grep 이용해서 디렉토리 검색

user0@pc0:~/linux_system_programming$ grep -nr "strerror (" /usr/include/

/usr/include/error.h:28:   if ERRNUM is nonzero, follow it with ": " and strerror (ERRNUM).

/usr/include/netdb.h:95:extern const char *hstrerror (int __err_num) __THROW;

/usr/include/netdb.h:671:extern const char *gai_strerror (int __ecode) __THROW;

/usr/include/string.h:413:extern char *strerror (int __errnum) __THROW;

user0@pc0:~/linux_system_programming$ grep -nr "int errno" /usr/include/

/usr/include/errno.h:46:extern int errno;

user0@pc0:~/linux_system_programming$ grep -nr "int open ("  /usr/include/

/usr/include/fcntl.h:146:extern int open (const char *__file, int __oflag, ...) __nonnull ((1));