stream is a utility that is a line oriented find and replace using C# Regular Expressions

stream.cs

#!/usr/bin/env -S dotnet --

// 1) Install dotnet sdk, e.g., sudo apt install dotnet-sdk-10.0
// 2) Copy gist to stream.cs
// 3) chmod a+x stream.cs
// 4) ./stream.cs -e 's#Joy#Wawa#'

using System.Text.RegularExpressions;

if (args.Length == 0 || args.Contains("--help"))
{
    Console.WriteLine(@"Description:
Process regular expression(s) over lines in a file.

Usage:
  stream [options]

Options:
  -e        A regular expression.
  -f        A file with regular expressions.
  --help    Display this help.");

    Environment.Exit(0);
}

// TODO: Class
List<Regex> RegexesFind = new();
List<string> RegexesReplace = new();
List<bool> RegexesReplaceAll = new();

foreach (string regex in GetRegexes(args))
{
    char splitOn = regex[1];

    RegexesFind.Add(new Regex(regex.Split(splitOn)[1], RegexOptions.None));
    RegexesReplace.Add(regex.Split(splitOn)[^2]);
    RegexesReplaceAll.Add(regex.ToLower().EndsWith('g'));
}

using (StreamReader stdin = new(Console.OpenStandardInput()))
{
    while (stdin.ReadLine() is string line)
    {
        foreach ((int index, Regex regex) in RegexesFind.Index())
        {
            line = regex.Replace(line, RegexesReplace[index], RegexesReplaceAll[index] ? Int32.MaxValue : 1);
        }

        Console.WriteLine(line);
    }
}

IEnumerable<string> GetRegexes(string[] args)
{
    bool prevDashE = false;
    bool prevDashF = false;

    foreach (string arg in args)
    {
        if (prevDashE)
        {
            prevDashE = false;

            yield return arg;
        }
        else if (prevDashF)
        {
            using (StreamReader stdin = new(File.OpenRead(arg)))
            {    
                while (stdin.ReadLine() is string line)
                {
                    yield return line;
                }
            }
        }
        else if (arg.Equals("-e"))
        {
            prevDashE = true;
        }
        else if (arg.Equals("-f"))
        {
            prevDashF = true;
        }
    }
}