Odd expansion behavior

Odd expansion behavior

[Dima Kogan]

Hi.

I'm observing something odd. It might be a bug, but I don't understand
it well-enough to call it that.

I see this:

$ x=(1 2 3); echo xxx${^x}
xxx1 xxx2 xxx3

This output makes sense. However something slightly different is strange:

$ x=(1 2 3); y=xxx${^x}; echo $y
xxx1 2 3

Here the ${^x} form turns on the RC_EXPAND_PARAM option, and it's
apparently not kicking in in the second (broken) case. Even if I setopt
it, I still don't have this working.

I asked on #zsh and osse helpfully pointed out that this can be made to
work by expressing the assignment as 'y=(xxx${^x})' instead, which does
work.

But shouldn't it work the other way as well? osse wasn't sure why the
original form wasn't working, so I'm reporting it here as a maybe-bug.

Thanks

dima

Re: Odd expansion behavior

[Peter Stephenson]

On Thu, 03 Jul 2014 00:43:23 -0700
Dima Kogan <dima@secretsauce.net> wrote:
> I'm observing something odd. It might be a bug, but I don't understand
> it well-enough to call it that.
> 
> I see this:
> 
> $ x=(1 2 3); echo xxx${^x}
> xxx1 xxx2 xxx3
> 
> This output makes sense. However something slightly different is strange:
> 
> $ x=(1 2 3); y=xxx${^x}; echo $y
> xxx1 2 3
> 
> I asked on #zsh and osse helpfully pointed out that this can be made to
> work by expressing the assignment as 'y=(xxx${^x})' instead, which does
> work.

That's the difference between a scalar and an array assignment.  In a
scalar assignment, arrays are forced immediately to scalars, i.e. single
strings joined (by default) with spaces.  So the $x gets turned
immediately into "1 2 3"; the "^" has no special effect because you're
just joining that string with the "xxx".

It's a little bit like (but not exactly the same as) putting double
quotes around the expression.

It might throw a little bit of extra light on this if you look at the
words that are coming out; you can do this with "print -l" which outputs
one word per line.  So in the first case and after array assignment you
get

xxx1
xxx2
xxx3

because you are getting three different words from ${^x}, each one
joined to xxx, while after the scalar expansion you get

xxx1 2 3

because you have a single word.

pws

Re: Odd expansion behavior

[Peter Stephenson]

On Thu, 03 Jul 2014 10:12:01 +0100
Peter Stephenson <p.stephenson@samsung.com> wrote:
> That's the difference between a scalar and an array assignment.

The doc is somewhat scattered.  This might help a bit.

diff --git a/Doc/Zsh/grammar.yo b/Doc/Zsh/grammar.yo
index 719f06a..77f0098 100644
--- a/Doc/Zsh/grammar.yo
+++ b/Doc/Zsh/grammar.yo
@@ -19,7 +19,11 @@ cindex(simple commands)
 cindex(commands, simple)
 A em(simple command) is a sequence of optional parameter
 assignments followed by blank-separated words,
-with optional redirections interspersed.
+with optional redirections interspersed.  For a description
+of assignment, see the beginning of
+ifnzman(noderef(Parameters))\
+ifzman(zmanref(zshparam)).
+
 The first word is the command to be executed, and the remaining
 words, if any, are arguments to the command.
 If a command name is given, the parameter assignments modify
diff --git a/Doc/Zsh/params.yo b/Doc/Zsh/params.yo
index 5bccdc2..dbac511 100644
--- a/Doc/Zsh/params.yo
+++ b/Doc/Zsh/params.yo
@@ -21,14 +21,20 @@ indent(var(name)tt(=)var(value))
 
 If the integer attribute, tt(-i), is set for var(name), the var(value)
 is subject to arithmetic evaluation.  Furthermore, by replacing `tt(=)'
-with `tt(+=)', a parameter can be added or appended to.  See
+with `tt(+=)', a parameter can be added or appended to.
+
+In scalar assignment, var(value) is expanded as a single string, in
+which the elements of arrays are joined together; filename expansion is
+not performed unless the option tt(GLOB_ASSIGN) is set.  See
 noderef(Array Parameters) for additional forms of assignment.
 
 To refer to the value of a parameter, write `tt($)var(name)' or
 `tt(${)var(name)tt(})'.  See
 ifzman(em(Parameter Expansion) in zmanref(zshexpn))\
 ifnzman(noderef(Parameter Expansion))
-for complete details.
+for complete details.  This section also explains the effect
+of the difference between scalar and array assignment on parameter
+expansion.
 
 In the parameter lists that follow, the mark `<S>' indicates that the
 parameter is special.

pws