U+001A "SUB" SUBSTITUTE Unicode Character

U+001A "SUB" SUBSTITUTE is a control character originally defined in the ASCII standard, intended to signal that a specific piece of data should be replaced or ignored, often used in communications and file transfer protocols to mark an erroneous or invalid character. In modern computing, it is most famously associated with its use in the CP/M and early MS-DOS operating systems, where it served as the end-of-file (EOF) marker, causing text editors and command-line tools to stop reading a file upon encountering it. Despite its historical importance, the SUB character is rarely used directly in contemporary text processing, as its role as a file terminator has largely been replaced by more explicit file system metadata.