execlp

execlp:
1）如果filename（即第一个参数）中包含了"/",则将其视为路径名，如果不包含，则在环境变量PATH中查看filename
2) 找到filename后便执行该文件，然后将第二个以后的参数当做该文件的argv[0]

execlp  ("ls",    "-al",  (char *)0);
filename    arg0      arg1
argv[0]  argv[1]
所以没有参数
不过这样子把argv[0] 的内容改掉了， 一般的main函数，argv［0］是可执行文件名，
所以按习惯应该是像  execlp("ls","ls","-al",(char *)0) 这样使用。

/*
 * main.c
 */
#include <stdio.h>

#include <unistd.h>

int
main(int argc, char *argv[])
{
        int r;

        r = execlp("./hello",
                        "What's your name?",
                        "What did you say?",
                        "What is your name?",
                        "Oh, call me World.",
                        (char *)0);
        return 0;
}
/*
 * hello.c
 */
#include <stdio.h>

int
main(int argc, char *argv[])
{
        int i;

        for (i = 0; i < argc; i++) {
                printf("%s\n", argv[i]);
        }

        return 0;
}
/*
 * The out put is as the following:
 *================================
$ make main hello && ./main
cc -g  main.c  -o main
cc -g  hello.c  -o hello
What's your name?
What did you say?
What is your name?
Oh, call me World.
$ 
 *================================
 */