问第二个输入char*产生无限循环

EN

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

#define MAXARG 7

int main()
{
    char buf[256];
    char* arg[MAXARG];
    char* s;
    char* save;
    int argv;

    static const char delim[] = " \t\n";
    int pid, status;

    while(1){
        printf("MyShell: ");
        fgets(buf, sizeof(buf), stdin);
        fflush(stdin);
        argv = 0;

        s = strtok_r(buf, delim, &save);

        while(s){
            arg[argv++] = s;
            s= strtok_r(NULL, delim, &save);
        }

        arg[argv] = (char*) 0;

        if(!strcmp(arg[0], "quit"))
            break;
        if((pid = fork()) == -1)
            perror("fork failed...");
        else if(pid != 0){
            pid = wait(&status);
        }
        else{
            execvp(arg[0], arg);
        }
    }
    return 0;
}