Perhaps it may surprise you that the Raspberry Pi comes with a built-in spell checker. aspell and ispell.
The standard word list is located in /usr/share/dict/
However, aspell has its own directory: /usr/lib/aspell
The standard aspell mode is by checking the spelling interactively. There is a way to do it with non-interactive method. This will let you dump misspelled words all at once.
- cat sample.txt | aspell list
list is a command that basically prints misspelled words coming in from standard input.