I did something similar as an AutoHotkey[1] script on Windows[2].

I just hit Win+N, a small window appears, I write a line of text, hit enter and it gets saved to the quicklog.txt.

[1] https://www.autohotkey.com/

[2] https://gist.github.com/knagy/4cdb5af48e23a6b33299d3f2fb2d4f...

edit: replaced the inline code with a Gist link