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
You can also decide at any point to trash the file you've been building.
This method calls its parent "close" in IO::File and then renames its temporary file as the original file name.
This method calls its parent "close" in IO::File and then deletes the temporary file.
Eryq (firstname.lastname@example.org). President, ZeeGee Software Inc (http://www.zeegee.com).
Dianne Skoll (email@example.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.