IO::AtomicFile - write a file which is updated atomically
use strict;
use warnings;
use feature 'say';
use IO::AtomicFile;
# Write a temp file, and have it install itself when closed:
my $fh = IO::AtomicFile->open("bar.dat", "w");
$fh->say("Hello!");
$fh->close || die "couldn't install atomic file: $!";
# Write a temp file, but delete it before it gets installed:
my $fh = IO::AtomicFile->open("bar.dat", "w");
$fh->say("Hello!");
$fh->delete;
# Write a temp file, but neither install it nor delete it:
my $fh = IO::AtomicFile->open("bar.dat", "w");
$fh->say("Hello!");
$fh->detach;
This module is intended for people who need to update files
reliably in the face of unexpected program termination.
For example, you generally don't want to be halfway in the middle of
writing /etc/passwd and have your program terminate! Even
the act of writing a single scalar to a filehandle is not atomic.
But this module gives you true atomic updates, via rename.
When you open a file /foo/bar.dat via this module, you are actually
opening a temporary file /foo/bar.dat..TMP, and writing your
output there. The act of closing this file (either explicitly
via close, or implicitly via the destruction of the object)
will cause rename to be called... therefore, from the point
of view of the outside world, the file's contents are updated
in a single time quantum.
To ensure that problems do not go undetected, the close method
done by the destructor will raise a fatal exception if the rename
fails. The explicit close just returns undef.
You can also decide at any point to trash the file you've been
building.
the IO::AtomicFile manpage inherits all methods from the IO::File manpage and
implements the following new ones.
$fh->close();
This method calls its parent close in the IO::File manpage and then renames its temporary file
as the original file name.
$fh->delete();
This method calls its parent close in the IO::File manpage and then deletes the temporary file.
$fh->detach();
This method calls its parent close in the IO::File manpage. Unlike delete in the IO::AtomicFile manpage it
does not then delete the temporary file.
Eryq (eryq@zeegee.com).
President, ZeeGee Software Inc (http://www.zeegee.com).
Dianne Skoll (dfs@roaringpenguin.com).
Copyright (c) 1997 Erik (Eryq) Dorfman, ZeeGee Software, Inc. All rights reserved.
This program is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.
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