1. A communication medium comprising: a storage unit configured to store files, definition information to control the files, a program designated by the definition information and settable for each of the files, and command execution information to execute command processing corresponding to a command; a receiving unit configured to receive the command; and an executing unit configured to interpret the command, and start the command processing, wherein in response to the start of the command processing, the executing unit executes the command processing based on the command execution information when the executing unit determines that the program does not exist based on the definition information settable for each of the files, and executes the program based on the definition information and executes the command processing based on the command execution information after the execution of the program when the executing unit determines that the program exists based on the definition information settable for each of the files.