A tiny shell program with job control

那天被布置了个作业，写SHELL
研究了老半天，下面这个是作业的标准答案

/*
 * tsh - A tiny shell program with job control
 *  
 *  Clara Raubertas
 * clara1
 */
#include
#include
#include
#include
#include
#include
#include
#include
#include

/* 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[MAXLINE];
  pid_t pid;
  sigset_t mask;
  int bg = parseline(cmdline, argv);
  // parses the command line and indicates whether the command is to run in the background       
  if (argv[0] == NULL) {
    return; // ignore blank lines
  }
  if ((sigemptyset(&mask)) < 0) {
    unix_error("sigemptyset error");
  }
  if ((sigaddset(&mask, SIGCHLD)) < 0) {
    unix_error("sigaddset error");
  }
  if (!(builtin_cmd(argv))) { // first check if it is a builtin command
    if ((sigprocmask(SIG_BLOCK, &mask, NULL)) < 0) {
      unix_error("sigprocmask error");
    }
    //fork off and execute the program in the child
    if ((pid = fork()) < 0) {
      unix_error("fork error");
    }
    else if (pid == 0) {
      if (setpgid(0, 0) < 0 ) {
    // make a new process group, check for error
    unix_error("setpgid error");
      }
      if (sigprocmask(SIG_UNBLOCK, &mask, NULL) < 0) {
    unix_error("sigprogmask error");
      }
      // printf("child process group is %d/n", getpgid(0));
      if  (execve(argv[0], argv, environ) < 0) {
    //error check execve
    printf("%s: Command not found./n", argv[0]);
    //return;
    exit(0);
      }
    }
  //   printf("parent process group is %d/n", getpgid(0));
    if (!bg) {
      // run the process in the foreground
        addjob(jobs, pid, FG, cmdline);
    if (sigprocmask(SIG_UNBLOCK, &mask, NULL) < 0) {
    unix_error("sigprocmask error");
    }
    waitfg(pid);  // wait for the foreground child to terminate.
    }
    else {
      // run the process in the background
      int jid;
      addjob(jobs, pid, BG, cmdline);
      if (sigprocmask(SIG_UNBLOCK, &mask, NULL) < 0) {
    unix_error("sigprocmask error");
      }
      jid = pid2jid(pid);
      printf("[%d] (%d) %s", jid, pid, cmdline);
    }
  }
  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.  
 */

int builtin_cmd(char **argv)

{
  //printf("builtin_cmd?/n");
  if (!strcmp("quit", argv[0])) {
    exit(0);
  }
  if (!strcmp("jobs", argv[0])) {
    listjobs(jobs);
    return 1;
  }
  if (!strcmp("bg", argv[0]) || !(strcmp("fg", argv[0]))) {
    do_bgfg(argv);
    return 1;
  }
  return 0;     /* not a builtin command */
}

/*
 * do_bgfg - Execute the builtin bg and fg commands
 */
void do_bgfg(char **argv)
{
  if (!(strcmp("bg", argv[0]))) {
     //make the job bg
    if(!(strncpy(argv[1], "%", 1))) {
      getjobjid(jobs, atoi(argv[1]));
    }
    else {
      kill(atoi(argv[1]), SIGCONT);
      (*(getjobpid(jobs, atoi(argv[1])))).state = BG;
    }
    //find out if it is a pid or jid
    //send the process a sigcont
    //set its state to bg
  }
  if (!(strcmp("fg", argv[0]))) {
    //make the job fg
    //find out if it is a pid or jid
    // send it a sigcont
    //set its state to fg
    //waitfg
  }
  printf("%s/n", argv[0]);
  return;
}

/*
 * waitfg - Block until process pid is no longer the foreground process
 */
void waitfg(pid_t pid)
{
  while
    (getjobpid(jobs, pid) != NULL) {
    if ((*(getjobpid(jobs, pid))).state == FG) {
      //      printf("%d/n", pid);
      sleep (1);
    }
  }
  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)
{
  int status;
  pid_t pid;
  //  pid = fgpid(jobs);
  while ((pid = waitpid(fgpid(jobs), &status, WNOHANG|WUNTRACED)) > 0) {
    //   printf("waitpid: %d/n", pid);
    deletejob(jobs, pid);
  }
  if (errno != ECHILD) {
    unix_error("sigchld_handler: waitpid error");
  }
  return;
}     

/*   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)
{
  int pid;
  int jid;
  pid = fgpid(jobs);
  if (pid != 0) {
    jid = pid2jid(pid);
    kill(-pid, SIGKILL);
    printf("Job [%d] (%d) terminated by signal %d/n", jid, pid, sig);
  }
  else {
  }
  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)
{
  int pid;
  int jid;
  int gid;
  pid = fgpid(jobs);

  if (pid != 0) {
    jid = pid2jid(pid);
    gid = -1 * pid;
    kill(-pid, SIGTSTP);
    (*(getjobpid(jobs, pid))).state = ST;
    printf("Stopped [%d] (%d) %s", jid, pid, (*(getjobpid(jobs, pid))).cmdline);
  }
  else {
  }
  return;
}
/* test05, test07, test08, test09, test10, test12, test13, test14, test15, test16 */
/*********************
 * 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 : %s/n", jobs[i].jid, jobs[i].pid, jobs[i].cmdline, 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);
}