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Postings from December 2011
frank cui wrote:
> hi,
Hello,
> I'm reading the book of "automating system administration with perl" and
> having doubts about this code snippets about file health check.
>
> # attempt to read the directory entry for this file
> my @stat = stat($name);
That should probably be:
my @stat = stat($name) or return 0;
> if ( !$stat[4] && !$stat[5] && !$stat[6] && !$stat[7] && !$stat[8] ) {
> return 0; # according to the code context, here it
> is saying the file is NOT ok
> }
>
> here $name refers to the file name and it's checking the stat of this file.
>
> stat[4:8] refers to the following from the "perldoc -f stat"
>
> 4 uid numeric user ID of file's owner
> 5 gid numeric group ID of file's owner
> 6 rdev the device identifier (special files only)
> 7 size total size of file, in bytes
> 8 atime last access time in seconds since the epoch
>
> so here the code is actually saying if all the above entries is 0 or
> undefined, then we declare this file to be NOT ok .
> and my question would be about this logic, why are we checking all of them
> with a AND relationship rather than OR, or maybe something else(like
> checking all the 0-12 entries) ?
That looks like a general heuristic that the author assumed would
indicated a bad file. As to whether it would work accurately is mute
(there are a lot of files with a UID, GID and RDEV of 0, assuming he is
reading from the whole file system.)
John
--
Any intelligent fool can make things bigger and
more complex... It takes a touch of genius -
and a lot of courage to move in the opposite
direction. -- Albert Einstein
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