Dry run first: rsync, find, git clean and sed

rsync -avn, find … -print and git clean -nd print exactly what the destructive version would do, and each is one flag away from the real thing. It is the same habit every time: run the command in show-me mode, read the list, then remove the flag. rm is the exception — it has no such mode, and the workaround matters.

1. rsync: -n shows what would be copied

$ clai show what rsync would copy without copying it→ rsync -avn src/ backup/sending incremental file listapp.pyutil.pylogs/logs/app.logsent 159 bytes  received 29 bytes  376.00 bytes/sectotal size is 8  speedup is 0.04 (DRY RUN)

The last two words, (DRY RUN), are the only difference in the output. The file list is identical to the real run — drop the -n and exactly these files get copied.

2. rsync --delete: the combination that bites

$ clai show what rsync would delete in the destination→ rsync -avn --delete src/ backup/sending incremental file listdeleting old-report.csvdeleting obsolete.py./notes.txtutil.pylogs/old.log

The deleting lines are the reason to bother with -n at all. Without it those two files vanish silently — verified: the same run without -n printed the same two lines and removed them.

3. find: -print first, -delete second

$ clai show logs older than 30 days without deleting them→ find src -name '*.log' -mtime +30 -printsrc/logs/old.log

find evaluates its tests left to right, so -print at the end shows precisely the list -delete would get. Never reorder them: -delete -name '*.log' deletes the whole tree first and filters afterwards.

4. git clean: -n prints what it would remove

$ clai show which untracked files git clean would remove→ git clean -ndWould remove backup/Would remove src/notes.txtWould remove tmpdir/

-n is the check, -d includes directories. Running git clean -fd without the -nd pass first is the quickest way to lose a file you forgot to stage.

5. sed: the preview is sed without -i

$ clai show how the replacement in conf.ini would look without changing the file→ sed 's/old/new/' conf.inihost=newport=80

Without -i, sed prints the result to the terminal and leaves the file alone — that is its built-in dry run. Verified: cat conf.ini afterwards still shows host=old.

6. When the edit does go in, keep a copy

$ clai replace in conf.ini but keep a backup→ sed -i.bak 's/old/new/' conf.ini

You get conf.ini.bak next to it with the original content. On macOS the suffix is mandatory even when empty (-i '') — the detail that breaks scripts moved over from Linux.

Gotchas

• rm has no dry run. The substitute is the same glob with ls: ls -1 src/logs/*.log shows exactly what rm src/logs/*.log would take. echo rm … works too, printing the full command instead of running it.
• -n means different things to different commands. For rsync it's dry run, for grep -n line numbers, for sort -n numeric sort. Don't carry the habit across blindly: find calls it -print, git calls it --dry-run.
• The check and the real run must differ by exactly one flag. If you also changed the path, the pattern or the argument order in between, you verified a different command. Delete the -n from the line you already typed instead of typing it again.

Related questions

Do package managers have a dry run? Yes: apt-get -s install pkg shows the plan without installing, dnf has --assumeno, and docker has docker system prune --dry-run.

How do I check what a script will do? bash -n script.sh checks the syntax without running anything; bash -x script.sh prints each command as it runs — note that it does run them.

Can I undo rsync --delete? No. The protections are -n beforehand, or --backup --backup-dir=…, which moves the doomed files aside instead of deleting them.

See also

• Delete files older than N days
• Copy files preserving the directory structure
• Find and replace across files

CliAI labels a destructive command CAUTION or DANGER and offers the dry-run form first, before anything runs. Install it in one line.