How to check if a string contains http:// at the start

Question

I want to be able to check a string to see if it has http:// at the start and if not to add it.

if (regex expression){
string = "http://"+string;
}

Does anyone know the regex expression to use?

David R Tribble · Accepted Answer · 2019-11-22T17:37:42.713

58

If you don't need a regex to do this (depending on what language you're using), you could simply look at the initial characters of your string. For example:

// C#
if (!str.StartsWith("http://"))
    str = "http://" + str;

// Java
if (!str.startsWith("http://"))
    str = "http://" + str;

// JavaScript/TypeScript
if (str.substring(0, 7) !== 'http://')
    str = 'http://' + str;

edited Nov 22 '19 at 17:37

answered Sep 08 '09 at 20:11

David R Tribble

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4

May many, many upvotes be bestowed upon you. Sometimes, regexes are overkill. – Samir Talwar Sep 08 '09 at 20:13
1

Thank you for the blessing. Yes, sometimes powerful language features are overused. Regex's are not as fast as simple string operations. – David R Tribble Sep 08 '09 at 20:42
@Ra91 - I added a JavaScript example, which does work in IE. – David R Tribble Nov 25 '19 at 17:39

score 8 · Answer 2 · answered Sep 08 '09 at 19:48

8

Should be:

/^http:\/\//

And remember to use this with ! or not (you didn't say which programming language), since you are looking for items which don't match.

answered Sep 08 '09 at 19:48

Adam Bellaire

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score 7 · Answer 3 · answered Sep 08 '09 at 19:47

7

In JavaScript:

if(!(/^http:\/\//.test(url)))
{
    string = "http://" + string;
}

answered Sep 08 '09 at 19:47

Chris Doggett

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score 6 · Answer 4 · answered Aug 09 '16 at 09:11

6

var url = "http://abcd";
var pattern = /^((http|https|ftp):\/\/)/;

if(!pattern.test(url)) {
    url = "http://" + url;
}

alert(url);

answered Aug 09 '16 at 09:11

Deepti Gehlot

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While this code may answer the question, providing additional context regarding *how* and/or *why* it solves the problem would improve the answer's long-term value. - [From Review](http://stackoverflow.com/review/low-quality-posts/13275385) – Michael Parker Aug 09 '16 at 16:16
Thank you so much! It helps me improve in processing – Blue Tram Feb 23 '19 at 07:26

score 3 · Answer 5 · edited Apr 03 '13 at 05:48

3

Something like this should work ^(https?://)

edited Apr 03 '13 at 05:48

Jignesh Rajput

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answered Sep 08 '09 at 19:49

Michael Ciba

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score 2 · Answer 6 · answered Oct 27 '09 at 16:10

2

yourString = yourString.StartWith("http://") ? yourString : "http://" + yourString

Is more sexy

answered Oct 27 '09 at 16:10

Nicolas Dorier

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score 1 · Answer 7 · answered Sep 08 '09 at 19:47

1

 /^http:\/\//

answered Sep 08 '09 at 19:47

scragar

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score 0 · Answer 8 · edited May 23 '17 at 12:01

0

If javascript is the language needed here, then look at this post which adds "startswith" property to the string type.

edited May 23 '17 at 12:01

Community

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answered Oct 27 '09 at 16:07

vsync

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score 0 · Answer 9 · answered Mar 26 '20 at 18:41

For me, with PHP these are the 2 I use just adding them here for completeness.

$__regex_url_no_http = "@[-a-zA-Z0-9\@:%._\+~#=]{1,256}\.[a-zA-Z0-9()]{1,6}\b([-a-zA-Z0-9()\@:%_\+.~#?&//=]*)@";

$__regex_url_http = "@https?:\/\/(www\.)?[-a-zA-Z0-9\@:%._\+~#=]{1,256}\.[a-zA-Z0-9()]{1,6}\b([-a-zA-Z0-9()\@:%_\+.~#?&//=]*)@";

I have a function like this to check:

/**
 * Filters a url @param url If @param protocol is true
 * then it will check if the url contains the protocol
 * portion in the url if it doesn't then false will be
 * returned.
 * 
 * @param string $url
 * @param boolean $protocol
 * @return boolean
 */   
public function filter_url($url, $protocol=false){
  $response = FALSE;

  $regex = $protocol == false ? $this->__regex_url_no_http:$this->__regex_url_http;

  if(preg_match($regex, $url)){
    $response = TRUE;
  }

  return $response;
}

I didn't create the regex. I found them someplace but seem to be compliant

How to check if a string contains http:// at the start

9 Answers9