EDT (text Editor) - Univac

Univac

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"

or

@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.
• sort
• search
• editing of plain text and files with line numbers
• direct on-disk editing of files too large to hold in memory