Regular Expression IsMatch() method in C#

Question

I compiled the code:

namespace TestRegExp
{
    class Program
    {
        static void Main(string[] args)
        {
            if (Regex.IsMatch(args[1], args[0]))
                Console.WriteLine("Input matches regular expression.");
            else
                Console.WriteLine("Input DOES NOT match regular expression.");
        }
    }
}

When I run:

TestRegExp.exe ^a\d{5}$ a12345 shows Input matches regular expression.
TestRegExp.exe ^a\d{5}$ aa12345 shows Input matches regular expression.
TestRegExp.exe ^^a\d{5}$ a12345 shows Input matches regular expression.
TestRegExp.exe ^^a\d{5}$ aa12345 shows Input DOES NOT match regular expression.

Why the second option shows Input matches regular expression.?

The '^' symbol represents the string init... alright? and why do I have to repeat this?

What CLI did you use? It sounds like command line interpretation problem. — luiges90
– luiges90, Commented Jun 9, 2013 at 1:27

Dave Cluderay · Accepted Answer · 2013-06-09 01:32:29Z

8

The ^ is used as an escape character in the Windows commandline environment. It tells the command interpreter to treat the next as a literal character (since some characters like <, > and | have special meanings otherwise).

^a evaluates to a when parsed.

^^ evaluates to ^ when parsed.

answered Jun 9, 2013 at 1:32

Dave Cluderay

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Comments

Diego Mijelshon · Accepted Answer · 2013-06-09 01:35:25Z

7

This has nothing to do with the regular expression itself.

If you print args[0] to the console, you'll see that it doesn't contain the ^. This is because Windows parses it as an escape character if the expression is not quoted.

If you call it like this:

TestRegExp.exe "^a\d{5}$" aa12345

You'll get the expected result.

edited Jun 9, 2013 at 1:35

answered Jun 9, 2013 at 1:28

Diego Mijelshon

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1 Comment

Kendall Frey Over a year ago

Can you clarify why the ^ is not included?

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