Rsync-based Perl script to incrementally mirror enormous directory trees.

Written originally by Matthew R. McEachen: https://matthew.mceachen.us/geek/gigasync/gigasync.pod.html

The original script builds a list of files descending from the root down to the source directory. When files are copied to target directory, the same exact tree is recreated on the target server. This is now changed so that relative directories are only created in target directory (effectively, making the source directory appear as the root.)

In addition, the 2nd parameter to 'gigasync' used to be a hostname. In this version, however, it's a destination directory (including any needed hostnames to be used with ssh) and is passed to rsync as-is.

I also supplied a short shell script to facilitate passing rsync options using the evironment variable RSYNC_OPTIONS.

The helper accepts 4 parameters, just run it without parameters to see a short usage help.