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content/articles/2023-09-24-introduction-to-programming-for-hvac-3.md

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+---
+tags: HVAC, programming, software
+---
+
+# Introduction to Programming for HVAC Part-3
+
+In this article we will put together some of the pieces from the last 2 articles, and build our first program. If you have missed the first
+articles, then you can catch up [here](https://mhoush.com/series/programming-for-hvac/) before continuing with this article.
+
+## Getting Started
+
+We are going to make our first script / program. This first program is really just setting up some building blocks for our next program we
+will write, that will remove the background from an image.
+
+### Creating a scripts directory
+
+We learned in the [first article](https://mhoush.com/posts/introduction-to-programming-for-hvac-1/) how to use our terminal. Today we are
+going to use some of the commands we learned to create a directory where we can store our script and future scripts that we write.
+
+**Create a directory**
+
+```bash
+mkdir -p ~/.local/bin
+```
+
+The above command will create a "hidden" directory in your home folder. We can go ahead and move into the directory we just created.
+
+> **Note:** The `-p` option allows us to create nested directories if the parent directory doesn't exist.
+
+```bash
+cd ~/.local/bin
+```
+
+### Hello World
+
+It is common in programming to start out with a "Hello World" program when learning a new scripting paradigm. So let's jump in and get
+started.
+
+**Creating our script file:**
+
+```bash
+touch hello-world.sh
+```
+
+**Now open the file:**
+
+```bash
+open hello-world.sh
+```
+
+The above command should open the file in the `TextEdit` application. In order to make the text edit application to not auto-capitalize
+words and play more nicely, we need to adjust some settings. Open the settings by pressing `⌘,`.
+
+In the **Format** section, select _Plain text_ and in the **Options** section de-select _Check spelling as you type_.
+
+![text-settings](/articles/images/2023-09-24-text-settings.png)
+
+At this point for changes to take place, you will need to close the file and re-open.
+
+> **Tip:** In your terminal you can run the last command in your history by using the `↑` (Up) arrow key.
+
+Now that the file is open again, we will write our hello-world program. The contents of your file should look like the following:
+
+```bash
+#!/bin/sh
+
+echo 'Hello World!'
+```
+
+The first line is referred to as the `shebang`, this tells your computer which shell interperter to run your file. I have not explained the
+shell yet, but it currently would just muddy the waters a bit, but there are several shell interperters on your computer with the `sh` posix
+shell being one of the most universal / lowest level ones, which is why I'm choosing this one (in other words this script would work on just
+about any machine you were on).
+
+The second line we are using the built-in `echo` command and passing it the 'Hello World!' argument.
+
+Now save and close the file `⌘s` (to save) `⌘q` (to quit the text edit application).
+
+**Run the program from your terminal:**
+
+```bash
+/bin/sh hello-world.sh
+```
+
+You should see that `Hello World!` was printed to your console.
+
+![hello-output](/articles/images/2023-09-24-hello-output.png)
+
+### Make Executable
+
+Now that we have our basic script working, let's make it an executable.
+
+**In your terminal, type the following:**
+
+```bash
+chmod u+x hello-world.sh
+```
+
+This will change the mode of the file type to be an executable.
+
+Now move / rename the file so we don't have to call it using `.sh` extension:
+
+```bash
+mv hello-world.sh hello-world
+```
+
+Now that the file is executable, we can execute it by just calling the name of the file.
+
+```bash
+./hello-world
+```
+
+> **Note:** We have to prefix the file name with `./` in the above command so that it knows where to find our file. The `./` is saying run
+> this file in our current directory. In the future we will setup our shell so that it knows to look in our `~/.local/bin` directory for
+> scripts, so that we can call them without this prefix.
+
+## Conclusion
+
+Congratulations, in this article we wrote our first program. We learned how to edit the file, set it's permissions, and execute the program
+from our terminal. I should mention that the `TextEdit` application is generally not how you would program, people typically use what is
+known as an `IDE (integrated development environment)`, however I chose to use the `TextEdit` application because it is built-in to `macOS`
+and allowed us to accomplish our goal without downloading other software.
+
+In our upcoming articles, we will write a program that I hope is useful to you / something that you can build upon and use for a long time.
+Thank you for reading to this point.