Regex to convert text URLs in Markdown to Links

user_194732 0
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I'm trying to convert text Links (with a FQDN i.e. no relative links) in markdown text to Markdown links. It is working fine except when the source markdown has already converted the text to links. For example this is the source text:

Login in to My site [https://example.com/](https://example.com/) and select Something > Select below details further.
(https://example.com/abc/1.html)

Also have a look at https://example.com/abc/1.html

My regex: /(?<!\]\()(\b(https?|ftp):\/\/[-A-Z0-9+&@#\/%?=~_|!:,.;]*[-A-Z0-9+&@#\/%=~_|])/gim.

Expected: match only the second and third link. Current outcome: matches 3 URLs.

I tried adding a negative lookahead at the end, similar to the negative lookbehind at the beginning but that just omits the last character of the URL which is a bummer!

I'm using this in NodeJS.

Here's a link to the regex101 with the sample data

regex-lookarounds node.js regex
2 Answers

You may choose to not specify a lookahead/lookbehind by simply not matching if the character before "http" is an opening bracket:

[^\[\(](https?|ftp):\/\/[^\s]*

But then if you strictly want to exclude all URLs in the format [x](y) then use this:

(?<!\]\()((?:https?|ftp):\/\/[^\s\]\)]*)(?:[\s\]\)](?!\()|$)

enter image description here

Where:

  • (?<!\]\() - Lookbehind assertion to ensure the this is not the y in [x](y)
  • ( - Capture URL part
    • (?:https?|ftp):\/\/ - Match the http/ftp part of the URL
    • [^\s\]\)]* - Match the remaining part of the URL.
  • ) - End of capturing of URL
  • (?: - Non-capturing group
    • [\s\]\)] - Match either a space character, closing bracket, or closing parenthesis. The reason we need to match the closing bracket/parenthesis is to allow URLs in the format e.g. (Check https://google.com) or [Check https://google.com]
    • (?!\() - Lookahead assertion to ensure the this is not the x in [x](y)
    • | - Or
    • $ - End of String
  • ) - End of non-capturing group
user_110438250

You can use a pattern to match what you do not want, and capture what you do want in group 1.

You can make use of the callback function of replace in the replacement.

You can check id group 1 exists. If it does, replace with you custom replacement. If it does not exist, replace with the full match

\[(?:https?|ftp):\/\/[^\]\[]+\]\([^()]*\)|((?:https?|ftp):\/\/\S+)

In parts the pattern matches:

  • \[ Match[
  • (?:https?|ftp):\/\/ Match one of the protocols and ://
  • [^\]\[]+ Match 1+ times any char except [ and ]
  • \] Match ]
  • \([^()]*\) Match from ( till )
  • | Or
  • ((?:https?|ftp):\/\/\S+) Capture in group 1 a url like format

Regex demo

To not match parenthesis in the url:

\[(?:https?|ftp):\/\/[^\]\[]+\]\([^()]*\)|((?:https?|ftp):\/\/[^()\s]+)

Regex demo

Or specifically capture a url between parenthesis:

\[(?:https?|ftp):\/\/[^\]\[]+\]\([^()]*\)|\(((?:https?|ftp):\/\/\S+)\)|((?:https?|ftp):\/\/[^()\s]+)

Regex demo

user_54249880
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