#(define path1 (ly:font-config-get-font-file "TeX Gyre Schola"))
#(define path2 (ly:font-config-get-font-file "nonsense"))

#(define (read-line port)
   (define (iterator prev)
     (let ((char (read-char port)))
       (if (or (eof-object? char) (equal? char #\nl))
           (if (and (eof-object? char) (null? prev))
               'eof
               prev)
           (iterator (cons char prev)))))
   (let ((rev-list (iterator '())))
     (if (equal? rev-list 'eof) 'eof
         (list->string (reverse rev-list)))))

#(define (file-contains? path expr)
   (define (iterator port)
     (let ((line (read-line port)))
       (if (equal? line 'eof)
           #f
           (if (string-contains line expr)
               #t
               (iterator port)))))
   (iterator (open-input-file path)))

#(display (file-contains? path1 "TeXGyreSchola"))
#(display (file-contains? path2 "nonsense"))