通过正则表达式检查空值答案

【问题标题】：Empty value check by Regular Expression通过正则表达式检查空值
【发布时间】：2019-06-11 02:14:08
【问题描述】：

我有一个如下格式的字符串。

var commandString = 'Campaign: {campaign value} Group: {group value} Sort_By: {sort by value}'

我有以下两个问题

var commandString = 'Campaign: {campaign value} Group: {group value} Sort_By: {}' 的输出是什么如果像 Sort_By 这样的值为空
var commandString = 'Group: {group value} Sort_By: {sort by value}' 的输出是什么如果像 Campaign 这样的值为空当第一个值为空时，则需要为第二个值（如 Group）删除空间。

我没有找到任何想法，你能帮帮我吗。

【问题讨论】：

标签： javascript regex typescript

【解决方案1】：

你可以使用这个正则表达式

(?:^|\s)[a-z_]+?:\s*\{\s*\}

(?:^|\s) - 字符串或空格字符的开头
[a-z_]+? - 匹配字母和_一次或多次
: - 匹配 :
\s*\{\s*\} - 匹配 {}

var str = 'Campaign: {campaign value} Group: {group value} Sort_By: {sort by value}'


let removeEmpty = (str) =>{
  return str.replace(/(?:^|\s)[a-z_]+?:\s*\{\s*\}/gi,"").trim()
}

console.log(removeEmpty(str))
console.log(removeEmpty("Campaign: {campaign value} Group: {}"))
console.log(removeEmpty("Campaign: {} Group: {}"))

【讨论】：

干净利落的解决方案，谢谢

【解决方案2】：

我们会设计可选组以涵盖可能或潜在的选项，例如，我们可以从类似于以下的表达式开始：

(Campaign:(\s+)?{(.+)?})?(\s+)?Group:(\s+)?{(.+)?}(\s+)?Sort_By:(\s+)?{(.+)?}

Demo 1

const regex = /(Campaign:(\s+)?{(.+)?})?(\s+)?Group:(\s+)?{(.+)?}(\s+)?Sort_By:(\s+)?{(.+)?}/gm;
const str = `Campaign: {campaign value} Group: {group value} Sort_By: {sort by value}
Campaign: {campaign value} Group: {group value} Sort_By: {}
Group: {group value} Sort_By: {sort by value}

Campaign: {campaign value}    Group:   {group value}    Sort_By: {sort by value}
Campaign: {campaign value} Group:   {group value}   Sort_By: {}
Group:   {group value} Sort_By:   {sort by value}`;
let m;

while ((m = regex.exec(str)) !== null) {
    // This is necessary to avoid infinite loops with zero-width matches
    if (m.index === regex.lastIndex) {
        regex.lastIndex++;
    }
    
    // The result can be accessed through the `m`-variable.
    m.forEach((match, groupIndex) => {
        console.log(`Found match, group ${groupIndex}: ${match}`);
    });
}

我们可以在我们希望有时拥有它的那些组的末尾使用?简单地添加更多可选空格，我们的表达式扩展为：

(Campaign(\s+)?:(\s+)?{(.+)?})?(\s+)?Group(\s+)?:(\s+)?{(.+)?}(\s+)?Sort_By(\s+)?:(\s+)?{(.+)?}

Demo 2

const regex = /(Campaign(\s+)?:(\s+)?{(.+)?})?(\s+)?Group(\s+)?:(\s+)?{(.+)?}(\s+)?Sort_By(\s+)?:(\s+)?{(.+)?}/gm;
const str = `Campaign: {campaign value} Group: {group value} Sort_By: {sort by value}
Campaign: {campaign value} Group: {group value} Sort_By: {}
Group: {group value} Sort_By: {sort by value}

Campaign: {campaign value}    Group:   {group value}    Sort_By: {sort by value}
Campaign: {campaign value} Group:   {group value}   Sort_By: {}
Group:   {group value} Sort_By:   {sort by value}

Campaign   :    {campaign value}    Group:   {group value}    Sort_By: {sort by value}
Campaign  : {campaign value} Group:   {group value}   Sort_By    : {}
Group    :   {group value} Sort_By    :   {sort by value}`;
let m;

while ((m = regex.exec(str)) !== null) {
    // This is necessary to avoid infinite loops with zero-width matches
    if (m.index === regex.lastIndex) {
        regex.lastIndex++;
    }
    
    // The result can be accessed through the `m`-variable.
    m.forEach((match, groupIndex) => {
        console.log(`Found match, group ${groupIndex}: ${match}`);
    });
}

正则表达式电路

jex.im 可视化正则表达式：

【讨论】：