Re: [Help-bash] Question about escaping in backquote string in double quoted strings

[KHMan]

On 5/15/2019 12:05 AM, Chet Ramey wrote:
> On 5/2/19 1:05 PM, KHMan wrote:
> > Hi all,
> >
> > I have a question about escaping of the double quote char in a backquote
> > command string nested inside a double quoted string. I have been trying out
> > an example from the Morbig paper[1] and looking at the bash ref man but
> > couldn't figure things out.
> >
> > Here is a slightly adjusted example from page 4, Example 2.5. Output is at
> > right after the comment #.
> >
> > echo "[` echo \" \\" \" `]"             # [ " ]      (A)
>
> OK, let's look at A. I have simplified the explanation by breaking things
> into separate steps, even if the code itself performs multiple steps in a
> single pass. All the quoted text snippets are from the POSIX standard.
>
> The parser takes this and applies the double-quoting rules. The command
> substitution rules enter the picture because POSIX leaves enough behavior
> undefined so that the double-quoted string can be terminated by a double
> quote in the backquoted command substitution (ksh93 does this, for
> instance).
>
> The bash parser doesn't allow quotes in a command substitution to terminate
> a double-quoted string that was started outside it, and doesn't remove
> backslashes until word expansion, so we have
[snip snip snip]

Thank you, I will spend some time to digest what you have written.

Please ignore my other posting on the source code, that was my 
last resort because everyone else was telling me to just use 
$(command). :-)

In recent years, this particular string nesting combination has 
caused problems with syntax highlighting for Scintilla-based 
editors (Geany, Notepad++, SciTE, etc.) Nested strings I sort of 
fixed, but char escaping in nested strings was a real headache 
that I postponed until now. While I could analyze and draw up 
behavioral charts, I couldn't find anything that clearly explained 
the process. So I have been doing a lot of groping in the dark. 
This is not a highlighting bug ticket that any other contributor 
want to touch, ha ha.

I'll probably implement a reasonable subset, then wait for the 
next bash syntax highlighting bug ticket.

Thanks again,
--
Cheers,
Kein-Hong Man (esq.)
Selangor, Malaysia