Command line and power tools

Comparing folders

Updated 2026-07-31 · 4 min read

Before deleting a supposed backup, prove it really is one.

Names only, fast

diff <(cd /path/A && find . -type f | sort) <(cd /path/B && find . -type f | sort)

Lines beginning < exist only in A; > only in B.

Contents too

diff -rq /path/A /path/B

-r recurses, -q reports only that files differ rather than printing the differences.

rsync dry run

rsync -avn --delete /path/A/ /path/B/

-n means dry run — it prints exactly what *would* be copied or deleted without touching anything. This is the safest way to answer "is B a complete copy of A?".

Note the trailing slash on the source; without it rsync nests the folder inside the destination.

Checksums, for certainty

cd /path/A && find . -type f -exec md5 -r {} \; | sort > /tmp/a.txt
cd /path/B && find . -type f -exec md5 -r {} \; | sort > /tmp/b.txt
diff /tmp/a.txt /tmp/b.txt

Slow, and definitive.

Before deleting an archive drive

Run the rsync dry run in both directions. Files present on the drive and not on the Mac are the ones that matter, and they are easy to miss when comparing only one way.

A search tool that keeps unmounted volumes in its index makes the spot-check afterwards possible without plugging the drive back in — which is the point at which "is it definitely backed up" stops being a leap of faith.

Common questions

What is the safest way to check a backup is complete?

rsync -avn --delete source/ destination/ — a dry run that prints exactly what would change without changing anything.

Why does rsync copy everything again?

Usually a trailing-slash difference on the source path, or timestamps not being preserved.