如何测试 Bash 4.2 中是否存在数组键？

Question

我得出的最接近的解决方案是：

declare -A foobar=([foo]=bar [bar]=foo)
(set -u; true ${foobar[foo]}) 2>/dev/null

理想情况下，我想使用test -v 来测试是否定义了数组键。但是test -v foobar[bar] 显然总是返回1。此外，我不想要全局 set +u 并冒着访问未定义变量的风险。

Answer 1

keys=" ${!foobar[*]} "
wanted=foo
if [[ $keys == *" $wanted "* ]]; then
    echo "foobar contains key $wanted"
else
    echo "key $wanted not present"
fi

如果键可能包含空格，或者如果想要的键恰好是“bar foo”或连续键的某种组合，这可能会失败。

更新： 这可能效率较低，但它既安全（空白）又更清晰：

for key in "${!foobar[@]}"; do
    if [[ $key = $wanted ]]; then
        echo "foobar contains key $wanted"
        break
    fi
done

Answer 2

从 bash 版本“4.2.39(1)-release”开始，我看不到如何使用 test -v 命令测试数组键是否存在。 test -v foobar[foo] 总是失败。对我来说，最好的选择似乎应该使用${foobar[foo]-bar} 参数替换进行测试。为了使用 shopt 的 nounset shell 选项和每个新版本重新测试 Bash 的行为，我编写了以下 Bash shell 脚本：

#!/bin/bash

shopt -os nounset

declare -ri colors=1
if (( "$colors" )); then
  declare -r bold="\e[1m"
  declare -r red="\e[41m"
  declare -r green="\e[42m"
  declare -r end="\e[0;m"
else
  declare -r bold=
  declare -r red=
  declare -r green=
  declare -r end=
fi
declare -ri a="${1:-0}"
case "$a" in
  1)
    echo -e "$a. Accessing ${bold}\"\$foobar\"${end} when unset should result in an error."
    echo "$foobar"
    ;;
  2)
    echo -e "$a. Accessing ${bold}\"\${foobar-bar}\"${end} when unset should result in the \"bar\" default value."
    echo "${foobar-bar}"
    ;;
  3)
    echo -e "$a. Accessing ${bold}\"\${foobar:-bar}\"${end} when unset should result in the \"bar\" default value."
    echo "${foobar:-bar}"
    ;;
  4)
    echo -e "$a. Accessing ${bold}\"\$foobar\"${end} when set to the NULL string should result in it (whitespace)."
    declare -r foobar=
    echo "$foobar"
    ;;
  5)
    echo -e "$a. Accesssing ${bold}\"\${foobar-bar}\"${end} when set to the NULL string should result in it (whitespace)."
    declare -r foobar=
    echo "${foobar-bar}"
    ;;
  6)
    echo -e "$a. Accesssing ${bold}\"\${foobar:-bar}\"${end} when set to the NULL string should result in the \"bar\" default value."
    declare -r foobar=
    echo "${foobar:-bar}"
    ;;
  7)
    echo -e "$a. Accessing ${bold}\"\$foobar\"${end} when set to the \"foo\" string should result in it."
    declare -r foobar=foo
    echo "$foobar"
    ;;
  8)
    echo -e "$a. Accessing ${bold}\"\${foobar-bar}\"${end} when set to the \"foo\" string should result in it."
    declare -r foobar=foo
    echo "${foobar-bar}"
    ;;
  9)
    echo -e "$a. Accessing ${bold}\"\${foobar:-bar}\"${end} when set to the \"foo\" string should result in it."
    declare -r foobar=foo
    echo "${foobar:-bar}"
    ;;
  10)
    echo -e "$a. Accessing ${bold}\"\${foobar[foo]}\"${end} when unset should result in an error."
    declare -rA foobar=()
    echo "${foobar[foo]}"
    ;;
  11)
    echo -e "$a. Accessing ${bold}\"\${foobar[foo]-bar}\"${end} when unset should result in the \"bar\" default value."
    declare -rA foobar=()
    echo "${foobar[foo]-bar}"
    ;;
  12)
    echo -e "$a. Accessing ${bold}\"\${foobar[foo]:-bar}\"${end} when unset should result in the \"bar\" default value."
    declare -rA foobar=()
    echo "${foobar[foo]:-bar}"
    ;;
  13)
    echo -e "$a. Accessing ${bold}\"\${foobar[foo]}\"${end} when set to the NULL string should result in it (whitespace)."
    declare -rA foobar=([foo]=)
    echo "${foobar[foo]}"
    ;;
  14)
    echo -e "$a. Accessing ${bold}\"\${foobar[foo]-bar}\"${end} when set to the NULL string should result in it (whitespace)."
    declare -rA foobar=([foo]=)
    echo "${foobar[foo]-bar}"
    ;;
  15)
    echo -e "$a. Accessing ${bold}\"\${foobar[foo]:-bar}\"${end} when set to the NULL string should result in the \"bar\" default value."
    declare -rA foobar=([foo]=)
    echo "${foobar[foo]:-bar}"
    ;;
  16)
    echo -e "$a. Testing with ${bold}\"test -v foobar\"${end} when unset should fail."
    test -v foobar
    ;;
  17)
    echo -e "$a. Testing with ${bold}\"test -v foobar\"${end} when set to the NULL string should succeed."
    declare -r foobar=
    test -v foobar
    ;;
  18)
    echo -e "$a. Testing with ${bold}\"test -v foobar\"${end} when set to the \"bar\" string should succeed."
    declare -r foobar=
    test -v foobar
    ;;
  19)
    echo -e "$a. Testing with ${bold}\"test -v foobar[foo]\"${end} when unset should fail."
    declare -rA foobar=()
    test -v foobar[foo]
    ;;
  20)
    echo -e "$a. Testing with ${bold}\"test -v foobar[foo]\"${end} when set to the NULL string should fail."
    declare -rA foobar=([foo]=)
    test -v foobar[foo]
    ;;
  21)
    echo -e "$a. Testing with ${bold}\"test -v foobar[foo]\"${end} when set to the \"bar\" string should succeed."
    declare -rA foobar=([foo]=bar)
    test -v foobar[foo]
    ;;
  0)
    echo -e "Testing shopt's \"nounset\" shell option with Bash version \"$BASH_VERSION\"."
    echo
    declare -i b
    for ((b=1; b<=21; b+=1)); do
      "$0" "$b"
      if (( "$?" )); then
        echo -e "${red}Failure.${end}"
      else
        echo -e "${green}Success.${end}"
      fi
      echo
    done
    ;;
esac