Within Sunview, the NOAO/IRAF gterm window provides a functional terminal to run SPA. However, there are several annoying characteristics associated with the gterm window. Just like any VT240 terminal, the standard input and output devices are left in the graphics window after the completion of some graphical output. Yet, any subsequent characters typed within the graphics window are not echoed. Thus, even though the command is properly read, one does not see what one is typing. There are predefined function keys which allow a user to readily switch between the two windows. If one is left in the graphics window, F9 returns standard input and output to the text window. If the standard input and output are already in the text window, F8 switches these into the graphics window.
To start the SPA program, one issues the command within the shell % spa SFILE TFILE where SFILE is the name of the SPA data file and TFILE is the optional read only archive disk file. If SFILE is not on the command line, the SPA startup script will prompt you for the name of the SFILE. The same script also checks whether the user has read and write permission to the requested file. If not, the script exits. If the user does not "own" the terminal or console window as is the case if one uses "su username" in UNIX, then the script exits. Finally, if the file does not exist, then the script prompts the user to quit or create the file. A carriage return activates the initialization program SPI (see Chapter 2). The SPA program is finally activated when a startup message is printed across the screen and the user is left with a prompt which identifies the current active subdirectory. The program remembers the state of the program when last used and restarts in the same state. For example, the current subdirectory when starting the program is the same current subdirectory when last used.
WARNING !! There is a major problem of writing to magnetic tapes with a SCSI tape drive in UNIX. The problem is the device driver which implicitly writes end of file markers after every write command and before a tape move operation. This driver is incompatible with the SPA tape format since a directory is written at the beginning of the tape and is updated after data is written to tape. The EOFs explicity written will mark the end of tape after the directory which effectively nullifies all of the remaining data on tape.