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if ($data_choice eq 'l' || $data_choice eq 'L') {
    open my $fh, '<', 'stations.dat'
...
        or warn "Trouble closing file lock for stations.dat";
    @data_lines = split /\n/, $stations_data;
}

    # update file if necessary:
    mirror( $url, 'stations.dat' );
...
        or die "Trouble opening stations.dat - $!";
    # LOCK_SH not necessary when using mirror()
    @data_lines = <$fh>;