Converting a specific regular expression pattern from java to c#

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Hello,

What would be the equivalence regular expression in c# for

Java

private static final Pattern verifiedSourcePattern = Pattern.compile("(\\QCustomer review from the Amazon Vine™ Program\\E)|(\\QAmazon Verified Purchase\\E)");

Which is in Java. I get an error when I write the same in C#:

C#

static Regex verifiedSourcePattern = new Regex("(\\QCustomer review from the Amazon Vine™\\E)|(\\QAmazon Verified Purchase\\E)");

Thank you
Saman

Posted 10-Nov-14 12:20pm

Saman With You

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PIEBALDconsult 10-Nov-14 18:40pm

What error?

Saman With You 10-Nov-14 18:44pm

Hi, parsing "(\QCustomer review from the Amazon Vine™\E)|(\QAmazon Verified Purchase\E)" - Unrecognized escape sequence \Q.

PIEBALDconsult 10-Nov-14 18:49pm

And what is the goal? Why are you use \Q and \E in that expression? As far as I can tell, they aren't serving any purpose.

PIEBALDconsult 10-Nov-14 19:10pm

Also, try Expresso, it might give some insight.
http://www.ultrapico.com/Expresso.htm

2 solutions

Solution 1

The problem is: your observation is incorrect. Probably, you just copied the text incorrectly, maybe even two times. In one place you have "(\\QCustomer ...)", in another place — "(\QCustomer ...)".
Both cases are incorrect.

First case: in C#, having string value = "(\\QCustomer ...\\E)";
It compiles. It means that value is "(\QCustomer ...\E)". But these two escape sequences do not exist in .NET regular expressions.

The second case: C# tries to replace "\Q" with something, but this is a non-existing escape syntax. You could use '@' again. But again, the regular expression would make not much sense.

[EDIT]

So, this code would be incorrect:

C#

using Regex = System.Text.RegularExpressions.Regex;

//...

// won't compile: 'Unrecognized escape sequence'
//Regex regexOne = new Regex("(\QAmazon Verified Purchase\E)");

// will compile, but this line will throw exception
Regex regexTwo = new Regex("(\\QAmazon Verified Purchase\\E)");
// 'Unrecognized escape sequence \Q'

[END EDIT]

Please fix it and try again. For further help, we would need to know the goal, formally and correctly described.

—SA

Posted 10-Nov-14 13:04pm

Sergey Alexandrovich Kryukov

Updated 11-Nov-14 4:20am

v3

Comments

PIEBALDconsult 10-Nov-14 19:07pm

\Q has a meaning in other implementations. I see it in my Perl book, but its meaning is not in the .net implementation and seems pointless in the given example.

Sergey Alexandrovich Kryukov 10-Nov-14 19:12pm

Really? And could you tell me what's that meaning?

Anyway, I'm glad to get the confirmation that '\Q' is meaningless in .NET (and in fact is equivalent to 'Q', where '\' is simply redundant). So, it keeps my answer valid and my advice applicable.

I must say, I did not check it up on .NET this time. I checked it with my own native code using 3rd-party regex. So far, I did not face any discrepancies with .NET, but yes, Rerl regex could be different.

—SA

PIEBALDconsult 10-Nov-14 20:41pm

By "verbose" you mean "verbatim".

In one place you have "(\\QCustomer ...)", in another place — "(\QCustomer ...)". --- I don't see that.

Sergey Alexandrovich Kryukov 10-Nov-14 21:40pm

Well, "verbatim", thank you.
Two places are: in OP's question and comment.
—SA

PIEBALDconsult 10-Nov-14 21:44pm

Ah, I ignored the comment; it's non-canon. :D

Sergey Alexandrovich Kryukov 10-Nov-14 23:30pm

Okay, but without this comment, we cannot explain the error with "(\\QCustom ...)" would be processed correctly.
The error tells me that OP actually tried "(\QCustom ...)"; it wasn't exception but was a compilation error. Do you see the point now? The problem faced so far is unrelated to regex...
—SA

PIEBALDconsult 11-Nov-14 9:14am

I don't think so. The expression failed to compile, not the code.

Sergey Alexandrovich Kryukov 11-Nov-14 10:22am

Ha! You are right. It looks like OP did not try what is written in the comment, because error message from a C# compiler is slightly different. I finally accurately tested it on runtime and fixed the answer.
Thank you very much.
—SA

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PIEBALDconsult · Accepted Answer · 2014-11-10T13:22:00

I have been unable to determine what the meaning of \Q is in Java, but in Perl, it's:

\Q          quote (disable) pattern metacharacters until \E
\E          end either case modification or quoted section,

This doesn't appear in the .net implementation and seems needless in your example.

Remove the \Q and \E and try again.

Edit: It means the same thing in Java...

There are two ways to force a metacharacter to be treated as an ordinary character:
•precede the metacharacter with a backslash, or
•enclose it within \Q (which starts the quote) and \E (which ends it).

https://docs.oracle.com/javase/tutorial/essential/regex/literals.html[^]

Also, as reference, here's some documentation of .net Regular Expressions
http://msdn.microsoft.com/en-us/library/az24scfc(v=vs.110).aspx[^]