C#

Environment.SetEnvironmentVariable(name, value, EnvironmentVariableTarget.User)

Environment.GetEnvironmentVariable("MYID", EnvironmentVariableTarget.User)

Reference Source[^]:

C#

// send a WM_SETTINGCHANGE message to all windows
IntPtr r = Win32Native.SendMessageTimeout(new IntPtr(Win32Native.HWND_BROADCAST), Win32Native.WM_SETTINGCHANGE, IntPtr.Zero, "Environment", 0, 1000, IntPtr.Zero);
if (r == IntPtr.Zero) BCLDebug.Assert(false, "SetEnvironmentVariable failed: " + Marshal.GetLastWin32Error());

Environment.SetEnvironmentVariable Method (System) | Microsoft Docs[^]:

If target is EnvironmentVariableTarget.User, the environment variable is stored in the HKEY_CURRENT_USER\Environment key of the local computer's registry. It is also copied to instances of File Explorer that are running as the current user. The environment variable is then inherited by any new processes that the user launches from File Explorer.
...
If target is User or Machine, other applications are notified of the set operation by a Windows WM_SETTINGCHANGE message.

string s = @"d1.8xlarge: 3 d1.xlarge: 0 c2.xlarge: 25
s1.medium: 1 c2.xlarge: 10 s1.large: 4 d1.8xlarge: 27";

string[] split = s.Split(new char[] {' ',':', '\r','\n'}, StringSplitOptions.RemoveEmptyEntries);

int limit = split.Length - 1;

var sorted = split.Select((string str, int ndx) => // declaration of auto-index
{
    int val;  // use of variable defined inside 'Select

    if (ndx < limit && int.TryParse(split[ndx + 1], out val))
    {
        return new {name = split[ndx], value = val};
    }
    else
    {
        return null; // you have to return something !
    }
})
.Where(itm => itm != null) // get rid of 'nulls
.GroupBy(itm => itm.name) // group on the 'name
.ToDictionary(grp => grp.Key, grp => grp.Sum(v => v.value)); // summation

([a-zA-z]\d\.\w+:\s\d)

public static Regex regex = new Regex("([a-zA-z]\\d\\.\\w+:\\s\\d)",
                                      RegexOptions.Multiline | RegexOptions.CultureInvariant | RegexOptions.Compiled);
...
            MatchCollection ms = regex.Matches(InputText);
            foreach (Match m in ms)
                {
                Console.WriteLine(m.Value);
                }