Re: Bash string substitution bug (?)

[Dmitry V Golovashkin]

either
       VALUE=host1.blah.com
       echo ${VALUE//.*}
or
    echo ${VALUE/.*}

is accepted by Bash and works exactly as I would expect it - meaning
it correctly produces "host1" - removes the dot (dot is just a character 
- we are not
in the regular expression world) - so the dot and the trailing domain
name are removed. Bash works fine in both above cases, produces expected 
output;
${VALUE/.*} naturally seems to be a valid parameter expansion.

Please try once more:

CLUSTER='host5 host1 host2';
VALUE=host1.blah.com;
echo ${CLUSTER//${VALUE%%.*}}

again works perfectly: Outputs  'host5 host2' just as i would expect it.
${VALUE%%.*} similarly to ${VALUE//.*} just removes the first
dot-and-the-trailing domain name.
it is logical to assume and the manual supports it that
    echo ${CLUSTER//${VALUE%%.*}}
is a valid parameter expansion. Again - it works fine.

Therefore it seems to be inconsistent that the nearly identical
expansion
      echo ${CLUSTER//${VALUE/.*}}

is throwing "bad substitution" exception.

To sum things up, consider these two lines (without the "dot"):

echo ${CLUSTER//${VALUE%%*}}
echo ${CLUSTER//${VALUE//*}}

the first works great. the second results in "bash: ${VALUE: bad 
substitution"

It really does seem remarkably inconsistent: We have parameter expansion
within parameter expansion, one works fine, nearly identical another one
throws an exception... Seems a bug to me.

Thanks!
dm

PS echo ${CLUSTER//${VALUE##.*}}
also works superb - in this case ${VALUE##.*} is empty - because VALUE 
does not start with a dot.
Bash works great here too.  It is only when "//" is used - Bash 
misbehaves...



Bernd Eggink wrote:
> Chet Ramey schrieb:
>   
> > Bernd Eggink wrote:
> >     
> > > >       prompt: CLUSTER='1 2'; echo ${CLUSTER/${HOSTNAME/.*}}
> > > >       output:             -bash: ${HOSTNAME: bad substitution
> > > >         
> > > Apparently bash interprets this as  ${parameter/pattern/string}
> > > where pattern = ${HOSTNAME. Looks like a bug; it works in ksh.
> > >       
> > That is, in fact, what is happening.  I'm not sure you can call it
> > a bug, though -- bash is behaving exactly as documented.
> >     
>
> Where exactly is that documented? The only statement I can find in the
> documentation referring to this problem is:
>
> "When braces are used, the matching ending brace is the first `}' not
> escaped by a backslash or within a quoted string,  and  not
> within an embedded arithmetic expansion, command substitution, or
> parameter expansion."
>
> I may be wrong, but to me this means that the first opening brace
> matches the last closing one, and that the token ${HOSTNAME/.*} is a
> correct parameter expansion.
>
> Bernd
>
> --
> Bernd Eggink
> monoped@sudrala.de
> http://sudrala.de
>