如何修正正则表达式以匹配含多空格的目标URL（如www.d em m.）

First, let's break down why your current regex isn't matching www.d em m.:

1. HTML Entity Instead of Literal &: Your regex uses & which matches the string & instead of the actual & character—this is a common slip-up when copying regex from HTML contexts.
2. Missing Lowercase Letters: The character classes only include A-Z (uppercase), so lowercase letters like d, e, m aren't being matched unless you use the case-insensitive flag.
3. Case Sensitivity: Without the i flag, the regex ignores lowercase URL components entirely.

Corrected Regex #

Here's the fixed version that addresses these gaps and will match your target URL www.d em m.:

(?:(?:https?|ftp|file):\/\/|www\.|ftp\.)[-a-zA-Z0-9+&@#\/%=~_|$?!:,.| ]*[a-zA-Z0-9+&@#\/%=~_|$]\.

Or, use the case-insensitive (i) flag to simplify the character classes (avoids repeating a-z):

/(?:(?:https?|ftp|file):\/\/|www\.|ftp\.)[-A-Z0-9+&@#\/%=~_|$?!:,.| ]*[A-Z0-9+&@#\/%=~_|$]\./i

Key Changes Explained #

• Replaced & with &: Now the regex correctly matches the & character in URLs.
• Added Lowercase Letters: Explicitly included a-z in character classes (or used the i flag) to cover lowercase components.
• Preserved Space in Character Class: The space remains allowed in the middle section to handle URLs with spaces between characters.

Testing the Regex #

When applied to www.d em m., here's how it works:

1. Starts with www. which hits the initial www\. group.
2. The middle section d em m is fully covered by the allowed characters (including spaces and lowercase letters).
3. Ends with m. where m matches the final character class, followed by the required dot.

Optional Adjustment #

If you need to allow URLs that end with a space before the dot (e.g., www.d em m .), modify the final part to permit spaces between the last valid character and the dot:

/(?:(?:https?|ftp|file):\/\/|www\.|ftp\.)[-A-Z0-9+&@#\/%=~_|$?!:,.| ]*[A-Z0-9+&@#\/%=~_|$](?:\s*)\./i

内容的提问来源于stack exchange，提问作者Alen.Toma