regular expression for anything but an empty string

Question

Is it possible to use a regular expression to detect anything that is NOT an \"empty string\" like this:

string s1 = \"\";
string s2 = \" \";
string s3 = \"          


        

Answer 1

We can also use space in a char class, in an expression similar to one of these:

(?!^[ ]*$)^\S+$
(?!^[ ]*$)^\S{1,}$
(?!^[ ]{0,}$)^\S{1,}$
(?!^[ ]{0,1}$)^\S{1,}$

depending on the language/flavor that we might use.

RegEx Demo

Test

using System;
using System.Text.RegularExpressions;

public class Example
{
    public static void Main()
    {
        string pattern = @"(?!^[ ]*$)^\S+$";
        string input = @"

            abcd
            ABCD1234
            #$%^&*()_+={}
            abc def
            ABC 123
            ";
        RegexOptions options = RegexOptions.Multiline;

        foreach (Match m in Regex.Matches(input, pattern, options))
        {
            Console.WriteLine("'{0}' found at index {1}.", m.Value, m.Index);
        }
    }
}

C# Demo

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If you wish to simplify/modify/explore the expression, it's been explained on the top right panel of regex101.com. If you'd like, you can also watch in this link, how it would match against some sample inputs.

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RegEx Circuit

jex.im visualizes regular expressions: