使用正则表达式来匹配左边的内容

Question

Train from London to Boston - match
Train from Boston to London
Train from Cardif to London
Bus from London to Paris - match

如果伦敦出现在任何其他具有正则表达式的城市之前，我该如何匹配？我可以使用JavaScript中的循环字符串匹配来完成它，但我认为正则表达式更好。

Answer 1

获取包含London to

的行

＆＃13;

＆＃13;

var str = `Train from London to Boston - match
Train from Boston to London
Train from Cardif to London
Bus from London to Paris - match`,
  city = 'london';

console.log(
  str.match(new RegExp('^.*\\b' + city + '\\sto\\b.*$', 'gmi'))
)

＆＃13;

＆＃13;

＆＃13;

<强> Regex explanation here

Answer 2

试试这个

\bLondon(?=\s*to\b)

Regex demo

<强>解释
\：逃脱一个特殊字符sample
(?=…)：积极前瞻sample
\s：＆＃34;空格字符＆＃34;：空格，制表符，换行符，回车符，垂直标签sample
*：零次或多次sample

的Javascript

var re = /\bLondon(?=\s*to\b)/g; 
var str = 'Train from London to Boston - match\nTrain from Boston to London\nTrain from Cardif to London\nBus from London to Paris - match';
var m;

while ((m = re.exec(str)) !== null) {
    if (m.index === re.lastIndex) {
        re.lastIndex++;
    }
    // View your result using the m-variable.
    // eg m[0] etc.
}