exec函数族的作用是根据指定的文件名找到可执行文件，并用它来取代调用进程的内容，换句话说，就是在调用进程内部执行一个可执行文件
exec函数族共6个函数:

1.

int execl(const char *path, const char *arg0, ... /*, (char *)0 */);

path:路径
arg0,arg1,...,argn:参数

#include <unistd.h>
int main(int argc,char **argv){
	int ret;
	ret = execl ("/bin/ls", "ls", "-1", (char *)0);
}

2.

int execv(const char *path, char *const argv[]);

path:路径
argv:参数集

#include <unistd.h>
int main(int argc,char **argv){
	int ret;
	char *cmd[] = { "ls", "-l", (char *)0 };
	ret = execv ("/bin/ls", cmd);
	return ret;
}

3.

int execle(const char *path, const char *arg0, ... /*,(char *)0, char *const envp[]*/);

path:路径
arg0,arg1,...,argn:参数
envp:环境变量

#include <unistd.h>
int main(int argc,char **argv){
	int ret;
	char *env[] = { "HOME=/usr/home", "LOGNAME=home", (char *)0 };
	ret = execle ("/bin/ls", "ls", "-l", (char *)0, env);
	return ret;
}

4.

int execve(const char *path, char *const argv[], char *const envp[]);

path:路径
argv:参数集
envp:环境变量

#include <unistd.h>
int main(int argc,char **argv){
	int ret;
	char *cmd[] = { "ls", "-l", (char *)0 };
	char *env[] = { "HOME=/usr/home", "LOGNAME=home", (char *)0 };
	ret = execve ("/bin/ls", cmd, env);
	return ret;
}

5.

int execlp(const char *file, const char *arg0, ... /*, (char *)0 */);

file:文件
arg0,arg1,...,argn:参数

#include <unistd.h>
int main(int argc,char **argv){
	int ret;
	ret = execlp ("ls", "ls", "-l", (char *)0);
	return ret;
}

6.

int execvp(const char *file, char *const argv[]);

file:文件
argv:参数集

#include <unistd.h>
int main(int argc,char **argv){
	int ret;
	char *cmd[] = { "ls", "-l", (char *)0 };
	ret = execvp ("ls", cmd);
	return ret;
}

函数名都是由exec+性质(l-可变参数,v-参数集,e-带环境变量,p-文件)组成

int execl(const char *path, const char *arg0, ... /*, (char *)0 */);
int execv(const char *path, char *const argv[]);
int execle(const char *path, const char *arg0, ... /*,(char *)0, char *const envp[]*/);
int execve(const char *path, char *const argv[], char *const envp[]);
int execvp(const char *file, char *const argv[]);
int execlp(const char *file, const char *arg0, ... /*, (char *)0 */);

exec函数族