Regex to parse inline Markdown links in Objective-C

ParseMarkdownLinks.m

- (void)parseMarkdownLinks:(NSString *)text {
    assert(text);
    NSError *error = NULL;
    NSString *pattern = @"\\[([^\\]]+)\\]\\(([^\\)\"\\s]+)(?:\\s+\"(.*)\")?\\)";

    NSRegularExpression *regex = [NSRegularExpression regularExpressionWithPattern:pattern options:0 error:&error];
    NSArray *matches = [regex matchesInString:text options:0 range:NSMakeRange(0, [text length])];

    for (NSTextCheckingResult* match in matches) {
        NSString *matchString = [text substringWithRange:[match range]];
        
        NSString *link, *url, *title;
        NSRange linkRange = [match rangeAtIndex:1];
        NSRange urlRange = [match rangeAtIndex:2];
        NSRange titleRange = [match rangeAtIndex:3];
        
        if (linkRange.length > 0) link = [text substringWithRange:linkRange];
        if (urlRange.length > 0) url = [text substringWithRange:urlRange];
        if (titleRange.length > 0) title = [text substringWithRange:titleRange];

        NSLog(@"Found: >%@<\nLink:  >%@<\nURL:   >%@<\nTitle: >%@<", matchString, link, url, title);
    }
    NSLog(@"Done!");
}

RegexExplanation.txt

NSString *pattern = @"\\[([^\\]]+)\\]\\(([^\\)\"\\s]+)(?:\\s+\"(.*)\")?\\)";

Note: escape needs to be doubled \\ when inside @"" for regex to interpret it as the escape char
https://developer.apple.com/library/ios/documentation/Foundation/Reference/NSRegularExpression_Class/index.html

\\[                Find a literal opening square bracket: \[
    (              (start 1st capturing group)
        [^         Followed by any character that is not…
            \\]    … A literal closing square bracket: \]
        ]          
        +          Repeated 1 or more times
    )              (stop 1st capturing group)
\\]                Followed by a literal closing square bracket: \]
\\(                Followed by a literal opening parenthesis: \)
    (              (start 2nd capturing group)
        [^         Followed by any character that is not…
            \\)    … A literal closing parenthesis: \)
            \"     … Nor, a double quote: "
            \\s    … Nor, any “space” type of character: \s
        ]          
        +          Repeated 1 or more times
    )              (stop 2nd capturing group)
    (?:            (start a non-capturing group)
        \\s        Followed by any “space” type of character: \s
        +          Repeated 1 or more times
        \"         Followed by a double quote: "
        (          (start 3rd capturing group)
            .      Followed by any character
            *      Repeated 0 or more times
        )          (stop 3rd capturing group)
        \"         Followed by a double quote: "
    )              (stop the non-capturing group)
    ?              (match the non-capturing group 0 or 1 times)
\\)                Ending in a literal closing parenthesis: \)

SampleInputFile.txt

LINKS

Markdown supports two styles for creating links: inline and reference. With both styles, you use square brackets to delimit the text you want to turn into a link.

Inline-style links use parentheses immediately after the link text. For example:

This is an[example link](http://example.com/).
Output:

<p>This is an <a href="http://example.com/">
example link</a>.</p>
Optionally, you may include a title attribute in the parentheses:

This is an [example link](http://example.com/  "With a Title"). Another "quoted" word.
Output:

<p>This is an <a href="http://example.com/" title="With a Title">
example link</a>.</p>
Reference-style links allow you to refer to your links by names, which you define elsewhere in your document:


This is an [example link](http://example.com/  "Title").
Output:

I get 10 times more traffic from [Google][1] than from
[Yahoo][2] or [MSN][3].

[1]: http://google.com/        "Google"
[2]: http://search.yahoo.com/  "Yahoo Search"
[3]: http://search.msn.com/    "MSN Search"
Output:

<p>I get 10 times more traffic from <a href="http://google.com/"
title="Google">Google</a> than from <a href="http://search.yahoo.com/"
title="Yahoo Search">Yahoo</a> or <a href="http://search.msn.com/"
title="MSN Search">MSN</a>.</p>
The title attribute is optional. Link names may contain letters, numbers and spaces, but are not case sensitive:

I start my morning with a cup of coffee and
[The New York Times][NY Times].

[ny times]: http://www.nytimes.com/
Output:

<p>I start my morning with a cup of coffee and
<a href="http://www.nytimes.com/">The New York Times</a>.</p>

SampleOutputFile.log

2015-06-10 09:14:18.640 example[39382:4738113] Found: >[example link](http://example.com/)<
Link:  >example link<
URL:   >http://example.com/<
Title: >(null)<
2015-06-10 09:14:18.641 example[39382:4738113] Found: >[example link](http://example.com/  "With a Title")<
Link:  >example link<
URL:   >http://example.com/<
Title: >With a Title<
2015-06-10 09:14:18.641 example[39382:4738113] Found: >[example link](http://example.com/  "Title")<
Link:  >example link<
URL:   >http://example.com/<
Title: >Title<
2015-06-10 09:14:18.642 example[39382:4738113] Done!