Regex battle between maximum and minimum munge

Greetings, I have file with the following strings:

string.Format("{0},{1}", "Having \"Two\" On The Same Line".Localize(), "Is Tricky For regex".Localize());

my goal is to get a m开发者_高级运维atch set with the two strings:

• Having \"Two\" On The Same Line
• Is Tricky For regex

My current regex looks like this:

private Regex CSharpShortRegex = new Regex("\"(?<constant>[^\"]+?)\".Localize\\(\\)");

My problem is with the escaped quotes in the first line I end up stopping at the quote and I get:

• On The Same Line
• Is Tricky For This Style Too

however attempting to ignore the escaped quotes is not working out because it makes the Regex greedy and I get

• Having \"Two\" On The Same Line".Localize(), "Is Tricky For regex"

We seem to be caught between maximum and minimum munge. Is there any hope? I have some backup plans. Can you Regex backwards? that would make it easier because I can start with the "()ezilacoL."

EDIT: To clarify. This is my lone edge case. Most of the time the string sits alone like:

var myString = "Hot Patootie".Localize()

---

This one works for me:

\"((?:[^\\"]|(?:\\\"))*)\"\.Localize\(\)

Tested on http://www.regexplanet.com/simple/index.html against a number of strings with various escaped quotes.

Looks like most of us who answered this one had the same rough idea, so let me explain the approach (comments after #s):

\"             # We're looking for a string delimited by quotation marks
(              # Capture the contents of the quotation marks
  (?:          #   Start a non-capturing group
    [^\\"]     #     Either read a character that isn't a quote or a slash
    |(?:\\\")  #     Or read in a slash followed by a quote.
  )*           #   Keep reading
)              # End the capturing group
\"             # The string literal ends in a quotation mark
\.Localize\(\) # and ends with the literal '.Localize()', escaping ., ( and )

For C# you'll need to escape the slashes twice (messy):

\"((?:[^\\\\\"]|(?:\\\\\"))*)\"\\.Localize\\(\\)

Mark correctly points out that this one doesn't match escaped characters other than quotation marks. So here's a better version:

\"((?:[^\\"]|(?:\\")|(?:\\.))*)\"\.Localize\(\)

And its slashed-up equivalent:

\"((?:[^\\\\\"]|(?:\\\\\")|(?:\\\\.))*)\"\\.Localize\\(\\)

Works the same way, except it has a special case that if encounters a slash but it can't match \", it just consumes the slash and the following character and moves on.

---

Thinking about it, it's better to just consume two characters at every slash, which is effectively Mark's answer so I won't repeat it.

---

Here's the regular expression you need:

@"""(?<constant>(\\.|[^""])*)""\.Localize\(\)"

A test program:

using System; using System.Text.RegularExpressions; using System.IO;

class Program
{
    static void Main()
    {
        Regex CSharpShortRegex =
            new Regex(@"""(?<constant>(\\.|[^""])*)""\.Localize\(\)");

        foreach (string line in File.ReadAllLines("input.txt"))
            foreach (Match match in CSharpShortRegex.Matches(line))
                Console.WriteLine(match.Groups["constant"].Value);
    }
}

Output:

Having \"Two\" On The Same Line
Is Tricky For regex
Hot Patootie

Notice that I have used @"..." to avoid having to escape backslashes inside the regular expression. I think this makes it easier to read.

---

Update:

My original answer (below the horizontal rule) has a bug: regular-expression matchers attempt alternatives in left-to-right order. Having [^"] as the first alternative allows it to consume the backslash, but then the next character to be matched is a quote, which prevents the match from proceeding.

Incompatibility note: Given the pattern below, perl backtracks to the other alternative (the escaped quote) and successfully finds a match for the Having \"Two\" On The Same Line case.

The fix is to try an escaped quote first and then a non-quote:

var CSharpShortRegex =
  new Regex("\"(?<constant>(\\\\\"|[^\"])*)\"\\.Localize\\(\\)");

or if you prefer the at-string form:

var CSharpShortRegex =
  new Regex(@"""(?<constant>(\\""|[^""])*)""\.Localize\(\)");

---

Allow for escapes:

private Regex CSharpShortRegex =
  new Regex("\"(?<constant>([^\"]|\\\\\")*)\"\\.Localize\\(\\)");

Applying one level of escaping to make the pattern easier to read, we get

"(?<constant>([^"]|\\")*)"\.Localize\(\)

That is, a string starts and ends with " characters, and everything between is either a non-quote or an escaped quote.

---

Looks like you're trying to parse code so one approach might be to evaluate the code on the fly:

var cr = new CSharpCodeProvider().CompileAssemblyFromSource(
    new CompilerParameters { GenerateInMemory = true }, 
    "class x { public static string e() { return " + input + "}}");

var result = cr.CompiledAssembly.GetType("x")
    .GetMethod("e").Invoke(null, null) as string;

This way you could handle all kinds of other special cases (e.g. concatenated or verbatim strings) that would be extremely difficult to handle with regex.

---

new Regex(@"((([^@]|^|\n)""(?<constant>((\\.)|[^""])*)"")|(@""(?<constant>(""""|[^""])*)""))\s*\.\s*Localize\s*\(\s*\)", RegexOptions.Compiled);

takes care of both simple and @"" strings. It also takes into account escape sequences.