Control characters in declare output

[Rob Foehl]

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. 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.

Similarly:

╶➤ y=$'\e[31m'"oops"$'\e[0m'

╶➤ declare -p y
declare -- y="oops"

String again in red. Compare with:

╶➤ set |grep ^y=
y=$'\E[31moops\E[0m'

No issues with the set output. As they can both be usefully re-read by
the shell, is there any possibility for similarly escaped output from the
declare builtin, instead of raw control characters?

-Rob

[Chet Ramey]

Post by Rob Foehl
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.

Post by Rob Foehl
╶➤ 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.

[L A Walsh]

Post by Rob Foehl
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
╶➤ 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

BTW, to keep that red from turning your terminal red, I used:
read _CRST <<<"$(tput sgr0)" #Reset
read _CRED <<<"$(tput setaf 1)" #RED
read _CGREEN <<<"$(tput setaf 2)" #GREEN
read _CBLD <<<"$(tput bold)" #Bold

And in usage:
[[ $UID -eq 0 ]] && {
_prompt_open="$_CBLD$_CRED"
_prompt="#"
_prompt_close="$_CRST"
}

----
That way I can display the file on a screen without the control
characters
actually changing the color of the terminal.

(just in case you might be looking for a way around that behavior).