Re: Is ":G" of ${name:s/l/r/:G} actually supported?

["Lawrence Velázquez" <larryv@zsh.org>]

On Mon, Feb 12, 2024, at 12:11 PM, Mark J. Reed wrote:
> Well, that was a shorter reply than I intended. But you should be able 
> to see that the section you linked (14.1.4 Modifiers) is part of 14.1, 
> History Expansion. Those modifiers don't apply to parameter 
> substitution.

They do.

	% var=foobar
	% print -- $var:s/o/x
	fxobar

This is documented in zshexpn(1) under "Modifiers":

	After the optional word designator, you can add a sequence
	of one or more of the following modifiers, each preceded
	by a `:'.  These modifiers also work on the result of
	_filename generation_ and _parameter expansion_, except
	where noted.

and "PARAMETER EXPANSION":

	In addition to the following operations, the colon modifiers
	described in the section `Modifiers' in the section `History
	Expansion' can be applied: for example, ${i:s/foo/bar/}
	performs string substitution on the expansion of parameter $i.


> For doing replacements with parameter expansion, you can just use the 
> slash modifier. One / replaces the first occurrence, two //s does all 
> of them:
>
>> *$ value=/dir/subdir/file.csv*
>> *$ echo ${value//dir/_G}*
>> */_G/sub_G/file.csv*
> 
> That's not a zsh-specific feature; ksh and bash have it as well. Zsh 
> likely has a different mechanism to accomplish the same thing, but I've 
> not needed it so am not familiar with it.

The :s and :gs history modifiers are similar but not exactly so.
Among other things, they perform literal searches by default, allow
referring to the matched text with "&", and apply nested expansions
differently.


>> On Mon, Feb 12, 2024 at 9:19 AM Joachim Ansorg <mail@bashsupport.com> wrote:
>>> Hi,
>>> I was reading about modifiers on page 
>>> https://zsh.sourceforge.io/Doc/Release/Expansion.html#Modifiers, which says:
>>> 
>>> >   The forms ‘gs/l/r’ and ‘s/l/r/:G’ perform global substitution, i.e. substitute every occurrence of r for l. Note that the g or :G must appear in exactly the position shown.
>>> 
>>> But zsh 5.9 doesn't seem to support this:
>>>   > value="/dir/subdir/file.csv"
>>>   > echo ${value:s/dir/_/:G}
>>>   zsh: unrecognized modifier `G'

It doesn't work on zsh 4.3.11 either, which means it hasn't worked
for at least 13 years.  (This probably says something about the
prevalence of applying :s/l/r/:G to parameter expansions.)


>>> Is ":G" actually supported or is the documentation outdated here?

I can't say for sure, but this feels like a bug to me.


-- 
vq