#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/wait.h>


struct list {
    int fd;
    char *filename;
    int mode;
    struct list *next;
} *top;

char *prog;

extern void buildlist(), getprog(), executeit(), freelist(struct list *p);
extern char *mygetline(), *estrsave(char *s);


int main()
{
    while (1) {
	buildlist();
	getprog();
	executeit();
	freelist(top);
    }
}


void buildlist()
{
    int fd;
    top = NULL;
    while (printf(
"Which file descriptor do you want to redirect?  -1 to end the list.\n")
	    , (fd = atoi(mygetline())) >= 0) {
	struct list *p = malloc(sizeof(struct list));
	if (p == NULL) {
	    fprintf(stderr, "out of memory!\n");
	    exit(1);
	}
	p->next = top;
	top = p;
	p->fd = fd;
	printf("Where do you want to redirect file descriptor %d to/from?\n",
		p->fd);
	p->filename = estrsave(mygetline());
	printf("Is %s to be opened for read or write?  ('r' or 'w')\n",
		p->filename);
	p->mode = (mygetline()[0] == 'r') ? O_RDONLY : (O_WRONLY|O_CREAT|O_TRUNC);
    }
}


void getprog()
{
    printf("What program do you want to execute?\n");
    prog = mygetline();
}


void executeit()
{
    int pid;

    printf("Executing:\n");
    fflush(stdout);
    
    if ((pid = fork()) < 0) {
	perror("fork");
	exit(1);
    } else if (pid == 0) {
	for (; top; top = top->next) {
	    int fd;
	    if ((fd = open(top->filename, top->mode, 0666)) < 0) {
		perror(top->filename);
		exit(126);
	    }
	    if (fd != top->fd) {
		dup2(fd, top->fd);
		close(fd);
	    }
	}
	execl("/bin/sh", "sh", "-c", prog, (char *)NULL);
	perror("/bin/sh");
	exit(125);
    } else {
	int status;
	if (wait(&status) < 0) {
	    perror("wait");
	    exit(1);
	}
	printf("exit status %d\n", WEXITSTATUS(status));
    }
}


void freelist(struct list *p)
{
    if (p) {
	free(p->filename);
	freelist(p->next);
	free(p);
    }
}



char *mygetline()
{
    static char buf[500];
    char *p;
    if (fgets(buf, sizeof buf, stdin) == NULL)
	exit(0);
    if ((p = strchr(buf, '\n')))
	*p = '\0';
    return(buf);
}

char *estrsave(char *s)
{
    char *q;
    if (!s)
	return(NULL);
    if ((q = malloc(strlen(s) + 1)) == NULL) {
	fprintf(stderr, "out of memory\n");
	exit(1);
    }
    strcpy(q, s);
    return(q);
}