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    Does not work with set -u: "unbound variable" - if the array is empty. Commented Apr 8, 2017 at 19:56
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    @Igor: Works for me in Bash 4.4. set -u; foo=(); [ ${#foo[@]} -eq 0 ] && echo empty. If I unset foo, then it prints foo: unbound variable, but that's different: the array variable doesn't exist at all, rather than existing and being empty. Commented Sep 17, 2017 at 4:22
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    Also tested in Bash 3.2 (OSX) when using set -u - as long as you declared your variable first, this works perfectly. Commented Aug 5, 2018 at 16:48
  • this one is more compatible for most shells, but found this arithmetic way also stackoverflow.com/a/65957757/1091853 Commented Sep 21, 2023 at 16:30
  • Why do I get a "unbound variable" if I declare the array using declare -a myarr, but it works if declared using myarr=() or declare -a myarr=()? Commented May 9, 2025 at 6:59