Distinguish unset variables from empty strings.
Bash Scripts: Omitting the colon tests only whether a variable is unset; including it also treats an empty value as missing.
set -euo pipefail
setting=""
printf "[%s] [%s]\n" "${setting-default}" "${setting:-default}"Expected output EXAMPLE
[] [default]
Details
Requires Bash 4 or later. Save as snippet.sh and run bash snippet.sh in an empty working directory. Omitting the colon tests only whether a variable is unset; including it also treats an empty value as missing.
Tested on Ubuntu 24.04.5 LTS · · 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
b70e786c972dbb67151c2d55b05c2726a6b877d39413cf71335ae887c93877bd- 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.
# No input files required.
Observed standard output
[] [default]
Exit code: 0. Standard error: empty. Validation: Exact stdout comparison. System-dependent values above are one recorded run.