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