grep: search all files, one file, or not in file
grep: search all files, one file, or not in file

erictleung/programming-notes,erictleung/programming-notes,erictleung/programming-notes,erictleung/programming-notes,erictleung/programming-notes,erictleung/programming-notes,erictleung/programming-notes,erictleung/programming-notes,erictleung/programming-notes