This file is indexed.

/usr/bin/vcf-isec is in vcftools 0.1.14+dfsg-2.

This file is owned by root:root, with mode 0o755.

The actual contents of the file can be viewed below.

  1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
#!/usr/bin/env perl
#
# Author: petr.danecek@sanger
#

use strict;
use warnings;
use Carp;
use Vcf;

my $opts = parse_params();
vcf_isec($opts);

exit;

#--------------------------------

sub error
{
    my (@msg) = @_;
    if ( scalar @msg )
    {
        croak @msg;
    }
    die
        "About: Create intersections, unions, complements on bgzipped and tabix indexed VCF or tab-delimited files.\n",
        "   Note that lines from all files can be intermixed together on the output, which can yield\n",
        "   unexpected results.\n",
        "Usage: vcf-isec [OPTIONS] file1.vcf file2.vcf ...\n",
        "Options:\n",
        "   -a, --apply-filters                 Ignore lines where FILTER column is anything else than PASS or '.'\n",
        "   -c, --complement                    Output positions present in the first file but missing from the other files.\n",
        "   -d, --debug                         Debugging information\n",
        "   -f, --force                         Continue even if the script complains about differing columns, VCF versions, etc.\n",
        "   -o, --one-file-only                 Print only entries from the left-most file. Without -o, all unique positions will be printed.\n",
        "   -n, --nfiles [+-=]<int>             Output positions present in this many (=), this many or more (+), or this many or fewer (-) files.\n",
        "   -p, --prefix <path>                 If present, multiple files will be created with all possible isec combinations. (Suitable for Venn Diagram analysis.)\n",
        "   -r, --regions <list|file>           Do only the given regions (comma-separated list or one region per line in a file).\n",
        "   -t, --tab <chr:pos:file>            Tab-delimited file with indexes of chromosome and position columns. (1-based indexes)\n",
        "   -w, --win <int>                     In repetitive sequences, the same indel can be called at different positions. Consider\n",
        "                                           records this far apart as matching (be it a SNP or an indel).\n",
        "   -h, -?, --help                      This help message.\n",
        "Examples:\n",
        "   bgzip file.vcf; tabix -p vcf file.vcf.gz\n",
        "   bgzip file.tab; tabix -s 1 -b 2 -e 2 file.tab.gz\n",
        "\n";
}


sub parse_params
{
    $0 =~ s{^.+/}{}; $0 .= "($Vcf::VERSION)";
    my $opts = { positions=>0, args=>[$0, @ARGV], force=>0, split=>0, report_from_all=>1, apply_filters=>0 };
    while (defined(my $arg=shift(@ARGV)))
    {
        if ( $arg eq '-p' || $arg eq '--prefix' ) 
        { 
            my $prefix = shift(@ARGV); 
            $$opts{prefix} = init_outdir($opts,$prefix);
            $$opts{split}  = 1;
            next; 
        }
        if ( $arg eq '-f' || $arg eq '--force' ) { $$opts{force}=1; next; }
        if ( $arg eq '-a' || $arg eq '--apply-filters' ) { $$opts{apply_filters}=1; next; }
        if ( $arg eq '-r' || $arg eq '--regions' ) { $$opts{chromosomes}=shift(@ARGV); next; }
        if ( $arg eq '-o' || $arg eq '--one-file-only' ) { $$opts{report_from_all}=0; next; }
        if ( $arg eq '-c' || $arg eq '--complement' ) { $$opts{complement}=1; next; }
        if ( $arg eq '-n' || $arg eq '--nfiles' )
        {
            my $nfiles = shift(@ARGV);
            if ( !($nfiles=~/^([\-+=])(\d+)$/) ) { error("Could not parse: [$nfiles]\n"); }
            $$opts{isec_op}     = $1;
            $$opts{isec_nfiles} = $2;
            next;
        }
        if ( $arg eq '-d' || $arg eq '--debug' ) { $$opts{debug}=1; next; }
        if ( $arg eq '-w' || $arg eq '--win' ) { $$opts{win}=shift(@ARGV); next; }
        if ( $arg eq '-t' || $arg eq '--tab' ) 
        { 
            my $tab = shift(@ARGV);
            my ($chr,$pos,$file) = split(/:/,$tab);
            push @{$$opts{files}}, Reader->new(file=>$file,chr=>$chr-1,pos=>$pos-1);
            next; 
        }
        if ( -e $arg ) { push @{$$opts{files}}, $arg; next }
        if ( $arg eq '-?' || $arg eq '-h' || $arg eq '--help' ) { error(); }
        error("Unknown parameter or non-existent file \"$arg\". Run -h for help.\n");
    }
    if ( !exists($$opts{files}) ) { error("What files should be intersected?\n") }
    if ( !$$opts{force} ) { $SIG{__WARN__} = sub { error(@_); } }
    return $opts;
}

sub init_outdir
{
    my ($opts,$prefix) = @_;
    if ( $prefix=~m{/} )
    {
        # A directory should be created. This will populate dir and prefix, for example
        #   prefix  -> dir      prefix
        #   ----------------------------
        #   out                 out.dump
        #   out/       out/     out/out.dump
        #   out/xxx    out/     out/xxx.dump 
        #
        my $dir = '';
        if ( $prefix=~m{/[^/]+$} ) { $dir=$`; }
        elsif ( $prefix=~m{/([^/]+)/$} ) { $dir = $`.'/'.$1; $prefix = $dir.'/'.$1; }
        elsif ( $prefix=~m{([^/]+)/?$} ) { $dir=$1; $prefix=$dir.'/'.$1; }
        if ( $dir ) { `mkdir -p $dir`; }
    }
    return $prefix;
}

sub read_chrom_list
{
    my ($fname) = @_;
    my @chroms;
    if ( -e $fname )
    {
        open(my $chrms,'<',$fname) or error("$fname: $!");
        while (my $line=<$chrms>)
        {
            chomp($line);
            push @chroms, $line;
        }
        close($chrms);
    }
    else
    {
        @chroms = split(/,/,$fname);
    }
    return (@chroms);
}

sub check_columns
{
    my ($opts,$vcfs) = @_;

    # Do the check for VCF files only
    for (my $ivcf=0; $ivcf<@$vcfs; $ivcf++)
    {
        if ( !exists($$vcfs[$ivcf]{has_column}) ) { next; }

        for (my $jvcf=0; $jvcf<$ivcf; $jvcf++)
        {
            if ( !exists($$vcfs[$jvcf]{has_column}) ) { next; }

            if ( scalar @{$$vcfs[$ivcf]{columns}} != scalar @{$$vcfs[$jvcf]{columns}} ) 
            {
                my @icols = @{$$vcfs[$ivcf]{columns}};
                my @jcols = @{$$vcfs[$jvcf]{columns}};
                warn("Warning: The number of sample columns is different:\n",
                    (@icols>9 ? scalar @icols - 9 : 0), ": ",
                    join(',',@icols[9..$#icols]),"\n",
                    scalar @jcols - 9, ": ",
                    join(',',@jcols[9..$#jcols]),"\n",
                    );
                return;
            }

            for my $cname (keys %{$$vcfs[$ivcf]{has_column}})
            {
                if ( !exists($$vcfs[$jvcf]{has_column}{$cname}) or $$vcfs[$ivcf]{has_column}{$cname}!=$$vcfs[$jvcf]{has_column}{$cname} ) 
                { 
                    my @icols = @{$$vcfs[$ivcf]{columns}};
                    my @jcols = @{$$vcfs[$jvcf]{columns}};
                    warn("Warning: The column names do not match (e.g. $cname):\n",
                        join(',',@icols[9..$#icols]),"\n",
                        join(',',@jcols[9..$#jcols]),"\n",
                        );
                    return;
                }
            }
            for my $cname (keys %{$$vcfs[$jvcf]{has_column}})
            {
                if ( !exists($$vcfs[$ivcf]{has_column}{$cname}) ) 
                { 
                    my @icols = @{$$vcfs[$ivcf]{columns}};
                    my @jcols = @{$$vcfs[$jvcf]{columns}};
                    warn("Warning: The column names do not match (e.g. $cname):\n",
                        join(',',@icols[9..$#icols]),"\n",
                        join(',',@jcols[9..$#jcols]),"\n",
                        );
                    return;
                }
            }
        }
    }
}

sub vcf_isec
{
    my ($opts) = @_;

    $$opts{match} = {};

    # Open the VCF files and initialize the list of chromosomes
    my @vcfs;
    my (@chroms,%has_chrom);
    if ( exists($$opts{chromosomes}) ) { @chroms = read_chrom_list($$opts{chromosomes}); }

    my $source;
    my $vcf_version;
    my $vcf_version_warned;
    for (my $ifile=0; $ifile<@{$$opts{files}}; $ifile++)
    {
        my $file = $$opts{files}[$ifile];
        my ($vcf,$file_name);
        if ( ref($file) eq '' )
        {
            $vcf = Vcf->new(file=>$file);
            $file_name = $file;
        }
        else
        {
            $vcf = $file;
            $file_name = $$file{file};
        }
        $vcf->parse_header();
        $vcf->close();
        $$vcf{nread} = 0;
        push @vcfs, $vcf;

        # Check if the VCF versions are identical
        if ( ref($file) eq '' )
        {
            if ( !defined $vcf_version ) { $vcf_version = $$vcf{version} }
            if ( $vcf_version ne $$vcf{version} && !$vcf_version_warned )
            {
                warn("Warning: Mixed VCF format versions, use vcf-convert to unify.\n");
                $vcf_version_warned = 1;
            }
        }

        # Update the list of known chromosomes
        if ( !exists($$opts{chromosomes}) )
        {
            my $chrms = $vcf->get_chromosomes();
            for my $chr (@$chrms)
            {
                if ( exists($has_chrom{$chr}) ) { next; }
                $has_chrom{$chr} = 1;
                push @chroms, $chr;
            }
        }

        if ( $ifile )
        {
            # To get the missig fields filled by the default values
            if ( !$vcfs[0]{delim} )
            {
                for my $hline (@{$$vcf{header_lines}})
                {
                    $vcfs[0]->add_header_line($hline,silent=>1);
                }
            }
            $source .= ',';
        }
        $source .= "$ifile:$file_name";
        $$vcf{vcf_isec_ID} = $ifile;
    }
    check_columns($opts,\@vcfs);
    $$opts{vcfs} = \@vcfs;

    if ( !$vcfs[0]{delim} && !$$opts{split} )
    {
        $vcfs[0]->add_header_line({key=>'source',value=>join(' ',@{$$opts{args}})},append=>'timestamp');
        $vcfs[0]->add_header_line({key=>'sourceFiles',value=>$source},append=>'timestamp');
        $vcfs[0]->add_header_line({key=>'INFO',ID=>'SF',Number=>-1,Type=>'String',Description=>'Source File (index to sourceFiles, f when filtered)'},silent=>1);
        print $vcfs[0]->format_header();
    }

    # Go through all the files simultaneously and get the stats.
    for my $chr (@chroms)
    {
        # Open files
        for my $vcf (@vcfs)
        {
            delete($$vcf{last_line});
            $vcf->open(region=>$chr);
            delete($$vcf{eof});
        }
        do_chrm_isec($opts,\@vcfs);
    }

    for my $vcf (@vcfs)
    {
        if ( !$$vcf{nread} ) { warn("Warning: Read 0 lines from $$vcf{file}, the tabix index may be broken.\n"); }
    }
}


sub do_chrm_isec
{
    my ($opts,$vcfs) = @_;

    my $debug = $$opts{debug} ? 1 : 0;
    my $win   = $$opts{win} ? $$opts{win} : 0;
    my $complement = $$opts{complement} ? 1 : 0;
    my $report_from_all = $$opts{report_from_all} ? 1 : 0;
    my $nfiles = scalar @{$$opts{files}};
    my $isec_nfiles = $nfiles;
    my $isec_op     = '=';
    if ( exists($$opts{isec_nfiles}) )
    {
        $isec_nfiles = $$opts{isec_nfiles};
        $isec_op     = $$opts{isec_op};
    }
    my $split = $$opts{split};

    while (1)
    {
        my $grp = read_next_group($opts,$vcfs,$win);
        if ( !$grp || !scalar @$grp ) { last }

        if ( $debug )
        {
            print "Group:\n";
            for my $rec (@$grp) { print "$$rec{chr}\t$$rec{pos}\t$$rec{vcf}{file}\n"; }
            print "\n";
        }

        my %files; 
        my %srcs;
        for my $rec (@$grp)
        {
            my $vcf = $$rec{vcf};
            my $src = $$vcf{vcf_isec_ID};

            push @{$files{$src}}, $rec;

            if ( !$$vcf{delim} )
            {
                # This is a VCF, check filters
                my $fltr = $$rec{line}[6];
                if ( !$split && $fltr ne $$vcf{filter_passed} && $fltr ne $$vcf{defaults}{default} ) { $src .= 'f'; }
            }
            $srcs{$$rec{pos}}{$src} = $rec;
        }
        if ( $split )
        {
            write_line($opts,$grp,\%srcs);
            next;
        }
        my $nmatches = scalar keys %files;
        if ( $complement )
        {
            my $src = $$vcfs[0]{vcf_isec_ID};
            if ( !exists($files{$src}) ) { next; }
            if ( $nmatches!=1 ) { next; }
        }
        elsif ( $isec_op eq '=' && $isec_nfiles!=$nmatches ) { next; }
        elsif ( $isec_op eq '+' && $isec_nfiles>$nmatches ) { next; }
        elsif ( $isec_op eq '-' && $isec_nfiles<$nmatches ) { next; }

        # The hits are sorted by position in @$grp
        my ($prev_chr,$prev_pos,$prev_id);
        for my $rec (@$grp) 
        { 
            if ( !$report_from_all && $$rec{vcf}{vcf_isec_ID}!=0 ) { next; }
            elsif ( defined $prev_chr && $prev_chr eq $$rec{chr} && $prev_pos eq $$rec{pos} && $prev_id ne $$rec{vcf}{vcf_isec_ID} ) { next; }

            if ( !$$rec{vcf}{delim} )
            {
                # This is a VCF file, add annotation
                my @tags = split(/;/,$$rec{line}[7]);
                my $i;
                for ($i=0; $i<@tags; $i++)
                {
                    if ( $tags[$i] eq '.' or $tags[$i]=~/^SF=/ ) { last; }
                }
                my $src = join(',',sort keys %{$srcs{$$rec{pos}}});
                $tags[$i] = 'SF='.$src;
                $$rec{line}[7] = join(';',@tags);
                print join("\t",@{$$rec{line}}) . "\n";
            }
            else
            {
                print $$rec{line};
            }

            $prev_chr = $$rec{chr};
            $prev_pos = $$rec{pos};
            $prev_id  = $$rec{vcf}{vcf_isec_ID};
        }
    }
}

sub write_line
{
    my ($opts,$grp,$srcs) = @_;
    for my $hash (values %$srcs)
    {
        my $src = join('_',sort keys %$hash);
        if ( !exists($$opts{out_files}{$src}) )
        {
            my $id  = (sort keys %$hash)[0];
            my $vcf = $$opts{vcfs}[$id];
            $$opts{out_vcfs}{$src} = $vcf;
            $$opts{out_recs}{$src} = $id;
            open($$opts{out_files}{$src},"| bgzip -c > $$opts{prefix}$src.vcf.gz") or error("| bgzip -c > $$opts{prefix}$src.vcf.gz: $!");

            if ( !exists($$opts{readme_fh}) ) 
            { 
                open($$opts{readme_fh},'>',"$$opts{prefix}_README") or error("$$opts{prefix}_README: $!"); 
                print {$$opts{readme_fh}} "# This file was produced by vcf-isec. The command line was:\n#\t",join(' ',@{$$opts{args}}),"\n#\n";
            }
            print {$$opts{readme_fh}} "Using file '$$opts{prefix}$src.vcf.gz' for records present in:\n";
            for my $rec (sort values %$hash)
            {
                print {$$opts{readme_fh}} "\t$$rec{vcf}{file}\n";
            }
            if ( !$$vcf{delim} )
            {
                my $fnames = join(',',sort values %$hash);
                $vcf->add_header_line({key=>'source',value=>join(' ',@{$$opts{args}})},append=>'timestamp');
                $vcf->add_header_line({key=>'sourceFiles',value=>$fnames},append=>'timestamp');
                print {$$opts{out_files}{$src}} $vcf->format_header();
            }
        }
    }

#use Data::Dumper; print Dumper($srcs);
    for my $pos (keys %$srcs)
    {
        my $src  = join('_',sort keys %{$$srcs{$pos}});
        my $fh   = $$opts{out_files}{$src};
        my $irec = $$opts{out_recs}{$src};
        my $vcf  = $$opts{out_vcfs}{$src};
        my $rec  = $$srcs{$pos}{$irec};

        if ( !$$vcf{delim} )
        {
            print $fh join("\t",@{$$rec{line}}) . "\n";
        }
        else
        {
            print $fh $$rec{line};
        }
    }
}

sub read_next_group
{
    my ($opts,$vcfs,$win) = @_;

    my @grp;
    my $prev_vcf;
    my $start;

    while (1)
    {
        my $min_vcf = get_min_position($opts,$vcfs);

        # No more lines in the buffer?
        if ( !$min_vcf ) { last; }

        # Nothing new has been added?
        if ( $prev_vcf && $prev_vcf eq $$min_vcf{buf}[0] ) { last; }
        $prev_vcf = $$min_vcf{buf}[0];

        # Read everything what falls in the window. The window moves to encompass complete clusters.
        if ( !$start or $start+$win >= $$min_vcf{buf}[0]{pos} )
        {
            my $rec = shift(@{$$min_vcf{buf}});
            push @grp,$rec;

            $start = $$rec{pos};
            next; 
        }
    }
    return \@grp;
}

# Return the minimum position across all opened files. If there is no line in the file's buffer, 
#   advance to the next line. 
sub get_min_position
{
    my ($opts,$vcfs) = @_;

    my ($min_pos,$min_vcf);
    for my $vcf (@$vcfs)
    {
        # Check if there is a line in the buffer, if not, read. If still empty, the file reached eof
        if ( !$$vcf{buf} or !scalar @{$$vcf{buf}} ) { read_line($opts,$vcf); }
        if ( !$$vcf{buf} or !scalar @{$$vcf{buf}} ) { next; }

        my $line = $$vcf{buf}[0];

        # Designate this position as the minimum of all the files if:
        # .. is this the first file?
        if ( !$min_pos )
        {
            $min_pos = $$line{pos};
            $min_vcf = $vcf;
            next;
        }

        # .. has this file lower position?
        if ( $min_pos>$$line{pos} )
        {
            $min_pos = $$line{pos};
            $min_vcf = $vcf;
            next;
        }
    }
    return $min_vcf;
}

# Read one line from a VCF or Reader, split it and save it to a buffer.
sub read_line
{
    my ($opts,$vcf) = @_;

    if ( $$vcf{eof} ) { return; }

    my $line = $vcf->next_line();
    if ( !$line )
    {
        $$vcf{eof} = 1;
        return;
    }

    $$vcf{nread}++;

    my ($chr,$pos,$ref,$alt);
    if ( $$vcf{delim} )
    {
        my @items = split($$vcf{delim},$line);

        # Reader object
        $chr  = $items[$$vcf{chr}];
        $pos  = $items[$$vcf{pos}];
        $ref  = '';
        $alt  = '';
    }
    else
    {
        # We are reading VCF, not a tab-delimited file. Apply filters when requested.
        my @items = split(/\t/,$line);
        while ( $$opts{apply_filters} && $items[6] ne 'PASS' && $items[6] ne '.' )
        {
            $line = $vcf->next_line();
            if ( !$line )
            {
                $$vcf{eof} = 1;
                return;
            }
            @items = split(/\t/,$line);
        }
        chomp($items[-1]);
        $chr  = $items[0];
        $pos  = $items[1];
        $ref  = $items[3];
        $alt  = $items[4];
        $line = \@items;
    }
    if ( $$vcf{buf} && @{$$vcf{buf}} )
    {
        my $prev = $$vcf{buf}[-1];
        if ( $$prev{pos} == $pos ) { warn("Position $chr:$pos appeared twice in $$vcf{file}\n"); }
    }

    push @{$$vcf{buf}}, { chr=>$chr, pos=>$pos, ref=>$ref, alt=>$alt, line=>$line, vcf=>$vcf };
    return;
}


#---------------------------------

package Reader;

use strict;
use warnings;
use Carp;

sub new
{
    my ($class,@args) = @_;
    my $self = @args ? {@args} : {};
    bless $self, ref($class) || $class;
    if ( $$self{cmd} ) 
    { 
        $$self{file} = '';
        open($$self{fh},$$self{cmd}) or $self->throw("$$self{cmd}: $!"); 
    }
    if ( !$$self{file} && !$$self{fh} ) { $self->throw("Expected the file or fh option.\n"); }
    if ( !$$self{delim} ) { $$self{delim} = qr/\t/; }
    if ( !$$self{chr} ) { $$self{chr} = 0; }    # the index of the chromosome column (indexed from 0)
    if ( !$$self{pos} ) { $$self{pos} = 1; }    # the index of the position column 
    return $self;
}

sub throw
{
    my ($self,@msg) = @_;
    confess @msg;
}

sub open
{
    my ($self,%args) = @_;
    if ( !$$self{file} ) { $self->throw(qq[The parameter "file" not set.\n]); }
    $self->close();
    if ( $$self{file}=~/\.gz$/i ) 
    { 
        if ( exists($args{region}) && defined($args{region}) )
        {
            open($$self{fh},"tabix $$self{file} $args{region} |") or $self->throw("tabix $$self{file}: $!");
        }
        else
        {
            open($$self{fh},"gunzip -c $$self{file} |") or $self->throw("gunzip -c $$self{file} |: $!"); 
        }
    }
    else
    {
        open($$self{fh},'<',$$self{file}) or $self->throw("$$self{file}: $!");
    }
}

sub close
{
    my ($self) = @_;
    if ( !$$self{fh} ) { return; }
    close($$self{fh});
    delete($$self{fh});
    delete($$self{buffer});
}

sub _unread_line
{
    my ($self,$line) = @_;
    unshift @{$$self{buffer}}, $line;
    return;
}

sub next_line
{
    my ($self) = @_;
    my $line;
    if ( $$self{buffer} && @{$$self{buffer}} ) { return shift(@{$$self{buffer}}); }
    return readline($$self{fh}); 
}

sub parse_header
{
    my ($self) = @_;
    $self->open();
    while (1)
    {
        my $line = $self->next_line();
        if ( !$line ) { last; }
        if ( $line=~/^#/ ) { push @{$$self{header}},$line; next; }
        $self->_unread_line($line);
        last;
    }
}

sub format_header
{
    my ($self) = @_;
    if ( $$self{header} ) { return join('',@{$$self{header}}); }
    return '';
}

sub get_chromosomes
{
    my ($self) = @_;
    if ( !$$self{file} ) { $self->throw(qq[The parameter "file" not set.\n]); }
    my (@out) = `tabix -l $$self{file}`;
    if ( $? )
    {
        $self->throw(qq[The command "tabix -l $$self{file}" exited with an error. Is the file tabix indexed?\n]);
    }
    for (my $i=0; $i<@out; $i++) { chomp($out[$i]); }
    return \@out;
}