if ( ! unlink $file ) {
    warn "Can't unlink '$file': $!\n";
    push @unlink_failures, $file;
}

##</code><code>##

@unlink_failures = grep { ! unlink } @files_to_unlink;
warn "unlink failed for '$_'\n" for @unlink_failures;

##</code><code>##

warn "unlink failed for '$_'\n"
    for ( @unlink_failures
             = grep { ! unlink } @files_to_unlink );