Give a function an optional argument.

Let callers omit a value while keeping nounset enabled.

set -euo pipefail
greet() {
  local name="${1:-friend}"
  printf "Hello, %s\n" "$name"
}
greet
greet Taylor

Expected output EXAMPLE

Hello, friend
Hello, Taylor

Details

Requires Bash 4 or later. Save as snippet.sh and run bash snippet.sh in an empty working directory. local limits the variable to the function; :- safely handles a missing positional argument.

✓ Verified

Tested on Ubuntu 24.04.5 LTS · 2026-11-02 18:21:08 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: a0c019bae0d3470f31ae5d1c7ec996805d170d9c3a75b3ec5a8dbd4f170327d4
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

Hello, friend
Hello, Taylor

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