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Command cat has a -t option

-t Display non-printing characters (see the -v option), and display tab characters as ^I.

The tab character is represented by ^I.
I searched an explanation as:

This is a common notation that means “Control-I” which, as it turns out, is the same as a tab character.

Apparently, there's no connections of I and tab in spelling and meaning.

How to understand it?

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    It comes from mapping the the ASCII value (decimal 09) of the control character to the 9th letter of the Latin alphabet (I) - see Control character: History Commented Mar 29, 2018 at 1:13

1 Answer 1

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How to understand it?

By reading a manual page that has been around since Version 7 UNIX:

man ascii

See the code for the (Horizontal Tab) character. Like most control codes, this can be typed on terminals with the chord ⎈ Control+I. Notice what you get if you subtract 64 from the code for the I character.

Observe the pattern with, say, ⎈ Control+J and (Line Feed). Realize, once you remember where @ is in a U.S. keyboard layout, why ⎈ Control+2 is thus .

I searched an explanation

Always check out the manual. The manual, certainly on the BSDs but in cases like this one on Linux operating systems as well, is your friend.

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