Re: excess braces ignored: bug or feature ?
On 02/17/12 20:51, Mike Frysinger wrote:
> FOO= BAR=bar
> : ${FOO:=${BAR}
> echo $FOO
Why should this be a bug? Your second line performs a parameter
expansion, all the remaining characters are joint into the token and
passed to ':'.
No bug.
Re: excess braces ignored: bug or feature ?
On 2/20/12 4:17 AM, Dan Douglas wrote: > On Sunday, February 19, 2012 04:25:46 PM Chet Ramey wrote: > >> I assume you mean the first one. It doesn't matter whether or not the >> variable is set as a side effect of the redirection -- it's in a >> subshell and disappears. >> >> Chet > > Forgot to mention though, It's possible in ksh there is no subshell created > if > you consider this: The best way to tell for sure is with a system call tracer. -- ``The lyf so short, the craft so long to lerne.'' - Chaucer ``Ars longa, vita brevis'' - Hippocrates Chet Ramey, ITS, CWRUc...@case.eduhttp://cnswww.cns.cwru.edu/~chet/
Re: excess braces ignored: bug or feature ?
On 2/20/12 2:32 AM, Dan Douglas wrote: >>> That one really is ignored. No variable named xxx... is actually set. >> >> I assume you mean the first one. It doesn't matter whether or not the >> variable is set as a side effect of the redirection -- it's in a >> subshell and disappears. >> >> Chet > > Oh so a subshell is created after all, and that really is a command > substitution + redirect! I just chalked it up to Bash recycling the way > redirects were parsed. Bash always forks for command substitution. It defers parsing the command between the parens until it's needed, and so doesn't notice that it's only a redirection until it has already forked. It is able to skip the exec and dump the file out directly. > > I think I ran across that quirk in trying to determine whether $( special command substitution or it's own kind of expansion but couldn't think > of a way to test it. It's a special command substitution (there are others). David has gone to great lengths to avoid forking in ksh93 wherever possible; I assume this is one of those places where he's managed to do so. Chet -- ``The lyf so short, the craft so long to lerne.'' - Chaucer ``Ars longa, vita brevis'' - Hippocrates Chet Ramey, ITS, CWRUc...@case.eduhttp://cnswww.cns.cwru.edu/~chet/
Re: excess braces ignored: bug or feature ?
On Sunday, February 19, 2012 04:25:46 PM Chet Ramey wrote:
> I assume you mean the first one. It doesn't matter whether or not the
> variable is set as a side effect of the redirection -- it's in a
> subshell and disappears.
>
> Chet
Forgot to mention though, It's possible in ksh there is no subshell created if
you consider this:
$ : "$(&2;})"
1
$ : $(: $( echo ${.sh.subshell} >&2))
2
It even works with the subshell-less command substitution, but there's no
typeset output, so either x is automatically unset, it's never set to begin
with, or ${ &2 | :
0
~ $ : | { echo $BASH_SUBSHELL >&2; } | :
1
~ $ : | ( echo $BASH_SUBSHELL >&2; ) | :
1
~ $ : | ( ( echo $BASH_SUBSHELL >&2; ) ) | :
2
~ $ : | { ( echo $BASH_SUBSHELL >&2; ) } | :
2
~ $ : | { { echo $BASH_SUBSHELL >&2; } } | :
1
--
Dan Douglas
Re: excess braces ignored: bug or feature ?
On Sunday, February 19, 2012 04:25:46 PM Chet Ramey wrote:
> On 2/17/12 6:22 PM, Dan Douglas wrote:
> > My favorite is probably the parser ignoring any valid redirection syntax
> > with the special command substitutions.
> >
> > ~ $ { echo "$({} >
> > hi
>
> Bash does the same thing as ksh93 here, though for the wrong reasons.
> I think ksh93 counts an input redirection that saves the file descriptor
> into a variable as sufficient to kick in the `equivalent to cat file'
> clause.
>
> > ~ $ { echo "$(11 >
> > hi
>
> This is a bug. It should be a file descriptor out of range error, or
> it should treat the string of digits as a word, since the value
> exceeds the largest intmax_t.
>
> > That one really is ignored. No variable named xxx... is actually set.
>
> I assume you mean the first one. It doesn't matter whether or not the
> variable is set as a side effect of the redirection -- it's in a
> subshell and disappears.
>
> Chet
Oh so a subshell is created after all, and that really is a command
substitution + redirect! I just chalked it up to Bash recycling the way
redirects were parsed.
I think I ran across that quirk in trying to determine whether $(&2;})"
...only to discover that ${ cmd;} also increments .sh.subshell anyway (like
BASH_SUBSHELL), and there was no BASHPID equivalent so that was a dead end.
--
Dan Douglas
Re: excess braces ignored: bug or feature ?
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Hash: SHA1
On 2/17/12 6:22 PM, Dan Douglas wrote:
> My favorite is probably the parser ignoring any valid redirection syntax with
> the special command substitutions.
>
> ~ $ { echo "$({} hi
Bash does the same thing as ksh93 here, though for the wrong reasons.
I think ksh93 counts an input redirection that saves the file descriptor
into a variable as sufficient to kick in the `equivalent to cat file'
clause.
> ~ $ { echo "$(11 hi
This is a bug. It should be a file descriptor out of range error, or
it should treat the string of digits as a word, since the value
exceeds the largest intmax_t.
> That one really is ignored. No variable named xxx... is actually set.
I assume you mean the first one. It doesn't matter whether or not the
variable is set as a side effect of the redirection -- it's in a
subshell and disappears.
Chet
- --
``The lyf so short, the craft so long to lerne.'' - Chaucer
``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, ITS, CWRUc...@case.eduhttp://cnswww.cns.cwru.edu/~chet/
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Re: excess braces ignored: bug or feature ?
On 2/17/12 2:51 PM, Mike Frysinger wrote:
> can't tell if this is a bug or a feature.
>
> FOO= BAR=bar
> : ${FOO:=${BAR}
> echo $FOO
>
> i'd expect an error, or FOO to contain those excess braces. instead, FOO is
> just "bar".
Neither. That's just how parameter expansion works. The braces are
contained in the remainder of the word expansion.
--
``The lyf so short, the craft so long to lerne.'' - Chaucer
``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, ITS, CWRUc...@case.eduhttp://cnswww.cns.cwru.edu/~chet/
Re: excess braces ignored: bug or feature ?
On Friday, February 17, 2012 02:51:27 PM Mike Frysinger wrote:
> can't tell if this is a bug or a feature.
>
> FOO= BAR=bar
>
> : ${FOO:=${BAR}
>
> echo $FOO
>
> i'd expect an error, or FOO to contain those excess braces. instead, FOO is
> just "bar".
> -mike
My favorite is probably the parser ignoring any valid redirection syntax with
the special command substitutions.
~ $ { echo "$({}
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Re: excess braces ignored: bug or feature ?
Greg Wooledge wrote:
> Mike Frysinger wrote:
> > can't tell if this is a bug or a feature.
> >
> > FOO= BAR=bar
> > : ${FOO:=${BAR}
> > echo $FOO
> >
> > i'd expect an error, or FOO to contain those excess braces. instead, FOO
> > is
> > just "bar".
>
> imadev:~$ : ${FOO:=BAR}
> imadev:~$ echo "$FOO"
> BAR
>
> It looks OK to me. You've got an argument word which happens to contain
> a substitution-with-side-effects as part of it.
Or slightly differently expressed it is this too:
$ echo ${FOO:=BAR}
BAR
$ echo ${FOO:=BAR}
BAR
$ echo ${FOO:=${BAR}
}}}
Seems reasonable to me. In that context the bracket isn't special in
any way and is just another character in the string. Just like this:
$ echo
Bob
Re: excess braces ignored: bug or feature ?
On Fri, Feb 17, 2012 at 02:51:27PM -0500, Mike Frysinger wrote:
> can't tell if this is a bug or a feature.
>
> FOO= BAR=bar
> : ${FOO:=${BAR}
> echo $FOO
>
> i'd expect an error, or FOO to contain those excess braces. instead, FOO is
> just "bar".
imadev:~$ : ${FOO:=BAR}
imadev:~$ echo "$FOO"
BAR
It looks OK to me. You've got an argument word which happens to contain
a substitution-with-side-effects as part of it.
excess braces ignored: bug or feature ?
can't tell if this is a bug or a feature.
FOO= BAR=bar
: ${FOO:=${BAR}
echo $FOO
i'd expect an error, or FOO to contain those excess braces. instead, FOO is
just "bar".
-mike
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