Filtering an array of file names

Filtering an array of file names

[Jesper Nygårds]

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Suppose I have an array of file names, generated from some external
program. Is there an zsh-idiomatic way of filtering this array to only keep
directories?

I suppose I am looking for something on the line of
${(M)files:#<something>}, but I can't figure out how to do it.

Re: Filtering an array of file names

[Bart Schaefer]

On Sep 29,  8:43am, Jesper Nygards wrote:
} 
} Suppose I have an array of file names, generated from some external
} program. Is there an zsh-idiomatic way of filtering this array to only
} keep directories?

Are these local file names that you can compare to the filesystem?  If
so, you can use rc-expand-param and globbing qualifiers:

  directories=( ${^allfiles}(/) )

(This didn't work on some old versions of the shell, where qualifiers
were interpreted only if the preceding word had a globbing character.)

If they don't refer to the local filesystem, you'll need the array to
have already marked them somehow, such as with a trailing slash, and
then ${(M)files:#*/} would work.

Re: Filtering an array of file names

[Jesper Nygårds]

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Thank you, Bart! This works perfectly.


On Thu, Sep 29, 2016 at 9:18 AM, Bart Schaefer <schaefer@brasslantern.com>
wrote:

> On Sep 29,  8:43am, Jesper Nygards wrote:
> }
> } Suppose I have an array of file names, generated from some external
> } program. Is there an zsh-idiomatic way of filtering this array to only
> } keep directories?
>
> Are these local file names that you can compare to the filesystem?  If
> so, you can use rc-expand-param and globbing qualifiers:
>
>   directories=( ${^allfiles}(/) )
>
> (This didn't work on some old versions of the shell, where qualifiers
> were interpreted only if the preceding word had a globbing character.)
>
> If they don't refer to the local filesystem, you'll need the array to
> have already marked them somehow, such as with a trailing slash, and
> then ${(M)files:#*/} would work.
>

Re: Filtering an array of file names

[Mikael Magnusson]

On Thu, Sep 29, 2016 at 9:18 AM, Bart Schaefer
<schaefer@brasslantern.com> wrote:
> On Sep 29,  8:43am, Jesper Nygards wrote:
> }
> } Suppose I have an array of file names, generated from some external
> } program. Is there an zsh-idiomatic way of filtering this array to only
> } keep directories?
>
> Are these local file names that you can compare to the filesystem?  If
> so, you can use rc-expand-param and globbing qualifiers:
>
>   directories=( ${^allfiles}(/) )

This should be
  directories=( ${^allfiles}(/N) )
unless you have nullglob set, otherwise it will either fail or fill up
the directories array with entries like "foo(/)" depending on if
nomatch is set.

-- 
Mikael Magnusson

Re: Filtering an array of file names

[Daniel Shahaf]

Bart Schaefer wrote on Thu, Sep 29, 2016 at 00:18:53 -0700:
>   directories=( ${^allfiles}(/) )

Use the (N) qualifier if it's possible to have zero matches:

    directories=( ${^allfiles}(/N) )

Re: Filtering an array of file names

[Bart Schaefer]

On Sep 29,  9:54am, Mikael Magnusson wrote:
}
} This should be
}   directories=( ${^allfiles}(/N) )
} unless you have nullglob set

Thanks, and to Daniel also, for pointing out this nuance for the general
case, but in the OP's specific example $allfiles contains only names of
known existing files, so globbing is not expected to fail and (N) would
not be necessary.