Command line and power tools

The one backup command worth learning

Updated 2026-08-08 · 5 min read

Finder copies everything every time and dies mid-way without apology. rsync copies only the difference, survives interruption, and can make a mirror provably identical — which is why every serious backup script is rsync at heart.

The core command

rsync -av --progress ~/Projects/ /Volumes/Backup/Projects/

-a (archive) preserves times, permissions and symlinks while recursing; -v --progress narrates. Run it twice: the second pass transfers almost nothing, because rsync skips files already identical — that is the entire magic, and what makes re-running after a failure free.

The trailing-slash rule

One rsync trap accounts for most accidents: a trailing slash on the *source* means "the contents of", no slash means "the folder itself".

rsync -av ~/Projects/ /Volumes/Backup/Projects/   # contents → contents
rsync -av ~/Projects  /Volumes/Backup/           # creates Backup/Projects

Both are correct for different intents; mixing them nests or scatters a backup. When unsure, add --dry-run — rsync then reports what it *would* do, verbatim, transferring nothing.

Mirroring, and the respect --delete deserves

By default rsync only adds and updates. For a true mirror — deletions propagate too:

rsync -av --delete --dry-run ~/Projects/ /Volumes/Backup/Projects/

--delete removes destination files absent from the source, which is exactly right for a mirror and exactly wrong with a mistyped path. The discipline: --dry-run first, read the deletion list, then run without it. A mirror with --delete is not an archive — it faithfully reproduces your mistakes — so it complements Time Machine rather than replacing it.

Mac-specific notes

The rsync Apple ships is old (or, on recent macOS, a rewrite with partial flag coverage). For daily driving install the current one: brew install rsync, which supports modern compression and, with -X, Mac extended attributes — relevant when Finder tags and quarantine flags should survive the copy. For network destinations, the same command works over SSH unchanged: rsync -av folder/ user@host:backup/.

Common questions

Is rsync a replacement for Time Machine?

No — it makes mirrors, not versioned history. Use it for explicit folder backups and drive migrations alongside Time Machine, not instead of it.

Why did rsync copy everything again?

Usually a changed path or slash placement made rsync see a different destination, or timestamps were not preserved on a prior copy made without -a.