They really, really aren’t. Let’s take a look at this command together:

curl -L [some url goes here] | tar -xz

Sorry the formatting's a bit messy, Lemmy's not having a good day today

This command will start to extract the tar file while it is being downloaded, saving both time (since you don’t have to wait for the entire file to finish downloading before you start the extraction) and disk space (since you don’t have to store the .tar file on disk, even temporarily).

Let’s break down what these scary-looking command line flags do. They aren’t so scary once you get used to them, though. We’re not scared of the command line. What are we, Windows users?

• curl -L – tells curl to follow 3XX redirects (which it does not do by default – if the URL you paste into cURL is a URL that redirects (GitHub release links famously do), and you don’t specify -L, it’ll spit out the HTML of the redirect page, which browsers never normally show)
• tar -x – eXtract the tar file (other tar “command” flags, of which you must specify exactly one, include -c for Creating a tar file, and -t for Testing a tar file (i.e. listing all of the filenames in it and making sure their checksums are okay))
• tar -z – tells tar that its input is gzip compressed (the default is not compressed at all, which with tar is an option) – you can also use -j for bzip2 and -J for xz
• tar -f which you may be familiar with but which we don’t use here – -f tells tar which file you want it to read from (or write to, if you’re creating a file). tar -xf somefile.tar will extract from somefile.tar. If you don’t specify -f at all, as we do here, tar will default to reading the file from stdin (or writing a tar file to stdout if you told it to create). tar -xf somefile.tar (or tar -xzf somefile.tar.gz if your file is gzipped) is exactly equivalent to cat somefile.tar.gz | tar -xz (or tar -xz < somefile.tar – why use cat to do something your shell has built-in?)
• tar -v which you may be familiar with but which we don’t use here – tells tar to print each filename as it extracts the file. If you want to do this, you can, but I’d recommend telling curl to shut up so it doesn’t mess up the terminal trying to show download progress also: curl -L --silent [your URL] | tar -xvz (or -xzv, tar doesn’t care about the order)

You may have noticed also that in the first command I showed, I didn’t put a - in front of the arguments to tar. This is because the tar command is so old that it takes its arguments BSD style, and will interpret its first argument as a set of flags regardless of whether there’s a dash in front of them or not. tar -xz and tar xz are exactly equivalent. tar does not care.