Remove tag from string variable using Regex

Question

Application have the

string

variable which contains

xml

data.

I trying to remove all tags

<product_desc></product_desc>

using

Regex

.

Here are the value of the

string

variable

<orderlines>

    <orderline>

        <id>1000001</id>

        <product_id>2004</product_id>

        <product_desc>ITEM2004

        Color: red

        Size: 150x10x10

        Material: iron

        </product_desc>

        <qnt>2</qnt>

    </orderline>

    <orderline>

        <id>1000002</id>

        <product_id>2012</product_id>

        <product_desc>ITEM2012</product_desc>

        <qnt>4</qnt>

    </orderline>

    <orderline>

        <id>1000003</id>

        <product_id>3000</product_id>

        <product_desc>DELIVERY</product_desc>

        <qnt>1</qnt>

    </orderline>

</orderlines>

When I using next pattern:

Dim pattern As String = "(<product_desc>[\s\S]*</product_desc>)"

Dim newvalue As String = Regex.Replace(originvalue, pattern, "")

I get result like this:

<orderlines>

    <orderline>

        <id>1000001</id>

        <product_id>2004</product_id>



        <qnt>1</qnt>

    </orderline>

</orderlines>

So problem is that

Regex

matches all values between first

<product_desc>

and last

</product_desc>

and replace them with empty string. This approach remove all

<orederline>

tags between them(check value of the

<qnt>

tag).

Can anybody give some tip of how limit removing to remove only specific tag. Content of the tag can contain all possible characters, newlines and even html code.

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Answer 1

The problem: [\s\S]* is greedy

It matches every single char to the end of the string, then the engine backtracks to allow </product_desc> to match. Therefore, there is one single match from the first opening tag to the last closing tag.

The solution (if we're doing regex): a lazy quantifier

With all the warnings and disclaimers about using regex to parse xml... You can do this:

Adding a ? to a quantifier makes it "lazy", so that it matches only as many chars as necessary.
You can use .*? in DOTALL mode (as in the sample code below) or [\s\S]*? (but there is no point).

Sample code

Dim ResultString As String
Try
    ResultString = Regex.Replace(SubjectString, "(?s)<product_desc>.*?</product_desc>", "")
Catch ex As ArgumentException
    'Syntax error in the regular expression
End Try

Reference

Remove tag from string variable using Regex

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