Caché ObjectScript Reference - InterSystems Documentation

Caché ObjectScript Special Variables$IOContains the ID of the current input/output device.$IO$IDescription$IO contains the device ID of the current device to which all input/output operations aredirected. (If the input and output devices are different, $IO contains the ID of the currentinput device.)Caché sets the value of $IO to the principal input/output device at login. $PRINCIPALcontains the ID of the principal device. You issue a USE command to change the currentdevice. Only the USE and CLOSE commands, a BREAK command, or a return to the programmerprompt can change this value.The $ZUTIL(96,14) function returns the device type of the current device.On UNIX and VMS systems, $IO contains the actual device name.On Windows systems, $IO contains a Caché-generated unique identifier for the principaldevice. For terminal devices (TRM, TNT, and LAT), this consists of a pseudo-device nameenclosed in vertical bars, a colon and another vertical bar, followed by the device's processID (pid) number. For non-terminal devices, the pseudo-device name is enclosed in verticalbars and followed by a unique numeric identifier.For a Caché terminal: |TRM|:|pidFor a Telnet terminal: |TNT|nodename:portnumber|pidFor a LAT terminal: |LAT|:|pidFor a file descriptor: |FD|file_descriptor_number(File descriptors are used with CALLIN/CALLOUT remote access.)For a TCP device: |TCP|unique_device_identifierFor a named pipe: |NPIPE|unique_device_identifierFor the default printer: |PRN|For a printer other than the default: |PRN|physical_device_name436 Caché ObjectScript Reference