while ( readdir $dirhandle ) {
    if ( -f $_ ) {
        if ( open $file{ $_ }, '<', $_ ) {
            warn sprintf q{I have %d files open from the working directory.}, scalar keys %file;
            # do stuff
        } else {
            delete $files{ $_ };
            # report error
        }
    }
}
my @files = keys %file;
for ( @files ) {
    # do something that for some reason requires all the files in the directory open at once
}
for ( @files ) {
    close $file{ $_ };
    delete $file{ $_ };
}