Use find:

find . -exec gunzip '{}' +

or you can look explicitly for files that have not been gunzipped yet:

find . -name \*.gz -exec gunzip '{}' +

Those will do it for everything in the current directory and below. If you want to restrict it to the current directory, add -maxdepth 1 to the options.

The single quotes around the braces are so that spaces in file and directory names are properly handled. That is why xargs will have issues when trying to solve problems like this.

How about just this?

$ gunzip *.txt.gz

gunzip will create a gunzipped file without the .gz suffix and remove the original file by default (see below for details). *.txt.gz will be expanded by your shell to all the files matching.

This last bit can get you into trouble if it expands to a very long list of files. In that case, try using find and -exec to do the job for you.

From the man page gzip(1):

gunzip takes a list of files on its command line and  replaces  each  file
whose  name  ends  with  .gz, -gz, .z, -z, or _z (ignoring case) and which
begins with the correct magic number with an uncompressed file without the
original  extension.

Note about 'original name'

gzip can store and restore the filename used at compression time. Even if you rename the compressed file, you can be surprised to find out it restores to the original name again.

From the gzip manpage:

By default, gzip keeps the original file name and timestamp in the compressed file. These are used when decompressing the file with the -N option. This is useful when the compressed file name was truncated or when the time stamp was not preserved after a file transfer.

And these file names stored in metadata can also be viewed with file:

$ echo "foo" > myfile_orig
$ gzip myfile_orig 
$ mv myfile_orig.gz myfile_new.gz 
$ file myfile_new.gz 
myfile_new.gz: gzip compressed data, was "myfile_orig", last modified: Mon Aug  5 08:46:39 2019, from Unix
$ gunzip myfile_new.gz        # gunzip without -N
$ ls myfile_*
myfile_new

$ rm myfile_*
$ echo "foo" > myfile_orig
$ gzip myfile_orig
$ mv myfile_orig.gz myfile_new.gz 
# gunzip with -N
$ gunzip -N myfile_new.gz     # gunzip with -N
$ ls myfile_*
myfile_orig

You can use below command.

Go to the directory where your .gz file is and run command:

for f in *.gz ; do gunzip -c "$f" > /home/$USER/"${f%.*}" ; done

It will extract all file with original name and store it to current user home directory(/home/username). You can change it to somewhere else.

EDIT :

gunzip *.gz

This command also will work. But, by default, it replaces original file.

If you want, for each of those, to launch "gzip -d" on them:

cd theparentdir && gzip -d $(find ./ -type f -name '*.gz')

and then, to gzip them back:

cd theparentdir && gzip $(find ./ -type f -name '*.csv')

This will however choke in many cases

• if filenames have some special characters (spaces, tabs, newline, etc) in them
• other similar cases
• or if there are TOO MANY files to be put after the gzip command!

A solution would be instead, if you have GNU find, to do :

find ... -print0 | xarsg -0 gzip -d # for the gunzip one, but still choke on files with "newline" in them

Another (arguably better?) solution, if you have GNU find at your disposal:

cd theparentdir && find ./ -type f -name '*.gz' -exec gzip -d '{}' '+'

and to re-zip all csv in that parentdir & all subdirs:

cd theparentdir && find ./ -type f -name '*.csv' -exec gzip '{}' '+'

"+" tells GNU find to try to put as many found files as it can on each gzip invocation (instead of doing 1 gzip incocation per file, very very ressource intensive and very innefficient and slow), similar to xargs, but with some benefits (1 command only, no pipe needed)

This should do it:

gunzip *.gz

gunzip file.txt.gz in Terminal.