negative pattern doesn't match empty string in globbing?

negative pattern doesn't match empty string in globbing?

[Han Pingtian]

Hello,

I just notice that negative pattern like this doesn't work:

    localhost% setopt extendedglob
    localhost% print /usr/**/bin/zsh
    /usr/bin/zsh /usr/local/bin/zsh
    localhost% print /usr/^local/bin/zsh
    zsh: no matches found: /usr/^local/bin/zsh
    localhost% ls /usr//bin/zsh
    /usr//bin/zsh
    localhost% 

I think if "^local" can match with empty string, then this should work.
But looks like it doesn't.

negative pattern doesn't match empty string in globbing?

[Peter Stephenson]

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On Friday, 19 September 2014, Han Pingtian <hanpt@linux.vnet.ibm.com
<javascript:_e(%7B%7D,'cvml','hanpt@linux.vnet.ibm.com');>> wrote:
> Hello,
>
> I just notice that negative pattern like this doesn't work:
>
>     localhost% setopt extendedglob
>     localhost% print /usr/**/bin/zsh
>     /usr/bin/zsh /usr/local/bin/zsh

>     localhost% print /usr/^local/bin/zsh
>     zsh: no matches found: /usr/^local/bin/zsh
>     localhost% ls /usr//bin/zsh
>     /usr//bin/zsh
>     localhost%
>
> I think if "^local" can match with empty string, then this should work.
> But looks like it doesn't.

Please excuse formatting,  I'm writing this on my phone at a
bus stop, or at least trying.  (I'm now half way to Truro and
on the third browser...)

Negative patterns are confusing, I've discovered over the years.
The way to think of them is "match anything but..."
In other words, first match something, and only then decide
what to exclude.

In this case,  the initial  "match anything" matches files in the directory
you've reached. Obviously there is no empty file. So the overall match fails
at that point.

Phew...  time to hit send...

pws

negative pattern doesn't match empty string in globbing?

[Peter Stephenson]

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On Friday, 19 September 2014, Han Pingtian <hanpt@linux.vnet.ibm.com
<javascript:_e(%7B%7D,'cvml','hanpt@linux.vnet.ibm.com');>> wrote:
> Hello,
>
> I just notice that negative pattern like this doesn't work:
>
>     localhost% setopt extendedglob
>     localhost% print /usr/**/bin/zsh
>     /usr/bin/zsh /usr/local/bin/zsh

>     localhost% print /usr/^local/bin/zsh
>     zsh: no matches found: /usr/^local/bin/zsh
>     localhost% ls /usr//bin/zsh
>     /usr//bin/zsh
>     localhost%
>
> I think if "^local" can match with empty string, then this should work.
> But looks like it doesn't.

Please excuse formatting,  I'm writing this on a phone on a bus
and have encountered a catalogue of problems...

Negative pattern matches are confusing.

Think about them as "match anything but..."

In other words,  first match something, then decide what to exclude.

In this case the matches are all the files in the directory (and not the
empty string).  So the overall match fails when you try to exclude
everything.

(The keyboard's completion keeps offering 'Scotland'.  Must turn off
trending phrases.)

Hope for a mobile cell soon...

pws