C# How to get SQL Server installation path programatically?

Question

How do I get the installation path for a given instance of SQL Server (default and name instances)

Answer 1

If you have the connection string, you may select the Directory with SQL

private string ServerRootDirectory(string connString)
    {
        string path = string.Empty;
        using (SqlConnection con = new SqlConnection(connString))
        {
            con.Open();
            SqlCommand cmd = new SqlCommand();
            cmd.Connection = con;
            cmd.CommandText = string.Format(@"DECLARE @InstanceName varchar(100), 
                                                        @InstanceLocation varchar(100),
                                                        @InstancePath varchar(100)

                                                SELECT @InstanceName = convert(varchar, ServerProperty('InstanceName'))
                                                EXEC master..xp_regread @rootkey='HKEY_LOCAL_MACHINE',
                                                    @key='Software\Microsoft\Microsoft SQL Server\Instance Names\SQL',
                                                    @value_name=@InstanceName,
                                                    @value=@InstanceLocation OUTPUT
                                                SELECT @InstanceLocation = 'Software\Microsoft\Microsoft SQL Server\'+@InstanceLocation+'\Setup'

                                                EXEC master..xp_regread @rootkey='HKEY_LOCAL_MACHINE',
                                                    @key=@InstanceLocation,
                                                    @value_name='SQLPath',
                                                    @value=@InstancePath OUTPUT
                                                SELECT @InstancePath as RootDirectoryPath");
            path = (string)cmd.ExecuteScalar();
            con.Close();
        }
        return path;
    }

Output of the above code:

c:\Program Files\Microsoft SQL Server\MSSQL14.SQLEXPRESS\MSSQL