126 lines
4.5 KiB
Markdown
126 lines
4.5 KiB
Markdown
---
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tags: HVAC, programming, software
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---
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# Introduction to Programming for HVAC Part-3
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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
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articles, then you can catch up [here](https://mhoush.com/series/programming-for-hvac/) before continuing with this article.
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## Getting Started
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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
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will write, that will remove the background from an image.
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### Creating a scripts directory
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We learned in the [first article](https://mhoush.com/posts/introduction-to-programming-for-hvac-1/) how to use our terminal. Today we are
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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.
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**Create a directory**
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```bash
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mkdir -p ~/.local/bin
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```
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The above command will create a "hidden" directory in your home folder. We can go ahead and move into the directory we just created.
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> **Note:** The `-p` option allows us to create nested directories if the parent directory doesn't exist.
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```bash
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cd ~/.local/bin
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```
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### Hello World
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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
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started.
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**Creating our script file:**
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```bash
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touch hello-world.sh
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```
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**Now open the file:**
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```bash
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open hello-world.sh
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```
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The above command should open the file in the `TextEdit` application. In order to make the text edit application to not auto-capitalize
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words and play more nicely, we need to adjust some settings. Open the settings by pressing `⌘,`.
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In the **Format** section, select _Plain text_ and in the **Options** section de-select _Check spelling as you type_.
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At this point for changes to take place, you will need to close the file and re-open.
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> **Tip:** In your terminal you can run the last command in your history by using the `↑` (Up) arrow key.
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Now that the file is open again, we will write our hello-world program. The contents of your file should look like the following:
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```bash
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#!/bin/sh
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echo 'Hello World!'
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```
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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
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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
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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
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about any machine you were on).
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The second line we are using the built-in `echo` command and passing it the 'Hello World!' argument.
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Now save and close the file `⌘s` (to save) `⌘q` (to quit the text edit application).
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**Run the program from your terminal:**
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```bash
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/bin/sh hello-world.sh
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```
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You should see that `Hello World!` was printed to your console.
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### Make Executable
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Now that we have our basic script working, let's make it an executable.
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**In your terminal, type the following:**
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```bash
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chmod u+x hello-world.sh
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```
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This will change the mode of the file type to be an executable.
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Now move / rename the file so we don't have to call it using `.sh` extension:
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```bash
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mv hello-world.sh hello-world
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```
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Now that the file is executable, we can execute it by just calling the name of the file.
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```bash
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./hello-world
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```
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> **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
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> 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
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> scripts, so that we can call them without this prefix.
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## Conclusion
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Congratulations, in this article we wrote our first program. We learned how to edit the file, set it's permissions, and execute the program
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from our terminal. I should mention that the `TextEdit` application is generally not how you would program, people typically use what is
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known as an `IDE (integrated development environment)`, however I chose to use the `TextEdit` application because it is built-in to `macOS`
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and allowed us to accomplish our goal without downloading other software.
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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.
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Thank you for reading to this point.
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