Program.cs

using System;
using System.IO;
using System.Text.RegularExpressions;
using System.Collections.Generic;
using System.Threading;
using System.Diagnostics;

namespace enswap
{
    class MainClass
    {
        static long ParseValue(string line)
        {
            long result = 0;
            int i = 0;
            for (; line[i] != ':'; i++) {}
            for (; line[i] < '0'  || line[i] > '9';  i++) {}
            for (; line[i] >= '0' && line[i] <= '9'; i++)
                result = result * 10  + (int)(line[i] - '0');
                
            return result;
        }
        
        static string[] captureStrs = new string[] { "MemTotal:", "MemAvailable:", "SwapTotal:" };
        static Random   rnd         = new Random();
        
        const long      minAvailableMemory = 1024*1024 * 3/2; // in kilobytes 1024*1024 = 1 Gb
        const int       intervalForCheck   = 500;
        public static int Main(string[] args)
        {
            if (args.Length != 1 && args.Length != 2)
            {
                Console.Error.WriteLine("Must be 1 or 2 arguments: script path for execute and script parameters in quotes");
                Console.Error.WriteLine("Example");
                Console.Error.WriteLine("/media/veracrypt1/swap.sh \"2G\"");

                return 1;
                // args = new string[] { "/media/veracrypt1/swap.sh", "2G" };
            }

            var exec = true;
            var Dict = new Dictionary<string, long>(2);
            Console.CancelKeyPress += (sender, e) => exec = false;

            while (exec)
            {
                Dict.Clear();
                Thread.Sleep(rnd.Next(50, intervalForCheck));

                // System.Diagnostics.Process.Start("free");
                var memInfoLines = File.ReadAllLines("/proc/meminfo");
    
                foreach (var line in memInfoLines)
                {
                    foreach (var captureStr in captureStrs)
                        if (line.StartsWith(captureStr, StringComparison.InvariantCulture))
                        {
                            Dict.Add(captureStr, ParseValue(line));
                        }
    
                    if (Dict.Count >= 3)
                        break;
                }

                if (Dict[captureStrs[1]] <= minAvailableMemory)
                {
                    // if (Dict[captureStrs[2]] <= 0)

                    Process pi = null;
                    if (args.Length == 1)
                        pi = System.Diagnostics.Process.Start(args[0]);
                    else
                        pi = System.Diagnostics.Process.Start(args[0], args[1]);

                    pi.WaitForExit();

                    return 0;
                }
            }
            
            return 0;
        }
    }
}