Date: Thu, 12 Apr 2018 12:01:06 -0700 From: Russ Allbery <eagle@...ie.org> To: oss-security@...ts.openwall.com Subject: Re: Re: Terminal Control Chars Ian Zimmerman <itz@...y.loosely.org> writes: > The term "invisible character" has some obvious (if perhaps informal) > meaning. But I don't really know what "control character" means. Is a > page separator (^L) a control character, for example? Is DEL one (ASCII > 127)? I think a useful definition of "control character" in this context (and I realize this doesn't exactly match the ASCII definition) is a character that results in an action other than insertion being taken, as opposed to a glyph (possibly invisible) being inserted (and not counting contexts such as vi outside of insert mode where basically all characters are interpreted as actions). CR and LF would not be control characters in that definition, since they insert a newline and don't cause an action. Similarly, TAB wouldn't be a control character in that definition. DEL would be if it deleted a character as opposed to inserting a ^? sequence. ESC would be if it changed terminal modes or colors or did all the other things escape sequences can do. BEL would be if it rung the terminal bell. And so forth. I think it's reasonable to expect that pasting something into a terminal will cause insertion of text, including whitespace, but will not cause the terminal to take *actions* that are not the insertion of text. Certainly, I think there are a lot of people in the world who do have that assumption. -- Russ Allbery (eagle@...ie.org) <http://www.eyrie.org/~eagle/>
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