RSYNC, an open source utility widely used in Unix-based systems (which include Linux and MacOS), has a powerful feature called the ‘—dry-run’ option. This option is used to review what changes would occur on the file system without actually implementing them.
According to the man page of RSYNC, one can access by typing ‘man rsync’ in the terminal, the ‘—dry-run’ option “performs a trial run that doesn’t make any changes (and produces mostly the same output as a real run). It is most commonly used in combination with -v (verbose) to see what an rsync command would do without taking any action.”
In other words, it simulates an RSYNC operation and provides a verbose output of the action it would take without actually modifying any data on the file system. It’s a safeguard to preview and verify the operations before carrying them out, preventing potential unwanted changes.
This becomes exceptionally useful in scenarios where massive amounts of data are to be synchronized or modified. Consider that you’re a system administrator intending to synchronize important data between two servers. Mistakenly deleting or overwriting crucial data is problematic. Hence, before running the actual command, the ‘—dry-run’ option can be used to illustrate what changes the actual command will make.
For instance, if you want to synchronize a directory from local to remote server, you can use:
`rsync —dry-run -az /path/to/source/ user@remote:/path/to/destination/`
Here, -a stands for archive mode which ensures permissions, links, modification times etc are preserved, -z stands for compression to save bandwidth during the transfer process.
The —dry-run option will show an output detailing file and directory names, sizes, timestamps etc., as well as an indication of whether the file would be transferred completely or whether its existing form on the destination would just be updated.
It’s important to note also that as no actual data-transferring or file-modifying operations take place when the ‘—dry-run’ option is in use, it’s not possible to see some features of rsync’s behavior. For example, the final statistics summary that rsync produces in real run.
The source that is often used to construct information about the ‘—dry-run’ option is the rsync man page, available in Unix-based systems. You can check this page by typing ‘man rsync’ in your terminal or you can check it online. These sources, together with various widely recognized Unix/Linux forums and guides (like the Unix & Linux Stack Exchange, the Linux Man-pages project, and the rsync.samba.org documentation pages), provide further real-world examples and applications of the ‘—dry-run’ option in rsync.
