使用参数展开:

如果参数为空或未设置，则什么都没有 替换，否则词的展开就会被替换。

declare -A myarray
myarray[hello]="world"

for i in hello goodbye 123
do
  if [ ${myarray[$i]:+_} ]
  then
    echo ${!myarray[$i]} ${myarray[$i]} 
  else
    printf "there is no %s\n" $i
  fi
done

我通常只使用:

inarray=$(echo ${haystack[@]} | grep -o "needle" | wc -w)

非零值表示找到了匹配。

．.． 实际上，为了解决它不能与needle1和needle2工作的问题，如果你只想要一个精确匹配，没有更多，没有更少，只需在-o后面添加一个w标志，用于整个单词匹配:

inarray=$(echo ${haystack[@]} | grep -ow "needle" | wc -w)

没有'grep'和循环的一行检查

if ( dlm=$'\x1F' ; IFS="$dlm" ; [[ "$dlm${array[*]}$dlm" == *"$dlm${item}$dlm"* ]] ) ; then
  echo "array contains '$item'"
else
  echo "array does not contain '$item'"
fi

这种方法既不使用grep这样的外部实用程序，也不使用循环。

这里发生的是:

we use a wildcard substring matcher to find our item in the array that is concatenated into a string; we cut off possible false positives by enclosing our search item between a pair of delimiters; we use a non-printable character as delimiter, to be on the safe side; we achieve our delimiter being used for array concatenation too by temporary replacement of the IFS variable value; we make this IFS value replacement temporary by evaluating our conditional expression in a sub-shell (inside a pair of parentheses)

别胡闹了!使您的解决方案简单、干净和可重用。

这些函数负责索引数组和关联数组。可以通过将搜索算法从线性搜索升级为二进制搜索(用于大型数据集)来改进它们。

##
# Determines if a value exists in an array.
###
function hasArrayValue ()
{
    local -r needle="{$1:?}"
    local -nr haystack="{$2:?}"  # Where you pass by reference to get the entire array in one argument.

    # Linear search. Upgrade to binary search for large datasets.
    for value in "${haystack[@]}"; do
        if [[ "$value" == "$needle" ]]; then
            return 0
        fi
    done

    return 1
}

##
# Determines if a value exists in an associative array / map.
###
function hasMapValue ()
{
    local -r needle="{$1:?}"
    local -nr haystack="{$2:?}"

    # Linear search. Upgrade to binary search for large datasets.
    for value in "${haystack[@]}"; do
        if [[ $value == $needle ]]; then
            return 0
        fi
    done

    return 1
}

是的，同样的逻辑，但在处理bash时，如果函数的名称可以让您知道迭代的对象(或不迭代的对象)，则可能(可能)有用。

扩展上面来自Sean DiSanti的答案，我认为下面是一个简单而优雅的解决方案，它避免了对数组进行循环，并且不会由于部分匹配而给出假阳性

function is_in_array {
    local ELEMENT="${1}"
    local DELIM=","
    printf "${DELIM}%s${DELIM}" "${@:2}" | grep -q "${DELIM}${ELEMENT}${DELIM}"
}

可以这样称呼:

$ haystack=("needle1" "needle2" "aneedle" "spaced needle")
$ is_in_array "needle" "${haystack[@]}"
$ echo $?
1
$ is_in_array "needle1" "${haystack[@]}"
$ echo $?
0

回答完之后，我读到了另一个我特别喜欢的答案，但它有缺陷，遭到了不好评。我受到了启发，这里有两种可行的新方法。

array=("word" "two words") # let's look for "two words"

使用grep和printf:

(printf '%s\n' "${array[@]}" | grep -x -q "two words") && <run_your_if_found_command_here>

使用:

(for e in "${array[@]}"; do [[ "$e" == "two words" ]] && exit 0; done; exit 1) && <run_your_if_found_command_here>

对于not_found结果，添加|| <run_your_if_notfound_command_here>