in Linux, Ubuntu

How do you gunzip a file and keep the .gz file?

You’re looking for:

gzcat x.txt.gz >x.txt

The gzcat command is equivalent to gunzip -c which simply writes the output stream to stdout. This will leave the compressed file untouched. So you can also use:

gunzip -c x.txt.gz >x.txt

Note that on some systems gzcat is also known as zcat so run like this instead:

zcat x.txt.gz >x.txt