How to find variable is empty in shell script

最新推荐文章于 2025-09-09 11:44:36 发布

转载最新推荐文章于 2025-09-09 11:44:36 发布 · 49 阅读

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原文链接：http://www.cnblogs.com/dyllove98/p/3144975.html

文章标签：

#shell

本文介绍了一种使用Shell脚本来检查变量是否为空或特定值的方法。通过三种不同的方式实现这一功能，包括直接条件判断、定义函数进行判断以及通过循环遍历数组元素来演示判断过程。该脚本适用于检测字符串、整数、浮点数等多种类型的数据。

(1).

var=""
if [ -n "$var" ]; then
echo "not empty"
else
echo "empty"
fi

(2).

function empty
{
local var="$1"

    # Return true if:
    # 1.    var is a null string ("" as empty string)
    # 2.    a non set variable is passed
    # 3.    a declared variable or array but without a value is passed
    # 4.    an empty array is passed
    if test -z "$var"
    then
        [[ $( echo "1" ) ]]
        return

    # Return true if var is zero (0 as an integer or "0" as a string)
    elif [ "$var" == 0 2> /dev/null ]
    then
        [[ $( echo "1" ) ]]
        return

    # Return true if var is 0.0 (0 as a float)
    elif [ "$var" == 0.0 2> /dev/null ]
    then
        [[ $( echo "1" ) ]]
        return
    fi

    [[ $( echo "" ) ]]
}
usage:
if empty "${var}"
    then
        echo "empty"
    else
        echo "not empty"
fi

(3).

#!/bin/bash

vars=(
    ""
    0
    0.0
    "0"
    1
    "string"
    " "
)

for (( i=0; i<${#vars[@]}; i++ ))
do
var="${vars[$i]}"

    if empty "${var}"
        then
            what="empty"
        else
            what="not empty"
    fi
    echo "VAR \"$var\" is $what"
done

exit
output:
VAR "" is empty
VAR "0" is empty
VAR "0.0" is empty
VAR "0" is empty
VAR "1" is not empty
VAR "string" is not empty
VAR " " is not empty

转载于:https://www.cnblogs.com/dyllove98/p/3144975.html