Bad File Descriptor Error

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

Esteemed Monks,

I have run into a strange problem that I can't seem to get to the bottom of on my own, so I come to the monestary seeking assistance.

I have a script that watches a directory, and modifies some files before moving them to an output directory. Fairly simple, and I have done similar work before without any problems. This time I am getting a bad file descriptor error when creating the output file. I have tried File::Copy, Win32::CopyFile and simply writing the data to the file during processing, and I get the same error each time. The really strange part is that when I use File::Copy or Win32::CopyFile, I get the output file as requested along with the error. When I use the standard print FILE $data, the write fails and I get no file.

Thanks for any assistance/pointers,
digger

            open(FILE,"<",$file);
            binmode(FILE);
            if (flock(FILE,LOCK_EX|LOCK_NB))
            {
                my $buf = "";
                report("Info: Processing $file");
                
                #make sure this is a pcl job file first
                #if not, move it and log it
                read(FILE,$buf,9);
                $printstring = $printstring.$buf;
                unless($buf =~ m/^\x1B\x25\x2D\x31\x32\x33\x34\x35\x58
+/)
                {
                    close(FILE);
                    my $errdir = "$dir\\ERR";
                    report ("Warning: $file is not a valid PCL file - 
+moving to ERR folder");
                    unless(-d $errdir){mkdir($errdir);}
                    move($file,$errdir);
                    next;
                }
                
                while(read(FILE,$buf,4096))
                {
                    fixtraycalls(\$buf);
                    $printstring= $printstring.$buf;
                }
                close FILE;#closing file flushes buffer and releases l
+ock
                
                if($keepfile)
                {
                    my $dest;
                    sleep 1;
                    eval{
                        $dest = $$appconfig{"destination"}."\\$filenam
+e";
                        Win32::CopyFile($file,$dest,1);
                    };
                    if($!)
                    {
                        report("Error: Unable to move file to destinat
+ion - ".$dest."\n $!");
                        #die;
                    }
                }
[download]

Comment on Bad File Descriptor Error Select or Download Code

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Re: Bad File Descriptor Error by Anno (Deacon) on Mar 19, 2007 at 17:20 UTC
... when I use File::Copy or Win32::CopyFile, I get the output file as requested along with the error. The error variable `$!` is only valid immediately after an actual system error, which must be recognized by other means. If `$!` is nonzero that doesn't indicate an error in the preceding code. The value can come from anywhere. So you are using it wrong in your code below. `if($keepfile) { my $dest; sleep 1; eval{ $dest = $$appconfig{"destination"}."\\$filename"; Win32::CopyFile($file,$dest,1); }; if($!) { report("Error: Unable to move file to destination - ".$dest."\ +n $!"); #die; } }` [download] Moreover, why do you run the critical statements under `eval()`? It will only mask some errors. If the `eval()` is there for a reason, you ought to inspect `$@`, not `$!` after eval finishes to detect possible errors. (`$@` is unlike `$!` in that respect, if it's set after an `eval()`, there was an error.) I believe your program is running just fine, the message in `$!` is irrelevant. Wy you can't copy the file using `print()` I don't know. Anno PS: The behavior of `$!` is as described in Unix systems. I don't know for sure about Windows.	[reply] [d/l] [select]
Re^2: Bad File Descriptor Error by digger (Friar) on Mar 20, 2007 at 13:18 UTC
Thanks for taking the time to explain my misunderstanding so clearly. I am writing more apps that run in environments outside of my control, so I am trying to make the error handling more robust. My understanding of using eval in this way is that it will trap errors that may be fatal, but allow me to handle them gracefully if possible. After re-reading the perldoc for eval, I see, as you said, that I have to check $@ for error messages. If I am misusing eval in this context, I would appreciate any pointers. Thanks again digger	[reply]
Re^3: Bad File Descriptor Error by Anno (Deacon) on Mar 20, 2007 at 14:58 UTC
Your `eval()` makes sense if `Win32::CopyFile()` throws exceptions at run time and you want to deal with that. I don't know if it does. The pure Perl operation `$dest = $$appconfig{"destination"}."\\$filename";` [download] does not belong there. If there was a fatal error in that line, it would be a program error and you'd have to correct the line. It doesn't make sense to catch programming errors in `eval()`. Anno	[reply] [d/l] [select]
Re^3: Bad File Descriptor Error by Bro. Doug (Monk) on Mar 20, 2007 at 18:26 UTC
These are just a couple of warnings for you (hopefully, you'll find this advice irrelevant ). I've run into problems with $@ on -some- Windows systems. However, you can always use $EVAL_ERROR ( $@ is shorthand for this ). I don't know where this bug comes from, sorry. Also, on the Emachine T2862 (and only this model, in my experience), I've had problems with: `print HANDLE $stuff ; # doesn't seem to work on T2862` [download] Hopefully, you're not dealing with one of those. Good luck. Bro. Doug :wq	[reply] [d/l]
Re: Bad File Descriptor Error by samtregar (Abbot) on Mar 19, 2007 at 17:12 UTC
Are you sure Win32::CopyFile uses $! to report errors? My guess is you're just seeing some left-over junk in there. Most modules use $@, which seems particularly likely given your use of eval{}. -sam	[reply]
Re: Bad File Descriptor Error by Moron (Curate) on Mar 19, 2007 at 16:53 UTC
It is a few years ago since I did a bit of Windows programming to season my CV, but as I recall, '\' as a directory separator might be the issue -- the Unix-style '/' is portable* using Perl. (* update: i.e. Windows-compatible). -M Free your mind	[reply]
Re: Bad File Descriptor Error by bingos (Vicar) on Mar 20, 2007 at 08:21 UTC
On MSWin32 you might more milage out of using the Win32 functions: `use Win32; Win32::FormatMessage( Win32::GetLastError() );` [download] instead of relying on $!	[reply] [d/l]