March 28, 2011

Control the Keyboard with Control Keys

Filed under: Main — admin @ 12:01 am

A long time ago, computer keyboards had some nifty shortcuts. If you were adept with your left pinky finger, and didn’t mind cluttering your head with useless trivia, you could forgo keys like Tab, Backspace, Escape, and Enter.

Back in the good old days, computer keyboards were designed with the Ctrl key above the left Shift key. The Caps Lock key, was somewhere else on the keyboard. No one cared about Caps Lock because the Ctrl key was far, far more important. There was quite a bit you could do with it.

You could use the Ctrl key at the command prompt, or at any time you entered text, to produce various shortcuts. The shortcuts worked because the early computer keyboard were mapped to the ASCII standard. So, effectively, certain Ctrl keys echoed the functions of other, specific keys on the keyboard.

For example:

Ctrl+C or ^C. The cancel key for DOS, which was mapped to the Break key on the keyboard. It was often easier to press Ctrl+C than to hunt down the location of the Break key (which changed often on the early PC keyboards.) Ctrl+C is still used today to cancel terminal programs in both DOS and Unix.

Ctrl+H or ^H. The Backspace key. You could type Ctrl+H instead of pressing Backspace.

Ctrl+I or ^I. Tthe Tab key. On the early PC keyboard, both keys were mapped the same. I remember using Ctrl+I often and baffling people who watched me type, wondering how I got a tab without pressing the Tab key.

Ctrl+J or ^J. The line feed character, which behaved differently depending on the terminal. In Unix, it was the Enter or Return character. In DOS, it was merely a line feed or “vertical tab.”

Ctrl+L or ^L. ThisL key combination cleared the terminal screen. ZAP! It was mapped to the Clear key on some early keyboards. In DOS you’d have to type ECHO ^L to get the job done. The code also worked on the printer, serving to eject a page. Back in the old days, when dot matrix line printers were popular, a page didn’t often fully eject after you were done printing. The DOS command ECHO ^L > PRN served as a page eject.

Ctrl+M or ^M. The carriage return, which essentially relocated the cursor to the start of the line. In DOS, however, Control+M was mapped to the Enter key.

Ctrl+S or ^S. The Control+S key was used to pause a text display. The early terminals were slow, so you could try to read and catch up. When things got too fast, you pressed Ctrl+S to pause the display. On the early PC keyboard, the Pause key did the same thing. To resume text scrolling, you would press Ctrl+Q, though most software also accepted another Ctrl+S/Pause key press to resume.

Ctrl+[ or ^[. The Control+[ key combination is the same as the Escape (Esc) key on the keyboard. It was a bit of reach to do a Ctrl+[, so most folks simply whacked the Esc key.

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