Why is backspace often represented with ^H?

Question

I don't see what ^H has in common with "backspace". Why is backspace represented that way in many locations?

It was also represented with ^W too. Still, I have no idea why ^H or ^W in particular. — AndrejaKo, Nov 19 '10 at 20:03
AndejaKo: `^W` is the word erase keystroke in readline in emacs mode (and possibly emacs itself). It erases back to the previous space. — Ignacio Vazquez-Abrams, Nov 19 '10 at 20:13

score 11 · Accepted Answer · answered Nov 19 '10 at 20:12

11

^ represents holding the Ctrl button. With any of the characters from @ to _, it generates a character 64 (0x40) positions earlier in the ASCII table.

answered Nov 19 '10 at 20:12

Ignacio Vazquez-Abrams

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I'll just add that back in the DOS days, the CTRL-H combo did work as the backspace key. I don't recall whether it *always* worked, or was software specific, but I do remember it working for something. – Nov 19 '10 at 20:39
Ctrl-H still works at the CMD prompt (and in Powershell) in Windows and at the shell prompt in most terminals. – Dennis Williamson Nov 20 '10 at 09:08

score 5 · Answer 2 · answered Nov 19 '10 at 20:04

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This is because of where it comes in the ASCII table, there is no significance it's assignment to H other than that's the order in which controls were assigned to the ASCII charachters.

See this wiki on ASCII; ASCII Explained

It appears so frequently in computing due to the commonality of ASCII and it's extensive use.

answered Nov 19 '10 at 20:04

mhollander38

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Backspace is `0x08`. What does that have to do with either `^` or `H`? – Billy ONeal Nov 19 '10 at 20:06
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for those who do not, H is the eighth letter in the alphabet. – Xantec Nov 19 '10 at 20:12

score 5 · Answer 3 · answered Nov 19 '10 at 20:19

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See http://en.wikipedia.org/wiki/Caret_notation - ^H simply means 0x08 because H is the 8th letter of the alphabet. There's nothing linking this to the backspace functionality except the fact that 0x08 was assigned the BS function code. It could just as easily have been 0x09, then we'd be writing ^G.

answered Nov 19 '10 at 20:19

vwegert

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FYI: ^G is/was the "bell" sound in a terminal and it's 0x07. – Chris Nava Nov 19 '10 at 20:33
Tab is 0x09 (^I). – Dennis Williamson Nov 20 '10 at 09:06

score 3 · Answer 4 · answered Nov 20 '10 at 00:48

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"This sequence is still used humorously for epanorthosis by computer literates, denoting the deletion of a pretended blunder, much like a strikethrough."

"My slave-dri^H^H^H^H^H^H^H^H^Hboss decided to stall the project."

Backspace - Wikipedia

@Matt - Queue the old folks, haha!

answered Nov 20 '10 at 00:48

Bratch

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This phenomenon is actually why I asked about it. – Billy ONeal Nov 20 '10 at 00:53
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Actually, I believe it was a slashdot comment on an article about a security exploit that worked on all operating systems (it broke DNS, IIRC), and someone wrote "Good thing I'm using Linux^H^H^H^H^HMac^H^H^HWindows^H^H^H^H^H^H^H Shit.") – Billy ONeal Nov 20 '10 at 01:00
Yep, in addition to the phenomenon, WikiPedia's article explains it well, including the 8th letter of the alphabet, etc. I've seen it on Slashdot many times. – Bratch Nov 20 '10 at 23:05

Why is backspace often represented with ^H?

4 Answers4