Re: strange expansion of <(cat p.main.{optional,extra})
Chet Ramey <[EMAIL PROTECTED]> writes:
> [EMAIL PROTECTED] wrote:
>
>> Bash Version: 3.1
>> Patch Level: 17
>> Release Status: release
>>
>> Description:
>> Hi,
>>
>> The expansion of echo <(cat /etc/{passwd,motd}) is rather surprising:
>> $ echo <(cat p.main.{optional,extra})
>> ++ cat p.main.optional
>> cat: p.main.optional: No such file or directory
>> ++ cat p.main.extra
>> cat: p.main.extra: No such file or directory
>> + echo /dev/fd/63 /dev/fd/62
>> /dev/fd/63 /dev/fd/62
>>
>> I would have expected to be expanded to <(cat /etc/passwd /etc/motd) first.
>
> That's not how it works. Brace expansion is the first expansion performed.
> The manual page says:
>
> "Brace expansion is performed before any other expansions, and any char-
> acters special to other expansions are preserved in the result. It is
> strictly textual. Bash does not apply any syntactic interpretation to
> the context of the expansion or the text between the braces."
If it would be done strictly textual, the resulting expansion would
actually be this:
$ echo <(cat p.main.optional) p.main.extra)
which would be a syntax error.
Andreas.
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SuSE Linux Products GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany
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Re: strange expansion of <(cat p.main.{optional,extra})
On 18/04/07 at 11:11 +0200, Andreas Schwab wrote:
> Chet Ramey <[EMAIL PROTECTED]> writes:
>
> > [EMAIL PROTECTED] wrote:
> >
> >> Bash Version: 3.1
> >> Patch Level: 17
> >> Release Status: release
> >>
> >> Description:
> >> Hi,
> >>
> >> The expansion of echo <(cat /etc/{passwd,motd}) is rather surprising:
> >> $ echo <(cat p.main.{optional,extra})
> >> ++ cat p.main.optional
> >> cat: p.main.optional: No such file or directory
> >> ++ cat p.main.extra
> >> cat: p.main.extra: No such file or directory
> >> + echo /dev/fd/63 /dev/fd/62
> >> /dev/fd/63 /dev/fd/62
> >>
> >> I would have expected to be expanded to <(cat /etc/passwd /etc/motd) first.
> >
> > That's not how it works. Brace expansion is the first expansion performed.
> > The manual page says:
> >
> > "Brace expansion is performed before any other expansions, and any char-
> > acters special to other expansions are preserved in the result. It is
> > strictly textual. Bash does not apply any syntactic interpretation to
> > the context of the expansion or the text between the braces."
>
> If it would be done strictly textual, the resulting expansion would
> actually be this:
>
> $ echo <(cat p.main.optional) p.main.extra)
>
> which would be a syntax error.
Well, no, because bash expands *parameters*, not words. So the prefix is
"<(cat /etc/", and the suffix is ")".
--
| Lucas Nussbaum
| [EMAIL PROTECTED] http://www.lucas-nussbaum.net/ |
| jabber: [EMAIL PROTECTED] GPG: 1024D/023B3F4F |
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Re: strange expansion of <(cat p.main.{optional,extra})
Lucas Nussbaum <[EMAIL PROTECTED]> writes: > Well, no, because bash expands *parameters*, not words. So the prefix is > "<(cat /etc/", and the suffix is ")". But that would not be a *strict textual* expansion. Andreas. -- Andreas Schwab, SuSE Labs, [EMAIL PROTECTED] SuSE Linux Products GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany PGP key fingerprint = 58CA 54C7 6D53 942B 1756 01D3 44D5 214B 8276 4ED5 "And now for something completely different." ___ Bug-bash mailing list Bug-bash@gnu.org http://lists.gnu.org/mailman/listinfo/bug-bash
Re: strange expansion of <(cat p.main.{optional,extra})
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 According to Andreas Schwab on 4/18/2007 4:01 AM: > Lucas Nussbaum <[EMAIL PROTECTED]> writes: > >> Well, no, because bash expands *parameters*, not words. So the prefix is >> "<(cat /etc/", and the suffix is ")". > > But that would not be a *strict textual* expansion. According to 'man bash', brace expansion is documented as being able to expand one word into many. <(...) forms a single word, even when ... contains unquoted spaces. Therefore, strict textual expansion occurred, and there was no syntax error. - -- Don't work too hard, make some time for fun as well! Eric Blake [EMAIL PROTECTED] -BEGIN PGP SIGNATURE- Version: GnuPG v1.4.5 (Cygwin) Comment: Public key at home.comcast.net/~ericblake/eblake.gpg Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQFGJgwE84KuGfSFAYARAgF/AJ0VUlTUe/SoCsHOEKKsNk/D4bQXhwCfbWYU ba0721NvVacYWFWx4ldk4Ng= =PmOq -END PGP SIGNATURE- ___ Bug-bash mailing list Bug-bash@gnu.org http://lists.gnu.org/mailman/listinfo/bug-bash
Re: strange expansion of <(cat p.main.{optional,extra})
Eric Blake <[EMAIL PROTECTED]> writes: > According to Andreas Schwab on 4/18/2007 4:01 AM: >> Lucas Nussbaum <[EMAIL PROTECTED]> writes: >> >>> Well, no, because bash expands *parameters*, not words. So the prefix is >>> "<(cat /etc/", and the suffix is ")". >> >> But that would not be a *strict textual* expansion. > > According to 'man bash', brace expansion is documented as being able to > expand one word into many. The documentation talks about strings, not words. > <(...) forms a single word, even when ... contains unquoted spaces. That requires syntactic interpretation to the context of the expansion, which is explicitly excluded. Andreas. -- Andreas Schwab, SuSE Labs, [EMAIL PROTECTED] SuSE Linux Products GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany PGP key fingerprint = 58CA 54C7 6D53 942B 1756 01D3 44D5 214B 8276 4ED5 "And now for something completely different." ___ Bug-bash mailing list Bug-bash@gnu.org http://lists.gnu.org/mailman/listinfo/bug-bash
Re: strange expansion of <(cat p.main.{optional,extra})
On Tue, Apr 17, 2007 at 08:16:53PM -0400, Chet Ramey wrote:
[...]
> > The expansion of echo <(cat /etc/{passwd,motd}) is rather surprising:
> > $ echo <(cat p.main.{optional,extra})
> > ++ cat p.main.optional
> > cat: p.main.optional: No such file or directory
> > ++ cat p.main.extra
> > cat: p.main.extra: No such file or directory
> > + echo /dev/fd/63 /dev/fd/62
> > /dev/fd/63 /dev/fd/62
> >
> > I would have expected to be expanded to <(cat /etc/passwd /etc/motd) first.
>
> That's not how it works. Brace expansion is the first expansion performed.
> The manual page says:
>
> "Brace expansion is performed before any other expansions, and any char-
> acters special to other expansions are preserved in the result. It is
> strictly textual. Bash does not apply any syntactic interpretation to
> the context of the expansion or the text between the braces."
[...]
How does it get exanded to
echo <(cat p.main.optional) <(cat p.main,extra)
though?
If it were textual, I would expect:
echo <(cat p.main.optional) p.main,extra)
And what about:
echo $(cat p.main.{optional,extra})
This resolves to
echo $(cat p.main.optional p.main.extra)
I can't see any reason why $(...) and <(...) should be treated
differently.
bash-3.1$ echo <(echo {a,b})
++ echo a
++ echo b
+ echo /dev/fd/63 /dev/fd/62
/dev/fd/63 /dev/fd/62
bash-3.1$ echo $(echo {a,b})
++ echo a b
+ echo a b
a b
All the other shells treat them the same in that regards.
Any expansion inside command or process subsitution should
be defered to the subshell I think.
% echo <(echo {a,b})
+zsh:1> echo a b
+zsh:1> echo /proc/self/fd/11
/proc/self/fd/11
% echo $(echo {a,b})
+zsh:1> echo a b
+zsh:2> echo a b
a b
--
Stéphane
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Re: strange expansion of <(cat p.main.{optional,extra})
On 18/04/07 at 14:37 +0200, Andreas Schwab wrote: > Eric Blake <[EMAIL PROTECTED]> writes: > > > According to Andreas Schwab on 4/18/2007 4:01 AM: > >> Lucas Nussbaum <[EMAIL PROTECTED]> writes: > >> > >>> Well, no, because bash expands *parameters*, not words. So the prefix is > >>> "<(cat /etc/", and the suffix is ")". > >> > >> But that would not be a *strict textual* expansion. > > > > According to 'man bash', brace expansion is documented as being able to > > expand one word into many. > > The documentation talks about strings, not words. Based on the behaviour, I think that bash first splits the command line into a list of parameters, then expands each parameter. <(...) is a single parameter. -- | Lucas Nussbaum | [EMAIL PROTECTED] http://www.lucas-nussbaum.net/ | | jabber: [EMAIL PROTECTED] GPG: 1024D/023B3F4F | ___ Bug-bash mailing list Bug-bash@gnu.org http://lists.gnu.org/mailman/listinfo/bug-bash
Re: strange expansion of <(cat p.main.{optional,extra})
Stephane Chazelas wrote:
> On Tue, Apr 17, 2007 at 08:16:53PM -0400, Chet Ramey wrote:
> How does it get exanded to
>
> echo <(cat p.main.optional) <(cat p.main,extra)
>
> though?
>
> If it were textual, I would expect:
>
> echo <(cat p.main.optional) p.main,extra)
It's still a word expansion. The parser splits the input into words
before brace expansion takes place.
>
> And what about:
>
> echo $(cat p.main.{optional,extra})
>
> This resolves to
>
> echo $(cat p.main.optional p.main.extra)
>
> I can't see any reason why $(...) and <(...) should be treated
> differently.
Yes, that's a separate issue worth consideration. There is already code
to treat command substitution specially and defer expansion to the
subshell. It might be a good idea to treat process substitution the same
way.
Chet
--
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Chet Ramey, ITS, CWRU[EMAIL PROTECTED]http://cnswww.cns.cwru.edu/~chet/
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