On unix, nothing. The file isn't deleted until all file handles to it are closed. Until then, removing the file only removes the entry in the directory, not the file itself.

Of course, it's a different story if another program alters the contents of the file or changes its size. That would affect your script, because it is indeed read into memory a bit at a time. (It's buffered, so it's actually more than one line at a time.)

Some "clever" programmers do this to create a working file for their application that nobody else can see; that's all very well until their application throws a wobbly and your disk fills up. As a sys. admin. I've been bitten by this a few times over the years. Your disk is full but you can do du commands until you are blue in the face but you can't see what file is causing the problem. If you can work out which application is causing the problem, killing it will close the filehandle and thereby free the disk space.

If your program is still running with the open filehandle, let it run. The data is still there on disk to be read.

Best of luck,

JohnGG

Most unix filesystems will keep the actual data intact as long as there is an open file descriptor. The file descriptor should stay open until you close the file. In other words, it appears you may have dodged a bullet. Just hope the program doesn't crash for any reason! :-)

Some platforms can’t delete or rename files held open by the system, this limitation may also apply to changing filesystem metainformation like file permissions or owners. Remember to "close" files when you are done with them. Don’t "unlink" or "rename" an open file. Don’t "tie" or "open" a file already tied or opened; "untie" or "close" it first.

Actually, it is possible. Kinda. If you set the right share permission, the file can be deleted. Actually, it only gets flagged as being deleted. The file still appears in the directory until all file handles to it are closed. Open file handles still function. New handles can't be created. ("Access denied".)

For example,

use Win32API::File qw( createFile ReadFile CloseHandle );

$|=1;

my $share = $ARGV[0];

print("share: $share\n");

{
   open(my $fh, '>', 'deleteme')
      or die("Unable to create file: $!\n");

   print $fh ("foo\n");
}

{
   my $h = createFile('deleteme', 'r', $share)
      or die("Unable to open file: $^E\n");

   {
      ReadFile($h, my $buf, 1, [], [])
         or die("Unable to read from file: $^E\n");

      print("Read $buf\n");
   }

   print("pre unlink dir: ");
   system('dir /b deleteme');

   print("pre unlink type: ");
   system('type deleteme');

   if (unlink('deleteme')) {
     print("File deleted\n");
   } else {
     print("Unable to delete file\n");
   }

   print("post unlink dir: ");
   system('dir /b deleteme');

   print("post unlink type: ");
   system('type deleteme');


   {
      ReadFile($h, my $buf, 1, [], [])
         or die("Unable to read from file: $^E\n");

      print("Read $buf\n");
   }

   print("pre CloseHandle dir: ");
   system('dir /b deleteme');

   print("pre CloseHandle type: ");
   system('type deleteme');

   CloseHandle($h);

   print("post CloseHandle dir: ");
   system('dir /b deleteme');

   print("post CloseHandle type: ");
   system('type deleteme');
}
[download]

outputs

>perl 549202.pl rw
share: rw
Read f
pre unlink dir: deleteme
pre unlink type: foo
Unable to delete file     <---
post unlink dir: deleteme
post unlink type: foo
Read o
pre CloseHandle dir: deleteme
pre CloseHandle type: foo
post CloseHandle dir: deleteme
post CloseHandle type: foo

>perl 549202.pl rwd
share: rwd
Read f
pre unlink dir: deleteme
pre unlink type: foo
File deleted              <---
post unlink dir: deleteme
post unlink type: Access is denied.
Read o
pre CloseHandle dir: deleteme
pre CloseHandle type: Access is denied.
post CloseHandle dir: File Not Found
post CloseHandle type: The system cannot find the file specified.
[download]

That's why we love UNIX so much.

Thanks. I can go home now.