Bidirectional File Synchronizer written in Perl.

psync [-dv] [options] <root_1> <root_2>
    -v --verbose     Verbose
    -d --debug       Debug output
    --tag <tagname>  Metadata Tag

Two roots are required, all options are optional.

Simply specify two roots that you need to synchronize. A root can be on the local filesystem e.g. /home/user/path or remote over ssh e.g. user@host:/path

To synchronize with a remote location, the psync script needs to be in the path on the remote system. The name of the script must be the same as the one used to initiate the sync.

Keep in mind that when the psync script is updated, the remote script also needs to be updated.

I recommend only using SSH Public Key Authentication to avoid any password interactions. Make sure SSH authentication between the systems works properly before using psync.

Using the --tag option it is possible to synchronize the same root to a multitude of other roots in any way you desire. You just have to specify a unique tagname for each unique pair of roots (leg). Not specifying a tagname or using the same tagname on different legs will result in unexpected syncronization problems.

Metadata that is needed to sync properly is stored in the .psync folder in each root.

When using the --tag option, additional metadata will be stored for each leg in the same .psync folder.

Keep in mind that the metadata of both roots of a leg have to remain in sync. Normally this will be the case so you don't need to worry about that. But when one of the roots is replaced by an older backup, the metadata becomes out of sync. This can result in some unexpected behavior including possible loss of some data. One way around this problem is to start using a new tagname after the leg became out of sync. This will cause both roots to be merged and no data will be lost (conflicts may occur though). If you expect only small differences between the two roots you can simply use the same tagname (or no tagname) as before, monitor the changes and make manual changes if needed. Make sure you make a backup of both roots before syncing.

Just synchronize two roots on localhost

psync /home/user/root1 /home/user/root2

Synchronize a local root with a remote root

psync /home/user/root user@remote:/home/user/root

Synchronize two remote roots

psync user@remote1:/home/user/root user@remote2:/home/user/root

Three-way sync

psync --tag leg1 /home/user/root user@remote1:/home/user/root
psync --tag leg2 /home/user/root user@remote2:/home/user/root

This script was developed with the following ideas in mind, please maintain those ideas when submitting pull-requests.

• The script should be a single file so it can be copied to other systems easily.
• The module dependencies should be kept low, only core and a few non-exotic modules are used.
• It should work with most Perl versions commonly in use (currently v5.10 is required)

psync has been working for me without major problems for over a year so it should be fairly stable.

• Only works on *NIX (only tested on OS X)
• Empty directories and deleted directories are not syncronized. Directories are only created when needed to copy a file and never deleted.
• Timestamps are not preserved or synchronized
• Possibly implement multidirectional (more then 2 roots) sync, probably as a separate script
• Improve code documentation
• Conflicts (simultaneous changes in both roots) are not handled by the script. They are just displayed to be handled manually directly on the filesystem.
• Eventhough psync is reasonably fast, it was not built for speed or efficiency rather it was made to be simple and reliable.
• Build in check to ensure local and remote psync scripts are compatible.
• Improve readability of the script output.
• A temp file (in the format .<filename>.<number>) could be left behind, probably when psync is interrupted during a transfer. This temp file will be synced on the next run (will be fixed in a while)
• Implement a lockfile to enforce only one sync at a time

When a file is changed on both roots and still has an equal size, it will be compared. A file will also be compared after being copied to ensure its integrety. Comparing is done using a SHA512 digest.