https://goalkicker.com/BashBook/
https://goalkicker.com/BashBook/BashNotesForProfessionals.pdf

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Iliev - introduction to Bash Scripting for Developers
    https://github.com/bobbyiliev/introduction-to-bash-scripting
    https://github.com/bobbyiliev/introduction-to-bash-scripting/raw/main/ebook/en/export/introduction-to-bash-scripting-light.pdf