Link: ASCII table and history (Or, why does Ctrl+i insert a Tab in my terminal?)

August 3, 2019

This ASCII table page (via) answers the question it poses in its title, and the answer is quite interesting. I have a long standing interest in this area, and this page's table explains things like why Ctrl-@ is a common way to generate a 0 byte. The table also makes it clear that at least one case is handled specially, that of Ctrl-? often being DEL. So now that I look at it, the table is interesting reading, not just the history.

(The straightforward implementation of Ctrl masks off bit 7, or perhaps bits 6 and 7, which turns @, binary 10 00000, into binary 00 00000 and thus gives you NUL. But you cannot go from ?, binary 01 11111, to DEL, binary 11 11111, by masking off bits; you have to turn on a bit instead. And notice that it is common to make Ctrl-_ generate byte 31, so we have binary 10 11111 turning into binary 00 11111 through masking, so this is not a general special treatment when the low five bits are 11111.)

PS: There's also this version of a four column ASCII table, but it doesn't have the history and doesn't look as nice as this new one.

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For possible future reference: there is also an ascii(7) manual page on Linux (and other Unixes).

Written on 03 August 2019.
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Last modified: Sat Aug 3 14:45:21 2019
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