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Re: [EXTERNAL] [perl #133931] File::Find find() with "follow" option

From:
mark.w.maimone via perl5-porters
Date:
March 22, 2019 00:16
Subject:
Re: [EXTERNAL] [perl #133931] File::Find find() with "follow" option
Message ID:
201903190056.x2J0umPs026691@shavian.jpl.nasa.gov
	Hi,
	
Tony Cook via RT wrote:
> 
> On Wed, 13 Mar 2019 15:21:38 -0700, mark.maimone@jpl.nasa.gov wrote:
> > I noticed a disconnect between Find::File documentation and
> > implementation.  It claims that "follow" and "preprocess" options can
> > be used independently, but if I invoke Find::Find's "find()" using
> > options that include "follow"ing symlinks, it never invokes the
> > corresponding "preprocess" coderef option.  Looking at the Find.pm
> > source, it's clear that only _find_dir() ever invokes "preprocess"
> > (via local $pre_process); _find_dir_symlink() (which is called instead
> > of _find_dir() when "follow" is set) never invokes it at all.
> 
> The documentation for File::Find states:
> 
>   =3Ditem C<preprocess>
>  =20
>   ...  When
>   I<follow> or I<follow_fast> are in effect, C<preprocess> is a no-op.
> 
> This text was added in perl-5.6.0-4056-g7e47e6ffb6 (in 2001)
> 
> Could you please quote the text that indicates they are independent?

  Mea culpa, I see that now.  I must've just read the "follow" text
  closely, which doesn't mention it.

  Maybe if the words "I<follow>" and "I<follow_fast>" in that
  paragraph had the same emphasis as "C<preprocsss>" it'd be even more
  obvious?  Your quote shows them as italic, which renders as plain
  text in my terminal, whereas C<> shows up in double quotes.

> 
> >=20
> > I was able to make things work (obeying "preprocess" hooks
> > regardless of whether "follow" is also set) by duplicating the
> > _find_dir() code in _find_dir_symlink(), adding the third line here:
> >=20
> > @filenames =3D readdir DIR;
> > closedir(DIR);
> > @filenames =3D $pre_process->(@filenames) if $pre_process;
> >=20
> > I would like to suggest including this or a similar change in
> > new releases of File::Find.pm
> 
> That said, we could possibly allow preprocess to work with follow, but it's=
>  an enhancement, not a bug fix.

   Understood.  It does seem like a helpful and simple fix, it'd be a
   nice enhancement.  I have a filesystem with lots of symlinks, and I
   found I wasn't able to get the search to terminate in a reasonable
   amount of time unless I took advantage of the "preprocess" hook to
   prune away unneeded search branches.

   Thanks much for your reply!

					Mark M.
					
-- 
------------------------------------------------------------------------------
Mark Maimone                              cell : +1 (818) 642 - 7334
NASA Jet Propulsion Lab, Caltech          fax:   +1 (818) 393 - 2346
http://www-robotics.jpl.nasa.gov/people/Mark_Maimone



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