C# Regex.Replace() swallowing part of original string

Question

I can't figure out what happens to the "FROM ROOT" when the Regex.Replace() happens:

static string query = @"
SELECT * 
FROM root
ORDER BY root['UtcTimestamp'] DESC";

static void Main(string[] args)
{
    var endsWithOrderBy = new Regex("^.+(\\s+ORDER\\s+BY\\s+.+)$",
        RegexOptions.Multiline | RegexOptions.IgnoreCase | RegexOptions.Compiled);

    query = query.Trim();

    var result = endsWithOrderBy.Replace(query, "$1");

    Console.Write(result);
    Console.Read();
}

I think it's because there's a \n instead of a space between "FROM root\nORDER BY". How can I tell the regex to include \n characters in \\s?

NOTE: Please refrain from discussions about the applicability of using regular expressions here, given that the example here is contrived.

What is your expected behavior here? What are you trying to do? — JLRishe
– JLRishe, Commented Mar 16, 2016 at 18:15
\s matches all kinds of whitespace characters, including \n. So that's definitely not your problem, but I don't get what you're trying to do. If you want the regex to match the whole string, add the Singleline option; if you want to match just last line, remove the ^.+ and the first \s+. And while you're at it, use verbatim string literals (@"...") so you don't have to escape the backslashes, and drop the Compiled option: you don't need it. — Alan Moore
– Alan Moore, Commented Mar 16, 2016 at 20:34

Richard Deeming · Accepted Answer · 2016-03-16 18:20:30Z

2

Looking at the documentation, since you've specified RegexOptions.Multiline, the ^ anchor matches the beginning of a line, not the beginning of the string.

As a result, your pattern matches:

FROM root
ORDER BY root['UtcTimestamp'] DESC

You then replace that with the value of the first capture, which is:

{\n}
ORDER BY root['UtcTimestamp'] DESC

which gives the result:

SELECT *

ORDER BY root['UtcTimestamp'] DESC

It's not clear what output you were expecting. If you just want to remove the entire ORDER BY clause, then add a group to capture the prefix:

var endsWithOrderBy = new Regex("^(.+)(\\s+ORDER\\s+BY\\s+.+)$", ...);

answered Mar 16, 2016 at 18:20

Richard Deeming

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Comments

Anderson Pimentel · Accepted Answer · 2016-03-16 18:35:01Z

1

You can use this:

\s*\n?\s*(ORDER\s+BY\s+.*)$

If you use an anchor for the start of the line (^) you cannot match when the ORDER BY is not preceded by a line break, i.e. SELECT * FROM root ORDER BY root['UtcTimestamp'] DESC.

Check here: https://regex101.com/r/gQ2rQ1/2

I'm using the g modifier so you can test multiple sentences, but you won't need it.

edited Mar 16, 2016 at 18:35

answered Mar 16, 2016 at 18:27

Anderson Pimentel

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