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Re: Control characters in declare output

From: Chet Ramey
Subject: Re: Control characters in declare output
Date: Thu, 1 Nov 2018 11:06:10 -0400
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:52.0) Gecko/20100101 Thunderbird/52.9.1

On 11/1/18 2:01 AM, Rob Foehl wrote:
> Prompted (pun intended) by the recent thread on detecting missing newlines
> in command output, I'd had another look at my own version, and discovered a
> potential issue with control characters being written as-is in declare
> output.  

I don't see it as much of an issue.

Minimal (harmless) reproducer:
> ╶➤ x () { echo $'\e[31m'"oops"$'\e[0m'; }
> ╶➤ declare -f x
> x ()
> {
>     echo ''"oops"''
> }
> Emits the string in red in a terminal.  Any instances with control
> sequences that do anything more invasive with the terminal cause more trouble.

As documented, $'...' strings are expanded and converted to single-quoted
strings by the parser. In this case, that means while the function
definition is read and parsed, so the actual definition includes raw
control characters. It's difficult to make a good case for escaping these
characters while printing the function definition, which has to print
commands, while printing variable values is much more limited in scope.

``The lyf so short, the craft so long to lerne.'' - Chaucer
                 ``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU    address@hidden    http://tiswww.cwru.edu/~chet/

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