mjhjmtu

I'd like to download, and extract an archive under a given directory. Here is how I've been doing it so far:

wget http://downloads.mysql.com/source/dbt2-0.37.50.3.tar.gz
tar zxf dbt2-0.37.50.3.tar.gz
mv dbt2-0.37.50.3 dbt2

I'd like instead to download and extract the archive on the fly, without having the tar.gz written to the disk. I think this is possible by piping the output of wget to tar, and giving tar a target, but in practice I don't know how to put the pieces together.

You can do it by telling wget to output its payload to stdout (with flag -O-) and supress its own output (with flag -q):

wget -qO- your_link_here | tar xvz -

To specify a target directory:

wget -qO- your_link_here | tar xvz - -C /target/directory

Update

If you happen to have GNU tar

wget -qO- your_link_here | tar --transform 's/^dbt2-0.37.50.3/dbt2/' -xvz

should allow you to do it all in one step.

-q quiet

-O - output to stdout

This oneliner does the trick:

tar xvzf -C /tmp/ < <(wget -q -O - http://foo.com/myfile.tar.gz)

short explanation:
the right side in the parenthesis is executed first (-q tells wget to do it quietly, -O - is used to write the output to stdout).

Then we create a named pipe using the process substitution operator from Bash <( to create a named pipe.
This way we create a temporary file descriptor and then direct the contents of that descriptor to tar using the < file redirection operator.

Another option is to use curl which writes to stdout by default:

curl -s some_url | tar xvz -C /tmp