Re: any plans for command substitution that preserves trailing newlines?

[Chet Ramey]

On 1/28/22 8:44 PM, Christoph Anton Mitterer wrote:

> On Fri, 2022-01-28 at 11:19 -0500, Chet Ramey wrote:
> > It's not good form to force your own locale on the user, who might
> > not
> > even have it installed. So some shells dodge the question entirely:
> > you get
> > what you got when the shell started.
>
> > Others, like bash, treat everything as
> > multibyte characters whose interpretation is subject to the current
> > locale.
>
> You mean if one has a fixed string like:
> foo="b€r"
> and changed the locale before, bash would parse "foo" still with the
> old, but "b€r" with the new locale?

No. It means that word consists of a series of (possibly multibyte)
characters, and those characters are interpreted based on the locale at
parsing and execution time. You're not going to have trouble with the
`foo=' differing between locales, but the multibyte character corresponding
to the euro symbol in one locale may not correspond to the same symbol in a
different locale. So the bytes will probably be the same; the output of
`echo "$foo"' might differ.


> That's what I'd have followed from POSIX' wording:
>
> "Changing the value of LC_CTYPE after the shell has started shall not
> affect the lexical processing of shell commands in the current shell
> execution environment or its subshells."

That bit with lexical processing of commands isn't really intended to
refer to this aspect of processing; the above is going to be an assignment
statement (ASSIGNMENT_WORD) in any locale.

The processing part is mostly, as I think I said in an earlier message,
about <blank>s and other metacharacters and how the shell breaks input into
tokens and parses them.

I would argue that if you change LC_CTYPE in a script, you intend for the
new locale to affect command execution, like for pattern matching.


> > It gets tricky. Say you unset LC_ALL, which the shell inherited from
> > the
> > environment, and that `unshadows' a value of, for instance, LC_CTYPE
> > that
> > the shell also inherited in its environment. Child processes will see
> > a
> > different value for that category than you may have intended.
>
> Sure that's clear,...but for that reason we only change the locale
> around the substitution, and we only unset LC_ALL afterwards, if it was
> already unset before.

Yes, but we were talking about temporarily controlling the locale a command
sees, in the general case, and addressing your "(even those that I don't
touch)" comment.

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