How to unzip a .vw.gz file in linux?

How can I unzip a .vw.gz file in Linux? tar -xvf filename throws errors.

.gz is a gzipped file and is not related to tar. You do, more often than not, see a tarred and gzipped file that is first tarred, then gzipped (like somfile.tar.gz) but those are two seperate operations that are supported by a single tar command.

To unzip a gzipped file you use the gunzip command.

gunzip filename.vw.gz

The confusion here is that many of us are used to .zip files. zip fulfills two needs.

1. The need to put multiple files into a single file (archive)
2. The need to compress the file/archive.

tar is an archiving program. If you check out it's manpage in Ubuntu man tar you'll see:

tar — The GNU version of the tar archiving utility

gzip is a compression program. It's manpage man gzip reads:

gzip, gunzip, zcat - compress or expand files

So in this case we have two programs to compress and archive.

The other confusing bit is that we almost always use the tar command to do both archiving and compressing, but you'll see in it's manpage that you can specify the compression program to use. For instance we can compress in tar using the bzip compression algorithm:

tar -jcvf archive_name.tar.bz2 /path/to/some/dir