My original question was "C# run Pip install in Venv programmatically" but it turns out there was no issue with C# code or the Pip thing. But with the Batch Script. SO first is the edited question to help others and then my original question for just a record.

Run a Batch script with a command to run another Batch file.

child.bat

@echo off
echo Child Batch File is running !!!
echo Doing some Important Child Batch Stuff here . . . .
echo ✔ Child Batch Completed it. Voila !!
echo Now exiting Child.bat

parent.bat

@echo off
echo Parent Batch File is running !!!
echo Doing some Important Stuff here . . . .
echo ✔ Completed it. Voila !!
echo Now running Child.bat . . .

echo -------------------------------------------------------

child.bat

// Comment: Some how below statements are not executing
echo -------------------------------------------------------

echo ✔ Completed it. Voila !!
echo I believe all the this are complete.
echo I am now exiting.

Output:

C:\Users\abc> parent.bat

Parent Batch File is running !!!
Doing some Important Stuff here . . . .
✔ Completed it. Voila !!. .
Now running Child.bat . . .
-------------------------------------------------------
Child Batch File is running !!!
Doing some Important Child Batch Stuff here . . . .
✔ Child Batch Completed it. Voila !!
Now exiting Child.bat

C:\Users\abc>

Where are the other parent.bat echo commands.

Expected Output:

Parent Batch File is running !!!
Doing some Important Stuff here . . . .
✔ Completed it. Voila !!. .
Now running Child.bat . . .
-------------------------------------------------------
Child Batch File is running !!!
Doing some Important Child Batch Stuff here . . . .
✔ Child Batch Completed it. Voila !!
Now exiting Child.bat
-------------------------------------------------------
Completed it. Voila !!
echo I believe all the this are complete.
echo I am now exiting.

Old Question for just a record

I have a C# application and it uses some python scripts. To run the python scripts I need to have some dependencies. So i created a batch file that creates a VENV. But it never runs PIP INSTALL COMMAND.

C# Code to run multiple cmd statements. It creates a batch file.

        public void abc() {
            var batFileName = Path.Combine(Path.GetTempPath(), $"{Guid.NewGuid()}.bat");
            using (var batFile = new StreamWriter(batFileName))
            {
                var pythonPath = Path.Combine(LocalAppData, ProjectGuid, HolocronFolders["HolocronPython"]);
                var venv = Path.Combine(LocalAppData, ProjectGuid, HolocronFolders["HolocronVenv"]);
                batFile.WriteLine($"{pythonPath}\\python.exe -m venv {venv}");
                batFile.WriteLine($"{venv}\\Scripts\\activate.bat");
                batFile.WriteLine($"pip install rich"); //  Not running in venv
            }
            var process = new Process();
            var startInfo = new ProcessStartInfo
            {
                FileName = "cmd.exe",
                Arguments = $"/C {batFileName}"
            };
            process.StartInfo = startInfo;
            process.Start();
            File.Delete(batFileName);
        }

batch file created

Path_to_python\python.exe -m venv path_to_venv_folder
Path_to_venv_folder\Scripts\activate.bat
pip install rich            --//-- Comments: Not running in Venv. Actually not running at all.

cmd output:

c:\user\abc> Path_to_python\python.exe -m venv path_to_venv_folder
c:\user\abc> Path_to_venv_folder\Scripts\activate.bat
(path_to_venv_folder) c:\user\abc>