How do I use $File::Find::prune?

Question

I have a need to edit cue files in the first directory and not go recursively in the subdirectories.

find(\&read_cue, $dir_source);
sub read_cue {
    /\.cue$/ or return;

    my $fd = $File::Find::dir;
    my $fn = $File::Find::name; 
    tie my @lines, 'Tie::File', $fn
      or die "could not tie file: $!";

    foreach (@lines) {
        s/some substitution//;
    }

    untie @lines;
}

I've tried variations of

$File::Find::prune = 1;
return;  

but with no success. Where should I place and define $File::Find::prune?

Thanks

Answer 1

If you don't want to recurse, you probably want to use glob:

for  (glob("*.cue")) {
   read_cue($_);
}

Answer 2

If you want to filter the subdirectories recursed into by File::Find, you should use the preprocess function (not the $File::Find::prune variable) as this gives you much more control. The idea is to provide a function which is called once per directory, and is passed a list of files and subdirectories; the return value is the filtered list to pass to the wanted function, and (for subdirectories) to recurse into.

As msw and Brian have commented, your example would probably be better served by a glob, but if you wanted to use File::Find, you might do something like the following. Here, the preprocess function calls -f on every file or directory it's given, returning a list of files. Then the wanted function is called only for those files, and File::Find does not recurse into any of the subdirectories:

use strict;
use File::Find;

# Function is called once per directory, with a list of files and
# subdirectories; the return value is the filtered list to pass to
# the wanted function.
sub preprocess { return grep { -f } @_; }

# Function is called once per file or subdirectory.
sub wanted { print "$File::Find::name\n" if /\.cue$/; }

# Find files in or below the current directory.
find { preprocess => \&preprocess, wanted => \&wanted }, '.';

This can be used to create much more sophisticated file finders. For example, I wanted to find all files in a Java project directory, without recursing into subdirectories starting with ".", such as ".idea" and ".svn", created by IntelliJ and Subversion. You can do this by modifying the preprocess function:

# Function is called once per directory, with a list of files and
# subdirectories; return value is the filtered list to pass to the
# wanted function.
sub preprocess { return grep { -f or (-d and /^[^.]/) } @_; }

Answer 3

If you only want the files in a directory without searching subdirectories, you don't want to use File::Find. A simple glob probably does the trick:

my @files = glob( "$dir_source/*.cue" );

You don't need that subroutine. In general, when you're doing a lot of work for a task that you think should be simple, you're probably doing it wrong. :)

Answer 4

Say you have a directory subtree with

/tmp/foo/file.cue
/tmp/foo/bar/file.cue
/tmp/foo/bar/baz/file.cue

Running

#! /usr/bin/perl

use warnings;
use strict;

use File::Find;

sub read_cue {
  if (-f && /\.cue$/) {
    print "found $File::Find::name\n";
  }
}

@ARGV = (".") unless @ARGV;
find \&read_cue => @ARGV;

outputs

found /tmp/foo/file.cue
found /tmp/foo/bar/file.cue
found /tmp/foo/bar/baz/file.cue

But if you remember the directories in which you found cue files

#! /usr/bin/perl

use warnings;
use strict;

use File::Find;

my %seen_cue;
sub read_cue {
  if (-f && /\.cue$/) {
    print "found $File::Find::name\n";
    ++$seen_cue{$File::Find::dir};
  }
  elsif (-d && $seen_cue{$File::Find::dir}) {
    $File::Find::prune = 1;
  }
}

@ARGV = (".") unless @ARGV;
find \&read_cue => @ARGV;

you get only the toplevel cue file:

found /tmp/foo/file.cue

That's because $File::Find::prune emulates the -prune option of find that affects directory processing:

-prune

True; if the file is a directory, do not descend into it.