exec

1. http://imxfox.appspot.com/?p=118002
2. exec家族比較, http://man7.org/linux/man-pages/man3/execl.3.html
3. http://tc.itkee.com/os/detail-1bae.html
4. http://linux.about.com/od/commands/l/blcmdln_exec.htm

#include <unistd.h>

extern char **environ;

int execl(const char *path, const char *arg, ...);

int execlp(const char *file, const char *arg, ...);

int execle(const char *path, const char *arg,..., char * const envp[]);

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

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

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