EDT (text editor)
There are at least two major text editors named EDT. One was made by Digital Equipment Corporation, the other by what was then Sperry Univac, which later became Unisys. Other than them both having the identical name, neither editor had any relation to each other either in method of operation, use, or functionality.
EDT was a text editor that was developed by Digital Equipment Corporation (DEC) for use on its PDP-11 series of computers (including RSX-11,RSTS/E and RT-11), and later for its VAX/VMS series as well.
The editor contained both line mode commands and a screen based editor. In screen mode, the default action for the user was to directly update text as he or she typed, with special commands available by pressing keypad commands. Arrow keys allowed for simple navigation, while keypad commands allowed for more complex navigation and searches. As with many user interfaces developed around this time, EDT used the "Gold Key" style of input first developed for the WPS-8 word processing system. "Gold Key" editing used the PF1 keypad key as a meta key allowing the introduction of a wide variety of commands using both the keypad keys and keys on the main keyboard. Pressing the PF2 keypad key would give on-screen help on the keypad and other key combinations:
/-----------------------------------\ /-----------------------------------\ | ^ | DOWN | | | | | | FNDNXT | DEL L | | | | | | <---- | ----> | | GOLD | HELP | | | | | | | | LEFT | RIGHT | | | | FIND | UND L | | UP | v | | | |--------+--------+--------+--------| \-----------------------------------/ | PAGE | SECT | APPEND | DEL W | DELETE Delete character | | | | | LINEFEED Delete to beginning of word | COMMAND| FILL | REPLACE| UND W | BACKSPACE Backup to beginning of line |--------+--------+--------+--------| CTRL/A Compute tab level | ADVANCE| BACKUP | CUT | DEL C | CTRL/D Decrease tab level | | | | | CTRL/E Increase tab level | BOTTOM | TOP | PASTE | UND C | CTRL/K Define key |--------+--------+--------+--------| CTRL/R Refresh screen | WORD | EOL | CHAR | | CTRL/T Adjust tabs | | | | ENTER | CTRL/U Delete to beginning of line |CHNGCASE| DEL EOL| SPECINS| | CTRL/W Refresh screen |-----------------+--------| | CTRL/Z Exit to line mode | LINE | SELECT | | | | | SUBS | Press a key for help on that key. | OPEN LINE | RESET | | To exit, press the spacebar. \-----------------------------------/
Users could configure default actions or define key sequences for their editor by placing EDT commands in an initialization file which would be executed upon starting the editor.
DEC later developed TPU, a powerful language for designing text editors on its VMS systems. TPU was used to produce a new standard text editor, EVE, as well as to rewrite EDT. EVE included an emulator of the EDT screen mode keypad for the benefit of those who were used to particular key functions. Both EVE and the TPU implementation of EDT are still distributed with OpenVMS.
EDT was also the name of the text editor running on the Unisys VS/9 operating system using the UNIVAC 90/60 series mainframe computer. Other than the fact that coincidentally they both had the same name, the programs were in no way similar, and that editor was not the same as the one made by Digital.
The Univac EDT editor was a line-based editor, in that it did not use function keys. Unlike editors such as Teco or Emacs, the program is always in text-entry mode, similar to today's word processors.
Commands were sent to the editor by typing in text in the same manner as entering regular text, but the first character of the line (other than a space) was the at sign ("@"). When a line began with an @, the remainder of the line was used as a text-editing command. To enter a line of text beginning with @ which was not an editor command, it was necessary to prefix the line with a second @ sign, in which case, the first @ would be stripped off, and the line taken as text rather than a command. It was also possible to issue a command that the @ sign command indicator be changed to a different character. One use for this feature would be to write scripts to have EDT perform various actions upon another file. The command set of the editor included the ability to create unattended programmable editing sessions through the use of test, comparison, branch and looping functions.
Even if line numbers were not present in the original file, the editor supplied a pseudo-line number for use in editing each line. Because of the ISAM file format which supported an 8-character index key, line numbers consisted of a floating-point number in the range of 0.0000 to 9999.9999. The usual line number supplied by EDT started at 1.000 and incremented by 1 as a new line was added. Lines could be inserted between other lines by using a fractional number as a command prefix. For example, line 1 of a file would be 1.0000, line 2 would be 2.0000, and to insert a line between 1 and 2, one could type @1.5: followed by the text of the line; the colon would be discarded and the line would be inserted at 1.5000, between 1 and 2. A renumber command was available to renumber all or part of the file.
Commands in EDT generally consisted of a command (which is case insensitive), which may be followed by a range of line numbers that the command was to act upon, and a subfunction indicating how the command was to act. The range was either expressed as a single line number, a range of lines separated by a dash, (e.g. 5-8 would mean any line numbered 5.0000 through 8.9999 inclusive), or a group of lines, each separated by a comma. Some symbols were available to represent various values, such as the ampersand "&" or the word "all" representing every line in the file.
For example, to alter every "To" in a document to the word "From" you would type in
@ON ALL CHANGE "To" TO "From"
@on & change "To" to "From"
followed by the transmit key (equivalent to Enter on a PC), and the editor would perform the action. Editing was basically full-screen, with actions not taking place until the user pressed the transmit key, a procedure very similar to today's practice of entering text into an input box in a web page, with no action being taken until the user clicks on the submit button.
Univac's EDT editor provided extremely powerful editing capabilities, including
- text formatting similar to Runoff (in which commands were given for text editing by preceding lines with a period)
- possibly one of the first programs (the Univac 90/60 goes back to the late 1960s and early 1970s) to support the use of plugins to allow other programs to use the text the editor held in memory, as well as send commands back to the editor for processing.
- editing of plain text and files with line numbers
- direct on-disk editing of files too large to hold in memory