Bash 检查变量数组是否有值

Question

我有一个变量数组。我想使用 for 循环检查变量是否具有值。

我正在将值放入循环中，但 if 条件失败

function check {
    arr=("$@")
    for var in "${arr[@]}"; do
        if [ -z $var ] ; then
            echo $var "is not available"
        else
            echo $var "is available"
        fi
    done
}

name="abc"
city="xyz"
arr=(name city state country)
check ${arr[@]}

对于上述，我得到的都是 可用

预期输出是

name is available
city is available
state is not available
country is not available

Answer 1

这是您任务的正确语法

if [ -z "${!var}" ] ; then
    echo $var "is not available"
else
    echo $var "is available"
fi

说明，这个方法使用了间接变量展开，这个构造 ${!var}将扩展为名称在 $var 中的变量的值.

已更改 check有点功能

check () {
    for var in "$@"; do
        [[ "${!var}" ]] && not= || not="not "
        echo "$var is ${not}available"
    done
}

另一个使用 declare 的变体

check () {
    for var in "$@"; do
        declare -p $var &> /dev/null && not= || not="not "
        echo "$var is ${not}available"
    done
}

来自 declare帮助

$ declare --help
declare: declare [-aAfFgilnrtux] [-p] [name[=value] ...]
    Set variable values and attributes.
    Declare variables and give them attributes.  If no NAMEs are given,
    display the attributes and values of all variables.
    ...
    -p  display the attributes and value of each NAME
    ...

实际上，可以使用它一次检查所有变量

check () {
    declare -p $@ 2>&1 | sed 's/.* \(.*\)=.*/\1 is available/;s/.*declare: \(.*\):.*/\1 is not available/'
}