Re: Incorrect alias expansion within command substitution

[Chet Ramey]

On 2/4/22 4:59 PM, Alex fxmbsw7 Ratchev wrote:
> On Fri, Feb 4, 2022 at 10:18 PM Robert Elz <kre@munnari.oz.au> wrote:
> >      Date:        Fri, 4 Feb 2022 21:06:11 +0100
> >      From:        Alex fxmbsw7 Ratchev <fxmbsw7@gmail.com>
> >      Message-ID:  
> > <CAALKErH2N+EiVW+=sVBNYrpYa5JiWVrVjCe1YT=NEgUuJcRitA@mail.gmail.com>
> >
> >
> >    | now changing this to dynamic eof marker
> >
> > There is no such thing.   Unlikely (*VERY* unlikely) there ever will be.
> >
> >    | cat <<$( printf leet )
> >    | $(  printf leet )
> >    | $( printf leet )
> >    | notice the two spaces in the middle to not match eof
> >
> > Yes, that is supposed to work, and "cat" should write a single
> > line containing "leet".   The end word is *never* expanded, not
> > the copy of it after the << operator, and not the one that terminates
> > the here doc data (the former gets quote removal, but there are none
> > here to remove).
>
> i guess thats not rendundant enough for bash, or yet too early
> cause it doesnt interpret at runtime much yet, it just maps text or
> chars to read until

What does `not redundant enough' mean here?

> also its a high security risk, how to say... to let $( and all << as
> separator is all nonsense

How, exactly? kre already said it doesn't cause any command execution.

> written twice.. to match eof matching, but why
> if you start your << with $( printf leet ) or $(  printf leet ) and
> just wanna end with 'leet' .. .. .. you need command subst ( aka same
> code ) to match instead of the resulting text ? 

Why would you write something that way? Or, more to the point, why would
you have that expectation?


> >    | but
> >    |
> >    | cat <<$(  printf end )
> >    | $( printf end )
> >    | # here it should already end the heredoc parser
> >
> > No it shouldn't.   The 2nd line there doesn't have enough spaces,
> > they're not the same.
>
> i didnt continue the last line that matched the same command substitution
> it was a try to example from a view of interpreting the text dynamically
> still a bit unclear to me

You still want the here-doc delimiter to undergo word expansion? And all
the lines in the here-document body? Before checking for the matching
delimiter. Yeah, that's a mess.

> > The end word (after <<) is parsed as a command substitution, to find its
> > end, but is never expanded (the code in it is never executed) - all the
> > parsing accomplishes in this case is to allow the correct ')' to be found
> > so the command substitution text ends at the correct place - beyond that
> > it is ignored.
>
> what are you saying isnt clear to me
> do you want $( to expand or not

Not.


> > Perhaps a different example - I'm sure you know that in $(( )) you can
> > embed an arithmetic expression, and if you try and do something like
> >
> >          $(( data 2 ))
> >
> > you'll get a syntax error, because "data 2" is not a valid arithmetic
> > expression.
>
> you get this cause alias parsing is disabled, cause $(( is a command
> an alias $(( would work

It would not. I know you know how alias expansion works, but here are the
three keys: it happens on a per-token basis, it happens only when a token
is in a command position or an immediately-previous alias expansion ends
with a space, and it doesn't happen in a quoted string. Keep in mind that
the contents of an arithmetic expansion are treated as a double-quoted
string.

Oh, and `$((' is not a command. A token in a command position might have
an alias expansion that results in `$((', but that's not the same thing.

> but bash doesnt handle the ending right yet

Please show your work here.

> hint to chet: its just sad it results yet early in a code parse error
>
> #!/usr/bin/env -S bash
>
> shopt -s expand_aliases
>
> alias -- \
> p='printf %s\\n ' \
> assign='assign=$(( ' begin='$(( ' end=')) ' \
> sep=', ' \
> plus=+\  minus=-\  div=/\  mul=\*\  \
>
> for d in "1 + 2" "1 plus 2"
> do
> alias -- data="$d "
> p begin data end
> done
>
> nevermind i realized its exactly the same and i understood why its erroring
>
> alias.sh: line 14: unexpected EOF while looking for matching `)'
> alias.sh: line 16: syntax error: unexpected end of file
>
> cause bash doesnt parse aliases yet into pre parse state
>
> yea i just wish it would, such as no code error for valid code

Sigh. It's not valid code, and I hope you understand why it's not.

--
``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/