get string between two strings with javascript [duplicate]

Question

How do I get a string between two strings using match with variables? The following code works well if I use match with strings Regular Expression to get a string between two strings in Javascript I also tried to apply the info at JavaScript - Use variable in string match :

var test = "My cow always gives milk";

var testRE = test.match("cow(.*)milk");
alert(testRE[1]);

But what if I have:

var firstvariable = "cow";
var secondvariable = "milk";

var test = "My cow always gives milk";

I've tried various things including:

var testRE = test.match("firstvariable(.*)secondvariable");
alert(testRE[1]);

and:

var testRE = testRE.match + '("' + firstvariable + "(.*)" + secondvariable +'")';
alert(testRE[1]);

Neither worked.

How should it handle a case like "My cow gives milk. I like milk". Should the match be not greedy: "cow gives milk" or greedy: "cow gives milk. I like milk"? — RobG
– RobG, Commented Dec 26, 2014 at 11:40
If you're gonna down vote, you could at least give a reason why. — user3080392
– user3080392, Commented Dec 26, 2014 at 12:22

myTerminal · Accepted Answer · 2014-12-26 11:38:51Z

58

Try this:

test.match(new RegExp(firstvariable + "(.*)" + secondvariable));

answered Dec 26, 2014 at 11:38

myTerminal

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5 Comments

Pini Cheyni Over a year ago

It returns two parameters, and the fist is the full string

Fenix Over a year ago

The result is an Array (or null if no match). There may be multiple matches depending on RegExp and tested text. The result contains 1.) all matching results and 2.) each matching group (parts matching regexp in parentheses). E.g.: "xxxxABCDEFxxxxx".match(new RegExp( "AB(CD)(EF)" )) returns ["ABCDEF","CD","EF"]

Fenix Over a year ago

Note 2: It is a greedy match (its result is the longest matching string). E.g.: "xxxxAAmCCmCCmCCxxxx".match(new RegExp( "AA(.*)CC" )) returns ["AAmCCmCCmCC","mCCmCCm"].

Nagaraj Jayaraman Over a year ago

How it works if string contains '\n' at middle?

tay Over a year ago

To make this non greedy so it matches the first instance instead then change "(.*)" to "(.*?)", so the full thing would be: test.match(new RegExp(firstvariable + "(.*?)" + secondvariable));

Mouser · Accepted Answer · 2024-02-08 09:29:11Z

14

Use this code

const regExString = new RegExp(`(?<=${firstVariable}).*?(?=${secondVariable})`, "ig"); //set ig flag for global search and case insensitive

const testRE = regExString.exec("My cow always gives milk.");
if (testRE && testRE.length > 0) //RegEx has found something and has at least one entry.
{  
    alert(testRE[0]); //is the matched group if found
}

This matches only the middle part of the sentence.

(?<="+firstvariable+") finds but does not capture cow :: lookbehind is possible now.
.*? captures all characters between cow and milk and saves it in a group. ? makes it lazy so it stops at milk.
(?="+secondvariable+") finds but does not capture milk. :: lookahead

You can test this below:

const test = document.getElementById("testStringDiv").textContent;
let firstVariable = "";
let secondVariable = "";
function testString()
{
    firstVariable = document.querySelectorAll("input")[0].value; //first input;
    secondVariable = document.querySelectorAll("input")[1].value; //second input;
    
    //build the regex:
    //lookbehind is possible in JavaScript now: (?<=) sees if the content in the matched group is preceded by the first       variable, but does not capture this.
    //for the second variable we use the (?=) which is a lookahead and does the same as the lookbehind.
    //If there is a match, the string returned will be the one in the captured group (.*?)
    let regExString = new RegExp(`(?<=${firstVariable}).*?(?=${secondVariable})`, "ig");
    const testRE = regExString.exec(test);

    if (testRE && testRE.length > 0)
    {  
      document.getElementById("showcase").textContent = testRE[0]; //return second result.
    }
}
document.getElementById("test").addEventListener("click", testString, true);

<div id="testStringDiv">My cow always gives milk</div>
<div id="showcase">Result will display here...</div>
<input placeholder="enter first var"/><input placeholder="enter second var"/><button id="test">Search in between...</button>

edited Feb 8, 2024 at 9:29

answered Dec 26, 2014 at 11:42

Mouser

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2 Comments

Alejandro Cotilla Over a year ago

Doesn't work if there are any newline characters in the base string. Any idea how to solve that?

Mouser Over a year ago

In modern browsers since 2018 add s to the modifiers to enable dot to match line breaks.

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