Unlink command for opened files

[Prasanth]

When a file is open does unlink automatically deletes the file or it
generates an error. Because I wrote a program to delete a file and
regenerate the file. if the file is not deleted the data simply gets
appended to the existing file. which results in wrong results

 

[Joost Diepenmaat]

When a file is open does unlink automatically deletes the file or it
generates an error. Because I wrote a program to delete a file and
regenerate the file. if the file is not deleted the data simply gets
appended to the existing file. which results in wrong results

Unlink removes inodes, and it should succeed in that even if the file is
opened by any process. It does not empty files, if that's what you mean.

 

[A. Sinan Unur]

@u36g2000prf.googlegroups.co
m:

When a file is open does unlink automatically deletes the file or
it generates an error. Because I wrote a program to delete a file
and regenerate the file. if the file is not deleted the data
simply gets appended to the existing file. which results in wrong
results

Hmmmm ... What is the question?

If you script opened the file, close it before calling unlink.

If the file is opened in exclusive mode by another process, I am not
sure deleting it is the correct action in the first place.

If you don't want your script to continue if unlink failed, you
should check the return value of unlink.

On the other hand, not that this will solve whatever problem you are
having, I would not have messed with unlink at all:

open my $out_h, '>', 'report.txt'
or die "Cannot open 'report.txt': $!";

That truncates the file if it can be opened and would die if it
cannot. Beats appending junk to a file.

There are just two many combinations of problems and solutions that
might apply to your post. Please elaborate after reading the posting
guidelines for this group and may be taking a look at the following
page:

http://blogs.msdn.com/oldnewthing/archive/2008/04/15/8397753.aspx

Sinan

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[A. Sinan Unur]

Unlink removes inodes, and it should succeed in that even if the
file is opened by any process. It does not empty files, if that's
what you mean.

I am guessing the OP is on Windows where

http://windowshelp.microsoft.com/Windows/en-US/help/47b3ce2b-3aec-401d-8be3-74434a1999831033.mspx

Sinan

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[Ben Morrow]

Unlink removes inodes, and it should succeed in that even if the file is
opened by any process. It does not empty files, if that's what you mean.

Unlink removes *filenames*. Inodes are refcounted, and self-destruct
when there are no refs to them (including open file descriptors).

This only applies to Unixish filesystems, of course. Win32 won't let
you unlink an open file (under normal circumstances).

Ben

 

[Jürgen Exner]

When a file is open does unlink automatically deletes the file or it
generates an error.

That depends on the file system and/or operating system that you are
using.

jue

 

[xhoster]

When a file is open does unlink automatically deletes the file or it
generates an error. Because I wrote a program to delete a file and
regenerate the file. if the file is not deleted the data simply gets
appended to the existing file. which results in wrong results

This depends on your OS.

Xho

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[Jürgen Exner]

This is not a Perl question, this is a question about the filesystem
semantics for your particular operating system; the answer can differ
from OS to OS. I'll talk about Unix/Linux, because that's the one I
understand . In Unix/Linux, when you delete the file, you actually
only delete the directory entry for the file.

This is getting somewhat off topic, but now you triggered my curiousity.
Does the behaviour really depend on the OS (as you seem to imply) or
does it depend on the file system? Or on both?
Example: FAT32 mounted on Linux. FAT32 does not have inodes or link
counts and I would guess that Linux would not allow deletion of a file
from a FAT32 partition as long as there is an open file descriptor
dangling. Is this true or does Linux simulate an inode and link count
structure on top of FAT?

jue

jue

 

[Ben Morrow]

This is getting somewhat off topic, but now you triggered my curiousity.
Does the behaviour really depend on the OS (as you seem to imply) or
does it depend on the file system? Or on both?
Example: FAT32 mounted on Linux. FAT32 does not have inodes or link
counts and I would guess that Linux would not allow deletion of a file
from a FAT32 partition as long as there is an open file descriptor
dangling. Is this true or does Linux simulate an inode and link count
structure on top of FAT?

For both FAT and NFS (which doesn't support close-behind either) Linux
will fake the unlink by renaming the file to something 'unique', and
really deleting it after it's closed. Grep the kernel source for
'sillyrename'.

I don't know if all OSen provide (or attempt to provide) consistent
semantics across all filesystems they support.

Ben