Regex string issue in making plain text urls clickable

Question

I need a working Regex code in C# that detects plain text urls (http/https/ftp/ftps) in a string and make them clickable by putting an anchor tag around it with same url. I

Answer 1

Try this

Regex regx = new Regex("(?))(http|https|ftp|ftps)://([\\w+?\\.\\w+])+([a-zA-Z0-9\\~\\!\\@\\#\\$\\%\\^\\&\\*\\(\\)_\\-\\=\\+\\\\\\/\\?\\.\\:\\;\\'\\,]*)?", RegexOptions.IgnoreCase);

It should work for your example.

(?)) is a negative lookbehind, that means the pattern matches only if it is not preceeded by "href='" or ">".

See lookarounds on regular-expressions.info

and the especially the zero-width negative lookbehind assertion on msdn

See something similar on Regexr. I had to remove the alternation from the look behind, but .net should be able to handle it.

Update

To ensure that there are also (maybe possible) cases like "

ftp://www.def.com

" correctly handled, I improved the regex

Regex regx = new Regex("(?]*>))(http|https|ftp|ftps)://([\\w+?\\.\\w+])+([a-zA-Z0-9\\~\\!\\@\\#\\$\\%\\^\\&\\*\\(\\)_\\-\\=\\+\\\\\\/\\?\\.\\:\\;\\'\\,]*)?", RegexOptions.IgnoreCase);

The lookbehind (?]*>)) is now checking that there is not a "href='" nor a tag starting with "

The output of the teststring

ttt ftp://www.abc.com abc 
ftp://www.def.com
 abbbbb http://www.ghi.com

is with this expression

ttt ftp://www.abc.com abc 
ftp://www.def.com
 abbbbb http://www.ghi.com