For anyone who might be tempted to fall for the guilt-tripping about authors, text books rarely generate any income for their authors and most would be happy to open source them (as many do nowadays). They’re interested in getting useful materials out there (and the name recognition that comes from having their name on useful texts). They do not rely on book sales to make a living.

You should not feel guilty about pirating text books but you can help the authors out by asking your library to stock the text, borrowing it if your library has it (even if you’ve pirated a copy for keeps), and recommending it to others (with text that will show up on searches) if you found it useful.