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lang-bash
[ -z "${VAR-set}" ].${VAR+foo}and${VAR:+foo}. The former would evaluate tofooonly ifVARis unset, and the version with:will also returnfooifVARis set to the empty string.set -uorset -o nounsetin bash, then the test will just result in the error "bash: VAR: unbound variable". See stackoverflow.com/a/13864829 for a more reliable unset check. My go-to check for whether a variable is null or unset is[ -z "${VAR:-}" ]. My check for whether a variable is non-empty is[ "${VAR:-}" ].