Refuse to overwrite an existing file with redirection.

Bash Scripts: Noclobber makes a plain greater-than redirection fail when the target already exists.

set -euo pipefail
if (set -C; printf "new\n" > existing.txt) 2>/dev/null; then
  printf "Written\n"
else
  printf "Preserved\n"
fi
cat existing.txt

Expected output EXAMPLE

Preserved
original

Details

Requires Bash 4 or later. Save as snippet.sh and run bash snippet.sh in an empty working directory. Noclobber makes a plain greater-than redirection fail when the target already exists.

✓ Verified

Tested on Ubuntu 24.04.5 LTS · 2026-11-02 18:22:56 UTC · GNU bash, version 5.2.21(1)-release (x86_64-pc-linux-gnu) · bash 5.2.21-2ubuntu4; coreutils 9.4-3ubuntu6.3

Test inputs, results and environment

The exact published code ran in a dedicated Linux test container with prepared inputs. Snippet process uid 65534 with a read-only root filesystem and temporary working files. Networking disabled. Fixtures and output records are isolated from the application database. Testing covers this example and its stated checks, not every input, operating system, or runtime version. The Linux container shares its host's kernel; this is not a native Windows test.

Architecture / host kernel: x86_64 / 6.18.54.1-microsoft-standard-WSL2
Snippet identity / locale: uid=65534, gid=65534 (unprivileged process) / C.UTF-8
Interpreter invocation: bash -euo pipefail -c <published code>
Container image ID: sha256:ec91410a8f6ec3e985830b5e3a0560306d36f8c1c5ccd91a6699abe707123fa3
Code SHA-256: a7fadc2d2252d8f3e9d5f9bf21b52ce7e2ff046072c2df9ed259a2f8bd71a308
Dependencies: bash 5.2.21-2ubuntu4; coreutils 9.4-3ubuntu6.3

Test input setup

These are the prepared inputs used by the test harness. See Details above for the prerequisites and how to run this example.

printf 'original\n' > existing.txt

Observed standard output

Preserved
original

Exit code: 0. Standard error: empty. Validation: Exact stdout comparison. System-dependent values above are one recorded run.

Additional assertions that passed

Checks recorded by the test harness. Where Python assertions are shown, browser cases use Playwright and simulator cases may inspect pin transitions: result.stdout is captured output, work is the temporary directory, and Path is pathlib.Path. The harness also imports json and csv.

assert Path('existing.txt').read_text() == 'original\n'