Here's a short elisp example to get file content into a string.
;; thanks to “Pascal J Bourguignon” and “TheFlyingDutchman <zzbba...@aol.com>”. 2010-09-02 (defun get-string-from-file (filePath) "Return FILEPATH's file content." (with-temp-buffer (insert-file-contents filePath) (buffer-string)))
And, remember, you can also get them into list of lines.
(defun read-lines (filePath) "Return a list of lines of a file at FILEPATH." (with-temp-buffer (insert-file-contents filePath) (split-string (buffer-string) "\n" t)))
For more about processing a file line by line, see: Process a File Line by Line in Emacs Lisp.