Regex to Retrieve Quoted String and Quote Character

Question

I have a language that defines a string as being delimited by either single or double quotes, where the delimiter is escaped within the string by doubling it. For example, all of the following are legal strings:

'This isn''t easy to parse.'
'Then John said, "Hello Tim!"'
"This isn't easy to parse."
"Then John said, ""Hello Tim!"""

I have a collection of strings (defined above), delimited by something that doesn't contain a quote. What I am attempting to do using regular expressions, is to parse each string in a list out. For example, here is an input:

"Some String #1" OR 'Some String #2' AND "Some 'String' #3" XOR
'Some "String" #4' HOWDY "Some ""String"" #5" FOO 'Some ''String'' #6'

The regular expression to determine whether a string is of such a form is trivial:

^(?:"(?:[^"]|"")*"|'(?:[^']|'')*')(?:\s+[^"'\s]+\s+(?:"(?:[^"]|"")*"|'(?:[^']|'')*')*

After running the above expression to test whether it is of such a form, I need another regular expression to get each delimited string from the input. I plan to do this as follows:

Pattern pattern = Pattern.compile("What REGEX goes here?");
Matcher matcher = pattern.matcher(inputString);
int startIndex = 0;
while (matcher.find(startIndex))
{
    String quote        = matcher.group(1);
    String quotedString = matcher.group(2);
    ...
    startIndex = matcher.end();
}

I would like a regular expression that captures the quote character in group #1, and the text within quotes in group #2 (I am using Java Regex). So, for the above input, I am looking for a regular expression that produces the following output within each loop iteration:

Loop 1: matcher.group(1) = "
        matcher.group(2) = Some String #1
Loop 2: matcher.group(1) = '
        matcher.group(2) = Some String #2
Loop 3: matcher.group(1) = "
        matcher.group(2) = Some 'String' #3
Loop 4: matcher.group(1) = '
        matcher.group(2) = Some "String" #4
Loop 5: matcher.group(1) = "
        matcher.group(2) = Some ""String"" #5
Loop 6: matcher.group(1) = '
        matcher.group(2) = Some ''String'' #6

Patterns I have tried thus far (un-escaped, followed by escaped for Java code):

(["'])((?:[^\1]|\1\1)*)\1
"([\"'])((?:[^\\1]|\\1\\1)*)\\1"

(?<quot>")(?<val>(?:[^"]|"")*)"|(?<quot>')(?<val>(?:[^']|'')*)'
"(?<quot>\")(?<val>(?:[^\"]|\"\")*)\"|(?<quot>')(?<val>(?:[^']|'')*)'"

Both of these fail when trying to compile the pattern.

Is such a regular expression possible?

Answer 1

Make a utility class that matches for you:

class test {
    private static Pattern pd = Pattern.compile("(\")((?:[^\"]|\"\")*)\"");
    private static Pattern ps = Pattern.compile("(')((?:[^']|'')*)'");
    public static Matcher match(String s) {
        Matcher md = pd.matcher(s);
        if (md.matches()) return md;
        else return ps.matcher(s);
    }
}