击试验，如果目录是可写把定的UID
问题说明
我们可以测试出目录是否由当前进程的UID可写的：
We can test if a directory is writable by the uid of the current process:
$ if [ -w $directory ] ; then echo 'Eureka!' ; fi
但是，任何人都可以提出一个方法来测试一个目录有写入一些的其他的UID？
我的情况是，我管理MySQL服务器的实例，我要临时更改慢查询日志文件的位置。我可以通过执行MySQL命令 SET GLOBAL slow_query_log_file ='$ new_log_filename做到这一点，然后禁用和放大器;启用查询日志记录，以的mysqld 开始使用该文件。
My scenario is that I am administering a MySQL Server instance, and I want to change the location of the slow-query log file temporarily. I can do this by executing a MySQL command SET GLOBAL slow_query_log_file='$new_log_filename' and then disable & enable query logging to make mysqld start using that file.
不过，我想我的脚本来检查的mysqld 进程的UID有权限创建新的日志文件。所以我想要做类似的信息（伪code）：
But I'd like my script to check that the uid of the mysqld process has permissions to create that new log file. So I'd like to do something like (pseudocode):
$ if [ -w-as-mysql-uid `basename $new_log_filename` ] ; then echo 'Eureka!' ; fi
不过，当然，这是一个虚构的测试predicate的。
But of course that's an imaginary test predicate.
的澄清：的我想是不依赖于苏的解决方案，因为我不能假设用户的我的脚本有苏特权。
Clarification: I would like a solution that doesn't rely on su because I can't assume the user of my script has su privilege.
正确答案
下面是检查的一个长期的，迂回的方式。
Here's a long, roundabout way of checking.
USER=johndoe
DIR=/path/to/somewhere
# Use -L to get information about the target of a symlink,
# not the link itself, as pointed out in the comments
INFO=( $(stat -cL "%a %G %U" $DIR) )
PERM=${INFO[0]}
GROUP=${INFO[1]}
OWNER=${INFO[2]}
ACCESS=no
if [[ $PERM & 0002 != 0 ]]; then
# Everyone has write access
ACCESS=yes
elif [[ $PERM & 0020 != 0 ]]; then
# Some group has write access.
# Is user in that group?
gs=( $(groups $USER) )
for g in "${gs[@]}"; do
if [[ $GROUP == $g ]]; then
ACCESS=yes
break
fi
done
elif [[ $PERM & 0200 != 0 ]]; then
# The owner has write access.
# Does the user own the file?
[[ $USER == $OWNER ]] && ACCESS=yes
fi
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