linux之access函数解析
[lingyun@localhost access_1]$ ls
access.c
实例一：
[lingyun@localhost access_1]$ cat access.c
/*********************************************************************************
* Copyright: (C) 2013 fulinux<fulinux@sina.com>
* All rights reserved.
*
* Filename: access.c
* Description: This file
*
* Version: 1.0.0(08/02/2013~)
* Author: fulinux <fulinux@sina.com>
* ChangeLog: 1, Release initial version on "08/02/2013 04:10:44 PM"
*
********************************************************************************/
#include <stdio.h>
#include <unistd.h>
int main(void)
{
if(access("/etc/passwd", R_OK) == 0)
printf("/etc/passwd can be read\n");
}
[lingyun@localhost access_1]$ gcc access.c
[lingyun@localhost access_1]$ ./a.out
/etc/passwd can be read
[lingyun@localhost access_1]$
实例二：
[lingyun@localhost access_2]$ vim access.c
+ access.c
/*********************************************************************************
* Copyright: (C) 2013 fulinux<fulinux@sina.com>
* All rights reserved.
*
* Filename: access.c
* Description: This file
*
* Version: 1.0.0(08/02/2013~)
* Author: fulinux <fulinux@sina.com>
* ChangeLog: 1, Release initial version on "08/02/2013 04:18:45 PM"
*
********************************************************************************/
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
int main(int argc, char *argv[])
{
if(argc < 2)
{
printf("Usave: ./test filename\n");
exit(1);
}
if(access(argv[1], F_OK) == -1)
{
puts("File not exists!");
exit(2);
}
if(access(argv[1], R_OK) == -1)
puts("You can't read the file!");
else
if(access(argv[1], R_OK|W_OK) != -1)
puts("You can read and write the file");
else
puts("You can read the file");
exit(0);
}
~
~
~
~
~
~
~/apue/access/access_2/access.c[+] CWD: /usr/local/src/lingyun/apue/access/access_2 Line: 41/42:12
"access.c" [New] 42L, 1090C written
[lingyun@localhost access_2]$ gcc access.c
[lingyun@localhost access_2]$ ./a.out /etc/passwd
You can read the file
[lingyun@localhost access_2]$ ./a.out access.c
You can read and write the file
[lingyun@localhost access_2]$
[lingyun@localhost access_3]$ vim access.c
+ access.c
/*********************************************************************************
* Copyright: (C) 2013 fulinux<fulinux@sina.com>
* All rights reserved.
*
* Filename: access.c
* Description: This file
*
* Version: 1.0.0(08/02/2013~)
* Author: fulinux <fulinux@sina.com>
* ChangeLog: 1, Release initial version on "08/02/2013 04:10:44 PM"
*
********************************************************************************/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <unistd.h>
#include <err.h>
int main(int argc, char *argv[])
{
if(argc != 2)
{
printf("usage: a.out <pathname>\n");
exit(1);
}
if(access(argv[1], R_OK) < 0)
{
warn("access error for %s", argv[1]);
}
else
printf("read access OK\n");
if(open(argv[1], O_RDONLY) < 0)
{
warn("open error for %s", argv[1]);
}
else
printf("open for reading OK\n");
exit(0);
}
~
~
~
~
~
~
~
~/apue/access/access_3/access.c[+] CWD: /usr/local/src/lingyun/apue/access/access_3 Line: 36/41:5
"access.c" 41L, 1065C written
[lingyun@localhost access_3]$ gcc access.c
[lingyun@localhost access_3]$ ./a.out
usage: a.out <pathname>
[lingyun@localhost access_3]$ ./a.out access.c
read access OK
open for reading OK
[lingyun@localhost access_3]$ ls -l /etc/shadow
---------- 1 root root 1151 Jun 4 23:16 /etc/shadow
[lingyun@localhost access_3]$ ./a.out /etc/shadow
a.out: access error for /etc/shadow: Permission denied
a.out: open error for /etc/shadow: Permission denied
[lingyun@localhost access_3]$ sudo su
[root@localhost access_3]# chown root a.out
[root@localhost access_3]# chmod u+s a.out
[root@localhost access_3]# ls -l a.out
-rwsr-xr-x 1 root trainning 7220 Aug 2 17:04 a.out
[root@localhost access_3]# exit
exit
[lingyun@localhost access_3]$ ./a.out /etc/shadow
a.out: access error for /etc/shadow: Permission denied
open for reading OK
[lingyun@localhost access_3]$
