Genozip has two separate capabilities of aggregating files, each with its pros and cons:

1. tar with –tar

Using the genozip --tar option, genozip compresses files directly into a standard tar file.

Each file is compressed independently and written directly into a standard tar file as it is being formed. This is faster and consumes less disk space than first genozipping files and then packaging them into a tar file, since no separate .genozip files are created - just the tar file.

Example 1:

> # Compressing
> genozip --tar mydata.tar sample1.bam sample2.bam variants.vcf

> # Listing the contents of the tar file
> tar tvf mydata.tar
-rw-rw-rw- USER/USER   3424847 2021-06-01 11:34 sample1.bam.genozip
-rw-rw-rw- USER/USER   6765323 2021-03-04 22:04 sample2.bam.genozip
-rw-rw-rw- USER/USER    765323 2021-03-04 22:08 variants.vcf.genozip

> # Unarchiving and decompressing all files
> tar xvf mydata.tar |& genounzip --files-from - --replace

Example 2: compress all files in a directory and its sub-directories, using --subdirs:

> genozip --tar mydata.tar --subdirs my-data-dir

Example 3: compress and archive all BAM files in the current directory and its sub-directories, preserving the directory struture:

> find . -name "*.bam" | genozip --tar mydata.tar -T-

Implementation note: Genozip implements the IEEE 1003.1-1988 (“ustar”) standard of tar files, with the size field in binary format for files 8GB or larger. The GNU-tar LongLink extension is used for file names longer than 99 characters. This is compatible with most modern tar implementations, including GNU tar.

2. Binding with –output

Binding files only works for files that are similar:
- The files must be of the same type (eg VCF, SAM/BAM, FASTQ etc)
- In case of VCF files: they must have the same samples
- In case of SAM/BAM files: they must have identical @SQ header lines (contigs).

Unlike --tar, binding does not record the directory structure.

Unlike tar that merely aggregates files, binding leverages similarities and data redundancies between files to improve compression - typically, the size of a bound file is smaller than the combined sizes of files compressed separately.

Binding also allows analyzing the combined file as a concatenated data set.


> # binding
> genozip chr1.vcf chr2.vcf --output variants.vcf.genozip

> # unbinding back to the original files
> genounzip variants.vcf.genozip

> # viewing the concatenated data
> genocat variants.vcf.genozip

> # extracting the first component (chr1.vcf in this case) from the bound file
> genocat --component 1 variants.vcf.genozip

> # listing the components of a bound file
> genols variants.vcf.genozip

In the following example, we bind all the BAM files in the current directory:

> # binding
> genozip *.bam --output mydata.bam.genozip

> # unbinding back to the original files
> genounzip mydata.bam.genozip

> # unbinding into a different directory
> genounzip mydata.bam.genozip --prefix=mydir/