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Re: Syntax Question...


From: Linda Walsh
Subject: Re: Syntax Question...
Date: Tue, 16 Aug 2011 15:41:19 -0700
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Ken Irving wrote:
On Mon, Aug 15, 2011 at 08:19:01PM -0700, Linda Walsh wrote:
today_snaps="$('ls' -1 ${snap_prefix} 2>/dev/null |tr "\n" " " )"
This one is so bad, I saved it for last. Ack! Pfffft! Wait, what? Why?  What 
the? Huh?
...
What would you do to search for files w/wild cards and return the output
in a list?
Maybe this?
    today_snaps=( ${snap_prefix} )
----
  but as you mention, that will put them into an array....sorry "imprecise
terminology".... list for me is some number of objects in a string separated by some
separator.

I don't use list to mean 'array', though I see now how it could have been taken that way.

e.g., given:
    $ ls note*
    note  note-to-bob  note-to-bob.txt
    $ unset foo bar; bar=note\*; foo=($bar); echo address@hidden; echo $foo
    note note-to-bob note-to-bob.txt
    note
This result is an array; if you really want a string,
----
You are about to tell me what I already did...
Look closely at the line...it's:

today_snaps="$( )"....
$() acts like a variable syntactically -- the results will be
separate words when re-evaluated unless there are quotes
around it like I have. So I think I'm already using the case
you mention next:

    $ unset foo bar; bar=note\*; foo="$bar"; echo address@hidden; echo $foo
    note note-to-bob note-to-bob.txt
    note note-to-bob note-to-bob.txt
From bash(1):
   Pathname Expansion ...[snip]

I'm guessing the 'Ack!' was maybe for 'useless use of subshell'?
maybe?   Maybe he had a hairball and it was like a can'ts Gack!?  ;-)


It seems to me that there are real bugs in applying set -e that can only
be fixed by handling more special cases in the bash code,and those cases
may vary for different scripts.

[snip]
    set ...
    -e  The shell does not exit if the command that fails is part of the
        command list immediately  following  a while or until keyword,
        part of the test following the if or elif reserved words,
        part of any command executed in a && or || list except the
        command following the final && or ||, any command in a pipeline
        but the  last,  or  if  the  command's return  value  is being
        inverted with !
A constructive contribution might be made by seeing if you can add your
special cases to that list, even better if you can help by identifying
where it might be done in the code.
-----
ARRGGG...these were not special cases, they were has bash normally
worked in in it's non-posix mode SINCE they were created! (3.0 and
up through 4.0).
****4.1 breaks the previous standard.**** -- it's not compatible with
bash 3.0 or 4.0 in this regard

Example:  from 2 different linux systems, one w/bash 4.0 and one w/
the broken 4.1 (which will likely be reverted to 4.0 very soon if 4.1
doesn't get a fix)..

Here is a working 'bash (4.0) vs.  current, below:

   Astarte:/tmp> rpm -q bash
   bash-4.0-18.4.1.i586
   Astarte:/tmp> ( set -e ; ((a=0)); echo "are we here?"  )
   are we here?
   Astarte:/tmp>

Now for the current behavior:

   Ishtar:/tmp> rpm -q bash
   bash-4.1-20.25.1.x86_64
   Ishtar:/tmp> ( set -e ; ((a=0)); echo "are we here?" )
   Ishtar:/tmp>

----
You see the difference?   In 4.0, the assignment didn't cause
an errexit. -- ((a=0)) has NEVER cause an errexit since it
was introduced in bash 3.x[0?]    This is the now broken behavior
and it was done to make one of bash's extended features compatible
with POSIX -- which is a very BAD reason, as Bash has a posix mode
for that -- and that POSIX mode changes shouldn't be
contaminating the BASH-extended set.

That's what I referred to about w/Chet being on the posix
committee, he might be losing perspective about the 'extended part'
of bash which has never been required to be posix compliant --
that's what the "--posix flag was for.

I'm not asking for something "new", I'm asking for compatibility with
the versions 3.0 -> 4.0

Here's the quote from 4.0 on set -e:

      set ....
             -e      Exit immediately if a pipeline (which may consist of a
                     single  simple  command),  a subshell command enclosed
                     in parentheses, or one of  the  commands  executed  as
                     part  of  a command list enclosed by braces (see SHELL
                     GRAMMAR above) exits  with  a  non-zero  status.   The
                     shell  does not exit if the command that fails is part
                     of the command list immediately following a  while  or
                     until  keyword,  part  of the test following the if or
                     elif reserved words, part of any command executed in a
                     &&  or  || list except the command following the final
                     && or ||, any command in a pipeline but the  last,  or
if the command's return value is being inverted with !

-----------------

Note the above -- says it will exit on a "pipeline".....
as 'let' and '(())' did not take or accept I/O, they wouldn't
normally be considered part of a pipeline -- and Greg has
mentioned that ((1)), is a 'complex' command not a simple command
(but it can't be used as part of a pipeline...)


Ranting, inferring that people have 'little minds', aren't good
or skilled programmers, etc., does little to make things better.
Excessive verbosity, lingo, abbrevs, etc., don't help either. ;
----
   Ranting -- ?  I've only been continuing because no one seems
to know that "-e" *worked* in 3.0-4.0  in a reasonably reliable and
respectable manner.   4.1 broke that.


   In regards to 'little minds',  in Hemingway's day it
referred more to someone who wasn't likely to think "outside
the box"  -- i.e. too rigid and run by the 'rules of consistency'
in their head...  It's wasn't about intelligence, at least that's
not my impression.








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