[Toybox] Would someone please explain what bash is doing here?

[Chet Ramey]

On 5/23/20 1:06 PM, Rob Landley wrote:
> On 5/23/20 9:41 AM, Chet Ramey wrote:
>> On 5/21/20 6:50 PM, Rob Landley wrote:
>>
>>>>> But the same command line in the current shell and in bash -c are parsing
>>>>> different despite presumably reading the same .bashrc and friends?
>>>>
>>>> My guess is that the interactive shell has extglob enabled somehow, whether
>>>> it was in .bashrc or interactively after it was started. The -c command
>>>> shell doesn't read startup files, so that doesn't matter.
>>>
>>> Mine too, but grep isn't finding extglob under /etc or ~/.*
>>
>> I can only suggest looking in your shell history.
> 
> It's there in each new terminal tab. It's not a thing I typed.

Maybe run `bash -x' or `bash --login -x' and see where it gets set.


> ... can aliases expand to unbalanced ( or { ?

Yes. The way to implement aliases is to check for an alias expansion in the
lexer before you return a WORD, and if you have one, push the expanded text
onto the input stack and restart the read.


>>>   $ potato\
>>>   > \
>>>   > (
>>>   bash: syntax error near unexpected token `newline'
>>>
>>> You're right, it does. I'm not doing that.
>>
>> There can't be any newlines between the word and the open paren. That's the
>> shell grammar.
> 
> But wasn't \ supposed to eat the newline?

Sorry, I misread it. That's not the newline it's complaining about. You
can't have any newlines between the parens.

function_definition : fname '(' ')' linebreak function_body

Something like

potato\
\
(\
)\
{ echo hello; }

works just fine.


>>> So in bash, $LINENO isn't the starting line of a multi-line span, and it isn't
>>> the ending line of a multi-line span, it's the SECOND line of a multi-line span.
>>
>> No. Consider one of the original examples:
>>
>> echo $LINENO \
>> $LINENO
>>
>> The shell has already recognized this as a simple command by the time it
>> sees the backslash-newline pair.
> 
>   $ echo $LINENO \
>   > $LINENO \
>   > $LINENO
>   1 1 1
> 
>   $ bash -c $'echo $LINENO \\\n$LINENO'
>   0 0
> 
> Wait, why's it not doing it now?

We already agreed that starting LINENO at 0 in -c command was a bug, and
I fixed it several weeks ago.


>> Universities are famous for cast-off hardware. I wrote a considerable
>> portion of bash-2.0 on an IBM RT in the basement of my first house running
>> a custom version of 4.3 BSD. I wrote a troff package to do APA style so my
>> wife could write her doctoral thesis on it.
> 
> Did you actually get to use IBM Academic OS?

Yes. That's what I started with, since I had source. I added things from
MIT and 4.3-tahoe and reno that IBM hadn't added and maintained the kernel
myself.

> 
> There was this whole "everybody used BSD in 1980-1984, then AT&T paid them to
> switch to System V" thing that isn't sufficiently documented, and I've never
> figured out if AOS->AIX is part of that or just IBM hadn't gotten into unix yet.

AOS was a side branch for IBM. They already had a version of AIX that, I
think, ISC did for them that ran on the RT. AOS was an offshoot of the
support IBM gave Project Athena, and was only available to higher ed with
the right Unix licenses. AIX 2.x was wretched; when IBM donated the RTs to
us, it came with AIX, and we swapped it for AOS as soon as I could get the
licensing straightened out and get the tapes.

Chet

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