Hi @gilbertosj, here is an iex session that may help you:

iex(1)> string = """
...(1)> Hi, gilbertosj! That's a great question.
...(1)> You can use EEx (https://github.com/elixir-lang/elixir/tree/master/lib/eex)
...(1)> EEx is part of the standard library and can help you with your task. 
...(1)> EEx + the File module (as stated above) would solve your problem.
...(1)> Here is an example of a variable: <%= variable %>
...(1)> Here is a lesson about this on ElixirSchool: https://elixirschool.com/en/lessons/specifics/eex 
...(1)> Hope this helps!   
...(1)> """
"Hi, gilbertosj! That's a great question.\nYou can use EEx (https://github.com/elixir-lang/elixir/tree/master/lib/eex)\nEEx is part of the standard library and can help you with your task.\nEEx + the File module (as stated above) would solve your problem.\nHere is an example of a variable: <%= variable %>\nHere is a lesson about this on ElixirSchool: https://elixirschool.com/en/lessons/specifics/eex\nHope this helps!\n"
iex(2)> content = EEx.eval_string(string, [variable: "EXAMPLE VARIABLE"])       
"Hi, gilbertosj! That's a great question.\nYou can use EEx (https://github.com/elixir-lang/elixir/tree/master/lib/eex)\nEEx is part of the standard library and can help you with your task.\nEEx + the File module (as stated above) would solve your problem.\nHere is an example of a variable: EXAMPLE VARIABLE\nHere is a lesson about this on ElixirSchool: https://elixirschool.com/en/lessons/specifics/eex\nHope this helps!\n"
iex(3)> File.write!("this_is_a_filename.txt", content)
:ok

Now, you can check the file we just created:

pdg :> cat this_is_a_filename.txt 
Hi, gilbertosj! That's a great question.
You can use EEx (https://github.com/elixir-lang/elixir/tree/master/lib/eex)
EEx is part of the standard library and can help you with your task.
EEx + the File module (as stated above) would solve your problem.
Here is an example of a variable: EXAMPLE VARIABLE
Here is a lesson about this on ElixirSchool: https://elixirschool.com/en/lessons/specifics/eex
Hope this helps!