Regex to Conditionally Replace Twitter Hashtags with Hyperlinks

Regex to conditionally replace Twitter hashtags with hyperlinks

(^|\s)#(\w*[a-zA-Z_]+\w*)

PHP

$strTweet = preg_replace('/(^|\s)#(\w*[a-zA-Z_]+\w*)/', '\1#<a href="http://twitter.com/search?q=%23\2">\2</a>', $strTweet);

This regular expression says a # followed by 0 or more characters [a-zA-Z0-9_], followed by an alphabetic character or an underscore (1 or more), followed by 0 or more word characters.

http://rubular.com/r/opNX6qC4sG <- test it here.

not autolinking all-numeric twitter hashtags in perl?

Your regexp wouldn't capture anchors that contain more than one letter separated by numbers, e.g. #a0a:

my @anchors = ($tweet =~ m/#(\w+)/g);
foreach my $anchor (@anchors)
{
    next unless $anchor =~ m/[a-z]/i;
    $tweet =~ s{#$anchor}{<a href="http://twitter.com/search?q=%23$anchor">#$anchor</a>}g;
}

e.g. consider my $tweet = "hello #123 hello #abc1a hello #a0a";

Your code produces hello #123 hello <a href="http://twitter.com/search?q=%23abc1">#abc1</a>a hello <a href="http://twitter.com/search?q=%23a9">#a0</a>a

and mine produces hello #123 hello <a href="http://twitter.com/search?q=%23abc1a">#abc1a</a> hello <a href="http://twitter.com/search?q=%23a9a">#a0a</a>

Improving a regex for the hashtag to generate a link

Adding a third group is easy:

(^|\s)(#(\w+))
|__1_|| |   ||
      | |_3_||
      |____2_|

Replace with

$1<a href="/hash/$3" class='hash_tag'>$2</a>

See proof.

Saving Twitter Like Hashtags with Regex Rails

Your first regex works totally, but you must use scan instead of split, so your code to assign the tags would be:

def tag_list=(names)
  self.tags = names.scan(/\B#\w+/).map do |tag|
    Tag.find_or_initialize_by(name: tag.remove('#'))
  end
  save!
end

The changes are:

• Use scan
• Use find_or_initialize_by instead of where then first_or_create!
• Use save! at the end to save once
• You may not need tag.remove('#') if you want to save the hashtag with # prefix

Replace hashtags in a single pass with regex

Here is a way to do it with a little hack:

String str = "#This is a #foo_bar #document about #nothing_but_tags!";
String res = str.replaceAll(" ?#|(?<=#\\w{0,100})_", " ").trim();

It would break with hashtags longer than 100 characters, and it would insert a space in place of hash in the tag if it happens to be the first thing in a string (hence a call to trim()).

Demo.

The 100 character limitation comes from {0,100} portion of lookbehind. This is a limitation of Java regex engine: unlike some other regex engines, it requires the lengths of look-aneads and look-behinds to have an explicit upper limit.

How do I replace all hashtags in a contenteditable div with a hyperlink while ignoring previously replaced hashtags?

This regex looks for all hashtags that are not already wrapped in a hyperlink. It also creates two groups that we can use to form the link of the hashtag.
https://regex101.com/r/EUNySg/13

/(?!\s*#\w+\s*<\/a>)(#(\w+))/g

JQuery

$(document).on("keyup", ".post-input-field", function (event) {
   if (event.keyCode === 32 || event.keyCode === 13) {
      let html = $(this).html();
      html = html.replace( /(?!\s*#\w+\s*<\/a>)(#(\w+))/g, "<a class='hashtag' href='https://google.com/$1'>$2</a> ").replace("<br>", ""); 
      $(this).html(html);
   }
});

Below you can see that all #hashtag get highlighed, but the #notahashtag do not get highlighted.

Regex for twitter hastags not linking properly?

Put the # symbol within the <a> tag as you did, but also take out the one preceding the tag...

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