Re: bash exorcism experiment ('bug' 762923 & 763012)

[Stephane Chazelas <stephane.chazelas@gmail.com>]

2014-10-07 15:03:05 +0200, Thorsten Glaser:
> On Sat, 4 Oct 2014, Russ Allbery wrote:
> 
> > >> If we were to decide that #309415 should be fixed in policy (and hence
> > >> posh), then it should be done by requiring support for the obsolescent
> 
> The problems with posh and dash are also the sheer number of bugs
> in corner cases, which the more actively developed shells fix.
> 
> posh inherited all bugs from pdksh which I fixed in mksh, partially
> by rewriting the parser… so it had to be restarted from newer code.
> 
> dash, well, just ugh.
> 
> tglase@tglase:~ $ cat x
> a='space divded  argument
> here'
> IFS=\  ; set -- $a
> IFS= ; q="$*" ; nq=$*
> printf '<%s>\n' "$*" $* "$q" "$nq"
> [ "$q" = "$nq" ] && echo =true || echo =false
> tglase@tglase:~ $ dash x
> <spacedivdedargument
> here>
> <spacedivdedargument
> here>
> <spacedivdedargument
> here>
> <spacedivdedargument
> here>
> =true

That's expected behaviour to me, and the intuitive continuation
of the Bourne shell.

In the Bourne shell, the * and @ variable were variables whose
content were the concatenation of the positional arguments with
" " in between. And, as a special case "$@" in list contexts
didn't undergo normal expansion, but instead expended to the
list of positional parameters as separate words.

$*, $@, "$*" were not special in any way. They just underwent
the same rules as other variables. Only "$@" was.

That's why for instance:

bourne-sh -c 'set a b; IFS=; printf "<%s>\n" $*'
<a b>

dash is the same except that $* and $@ are the concatenation of
the positional parameters with the first character of IFS.

ksh introduced its bogus array feature and modified the meaning
of $* and $@ which are no longer normal variables (and in my
opinion make a lot less sense than the ash behaviour).

Now all shells have varying behaviours for corner cases of those
which means  that for portability, you should only use $* and
$@ quoted and only use "$@" in list contexts.

The behaviour for a=$@ of ${a#$*} or ${a#$@} varies from shell
to shell.

-- 
Stephane