#include<stdlib.h>
void my_exit(void)
{
    printf(“before exit () !\n”);
}
main()
{
    atexit (my_exit);
    exit(0);
}

#include<unistd.h>
main()
{
    execl(“/bin/ls”,”ls”,”-al”,”/etc/passwd”,(char * )0);
}

/* 执行结果ls -al /etc/passwd execlp()会依PATH 变量中的/bin找到/bin/ls*/
#include<unistd.h>
main()
{
    execlp(“ls”,”ls”,”-al”,”/etc/passwd”,(char *)0);
}

/* 执行结果/bin/ls -al /etc/passwd */
#include<unistd.h>
main()
{
    char * argv[ ]={“ls”,”-al”,”/etc/passwd”,(char*) }};
    execv(“/bin/ls”,argv);
}

#include<unistd.h>
main()
{
    char * argv[ ]={“ls”,”-al”,”/etc/passwd”,(char *)0};
    char * envp[ ]={“PATH=/bin”,0}
    execve(“/bin/ls”,argv,envp);
}

/*请与execlp（）使用示例对照*/
#include<unistd.h>
main()
{
    char * argv[ ] ={ “ls”,”-al”,”/etc/passwd”,0};
    execvp(“ls”,argv);
}

#include<unistd.h>
main()
{
    if(vfork() = =0)
    {
        printf(“This is the child process\n”);
    }else{
        printf(“This is the parent process\n”);
    }
}

/*取得init 进程（pid＝1）的组识别码*/
#include<unistd.h>
mian()
{
    printf(“init gid = %d\n”,getpgid(1));
}

#include<unistd.h>
main()
{
    printf(“my gid =%d\n”,getpgrp());
}

#include<unistd.h>
main()
{
    printf(“pid=%d\n”,getpid());
}

#include<unistd.h>
main()
{
    printf(“My parent ‘pid =%d\n”,getppid());
}

#include<stdlib.h>
void my_exit(int status,void *arg)
{
    printf(“before exit()!\n”);
    printf(“exit (%d)\n”,status);
    printf(“arg = %s\n”,(char*)arg);
}
main()
{
    char * str=”test”;
    on_exit(my_exit,(void *)str);
    exit(1234);
}

#include<stdlib.h>
main()
{
    system(“ls -al /etc/passwd /etc/shadow”);
}

#include<stdlib.h>
#include<unistd.h>
#include<sys/types.h>
#include<sys/wait.h>
main()
{
    pid_t pid;
    int status,i;
    if(fork()= =0){
        printf(“This is the child process .pid =%d\n”,getpid());
        exit(5);
    }else{
        sleep(1);
        printf(“This is the parent process ,wait for child...\n”;
        pid=wait(&status);
        i=WEXITSTATUS(status);
        printf(“child’s pid =%d .exit status=^d\n”,pid,i);
    }
}

#include<stdio.h>
main()
{
    int i = 150;
    int j = -100;
    double k = 3.14159;
    fprintf(stdout,”%d %f %x \n”,j,k,i);
    fprintf(stdout,”%2d %*d\n”,i,2,i);
}

#include<stdio.h>
main()
{
    int i;
    unsigned int j;
    char s[5];
    fscanf(stdin,”%d %x %5[a-z] %*s %f”,&i,&j,s,s);
    printf(“%d %d %s \n”,i,j,s);
}

#include<stdio.h>
main()
{
    int i = 150;
    int j = -100;
    double k = 3.14159;
    printf(“%d %f %x\n”,j,k,i);
    printf(“%2d %*d\n”,i,2,i); /*参数2 会代入格式*中，而与%2d同意义*/
}

#include <stdio.h>
      main()
      {
      int i;
      unsigned int j;
      char s[5];
      scanf(“%d %x %5[a-z] %*s %f”,&i,&j,s,s);
      printf(“%d %d %s\n”,i,j,s);
      }

#include<stdio.h>
main()
{
    char * a=”This is string A!”;
    char buf[80];
    sprintf(buf,”>>> %s<<<\n”,a);
    printf(“%s”.buf);
}

#include<stdio.h>
main()
{
    int i;
    unsigned int j;
    char input[ ]=”10 0x1b aaaaaaaa bbbbbbbb”;
    char s[5];
    sscanf(input,”%d %x %5[a-z] %*s %f”,&i,&j,s,s);
    printf(“%d %d %s\n”,i,j,s);
}

#include<stdio.h>
#include<stdarg.h>
int my_printf( const char *format,……)
{
    va_list ap;
    int retval;
    va_start(ap,format);
    printf(“my_printf( ):”);
    retval = vprintf(format,ap);
    va_end(ap);
    return retval;
}
main()
{
    int i = 150,j = -100;
    double k = 3.14159;
    my_printf(“%d %f %x\n”,j,k,i);
    my_printf(“%2d %*d\n”,i,2,i);
}