using System;

using System.Collections.Generic;

using System.Diagnostics;

using System.IO;

using System.Linq;

using System.Threading;

using System.Threading.Tasks;

using System.Text.RegularExpressions;

public class Test

{

    public static void Main()

    {

        var ssbpowoffset_cmd="set beampattern 0 ss-pbchindex=1 beamset-index=1 power=-3.5dB";

        decimal ssbpowoffset_val ;

​

        var key = "power";

        var targetStr = ssbpowoffset_cmd.Split(' ').FirstOrDefault(str => str.Contains(key)) ?? string.Empty;

        var Match = new Regex(@"^\D*?((-?(\d+(\.\d+)?))|(-?\.\d+)).*").Match(targetStr);

        ssbpowoffset_val = Match.Success ? Convert.ToDecimal(Match.Groups[1].Value) : 0;

        Console.WriteLine(targetStr);

        Console.WriteLine(Match);

        Console.WriteLine(ssbpowoffset_val);

    }

}