Hello Efstathios,

Yes, you should be able to cat together BGZF files and have a
valid BGZF file. (Likewise you should be able to cat together
any gzipped files and have a valid gzip file).

However, there are two important provisos. First, the internal
data format must allow concatenation (e.g. you cannot cat
together two BAM files since that would result in an extra
header in the middle of the data). Second, some tools fail
to cope with concatenated gzip block (e.g. some Java
libraries break).

Can you reproduce this with a public sample VCF file?

Peter

On Wed, May 13, 2015 at 12:17 PM, Kanterakis, Efstathios
<ekantera...@illumina.com> wrote:
> Hello,
> The following routine seems to produce invalid tabix indices (samtools 1.2):
> zgrep '^chr1' some.vcf.gz > chr1.vcf
> zgrep '^chr2' some.vcf.gz > chr2.vcf
> zgrep '^#' some.vcf.gz > header.vcf
> cat header.vcf chr1.vcf > chr1_h.vcf
> bgzip chr1_h.vcf
> bgzip chr2.vcf
> cat chr1_h.vcf.gz chr2.vcf.gz > test.vcf.gz
> tabix test.vcf.gz
> tabix test.vcf.gz chr2 # blank
> tabix test.vcf.gz chr1 # works
>
> bgzip -d test.vcf.gz
> bgzip test.vcf
> tabix test.vcf.gz
> tabix test.vcf.gz chr2 # works now
>
> I was under the impression that bgzipped files are directly cat'able. Is this 
> a bug?
>
> Thank you,
> Stathis

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