* Array expansion interacts with brace expansion in the wrong order
@ 2017-07-13 22:45 Anders Kaseorg
2017-07-13 23:48 ` Bart Schaefer
0 siblings, 1 reply; 6+ messages in thread
From: Anders Kaseorg @ 2017-07-13 22:45 UTC (permalink / raw)
To: zsh-workers
Given a=(1 2 3), I would expect {$^a,4,5,6} to expand to 1 2 3 4 5 6, but
it doesn’t. Instead the 4 5 6 is duplicated for every element of $^a:
% echo $ZSH_PATCHLEVEL
zsh-5.3.1-240-ga3b3f0057
% echo {{1,2,3},4,5,6}
1 2 3 4 5 6
% a=(1 2 3)
% echo {$^a,4,5,6}
1 4 5 6 2 4 5 6 3 4 5 6
Anders
^ permalink raw reply [flat|nested] 6+ messages in thread* Re: Array expansion interacts with brace expansion in the wrong order 2017-07-13 22:45 Array expansion interacts with brace expansion in the wrong order Anders Kaseorg @ 2017-07-13 23:48 ` Bart Schaefer 2017-07-14 1:42 ` Anders Kaseorg 0 siblings, 1 reply; 6+ messages in thread From: Bart Schaefer @ 2017-07-13 23:48 UTC (permalink / raw) To: Anders Kaseorg; +Cc: zsh-workers On Thu, Jul 13, 2017 at 3:45 PM, Anders Kaseorg <andersk@mit.edu> wrote: > Given a=(1 2 3), I would expect {$^a,4,5,6} to expand to 1 2 3 4 5 6, but > it doesn’t. Instead the 4 5 6 is duplicated for every element of $^a Your expectation is wrong. Brace expansion happens last of all (except for globbing), so {$^a,4,5,6} is {1,4,5,6} {2,4,5,6} {3,4,5,6}. This is documented. Even if this happened in the order you expect, the way you've written it would have given 1 4 1 5 1 6 2 4 2 5 2 6 3 4 3 5 3 6 because of the meaning of $^a. What you are after is simply {"$a",4,5,6}. ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Array expansion interacts with brace expansion in the wrong order 2017-07-13 23:48 ` Bart Schaefer @ 2017-07-14 1:42 ` Anders Kaseorg 2017-07-14 8:48 ` Peter Stephenson 0 siblings, 1 reply; 6+ messages in thread From: Anders Kaseorg @ 2017-07-14 1:42 UTC (permalink / raw) To: Bart Schaefer; +Cc: zsh-workers On Thu, 13 Jul 2017, Bart Schaefer wrote: > On Thu, Jul 13, 2017 at 3:45 PM, Anders Kaseorg <andersk@mit.edu> wrote: > > Given a=(1 2 3), I would expect {$^a,4,5,6} to expand to 1 2 3 4 5 6, but > > it doesn’t. Instead the 4 5 6 is duplicated for every element of $^a > > Your expectation is wrong. Brace expansion happens last of all > (except for globbing), so {$^a,4,5,6} is {1,4,5,6} {2,4,5,6} > {3,4,5,6}. This is documented. > > Even if this happened in the order you expect, the way you've written > it would have given 1 4 1 5 1 6 2 4 2 5 2 6 3 4 3 5 3 6 because of the > meaning of $^a. The documentation for ${^spec} says “Internally, each such expansion is converted into the equivalent list for brace expansion. E.g., ${^var} becomes {$var[1],$var[2],...}, and is processed as described in Brace Expansion below.” That would seem to support my expectation that {$^a,4,5,6} should become {{1,2,3},4,5,6}, which expands to 1 2 3 4 5 6. > What you are after is simply {"$a",4,5,6}. That produces 4 words ("1 2 3" 4 5 6), and doesn’t generalize (e.g. I would expect {$^a,4,5,6}{x,y} = {{1,2,3},4,5,6}{x,y} = 1x 1y 2x 2y 3x 3y 4x 4y 5x 5y 6x 6y). Anders ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Array expansion interacts with brace expansion in the wrong order 2017-07-14 1:42 ` Anders Kaseorg @ 2017-07-14 8:48 ` Peter Stephenson 2017-07-14 9:45 ` Peter Stephenson 0 siblings, 1 reply; 6+ messages in thread From: Peter Stephenson @ 2017-07-14 8:48 UTC (permalink / raw) To: zsh-workers On Thu, 13 Jul 2017 21:42:50 -0400 Anders Kaseorg <andersk@mit.edu> wrote: > The documentation for ${^spec} says > > “Internally, each such expansion is converted into the equivalent list for > brace expansion. E.g., ${^var} becomes {$var[1],$var[2],...}, and is > processed as described in Brace Expansion below.” > > That would seem to support my expectation that {$^a,4,5,6} should become > {{1,2,3},4,5,6}, which expands to 1 2 3 4 5 6. What it means is the effect similar to brace expansion is *performed* immediately, not simply recorded as happening below with the other brace expansion. So by the time the shell even looks to see if there's any (actual) brace expansion to do, the array has already been expended using its own similar rules and the shell is looking at: {1,4,5,6} {2,4,5,6] {3,4,5,6} There's no likelihood of the big rewrite that would be necessary to transform the array expansion into such a form that it actually happens with the brace expansion; indeed the brace expansion code is quite ad hoc, as I rediscovered only yesterday. The ordering of diferent sorts of expansion in the shell is always a big source of confusion and in head scratching about how to get things to work, but the key is to think of array expansion and brace expansion as completely separate stages. I can't think of an easy workaround for your case except by constructing an array b=($a 4 5 6) which is obviously rather more verbose. pws ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Array expansion interacts with brace expansion in the wrong order 2017-07-14 8:48 ` Peter Stephenson @ 2017-07-14 9:45 ` Peter Stephenson 2017-07-15 17:19 ` Peter Stephenson 0 siblings, 1 reply; 6+ messages in thread From: Peter Stephenson @ 2017-07-14 9:45 UTC (permalink / raw) To: zsh-workers This might be worth saying explicitly --- though things like this are implicit throughout zsh's expansion rules. diff --git a/Doc/Zsh/expn.yo b/Doc/Zsh/expn.yo index d161b0b..c45f83a 100644 --- a/Doc/Zsh/expn.yo +++ b/Doc/Zsh/expn.yo @@ -856,8 +856,9 @@ all arguments to be removed. Internally, each such expansion is converted into the equivalent list for brace expansion. E.g., tt(${^var}) becomes tt({$var[1],$var[2],)...tt(}), and is processed as described in -noderef(Brace Expansion) below. -If word splitting is also in effect the +noderef(Brace Expansion) below: note, however, the expansion +happens immediately, with any explicit brace expansion +happening later. If word splitting is also in effect the tt($var[)var(N)tt(]) may themselves be split into different list elements. ) pws ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Array expansion interacts with brace expansion in the wrong order 2017-07-14 9:45 ` Peter Stephenson @ 2017-07-15 17:19 ` Peter Stephenson 0 siblings, 0 replies; 6+ messages in thread From: Peter Stephenson @ 2017-07-15 17:19 UTC (permalink / raw) To: zsh-workers On Fri, 14 Jul 2017 10:45:55 +0100 Peter Stephenson <p.stephenson@samsung.com> wrote: > This might be worth saying explicitly --- though things like this are > implicit throughout zsh's expansion rules. I wonder if it's also worth expanding the following? Having reread it in the light of Anders' query I realised "in one step" might be a bit misleading. Other suggestions welcome. I'm not, to be honest, quite sure what "in one step" really meant. I think it meant the each command line argument was changed completely before moving onto the next. But even if it did, that's not *quite* right if you consider that you might generate extra arguments from an earlier step which then need processing themselves in left to right order. All in all, I think obscuring the fact that the expansions happen one after the other is unhelpful, however we tackle it. pws diff --git a/Doc/Zsh/expn.yo b/Doc/Zsh/expn.yo index d161b0b..5b26f36 100644 --- a/Doc/Zsh/expn.yo +++ b/Doc/Zsh/expn.yo @@ -21,9 +21,12 @@ xitem(em(Parameter Expansion)) xitem(em(Command Substitution)) xitem(em(Arithmetic Expansion)) item(em(Brace Expansion))( -These five are performed in one step in left-to-right fashion. After -these expansions, all unquoted occurrences of the characters `tt(\)', -`tt(')' and `tt(")' are removed. +These five are performed in left-to-right fashion. On each argument, +any of the five steps that are needed are performed one after the other. +Hence, for example, all the parts of parameter expansion are completed +before command substitution is started. After these expansions, all +unquoted occurrences of the characters `tt(\)',`tt(')' and `tt(")' are +removed. ) item(em(Filename Expansion))( If the tt(SH_FILE_EXPANSION) option is set, the order of expansion is ^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2017-07-15 17:27 UTC | newest] Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2017-07-13 22:45 Array expansion interacts with brace expansion in the wrong order Anders Kaseorg 2017-07-13 23:48 ` Bart Schaefer 2017-07-14 1:42 ` Anders Kaseorg 2017-07-14 8:48 ` Peter Stephenson 2017-07-14 9:45 ` Peter Stephenson 2017-07-15 17:19 ` Peter Stephenson
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