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Re: activate alias inside subshell

On 08/04/18 12:39 AM, Bart Schaefer wrote:
I'm not going to try to respond blow-by-blow to your messages, because
there still seem to be some concepts about aliasing that we've
discussed in past threads that you don't appear to be applying.

It does take a while for some things to stick, but they do stick eventually.  There are so many things assumed to be understood in the culture.  Misunderstood, answers don't really gel, the mind hunts for a 'get it' but the 'get it' is false.  Like only recently do I finally really get it as to bleeding newlines in arrays -- not there!
Firstly, though, there's something that doesn't add up about your
"test1" example; as you quoted it, "yelline" references a variable
$yel that's never assigned,
Pardon, I try to copy in all the relevant bits and pieces from my environment.  That's just the code for 'yellow' of course.  What's the best way to run something as a test for fitness to export it, as to here, for example?  I mean a way of ensuring that it's entirely self-contained as to things like that and nothing has been left out or assumed?
I suspect you're using a shell in which you've been running other
tests and something from an earlier experiment is spilling over to
confuse you.  Either that, or you haven't actually shown us the full
contents of the "test1" file.
Sure.  As above, I'm always worried that there's some local setting or glitch that makes my code invalid as far as other people pasting it from an email and getting the same results.  I need a sort of 'virgin' test before sending these things on.  Should have got that squared away years ago.
The fundamental thing you're forgetting is that aliases act by text
replacement.  "whence" will tell you whether an alias WILL replace
text the NEXT time the lexer is invoked, but that has no meaning for
text that has previously been parsed.  Function definitions are always
fully lexed+parsed before they are executed, so once a function is
defined any aliases it may have used have been replaced by the
expanded text of the alias and can never expand again.
Ok, so whence is simply obeying the 'not active till next time' rule.  Not very friendly but it is consistent with the law of aliases.
% alias msg='echo this is an alias'
% test1() { msg in test1 }
% functions test1
test1 () {
     echo this is an alias in test1

See how the use of the alias is no longer present in the stored
definition of test1?

That at least is exactly as I expect, it's a macro.

Note that it's important that the alias and the
function were defined separately (in this example at separate PS1
prompts), so that the parser was run a second time AFTER the alias was

Compare running the parser only once, by using a multi-line construct
(I have started a fresh "zsh -f" for each of these examples even
though I've changed the function names to differentiate them):

Is 'zsh -f' the answer to the above -- a truly clean test of something?

Here test2 was parsed at the same time as the alias command, so the
alias was not yet "active" when the body of test2 was read, and thus
the alias definition is both not expanded in test2 and also irrelevant
at the time the function is executed.


$ alias msg ... ; test2 () { msg }


$ alias msg ...
$ test2 () { msg }

... are very different!  In the former the alias is 'pending' in the latter, it is active, yes?  That's easy not to know.

Something like this must be involved in producing the "nulled" output
from the example you posted.

Ok, let me hack away at it a bit more.  Nevermind whence, the only serious issue is the way the redefined function seems to kill the alias within the subshell within the calling function.  Again, it turns out that this is exactly what I want, but not something I understand.  It is as if the fact that the redefined function has the same name as the alias overwrites the namespace within the subshell so the alias vanishes.  If so, that could be seen as a feature not a bug.

BTW, results are hugely different if the redefined message function is redefined with or without 'function' prepended: " function msg () ... " vs. " msg () ... ".  Most comments found on the internet suggest there should be no difference but that is not so, one changes things externally, the other does not.  It added to the confusion.

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