The first two lines are identical to FLEX since the first would default to an extension of CMD. The third line would load the binary file 'LOOKUP.BIN' into memoy and, assuming the file contained a transfer address, the program would be executed. A transfer address tells the program loader where to start the program executing after it has been loaded. If you try to load and execute a program in the above manner and no transfer address is present, the message 'NO LINK' will be output to the terminal, where 'link' refers to the transfer address. Some other error messages which can occur are 'WHAT?' if an illegal file specification has been typed as the first part of a command line, and 'NOT THERE' if the file typed does not exist on the disk.
During the typing of a command line, the system simply accepts all characters until a 'RETURN' key is typed. Any time before typing the RETURN key, the user may use one of two special characters to correct any mistyped characters. One of these characters is the 'back space' and allows deletion of the previously typed character. Typing two back spaces will delete the previous two characters. The back space is initially defined to be a 'control H' but may be redefined by the user using the TTYSET utility command. The second special character is the line 'delete' character. Typing this character will effectively delete all of the characters which have been typed on the current line. A new prompt will be output to the terminal, but instead of the usual '+++' prompt, to show the action of the delete character, the prompt will be '???'. Any time the delete character is used, the new prompt will be '???', and signifies that the last line typed did not get entered into the computer. The delete character is initially a 'control X' but may also be redefined using TTYSET.
As mentioned earlier, the first name on a command line is always interpreted as a command. Following the command is an optional list of names and parameters, depending on the particular command being entered. The fields of a command line must be spearated by either a space or a comma. The general format of a command line is:
<command>[,<list of names and parameters>]
A comma is shown, but a space may be used. FLEX also allows several commands to be entered on one command line by use of the 'end of line' character. This character is initially a colon (':'), but may be user defined with the TTYSET utility. By ending a command with the end of line character, it is possible to to follow it immediately with another command. FLEX will execute all commands on the line before returning with the next '+++' prompt. An error in any of the command entries will cause the system to terminate operation of that command line and return with the prompt. Some examples of valid command lines follow:
+++CAT 1:ASN S=1
+++LIST LIBRARY:CAT 1:CAT 0
As many commands may be typed in one command line as desired, but the total number of characters typed must not exceed 128. Any excess characters will be ignored by FLEX.
One last system feature to be described is the idea of 'system' and 'working' drives. As stated earlier, if a file specification does not specifically designate a drive number, it will assume a default value. The default value will either be the current 'system' drive assignment or the current 'working' drive assignment. The system drive is the default for all command names, or in other words, all file names which are typed first on a command line. Any other file name in the command line will default to the working drive. This version of FLEX also supports automatic drive searching. When in the auto search mode if no drive numbers are specified, the operating system will first search drive 0 for the file. If the file is not found, drive 1 will be searched and so on. When the system is first initialized the auto drive searching mode will be selected. At this time, all drive defaults will be to drive 0. It is sometimes convenient to assign drive 1 as the working drive in which case all file references, except commands, will automatically look on drive 1. It is then convenient to have a diskette in drive 0 with all the system utility commands on it (the 'system drive'), and a disk with all the files being worked on in drive 1 (the 'working drive'). If the system drive is 0 and the working drive is 1, and the command line was:
FLEX would go to drive 0 for the command LIST and to drive 1 for the file TEXTFILE. The actual assignment of drives is performed by the ASN utility. See its description for details.