• Use File::Spec->catfile for building the directory locations and pathnames
• Dont use constant open form, see open ( my $fh, $rw, $perm ) format
• I think reading in the whole file is probably better for whatever you want, on a modern system
• Don't grep for a file_path if the call requires it to be there

#!/usr/bin/perl -l
use strict;
use File::Find;
use File::Spec;

use constant DIRECTORY => '/tmp/rja/find_test';

my @files;

find( \&findsub, __PACKAGE__->DIRECTORY );

@files = grep is_dos_format($_), @files;

foreach my $file (@files) {
    print "FAILED FILE - $file";
}

sub findsub {
    push @files, $File::Find::name;
}

sub is_dos_format {
    my $abs_path = shift;

    open ( my $fh, '<', $abs_path )
        or die "open $abs_path: $!"
    ;

    if ( grep m/\r\n/s, <$fh> ) {
        return 1;
    }

    return undef;

}
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