Mike Doherty > File-Symlink-Atomic-0.002 > File::Symlink::Atomic

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Module Version: 0.002   Source  

NAME ^

File::Symlink::Atomic - an atomic drop-in replacement for CORE::symlink

VERSION ^

version 0.002

SYNOPSIS ^

    use File::Symlink::Atomic;   # imports replacement symlink
    symlink "target", "name1";   # easy peasy
    symlink "bullseye", "name1"; # now atomic

DESCRIPTION ^

Actually creating a symlink is not problematic, but making an existing one point at a new target may not be atomic on your system. For example, on Linux, the system does unlink and then symlink. In between, no symlink exists. If something goes wrong, you're left with nothing.

In your shell, you probably want to do something like:

    mkdir old-target new target # Create your targets
    ln -s old-target link       # Create your initial symlink
    # ln -sf new-target link    # NOT atomic!
    ln -s new-target link-tmp && mv -Tf link-tmp link

Moving the symlink to the new name makes it atomic, because under the hood, the mv command does rename, which is guaranteed to be atomic by POSIX.

File::Symlink::Atomic attempts to do the same thing in Perl what the command shown above does for your shell.

FUNCTIONS ^

symlink OLDFILE,NEWFILE

Creates a new filename symbolically linked to the old filename. Returns 1 for success, 0 otherwise. This drop-in replacement for CORE::symlink creates a symlink with a temporary name, then renames it to the name you requested - this ensures that if a symlink by the requested name already existed, then its target is updated atomically.

CAVEATS ^

This module is not guaranteed to be portable. I have no idea what this will do on any platform other than Linux. Feel free to run the test suite to find out!

AVAILABILITY ^

The project homepage is http://metacpan.org/release/File-Symlink-Atomic/.

The latest version of this module is available from the Comprehensive Perl Archive Network (CPAN). Visit http://www.perl.com/CPAN/ to find a CPAN site near you, or see https://metacpan.org/module/File::Symlink::Atomic/.

SOURCE ^

The development version is on github at http://github.com/doherty/File-Symlink-Atomic and may be cloned from git://github.com/doherty/File-Symlink-Atomic.git

BUGS AND LIMITATIONS ^

You can make new bug reports, and view existing ones, through the web interface at https://github.com/doherty/File-Symlink-Atomic/issues.

AUTHOR ^

Mike Doherty <doherty@cpan.org>

COPYRIGHT AND LICENSE ^

This software is copyright (c) 2012 by Mike Doherty.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.

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