在Bash中,测试数组是否包含某个值的最简单方法是什么?
当前回答
这对我来说很管用:
# traditional system call return values-- used in an `if`, this will be true when returning 0. Very Odd.
contains () {
# odd syntax here for passing array parameters: http://stackoverflow.com/questions/8082947/how-to-pass-an-array-to-a-bash-function
local list=$1[@]
local elem=$2
# echo "list" ${!list}
# echo "elem" $elem
for i in "${!list}"
do
# echo "Checking to see if" "$i" "is the same as" "${elem}"
if [ "$i" == "${elem}" ] ; then
# echo "$i" "was the same as" "${elem}"
return 0
fi
done
# echo "Could not find element"
return 1
}
示例调用:
arr=("abc" "xyz" "123")
if contains arr "abcx"; then
echo "Yes"
else
echo "No"
fi
其他回答
如果你需要性能,你不希望每次搜索时都要遍历整个数组。
在这种情况下,您可以创建一个表示该数组索引的关联数组(哈希表或字典)。也就是说,它将每个数组元素映射到它在数组中的索引:
make_index () {
local index_name=$1
shift
local -a value_array=("$@")
local i
# -A means associative array, -g means create a global variable:
declare -g -A ${index_name}
for i in "${!value_array[@]}"; do
eval ${index_name}["${value_array[$i]}"]=$i
done
}
然后你可以这样使用它:
myarray=('a a' 'b b' 'c c')
make_index myarray_index "${myarray[@]}"
并像这样测试成员:
member="b b"
# the "|| echo NOT FOUND" below is needed if you're using "set -e"
test "${myarray_index[$member]}" && echo FOUND || echo NOT FOUND
或者:
if [ "${myarray_index[$member]}" ]; then
echo FOUND
fi
请注意,即使在测试值或数组值中存在空格,该解决方案也能正确执行。
作为奖励,您还可以通过以下方式获得数组中值的索引:
echo "<< ${myarray_index[$member]} >> is the index of $member"
以下是我对这个问题的看法。以下是简短的版本:
function arrayContains() {
local haystack=${!1}
local needle="$2"
printf "%s\n" ${haystack[@]} | grep -q "^$needle$"
}
长一点的版本,我觉得看起来更舒服。
# With added utility function.
function arrayToLines() {
local array=${!1}
printf "%s\n" ${array[@]}
}
function arrayContains() {
local haystack=${!1}
local needle="$2"
arrayToLines haystack[@] | grep -q "^$needle$"
}
例子:
test_arr=("hello" "world")
arrayContains test_arr[@] hello; # True
arrayContains test_arr[@] world; # True
arrayContains test_arr[@] "hello world"; # False
arrayContains test_arr[@] "hell"; # False
arrayContains test_arr[@] ""; # False
如果您想做一个快速而复杂的测试,看看是否值得遍历整个数组以获得精确匹配,Bash可以像对待标量一样对待数组。测试标量中的匹配项,如果没有,则跳过循环节省时间。显然你会得到假阳性。
array=(word "two words" words)
if [[ ${array[@]} =~ words ]]
then
echo "Checking"
for element in "${array[@]}"
do
if [[ $element == "words" ]]
then
echo "Match"
fi
done
fi
这将输出“Checking”和“Match”。使用array=(word "two words" something),它只会输出"Checking"。使用array=(单词“two widgets”什么的)将没有输出。
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 == $needle ]]; then
return 0
fi
done
return 1
}
是的,同样的逻辑,但在处理bash时,如果函数的名称可以让您知道迭代的对象(或不迭代的对象),则可能(可能)有用。
我的版本的正则表达式技术,已经建议:
values=(foo bar)
requestedValue=bar
requestedValue=${requestedValue##[[:space:]]}
requestedValue=${requestedValue%%[[:space:]]}
[[ "${values[@]/#/X-}" =~ "X-${requestedValue}" ]] || echo "Unsupported value"
What's happening here is that you're expanding the entire array of supported values into words and prepending a specific string, "X-" in this case, to each of them, and doing the same to the requested value. If this one is indeed contained in the array, then the resulting string will at most match one of the resulting tokens, or none at all in the contrary. In the latter case the || operator triggers and you know you're dealing with an unsupported value. Prior to all of that the requested value is stripped of all leading and trailing whitespace through standard shell string manipulation.
我相信它是干净而优雅的,尽管如果支持的值数组特别大,我不太确定它的性能如何。