How to test if a file is readable on Win64?

rhardy has asked for the wisdom of the Perl Monks concerning the following question:

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Re: How to test if a file is readable on Win64? by Anonymous Monk on Mar 09, 2014 at 23:29 UTC
Hi , I have some ideas :) Unfortunately this doesn't work on Windows resulting in my script crashing due to Permission Denied trying to read a protected file. Try Win32API::File , for example `sub is_readable { use Win32API::File (); my $oldMode = Win32API::File::SetErrorMode(2); my $readable = -r $_[0]; Win32API::File::SetErrorMode( $oldMode ); return $readable; }` [download] Also try cacls.exe for changing permissions ... Also, I remember hearing about starting win32 programs with "dropped privileges" (psexec.exe -d -l ) ... so the program doesn't use all the permissions you have ... :) Thats my ideas	[reply] [d/l]
Re^2: How to test if a file is readable on Win64? by rhardy (Acolyte) on Mar 10, 2014 at 01:16 UTC
Unfortunately this did not seem to work. I implemented your suggestions but my script fails in the exact same way i.e. it gets to a file which it cannot read but the is_readable function returns that it is readable and my program proceeds to try and execute code which can't possibly succeed i.e. diffing two files, one of which it can't read.	[reply]
Re^3: How to test if a file is readable on Win64? by Anonymous Monk on Mar 10, 2014 at 01:53 UTC
but the is_readable function returns that it is readable wait a minute, did the original code do that as well? Like I said earlier, newer versions of windows can have files which stat like readable but it won't let you read them (this is normal) -r doesn't check for these things (this is normal) you have to check for these things ... I've never dealt with this ... the win32api docs explain some of it as does tye :) (tye)Re: Opening a locked file for reading (tye)Re: Unable to write to a file opened in read only mode http://live.sysinternals.com/handle.exe and http://live.sysinternals.com/procexp.exe can help you see some diagnostic stuff If you SetErrorMode to 2 you won't get error popups that interrupt the program (but you won't be able to read file either) if you use cacls you can see or change the ACL (permissions) if that is a problem Good luck	[reply]
Re: How to test if a file is readable on Win64? by Discipulus (Canon) on Mar 10, 2014 at 08:00 UTC
Hello, you have to be sure you are not falled in such type of pit. The `-e` test is passing? Are file that you are testing inside some system dir? or fake ones? HtH L* There are no rules, there are no thumbs.. Reinvent the wheel, then learn The Wheel; may be one day you reinvent one of THE WHEELS.	[reply] [d/l] [select]
Re: How to test if a file is readable on Win64? by jellisii2 (Hermit) on Mar 10, 2014 at 14:48 UTC
eval the test: `eval {-r "$File1"}; if ($@) { $Debug && print "File $File1 is not readable! Return was $@.\n"; return 1; }` [download]	[reply] [d/l]
Re^2: How to test if a file is readable on Win64? by rhardy (Acolyte) on Mar 10, 2014 at 23:52 UTC
I'm puzzled. Why would an eval make any difference?	[reply]
Re^3: How to test if a file is readable on Win64? by Anonymous Monk on Mar 10, 2014 at 23:58 UTC
No, eval wouldn't make any difference If the -r test is causing the popup Win32API::File::SetErrorMode(2); should silence it	[reply]
Re^3: How to test if a file is readable on Win64? by jellisii2 (Hermit) on Mar 11, 2014 at 16:55 UTC
It's my understanding that wrapping code in an eval will effectively fork and return the result code, setting $@ on an error. It should sidestep the crash nicely allowing for the catch that the OP appears to be digging for. That said, I could be answering the wrong question.	[reply]
Re^4: How to test if a file is readable on Win64? by Anonymous Monk on Mar 12, 2014 at 11:00 UTC
Re^5: How to test if a file is readable on Win64? by jellisii2 (Hermit) on Mar 12, 2014 at 11:24 UTC
Re: How to test if a file is readable on Win64? by locked_user sundialsvc4 (Abbot) on Mar 11, 2014 at 13:46 UTC
In my experience, there are so many possible factors that could influence “the ability to access a file,” and so many ways for the system to (rudely) inform you that you can’t, that you’re going to have to use logic that can handle the possibility that an exception might be thrown. The simplest way to do that in Perl is with the `eval { ... }` construct. Wrap the entire thing up in a subroutine which will always survive and which will return True or False. Within that subroutine, do this ... attempt the test, and if the test succeeds without an exception, use the result that it obtained. If it does not, catch the exception, squash it, and say that access is denied. Don’t attempt to write logic that avoids the possibility of an exception being thrown, because that probably can’t be avoided in the general case. Many CPAN modules already incorporate this kind of logic.
Re^2: How to test if a file is readable on Win64? by Anonymous Monk on Mar 12, 2014 at 11:03 UTC
In my experience,... Do you own a windows operating system? Since when does eval handle errors generated by microsoft c runtime? sundialsvc4 stop that	[reply]
Re^2: How to test if a file is readable on Win64? by eyepopslikeamosquito (Archbishop) on Mar 12, 2014 at 10:50 UTC
there are so many possible factors that could influence “the ability to access a file,” and so many ways for the system to (rudely) inform you that you can’t, you’re going to have to use logic that can handle the possibility that an exception might be thrown Really? In Perl? Which Perl file handling functions or operators might throw an exception? I'm not aware of any (unless, of course, you are using autodie).	[reply]