Simple shell written for NYU CSO course in Spring 2013

tsh.c

/* 
* tsh - A tiny shell program with job control
* 
* Michael Garate | mg3626
* 
* Book code found here: http://csapp.cs.cmu.edu/public/code.html
* 
*/
#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 */


/* verbose */

#define DEBUG 0	/* printf and flush, verbose, debug */

/* 
* 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 */

/*Error handling wrappers */
pid_t Fork(void);
int Execve(const char *filename, char *const argv[], char *const envp[]);
int Kill(pid_t pid, int sig);
int Setpgid(pid_t pid, pid_t pgid);
int Sigemptyset(sigset_t *set);
int Sigaddset(sigset_t *set, int signo);
int Sigprocmask(int how, const sigset_t *set, sigset_t *oldset);

/* 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);

/* error wrappers */
/* Based on book code pg 752*/
pid_t Fork(void)
{
	pid_t pid;
	if ((pid = fork()) < 0)
	unix_error("Fork error");
	return pid;
}
int Execve(const char *filename, char *const argv[], char *const envp[])
{
	if(execve(filename, argv, envp) < 0)
	printf("%s: Command not found\n", argv[0]);
	exit(0);	
}
int Kill(pid_t pid, int sig)
{
	if (kill(pid, sig) < 0)
	unix_error("Kill error");
	return 0;
}
int Setpgid(pid_t pid, pid_t pgid)
{
	if (setpgid(pid, pgid) < 0)
	unix_error("Setpgid error");
	return 0;
}
int Sigemptyset(sigset_t *set)
{
	if (sigemptyset(set) < 0)
	unix_error("Setpgid error");
	return 0;
}
int Sigaddset(sigset_t *set, int signo)
{
	if (sigaddset(set, signo) < 0)
	unix_error("Setpgid error");
	return 0;
}
int Sigprocmask(int how, const sigset_t *set, sigset_t *oldset)
{
	if (sigprocmask(how, set, oldset) < 0)
	unix_error("Setpgid error");
	return 0;
}
/*
* 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)  /* Based on book code shellex.c and procmask2.c */
{
	char *argv[MAXARGS]; /* Argument list execve() */
	char buf[MAXLINE];   /* Holds modified command line */
	int bg;              /* Should the job run in bg or fg? */
	pid_t pid;           /* Process id */
	sigset_t mask;
	int state = 0;		 /* 1 is FG, 2 is BG, 3 is STopped, and 0 is undefined */
	
	strcpy(buf, cmdline);
	bg = parseline(buf, argv); 
	if (argv[0] == NULL)  
	return;   										/* Ignore empty lines */
	

	if (!builtin_cmd(argv)) { 
		
		Sigemptyset(&mask);
		Sigaddset(&mask, SIGCHLD);
		Sigprocmask(SIG_BLOCK, &mask, NULL); 		/* Block SIGCHILD */
		
		if ((pid = Fork()) == 0) {   				/* Child runs user job */
			Setpgid(0, 0); 							/* Give process own group id */
			Sigprocmask(SIG_UNBLOCK, &mask, NULL); 	/* Unblock SIGCHILD for excecve */
			Execve(argv[0], argv, environ);
		}
		
		if (bg){ 		/* Convert bg to state syntax for job control */
			state = 2;  /* Background */
		}
		else{
			state = 1;	/* Foreground */
		}
		if (!bg) {
			addjob(jobs, pid, state, cmdline); 			/* Add this fg job to the jobs list */
			Sigprocmask(SIG_UNBLOCK, &mask, NULL); 		/* Unblock SIGCHILD */
			waitfg(pid);
		}
		else{
			addjob(jobs, pid, state, cmdline); 			/* Add this bg job to the jobs list */
			struct job_t* job = getjobpid(jobs, pid); 	/* Point to address of current job information */
			Sigprocmask(SIG_UNBLOCK, &mask, NULL); 		/* Unblock SIGCHILD */
			printf("[%d] (%d) %s", job->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) /* quit, ignore, and 'not builtin cmd' based on book code */
{
	if(DEBUG){printf("Begin: builtin_cmd\n"); fflush(stdout);}
	
	if (!strcmp(argv[0], "quit")){ 		/* quit command */
		exit(0);  
	}
	if (!strcmp(argv[0], "&"))    		/* Ignore singleton & */
		return 1;
	if (!strcmp(argv[0], "jobs")){    	/* jobs command & */
		listjobs(jobs);
		return 1;
	}
	if (!strcmp(argv[0], "bg")){    	/* bg command */
		do_bgfg(argv);
		return 1;
	}
	if (!strcmp(argv[0], "fg")){    	/* fg command */
		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(DEBUG){printf("Begin: do_bgfg?\n"); fflush(stdout);}

	char* idString = argv[1];				/* Hold the input id, including % sign (for now) */
	int id = -1;							/* Hold the input jid or pid */
	int is_pid = 1;							/* Boolean to remember if pid or jid */
	int i;									/* Counter for loops */
	int found;
	struct job_t* job;						/* Hold current job */
	int argc = 1;

	while(argv[argc]!=NULL && argc < 4){	/* Count the number of arguments. No need to go past 4. */
		argc++;
	}
	
	/* Handle invalid inputs and parse input */
	if (argc!=2){							/* Print error if more/less than 2 args */
		printf("%s command requires PID or %%jobid argument\n", argv[0]);
		return;
	}
	if (idString[0] == '%'){    			/* Check for '%' to see if jid */
		idString = idString + 1; 			/* Inc. pointer to skip '%' symbol */
		is_pid = 0;							/* Remember if not pid */
	}
	for (i=0;idString[i]!=0;i++){ 			/* Check that string is only digits */
		if (!isdigit(idString[0])){	
			printf("%s: argument must be a PID or %%jobid\n", argv[0]);
			return;
		}
	}
	id = atoi(idString);									/* Cast String to integer */
	if(is_pid){
		found=0;
		if (id < 1) printf("(%i): No such process\n", id); 	/* Immediately deal with impossible PID */
		for (i = 0; i < maxjid(jobs); i++){					/* Check that this pid exists in currently active jobs */
			if (jobs[i].pid == id) {
				found = 1;
			}
		}
		if (!found) {
			printf("(%i): No such process\n", id);
			return;
		}
		job = getjobpid(jobs, id);							/* Get current job by pid */
	}
	else{
		found=0;
		if (id < 1) printf("(%i): No such process\n", id);	/* Immediately deal with impossible JID */
		for (i = 0; i < maxjid(jobs); i++){					/* Check that this jid exists in currently active jobs */
			if (jobs[i].jid == id) {
				found = 1;
			}
		}
		if (!found) {
			printf("%%%i: No such job\n", id);
			return;
		}
		job = getjobjid(jobs, id);			/* Get current job by jid */
	}
	pid_t pid = job->pid;
	if (!strcmp(argv[0], "bg")){ 			/* Set state to bg and send SIGCONT signal */
		job->state = BG;
		Kill(-pid, SIGCONT);
		printf("[%d] (%d) %s", job->jid, pid, job->cmdline);
	}
	else if (!strcmp(argv[0], "fg")){  		/* Set state to fg, send SIGCONT signal, and enter waitfg() loop */
		job->state = FG;
		Kill(-pid, SIGCONT);
		waitfg(pid);
	}
	return;
}

/* 
* waitfg - Block until process pid is no longer the foreground process
*/
void waitfg(pid_t pid)
{
	if(DEBUG){ printf("Begin: waitfg\n"); listjobs(jobs); fflush(stdout);}
	/* Wait for fg job to terminate */
	while (pid == fgpid(jobs)){
		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)  	/* Code adapted from pg 761, waitpid1.c and linux man page for waitpid */
{	
	if(DEBUG){ printf("Caught SIGCHLD\n"); listjobs(jobs); fflush(stdout);}
	
	/* Get pgid of fg process */
	pid_t pid, w;
	pid = fgpid(jobs);
	int status = getpgid(pid);
	
	/* Do waitpid() for all exited children. Adapted from man page example code. */
	do {
		w = waitpid(-1, &status,WUNTRACED|WNOHANG);
		if (w == -1) {
			perror("waitpid");
			exit(EXIT_FAILURE);
		}
		if(WIFEXITED(status)){ 						/* Silently reap exited child */
				if(DEBUG){ printf("%i reaped, status=%d\n", w, WEXITSTATUS(status)); fflush(stdout);}
			deletejob(jobs, w);
		}
		else if (WIFSIGNALED(status)){ 				/* Run deletejob() for terminated jobs */
			if(WTERMSIG(status) == 2)				/* Only print for signal 2 */
			{
				printf("Job [%i] (%i) terminated by signal %d\n",pid2jid(w), w, WTERMSIG(status));
			}
			deletejob(jobs, w);
		}
		else if (WIFSTOPPED(status) && WSTOPSIG(status)==20){	/* Change job state for stop signal */
			int i;
			for (i = 0; i < MAXJOBS; i++){						/* Get current process and change state */
				if (jobs[i].pid == w) {
					jobs[i].state=ST;
					printf("Job [%i] (%i) stopped by signal 20\n",pid2jid(w), w);
					return;
				}
			}
			printf("WIFSTOPPED error\n" );
			return;
		}
		else if (WIFCONTINUED(status)) {
			printf("continued\n");
		}
	} while (!WIFEXITED(status) && !WIFSIGNALED(status));
	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) /* based on book code pg 779, sigint1.c */
{
	if(DEBUG){printf("Caught SIGINT\n"); listjobs(jobs); fflush(stdout);}
	
	/* Send SIGINT to -pgid*/
	pid_t pid = fgpid(jobs);
	int pgid = getpgid(pid);
	if(pgid < 0) unix_error("getpgid error"); 				/* Catch system call error */
	Kill(-pgid, SIGINT);
}

/*
* 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) 
{
	if(DEBUG){printf("Caught SIGTSTP\n"); listjobs(jobs); fflush(stdout);}
	
	/* Send SIGTSTP to -pgid*/
	pid_t pid = fgpid(jobs);
	int pgid = getpgid(pid);
	if(pgid < 0) unix_error("getpgid error"); 				/* Catch system call error */
	Kill(-pgid, SIGTSTP);
}

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