Copy without overwriting

Copy without overwriting an existing file with cp -n. In GNU coreutils 9.1 it skips the copy and still exits 0, a status that later releases changed.

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Summarize in AI

A copy should leave files in the destination alone when they are already there, so a rerun cannot destroy changes.

Shell

mkdir -p src dst
echo new > src/a.txt
echo keep > dst/a.txt
cp -n src/a.txt dst/
echo "exit status: $?"
cat dst/a.txt

Text

exit status: 0
keep

-n is --no-clobber in GNU cp. The existing file wins and the command reports success, so a repeated run cannot overwrite local edits. The alternative, -i, stops to ask, which does not suit a script.

The exit status of a skipped copy has changed between coreutils releases, and the status of 0 shown here is from coreutils 9.1 on Debian 12, so check the release notes of the version you deploy before testing $? in a script. For a guarantee of what was copied, rsync --ignore-existing is the clearer tool.

Taggedfile system idempotent