exec
execl( char *pathname, char *arg0, ... , (char*) 0 );
execv( char *pathname, char *argv[] );
execle( char *pathname, char *arg0, ..., (char*) 0,
char *envp[] );
execve( char *pathname, char *argv[],
char *envp[] );
execlp( char *filename, char *arg0, ..., (char*) 0 );
execvp( char *filename, char *argv[] );