[Unix; common]
1. Something passed between routines or programs that enables the receiver to perform some operation; a capability ticket or opaque identifier. Especially used of small data objects that contain data encoded in a strange or intrinsically machine-dependent way. E.g., on non-Unix OSes with a non-byte-stream model of files, the result offtell(3) may be a magic cookie rather than a byte offset; it can be passed tofseek(3), but not operated on in any meaningful way. The phraseit hands you a magic cookie means it returns a result whose contents are not defined but which can be passed back to the same or some other program later.
2. An in-band code for changing graphic rendition (e.g., inverse video or underlining) or performing other control functions (see alsocookie). Some older terminals would leave a blank on the screen corresponding to mode-change magic cookies; this was also called aglitch (or occasionally aturd; comparemouse droppings). See alsocookie.
