In general, please always define "it's not working" with the error message..

Your grep arguments are backwards:

@files = grep  { /\errors.txt$/ && -f $_ }, @files;
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Related topics: glob, File::Find, File::Find::Rule (example below)

my @files = File::Find::Rule->file()->name('errors.txt')->maxdepth(1)-
+>in($dir);
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Also, if you're going for just one specific file, no need to read the directory -- just check directly if the file exists:

my $file = $dir . '/errors.txt';
push @files, $file if -f $file;
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