
#define ST 3    /* stopped */

/*
 * Jobs states: FG (foreground), BG (background), ST (stopped)
 * Job state transitions and enabling actions:
 *     FG -> ST  : ctrl-z
 *     ST -> FG  : fg command
 *     ST -> BG  : bg command
 *     BG -> FG  : fg command
 * At most 1 job can be in the FG state.
 */

/* Global variables */
extern char **environ;      /* defined in libc */
char prompt[] = "tsh> ";    /* command line prompt (DO NOT CHANGE) */
int verbose = 0;            /* if true, print additional output */
int nextjid = 1;            /* next job ID to allocate */
char sbuf[MAXLINE];         /* for composing sprintf messages */

struct job_t {              /* The job struct */
    pid_t pid;              /* job PID */
    int jid;                /* job ID [1, 2, ...] */
    int state;              /* UNDEF, BG, FG, or ST */
    char cmdline[MAXLINE];  /* command line */
};
struct job_t jobs[MAXJOBS]; /* The job list */
/* End global variables */


/* Function prototypes */

/* Here are the functions that you will implement */
void eval(char *cmdline);
int builtin_cmd(char **argv);
void do_bgfg(char **argv);
void waitfg(pid_t pid);

void sigchld_handler(int sig);
void sigtstp_handler(int sig);
void sigint_handler(int sig);

/* Here are helper routines that we've provided for you */
int parseline(const char *cmdline, char **argv);
void sigquit_handler(int sig);

void clearjob(struct job_t *job);
void initjobs(struct job_t *jobs);
int maxjid(struct job_t *jobs);
int addjob(struct job_t *jobs, pid_t pid, int state, char *cmdline);
int deletejob(struct job_t *jobs, pid_t pid);
pid_t fgpid(struct job_t *jobs);
struct job_t *getjobpid(struct job_t *jobs, pid_t pid);
struct job_t *getjobjid(struct job_t *jobs, int jid);
int pid2jid(pid_t pid);
void listjobs(struct job_t *jobs);

void usage(void);
void unix_error(char *msg);
void app_error(char *msg);
typedef void handler_t(int);
handler_t *Signal(int signum, handler_t *handler);

/*
 * main - The shell's main routine
 */
int main(int argc, char **argv)
{
    char c;
    char cmdline[MAXLINE];
    int emit_prompt = 1; /* emit prompt (default) */

    /* Redirect stderr to stdout (so that driver will get all output
     * on the pipe connected to stdout) */
    dup2(1, 2);

    /* Parse the command line */
    while ((c = getopt(argc, argv, "hvp")) != EOF) {
        switch (c) {
        case 'h':             /* print help message */
            usage();
	    break;
        case 'v':             /* emit additional diagnostic info */
            verbose = 1;
	    break;
        case 'p':             /* don't print a prompt */
            emit_prompt = 0;  /* handy for automatic testing */
	    break;
	default:
            usage();
	}
    }

    /* Install the signal handlers */

    /* These are the ones you will need to implement */
    Signal(SIGINT,  sigint_handler);   /* ctrl-c */
    Signal(SIGTSTP, sigtstp_handler);  /* ctrl-z */
    Signal(SIGCHLD, sigchld_handler);  /* Terminated or stopped child */

    /* This one provides a clean way to kill the shell */
    Signal(SIGQUIT, sigquit_handler);

    /* Initialize the job list */
    initjobs(jobs);

    /* Execute the shell's read/eval loop */
    while (1) {

	/* Read command line */
	if (emit_prompt) {
	    printf("%s", prompt);
	    fflush(stdout);
	}
	if ((fgets(cmdline, MAXLINE, stdin) == NULL) && ferror(stdin))
	    app_error("fgets error");
	if (feof(stdin)) { /* End of file (ctrl-d) */
	    fflush(stdout);
	    exit(0);
	}

	/* Evaluate the command line */
	eval(cmdline);
	fflush(stdout);
	fflush(stdout);
    }

    exit(0); /* control never reaches here */
}

/*
 * eval - Evaluate the command line that the user has just typed in
 *
 * If the user has requested a built-in command (quit, jobs, bg or fg)
 * then execute it immediately. Otherwise, fork a child process and
 * run the job in the context of the child. If the job is running in
 * the foreground, wait for it to terminate and then return.  Note:
 * each child process must have a unique process group ID so that our
 * background children don't receive SIGINT (SIGTSTP) from the kernel
 * when we type ctrl-c (ctrl-z) at the keyboard.
*/
void eval(char *cmdline)
{
    char *argv[MAXARGS]; // List of arguments for execve()
    char buf[MAXLINE]; // Parsed command line
    int bg; // 1 if background job, 0 if foreground
    pid_t pid; // Process id
    sigset_t set; // List of signals


    strcpy(buf, cmdline);
    bg = parseline(buf, argv); // Parse command line, determine whether background job or not
    if (argv[0] == NULL)
      return; // ignore empty lines

    if (!builtin_cmd(argv)) // User input is not a built in command
    {
        sigemptyset(&set); // Initialize signal set
        sigaddset(&set, SIGCHLD); // Add SIGCHLD to set
        sigprocmask(SIG_BLOCK, &set, NULL); // Block SIGCHLD


        if ((pid = fork()) < 0)
        {
          // pid is less than zero, error during forking
          unix_error("fork error");
          return;
        }

        if (pid == 0)
          {   /* Child runs user job */
              setpgid(0,0); // Set children id to 0
              sigprocmask(SIG_UNBLOCK,&set, NULL); // Unblock SIGCHLD
              if (execve(argv[0], argv, environ) < 0) // execute command
              {
                printf("%s: Command not found\n", argv[0]); // error if first element of argv is less than zero
                exit(0);
              }
          }

      /* Parent waits for foreground job to terminate */
        if (!bg)
          {
            addjob(jobs, pid, FG,cmdline); // Add to job list as foreground job
            sigprocmask(SIG_UNBLOCK,&set, NULL); // Unblock SIGCHLD
            waitfg(pid); // Let foreground job finish


          }
          else
          {
            addjob(jobs, pid, BG,cmdline); // Add to job list as background job
            sigprocmask(SIG_UNBLOCK,&set, NULL); // Unblock SIGCHLD
            printf("[%d] (%d) %s", pid2jid(pid), (int)pid, cmdline); // Print process info
          }

      }
        return;
}

/*
 * parseline - Parse the command line and build the argv array.
 *
 * Characters enclosed in single quotes are treated as a single
 * argument.  Return true if the user has requested a BG job, false if
 * the user has requested a FG job.
 */
int parseline(const char *cmdline, char **argv)
{
    static char array[MAXLINE]; /* holds local copy of command line */
    char *buf = array;          /* ptr that traverses command line */
    char *delim;                /* points to first space delimiter */
    int argc;                   /* number of args */
    int bg;                     /* background job? */

    strcpy(buf, cmdline);
    buf[strlen(buf)-1] = ' ';  /* replace trailing '\n' with space */
    while (*buf && (*buf == ' ')) /* ignore leading spaces */
	buf++;

    /* Build the argv list */
    argc = 0;
    if (*buf == '\'') {
	buf++;
	delim = strchr(buf, '\'');
    }
    else {
	delim = strchr(buf, ' ');
    }

    while (delim) {
	argv[argc++] = buf;
	*delim = '\0';
	buf = delim + 1;
	while (*buf && (*buf == ' ')) /* ignore spaces */
	       buf++;

	if (*buf == '\'') {
	    buf++;
	    delim = strchr(buf, '\'');
	}
	else {
	    delim = strchr(buf, ' ');
	}
    }
    argv[argc] = NULL;

    if (argc == 0)  /* ignore blank line */
	return 1;

    /* should the job run in the background? */
    if ((bg = (*argv[argc-1] == '&')) != 0) {
	argv[--argc] = NULL;
    }
    return bg;
}

/*
builtin_cmd - If the user has typed a built-in command then execute
it immediately.

Recall that tsh should support the following built-in commands:
    The quit command terminates the shell.
    The jobs command lists all background jobs.
    The bg <job> command restarts <job> by sending it a SIGCONT signal, and then runs it in the background.
    The fg <job> command restarts <job> by sending it a SIGCONT signal, and then runs it in the foreground.
 */

 int builtin_cmd(char **argv)
 {
   // quit command terminate the shell
   if (!strcmp(argv[0], "quit"))
     {
         exit(0); // exit shell
     }

   // jobs command lists all the background jobs
   else if (!strcmp(argv[0], "jobs"))
     {
       listjobs(jobs);
       return 1;
     }

   // bg <job> command restarts <job> by sending it a SIGCONT signal and then runs
   // it in the background.
   else if (!strcmp(argv[0], "bg") || !strcmp(argv[0], "fg"))
     {
       do_bgfg(argv);
       return 1;
     }


   return 0; // not a builtin command
 }

/*
 * do_bgfg - Execute the builtin bg and fg commands
 * The bg <job> command restarts <job> by sending it a SIGCONT signal, and then runs it in the background. The <job> argument can be either a PID or a JID.
 * The fg <job> command restarts <job> by sending it a SIGCONT signal, and then runs it in the foreground. The <job> argument can be either a PID or a JID.
*/
void do_bgfg ( char **argv )
{
    struct job_t *job;
    char *arg;
    pid_t pid = 0;

    arg = argv[1];


    if ( arg == NULL )
    { //no argument
      printf("%s command requires PID or %%jobid argument\n", argv[0]);
      return;
    }

    if ( arg[ 0 ] == '%' ) // jid identifies job
     {
        int jid = atoi(&arg[1]); // set job id
        job = getjobjid(jobs, jid); // set associated job

        if ( job == NULL ) // check if jid identifies a valid job
        {
            printf ( "%s: No such job\n", arg );
            return;
        }
        else
        {
            pid = job->pid; // set process id
        }
    }

    else if ( isdigit ( arg[ 0 ] ) ) // pid identifies job
    {
        pid = (pid_t) atoi(arg); // set pid
        job = getjobpid(jobs, pid); // set associated job

        if ( job == NULL ) // check if process id identifies a valid job
        {
            printf ( "(%d): No such process\n", pid );
            return;
        }
    }
    else { // argument is neither a PID or JID
      printf("%s: argument must be a PID or %%jobid\n", argv[0]);
      return;
    }

    if (kill(-pid, SIGCONT) < 0) // Send SIGCONT signal
      unix_error("do_bgfg ERROR"); // error when kill

      if (!strcmp(argv[0], "bg"))
      {
        job->state = BG; // change job state to background
        printf("[%d] (%d) %s", job->jid, job->pid, job->cmdline);
      }
      else
      {
        job->state = FG; // put job to foreground
        waitfg(job->pid); // wait until foreground job is done
      }

    return;
}

/*
 * waitfg - Block until process pid is no longer the foreground process
 */
 void waitfg ( pid_t pid )
 {
   while (1) // loop
   {
       if (pid != fgpid(jobs)) break; // stop waiting when job isn't in foreground anymore
       else sleep(1); // wait
   }
   return;
 }

/*****************
 * Signal handlers
 *****************/

/*
 * sigchld_handler - The kernel sends a SIGCHLD to the shell whenever
 *     a child job terminates (becomes a zombie), or stops because it
 *     received a SIGSTOP or SIGTSTP signal. The handler reaps all
 *     available zombie children, but doesn't wait for any other
 *     currently running children to terminate.
 */
 void sigchld_handler(int sig)
 {
     pid_t pid;
     int status;

     while((pid = waitpid(-1, &status, WNOHANG | WUNTRACED)) > 0) // find all zombie children
       {
         // if child job terminated because it recieved a signals or
         // if child becomes a zombie
         // then it should be deleted from the job list
         if (WIFEXITED(status)) { // child terminated normally
             deletejob(jobs, pid); // Delete the child from the job list
         }

         else if (WIFSIGNALED(status)) { // signal caused child to terminate
           printf("Job [%d] (%d) terminated by signal %d\n",  pid2jid(pid), (int) pid, WTERMSIG(status)); // print which signal caused termination
           deletejob(jobs,pid);
	 }

         else if(WIFSTOPPED(status)) // child is stopped
           {
             getjobpid(jobs, pid)->state =ST; // change state to stopped
             printf("Job [%d] (%d) stopped by signal %d\n", pid2jid(pid), (int) pid, WSTOPSIG(status));
           }
       }

 }

/*
 * sigint_handler - The kernel sends a SIGINT to the shell whenver the
 *    user types ctrl-c at the keyboard.  Catch it and send it along
 *    to the foreground job.
 */
void sigint_handler(int sig)
{

  //  When you implement your signal handlers, be sure to send SIGINT and SIGTSTP signals
  //  to the entire foreground process group, using ”-pid” instead of ”pid” in the argument
  //  to the kill function
  pid_t pid = fgpid(jobs); // current foreground jobs
  if(pid != 0)
    {
      if (kill(-pid, sig) < 0) // send signal 'sig' to entire foreground process group
        unix_error("SIGINT ERROR");
    }
  return;
}

/*
 * sigtstp_handler - The kernel sends a SIGTSTP to the shell whenever
 *     the user types ctrl-z at the keyboard. Catch it and suspend the
 *     foreground job by sending it a SIGTSTP.
 */
void sigtstp_handler(int sig)
{
  //  When you implement your signal handlers, be sure to send SIGINT and SIGTSTP signals
  //  to the entire foreground process group, using ”-pid” instead of ”pid” in the argument
  //  to the kill function

    pid_t pid = fgpid(jobs); // foreground jobs
    if(pid != 0)
      {
        if (kill(-pid,sig) < 0) // send sig to entire foreground process group
          unix_error("SIGSTOP ERROR");
      }
    return;
}

/*********************
 * End signal handlers
 *********************/

/***********************************************
 * Helper routines that manipulate the job list
 **********************************************/

/* clearjob - Clear the entries in a job struct */
void clearjob(struct job_t *job) {
    job->pid = 0;
    job->jid = 0;
    job->state = UNDEF;
    job->cmdline[0] = '\0';
}

/* initjobs - Initialize the job list */
void initjobs(struct job_t *jobs) {
    int i;

    for (i = 0; i < MAXJOBS; i++)
	clearjob(&jobs[i]);
}

/* maxjid - Returns largest allocated job ID */
int maxjid(struct job_t *jobs)
{
    int i, max=0;

    for (i = 0; i < MAXJOBS; i++)
	if (jobs[i].jid > max)
	    max = jobs[i].jid;
    return max;
}

/* addjob - Add a job to the job list */
int addjob(struct job_t *jobs, pid_t pid, int state, char *cmdline)
{
    int i;

    if (pid < 1)
	return 0;

    for (i = 0; i < MAXJOBS; i++) {
	if (jobs[i].pid == 0) {
	    jobs[i].pid = pid;
	    jobs[i].state = state;
	    jobs[i].jid = nextjid++;
	    if (nextjid > MAXJOBS)
		nextjid = 1;
	    strcpy(jobs[i].cmdline, cmdline);
  	    if(verbose){
	        printf("Added job [%d] %d %s\n", jobs[i].jid, jobs[i].pid, jobs[i].cmdline);
            }
            return 1;
	}
    }
    printf("Tried to create too many jobs\n");
    return 0;
}

/* deletejob - Delete a job whose PID=pid from the job list */
int deletejob(struct job_t *jobs, pid_t pid)
{
    int i;

    if (pid < 1)
	return 0;

    for (i = 0; i < MAXJOBS; i++) {
	if (jobs[i].pid == pid) {
	    clearjob(&jobs[i]);
	    nextjid = maxjid(jobs)+1;
	    return 1;
	}
    }
    return 0;
}

/* fgpid - Return PID of current foreground job, 0 if no such job */
pid_t fgpid(struct job_t *jobs) {
    int i;

    for (i = 0; i < MAXJOBS; i++)
	if (jobs[i].state == FG)
	    return jobs[i].pid;
    return 0;
}

/* getjobpid  - Find a job (by PID) on the job list */
struct job_t *getjobpid(struct job_t *jobs, pid_t pid) {
    int i;

    if (pid < 1)
	return NULL;
    for (i = 0; i < MAXJOBS; i++)
	if (jobs[i].pid == pid)
	    return &jobs[i];
    return NULL;
}

/* getjobjid  - Find a job (by JID) on the job list */
struct job_t *getjobjid(struct job_t *jobs, int jid)
{
    int i;

    if (jid < 1)
	return NULL;
    for (i = 0; i < MAXJOBS; i++)
	if (jobs[i].jid == jid)
	    return &jobs[i];
    return NULL;
}

/* pid2jid - Map process ID to job ID */
int pid2jid(pid_t pid)
{
    int i;

    if (pid < 1)
	return 0;
    for (i = 0; i < MAXJOBS; i++)
	if (jobs[i].pid == pid) {
            return jobs[i].jid;
        }
    return 0;
}

/* listjobs - Print the job list */
void listjobs(struct job_t *jobs)
{
    int i;

    for (i = 0; i < MAXJOBS; i++) {
	if (jobs[i].pid != 0) {
	    printf("[%d] (%d) ", jobs[i].jid, jobs[i].pid);
	    switch (jobs[i].state) {
		case BG:
		    printf("Running ");
		    break;
		case FG:
		    printf("Foreground ");
		    break;
		case ST:
		    printf("Stopped ");
		    break;
	    default:
		    printf("listjobs: Internal error: job[%d].state=%d ",
			   i, jobs[i].state);
	    }
	    printf("%s", jobs[i].cmdline);
	}
    }
}
/******************************
 * end job list helper routines
 ******************************/


/***********************
 * Other helper routines
 ***********************/

/*
 * usage - print a help message
 */
void usage(void)
{
    printf("Usage: shell [-hvp]\n");
    printf("   -h   print this message\n");
    printf("   -v   print additional diagnostic information\n");
    printf("   -p   do not emit a command prompt\n");
    exit(1);
}

/*
 * unix_error - unix-style error routine
 */
void unix_error(char *msg)
{
    fprintf(stdout, "%s: %s\n", msg, strerror(errno));
    exit(1);
}

/*
 * app_error - application-style error routine
 */
void app_error(char *msg)
{
    fprintf(stdout, "%s\n", msg);
    exit(1);
}

/*
 * Signal - wrapper for the sigaction function
 */
handler_t *Signal(int signum, handler_t *handler)
{
    struct sigaction action, old_action;

    action.sa_handler = handler;
    sigemptyset(&action.sa_mask); /* block sigs of type being handled */
    action.sa_flags = SA_RESTART; /* restart syscalls if possible */

    if (sigaction(signum, &action, &old_action) < 0)
	unix_error("Signal error");
    return (old_action.sa_handler);
}

/*
 * sigquit_handler - The driver program can gracefully terminate the
 *    child shell by sending it a SIGQUIT signal.
 */
void sigquit_handler(int sig)
{
    printf("Terminating after receipt of SIGQUIT signal\n");
    exit(1);
}