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content/articles/2023-09-26-introduction-to-programming-for-hvac-4.md

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+---
+tags: HVAC, programming, software
+---
+
+# Introduction to Programming for HVAC Part-4
+
+This article builds upon our [last](https://mhoush.com/posts/introduction-to-programming-for-hvac-3/) article, so make sure to catch up
+before continuing with this article.
+
+## Arguments
+
+Before we start creating our program that will remove the background from images let's go over arguments in shell scripts. Arguments are
+supplied to shell scripts are separated by a space `" "`, as opposed to options which start with a `-<character>` or `--<word>`.
+
+To illustrate this, let's change our `hello-world` script we wrote in the last article.
+
+**Move into our scripts directory:**
+
+```bash
+cd ~/.local/bin
+```
+
+**Make a copy of the hello-world script:**
+
+```bash
+cp hello-world greet
+```
+
+Above we make a copy of the hello-world file and name the copy `greet`.
+
+**Open the greet file:**
+
+```bash
+open -a TextEdit greet
+```
+
+> **Note:** Because the greet file is an executable, in order to open it in the `TextEdit` application we must supply the `-a` option.
+> Otherwise it will just run our `greet` program in another terminal. Use `man open` to read more about the open command.
+
+**Edit the greet file:**
+
+```bash
+#!/bin/sh
+
+echo "Hello, ${1}!"
+```
+
+Make sure to save `⌘s` the file.
+
+Take note that the quotes need to be changed to `"` (double quotes) from our original `hello-world` program.
+
+The `${1}` is indicating that we will insert / interpret the first argument passed to our program and insert it at that location. Arguments
+are interpreted in order they are passed in with `${0}` always representing the filename of the program that is called (generally not needed
+/ used in your scripts).
+
+**Test it out:**
+
+```bash
+./greet Michael
+```
+
+![greet-output](/articles/images/2023-09-26-greet-output.png)
+
+If you'd like to supply multiple words (or arguments that contain spaces) as a single argument then you can wrap them in quotes.
+
+```bash
+./greet "Michael Housh"
+```
+
+> **Tip:** Wrapping in quotes is especially useful for commands that take file paths, if any of the folders or file names contain spaces.
+
+## More Useful Program
+
+At this point, it's time to build a more useful program that we can use. First, we must download some dependencies for our program.
+
+**Install imagemagick:**
+
+```bash
+brew install imagemagick
+```
+
+> **Note:** If you'd like to check out the documentation / website for imagemagick you can run `brew home imagemagick`.
+
+This will take a bit for brew to install imagemagick and it's dependencies. When it's completed, we can check to make sure that imagemagick
+is installed by running the following command.
+
+```bash
+magick --version
+```
+
+It should output something along the lines of this below.
+
+```bash
+Version: ImageMagick 7.1.1-17 Q16-HDRI aarch64 21569 https://imagemagick.org
+Copyright: (C) 1999 ImageMagick Studio LLC
+License: https://imagemagick.org/script/license.php
+Features: Cipher DPC HDRI Modules OpenMP(5.0)
+Delegates (built-in): bzlib fontconfig freetype gslib heic jng jp2 jpeg jxl lcms lqr ltdl lzma openexr png ps raw tiff webp xml zlib
+Compiler: gcc (4.2)
+```
+
+> **Tip:** Don't forget, you can use the `clear` command to clear the terminal.
+
+**Create our script:**
+
+```bash
+touch mktrans
+```
+
+We are going to name our script `mktrans` as a short for make transparent.
+
+**Open the file:**
+
+```bash
+open mktrans
+```
+
+**The program:**
+
+```bash
+#!/bin/bash
+
+# The input file path, passed in as the first argument.
+inputfile="${1}"
+
+# The color to make transparent, optionally passed in as the second argument.
+# by default we handle / make white backgrounds transparent.
+color="${2:-white}"
+
+# Use the built-in basename command to normalize the input file name
+# this will convert a file path, such as ~/Pictures/my-image.png to my-image.png.
+fullfilename=$(basename -- "$inputfile")
+
+# Use the text of the `fullfilename` up to the first '.' as the file name.
+filename="${fullfilename%%.*}"
+
+# Use the text after the last '.' as the file extension.
+extension="${fullfilename##*.}"
+
+# Create the output file name to use.
+#
+# For an input file of `input.png`, our output name would be
+# `input-transparent.png`.
+#
+# This will output the file in the directory that we are
+# in when we use our script (which may different than where
+# the image is located)
+outputfile="${filename}-transparent.${extension}"
+
+# Make the magick happen :)
+convert "${inputfile}" -fuzz 10% -transparent "${color}" "${outputfile}"
+
+```
+
+I've included comments in the program above, which is good practice, as there is high odds that you will forget what is going on when / if
+you open the file up in the future to look at it. We are using a lot of what is called parameter expansion magic in this file. You can read
+up more on what we are doing in the [bash documentation](https://www.gnu.org/software/bash/manual/html_node/Shell-Parameter-Expansion.html).
+
+This script is far from perfect, there are a lot of things to be improved upon. For example, if you download / save the banner image of this
+post and run this script, it will also remove some color in the wizards beard, eyes, and eye brows. However, it does work very well for my
+general use case, which is to remove the background from screenshots of pdf documents. It should be noted that it will not work on all types
+of images, some image types do not allow transparency, so it is safest to call this with input image being a `.png` image type, however you
+can use the `imagemagick` program that we downloaded to convert other image types to `.png`, but that will be left up to you to figure out.
+
+## Using Our Program
+
+This is going to assume that you have download the banner image at the top of this article. You can do this by right-clicking and choosing
+`Save As`. This should save the image in your downloads folder, and you can keep the name of `part4-banner.png`.
+
+**Make the program executable:**
+
+```bash
+chmod u+x mktrans
+```
+
+**Make the image background transparent:**
+
+```bash
+./mktrans ~/Downloads/part4-banner.png
+```
+
+**Open the image:**
+
+```bash
+open part4-banner-transparent.png
+```
+
+It should look like below.
+
+![banner-transparent](/articles/images/2023-09-26-part4-banner-transparent.png)
+
+> **Note:** If you are viewing this site in _light_ mode, the image does not look that bad. Hit the moon button in the top above my profile
+> image to see some of the flaws of our program.
+
+---
+
+> **Tip:** Remove the image from the `~/.local/bin` by using `rm part4-banner-transparent.png`. Be aware that the `rm` command can not be
+> undone, so use with caution / knowledge. It is safer, until you are more comfortable to use the `Finder` application and move the file to
+> the trash. In `Finder`, you can show hidden directories by typing `⌘.` or go directly to the folder by typing `⇧⌘G` (shift + command + G)
+> and in the pop-up typing `~/.local/bin`.
+
+---
+
+That is it for this article. In the upcoming articles we will setup our `shell` environment so that we can use the commands we've built
+without having to navigate to the `~/.local/bin` directory. Thank you for reading to the end, I hope you're finding this series helpful.