tsh.c

/* 
 * tsh - A tiny shell program with job control
 * 
 */
#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>
#include <fcntl.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 */

/* 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 */
char sbuf[MAXLINE];         /* for composing sprintf messages */

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

volatile sig_atomic_t ready; /* Is the newest child in its own process group? */

/* End global variables */


/* Function prototypes */

/* Here are the functions that you will implement */
void eval(char *cmdline);
int builtin_cmd(char **argv, int argc);
void do_bgfg(char **argv);
void waitfg(pid_t pid);
void sigchld_handler(int sig);
void sigint_handler(int sig);
void sigtstp_handler(int sig);
void recursive_pipes(int start, int commands_to_process, int *command_indexes, char **argv);

/* Here are helper routines that we've provided for you */
int parseline(const char *cmdline, char **argv); 
void sigquit_handler(int sig);
void sigusr1_handler(int sig);

void clearjob(struct job_t *job);
void initjobs(struct job_t *jobs);
int freejid(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(STDOUT_FILENO, STDERR_FILENO);

    /* Parse the command line */
    while ((c = getopt(argc, argv, "hvp")) != -1) {
        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 */

    Signal(SIGUSR1, sigusr1_handler); /* Child is ready */

    /* 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);
    } 

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

/*
 * Recursive pipes implementation /bin/ls -l | /bin/cat | /bin/wc
 */
void recursive_pipes(int start, int commands_to_process, int *command_indexes, char **argv) {
    // start = 0, commands_to_process = 1, command_indexes = [0,3,5] 
    int fd[2];
    int fork_return;
    if ((pipe(fd)) == -1) {
        perror("pipe");
        exit(1);
    }
    fork_return = fork();
    if (fork_return > 0) {
        if ((dup2(fd[1], fileno(stdout))) == -1) {
            perror("dup2");
            exit(1);
        }
        if ((close(fd[0])) == -1) {
            perror("close");
        }
        if ((close(fd[1])) == -1) {
            perror("close");
        }
        execve(argv[command_indexes[start]], argv + command_indexes[start], NULL);
    } else if (fork_return == 0) {
        if ((dup2(fd[0], fileno(stdin))) == -1) {
            perror("dup2");
            exit(1);
        }
        if ((close(fd[1])) == -1) {
            perror("close");
        }
        if ((close(fd[0])) == -1) {
            perror("close");
        }
        commands_to_process--;
        start++;
        if (commands_to_process == 0) {
            execve(argv[command_indexes[start]], argv + command_indexes[start], NULL);
        } else {
            recursive_pipes(start, commands_to_process, command_indexes, argv);
        }

    }
}

/* 
 * 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) {
    pid_t child_pid;
    char *argv[MAXARGS];
    int argc = parseline(cmdline, argv);
    int output_redirection = -1;
    int input_redirection = -1;
    for (int a = 0; a < argc; a++) {
        if (*(argv[a]) == '>') {
            output_redirection = a;
        } else if (*(argv[a]) == '<') {
            input_redirection = a;
        }
    }
    int num_commands = 1;
    int pipes_exist = 0;
    int command_indexes[argc];
    pid_t fork_return;
    command_indexes[0] = 0;
    int status_p;
    for (int i = 0; i < argc; i++) {
        if (*(argv[i]) == '|') {
            argv[i] = NULL;
            pipes_exist = 1;
            command_indexes[num_commands++] = i + 1;
        }
    }
    if (pipes_exist == 1) {
	
        fork_return = fork();
        if (fork_return == 0) {
	    
            recursive_pipes(0, num_commands-1, command_indexes, argv);
        } else if (fork_return > 0) {
	   wait(&status_p);   
        }
        return;
    }
    if (builtin_cmd(argv, argc) == 0) {
	sigset_t blockSet, prevMask;
        sigemptyset(&blockSet);
        sigaddset(&blockSet, SIGINT);
        sigaddset(&blockSet, SIGTSTP);
        sigaddset(&blockSet, SIGCHLD);
        sigprocmask(SIG_BLOCK, &blockSet, &prevMask);
        if (*(argv[argc-1]) == '&') {
            argv[argc-1] = NULL;
            child_pid = fork();
            if (child_pid < 0) {
                perror("fork failed");
                exit(EXIT_FAILURE);
            } else if (child_pid == 0) {
		setpgid(0, 0);
		sigprocmask(SIG_SETMASK, &prevMask, NULL);
		if (output_redirection != -1) { 
                    int filefd = open(argv[output_redirection + 1], O_RDWR | O_CREAT | O_TRUNC, S_IRWXU);
                    if (filefd == -1) {
			perror("open");
		    }
                    if (dup2(filefd, fileno(stdout)) == -1) {
			perror("dup2");
		    }
		    close(filefd);

                }
                if (input_redirection != -1) {
                    int filefd1 = open(argv[input_redirection + 1], O_RDWR | O_CREAT, S_IRWXU);
                    if (filefd1 == -1) {
		        perror("open");
		    }
                    if (dup2(filefd1, fileno(stdin)) == -1) {
		        perror("dup2");
		    }
		    close(filefd1);
                }
		if (input_redirection != -1 && output_redirection != -1) {
                    argv[argc-4] = NULL;
                } else if (input_redirection != -1 || output_redirection != -1) {
                    argv[argc-2] = NULL;
                }
                if (execve(argv[0], argv, NULL) == -1) {
		    printf("%s: Command not found\n", argv[0]);
                    exit(EXIT_FAILURE);
                }
            } else {
                addjob(jobs, child_pid, BG, cmdline);
		sigprocmask(SIG_SETMASK, &prevMask, NULL);
		printf("[%d] (%d) %s", pid2jid(child_pid), child_pid, cmdline);
            }
        } else {
            child_pid = fork();
            if (child_pid < 0) {
                perror("fork failed");
                exit(EXIT_FAILURE);
            } else if (child_pid == 0) {
		setpgid(0, 0);
		sigprocmask(SIG_SETMASK, &prevMask, NULL);
		if (output_redirection != -1) {
                    int filefd = open(argv[output_redirection + 1], O_RDWR | O_CREAT | O_TRUNC, S_IRWXU);
                    if (filefd == -1) {
			perror("open");
		    }
                    if (dup2(filefd, fileno(stdout)) == -1) {
			perror("dup2");
		    }
		    close(filefd);
                }
                if (input_redirection != -1) {
                    int filefd1 = open(argv[input_redirection + 1], O_RDWR | O_CREAT, S_IRWXU);
                    if (filefd1 == -1) {
			perror("open");
		    }
                    if (dup2(filefd1, fileno(stdin)) == -1) {
			perror("dup2");
		    }
		    close(filefd1);
                }
		if (input_redirection != -1 && output_redirection != -1) {
                    argv[argc-4] = NULL;
                } else if (input_redirection != -1 || output_redirection != -1) {
                    argv[argc-2] = NULL;
                }
                if (execve(argv[0], argv, NULL) == -1) {
		    printf("%s: Command not found\n", argv[0]);
                    exit(EXIT_FAILURE);
                }
            } else {
                addjob(jobs, child_pid, FG, cmdline);
		sigprocmask(SIG_SETMASK, &prevMask, NULL);
                waitfg(child_pid);
            }
        }
    }
    return;
}

/* 
 * parseline - Parse the command line and build the argv array.
 * 
 * Characters enclosed in single quotes are treated as a single
 * argument.  Return number of arguments parsed.
 */
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 space or quote delimiters */
    int argc;                   /* number of args */

    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;
    
    return argc;
}

/* 
 * builtin_cmd - If the user has typed a built-in command then execute
 *    it immediately.  
 */
int builtin_cmd(char **argv, int argc) {
    if (argv[0] == NULL) {
	return 1;
    }
    if (strcmp(argv[0], "quit") == 0) {
        exit(0);
    } else if (strcmp(argv[0], "jobs") == 0) {
        listjobs(jobs);
        return 1;
    } else if (strcmp(argv[0], "bg") == 0) {
	if (argc != 2) {
	    printf("bg command requires PID or %%jid argument\n");
	} else {
	    do_bgfg(argv);
	}
        return 1;
    } else if (strcmp(argv[0], "fg") == 0) {
	if (argc != 2) {
            printf("fg command requires PID or %%jid argument\n");
        } else {
            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) {
    int num;
    char *argv_1 = argv[1];
    if (argv_1[0] == '%') {
	argv_1 = argv_1 + 1;
        num = strtol(argv_1, NULL, 10);
	if (num == 0) {
	    printf("%s: argument must be a PID or %%jid\n", argv[0]);
	    return;
	}
        struct job_t *job1 = getjobjid(jobs, num);
        if (job1 == NULL) {
            printf("%s: No such job\n", argv[1]);
        } else {
            if (strcmp(argv[0], "bg") == 0) {
                kill(-(job1->pid), SIGCONT);
                job1->state = BG;
		printf("[%d] (%d) %s",job1->jid, job1->pid, job1->cmdline);
            } else if (strcmp(argv[0], "fg") == 0) {
                job1->state = FG;
                kill(-(job1->pid), SIGCONT);
                waitfg(job1->pid);
            }
        }
    } else {
        num = strtol(argv_1, NULL, 10);
	if (num == 0) {
            printf("%s: argument must be a PID or %%jid\n", argv[0]);
            return;
        }
        struct job_t *job1 = getjobpid(jobs, num);
        if (job1 == NULL) {
            printf("(%d): No such process\n", num);
        } else {
            if (strcmp(argv[0], "bg") == 0) {
                kill(-(job1->pid), SIGCONT);
                job1->state = BG;
		printf("[%d] (%d) %s",job1->jid, job1->pid, job1->cmdline);
            } else if (strcmp(argv[0], "fg") == 0) {
                job1->state = FG;
                kill(-(job1->pid), SIGCONT);
                waitfg(job1->pid);
            }
        }
    }
    return;
}

/* 
 * waitfg - Block until process pid is no longer the foreground process
 */
void waitfg(pid_t pid) {
    sigset_t set;
    sigemptyset(&set);
    int job_still_here = 0;
    int no_longer_FG = 0;
    while (1) {
	job_still_here = 0;
	no_longer_FG = 0;
        sigsuspend(&set);
        for (int i = 0; i < MAXJOBS; i++) {
            if (jobs[i].pid == pid) {
                job_still_here = 1;
                if (jobs[i].state != FG) {
                    no_longer_FG = 1;
                    return;
                }
            }
        }
        if (job_still_here == 0 || no_longer_FG == 1) {
            return;
        }
    }
    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 wpid;
    int status;
    wpid = waitpid(-1, &status, WNOHANG | WUNTRACED);
    if (wpid == -1) {
        // Error occurred while waiting
        perror("waitpid");
	exit(1);
    } else if (wpid == 0) {
	
    }
    if (wpid > 0) {
	if (WIFEXITED(status)) {
	    deletejob(jobs, wpid);
	} else if (WIFSTOPPED(status)) {
            for (int k = 0; k < MAXJOBS; k++) {
		if (jobs[k].state == FG) {
		    jobs[k].state = ST;
		    //printf("Job [%d] (%d) stopped by signal %d\n", jobs[k].jid, jobs[k].pid, SIGTSTP);
		}
		
	    }
        }
	if (WIFSIGNALED(status)) {
	    int sig = WTERMSIG(status);
            if (sig == SIGINT) {
		//printf("Job [%d] (%d) terminated by signal %d\n",pid2jid(wpid),wpid,SIGINT);
                deletejob(jobs, wpid);
            }
	}
    }
    return;
}

/* 
 * sigint_handler - The kernel sends a SIGINT to the shell whenever the
 *    user types ctrl-c at the keyboard.  Catch it and send it along
 *    to the foreground job.  
 */
void sigint_handler(int sig) {
    for (int i = 0; i < MAXJOBS; i++) {
        if (jobs[i].state == FG) {
	    printf("Job [%d] (%d) terminated by signal %d\n", jobs[i].jid, jobs[i].pid, SIGINT);
            kill(-(jobs[i].pid), SIGINT);
	    deletejob(jobs, jobs[i].pid);
        }
    }
    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) {
    for (int i = 0; i < MAXJOBS; i++) {
        if (jobs[i].state == FG) {
            printf("Job [%d] (%d) stopped by signal %d\n", jobs[i].jid, jobs[i].pid, SIGTSTP);
            jobs[i].state = ST;
            kill(-(jobs[i].pid), SIGTSTP);
        }
    }
    return;
}


/*
 * sigusr1_handler - child is ready
 */
void sigusr1_handler(int sig) {
    ready = 1;
}


/*********************
 * 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]);
}

/* freejid - Returns smallest free job ID */
int freejid(struct job_t *jobs) {
    int i;
    int taken[MAXJOBS + 1] = {0};
    for (i = 0; i < MAXJOBS; i++)
        if (jobs[i].jid != 0) 
        taken[jobs[i].jid] = 1;
    for (i = 1; i <= MAXJOBS; i++)
        if (!taken[i])
            return i;
    return 0;
}

/* 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;

    int free = freejid(jobs);
    if (!free) {
        printf("Tried to create too many jobs\n");
        return 0;
    }
    for (i = 0; i < MAXJOBS; i++) {
        if (jobs[i].pid == 0) {
            jobs[i].pid = pid;
            jobs[i].state = state;
            jobs[i].jid = free;
            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;
        }
    }
    return 0; /*suppress compiler warning*/
}

/* 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]);
            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 and terminate
 */
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);
}