Parsing text between quotes with .NET regular expressions

Question

I have the following input text:

@"This is some text @foo=bar @name=""John \""The Anonymous One\"" Doe"" @age=38"

I would like to parse the values with the @name=value syntax as name/value pairs. Parsing the previous string should result in the following named captures:

name:"foo"
value:"bar"

name:"name"
value:"John \""The Anonymous One\"" Doe"

name:"age"
value:"38"

I tried the following regex, which got me almost there:

@"(?:(?<=\s)|^)@(?<name>\w+[A-Za-z0-9_-]+?)\s*=\s*(?<value>[A-Za-z0-9_-]+|(?="").+?(?=(?<!\\)""))"

The primary issue is that it captures the opening quote in "John \""The Anonymous One\"" Doe". I feel like this should be a lookbehind instead of a lookahead, but that doesn't seem to work at all.

Here are some rules for the expression:

• Name must start with a letter and can contain any letter, number, underscore, or hyphen.

• Unquoted must have at least one character and can contain any letter, number, underscore, or hyphen.

• Quoted value can contain any character including any whitespace and escaped quotes.

Edit:

Here's the result from regex101.com:

(?:(?<=\s)|^)@(?<name>\w+[A-Za-z0-9_-]+?)\s*=\s*(?<value>(?<!")[A-Za-z0-9_-]+|(?=").+?(?=(?<!\\)"))

(?:(?<=\s)|^) Non-capturing group
@ matches the character @ literally
(?<name>\w+[A-Za-z0-9_-]+?) Named capturing group name
\s* match any white space character [\r\n\t\f ]
= matches the character = literally
\s* match any white space character [\r\n\t\f ]
    Quantifier: * Between zero and unlimited times, as many times as possible, giving back as needed [greedy]
(?<value>(?<!")[A-Za-z0-9_-]+|(?=").+?(?=(?<!\\)")) Named capturing group value
    1st Alternative: [A-Za-z0-9_-]+
        [A-Za-z0-9_-]+ match a single character present in the list below
            Quantifier: + Between one and unlimited times, as many times as possible, giving back as needed [greedy]
            A-Z a single character in the range between A and Z (case sensitive)
            a-z a single character in the range between a and z (case sensitive)
            0-9 a single character in the range between 0 and 9
            _- a single character in the list _- literally
    2nd Alternative: (?=").+?(?=(?<!\\)")
        (?=") Positive Lookahead - Assert that the regex below can be matched
            " matches the characters " literally
        .+? matches any character (except newline)
            Quantifier: +? Between one and unlimited times, as few times as possible, expanding as needed [lazy]
        (?=(?<!\\)") Positive Lookahead - Assert that the regex below can be matched
            (?<!\\) Negative Lookbehind - Assert that it is impossible to match the regex below
                \\ matches the character \ literally
            " matches the characters " literally

Answer 1

You can use a very useful .NET regex feature where multiple same-named captures are allowed. Also, there is an issue with your (?<name>) capture group: it allows a digit in the first position, which does not meet your 1st requirement.

So, I suggest:

(?si)(?:(?<=\s)|^)@(?<name>\w+[a-z0-9_-]+?)\s*=\s*(?:(?<value>[a-z0-9_-]+)|(?:"")?(?<value>.+?)(?=(?<!\\)""))

See demo

Note that you cannot debug .NET-specific regexes at regex101.com, you need to test them in .NET-compliant environment.