#include <unistd.h>
main()
{
	char *envp[]={"PATH=/tmp",
			"USER=lei",
			"STATUS=testing",
			NULL};
	char *argv_execv[]={"echo", "excuted by execv",	NULL};
	char *argv_execvp[]={"echo", "executed by execvp", NULL};
	char *argv_execve[]={"env", NULL};
	if(fork()==0)
		if(execl("/bin/echo", "echo", "executed by execl", NULL)<0)
			perror("Err on execl");
	if(fork()==0)
		if(execlp("echo", "echo", "executed by execlp", NULL)<0)
			perror("Err on execlp");
	if(fork()==0)
		if(execle("/usr/bin/env", "env", NULL, envp)<0)
			perror("Err on execle");
	if(fork()==0)
		if(execv("/bin/echo", argv_execv)<0)
			perror("Err on execv");
	if(fork()==0)
		if(execvp("echo", argv_execvp)<0)
			perror("Err on execvp");
	if(fork()==0)
		if(execve("/usr/bin/env", argv_execve, envp)<0)
			perror("Err on execve");
}