for the ls parsing example, you can do

shopt -s nocaseglob

ls ~/Downloads/*.{png,jpg,jpeg,gif,webp}

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for command line tools (grep/sed/awk/sort/etc), you can refer my ongoing project (https://github.com/learnbyexample/Command-line-text-processi...) as resource :)

I just have to ask. Doesn't the above comment kind of defeats the article premise?