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You should read through the PCRE section of the manual to get an idea of what the various things in the patterns do, and what is available to use when constructing patterns. Using an online regex debugger can help you as well by letting you easily try patterns and break them down into their components.

Throwing syntax at the function and seeing if it does what you want isn't a very efficient way of programming. Do you understand how those regular expressions work? What the various symbols mean? Again: one step at a time. This ~(\bhttps?://\S+)(?:\s+\[([^]]+)\])?~i is a good enough regular expression that will match these: http://www.google.com https://www.google.com http://www.google.com [Link text here] https://www.google.com [Link text here] Did you know about the [text] bit at the end? Do you want that?