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 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 $(file) was a 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 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 2/17/12 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 ?
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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 $({}/dev/stdin); } 'hi'
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/dev/stdin); } 'hi'
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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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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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.
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 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 $({}/dev/stdin); } 'hi'
hi
~ $ { echo $(11/dev/stdin); } 'hi'
hi
That one really is ignored. No variable named xxx... is actually set.
--
Dan Douglas
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