Question: How do I uncompress a *.7z file ( 7zip file ) in UNIX/Linux ?Can you explain with a simple example?
Answer: Use 7za command to unzip a 7z file ( 7zip file ) on Unix platform as shown below.

Verify whether you have 7za command on your system.

# whereis 7za
7za: /usr/bin/7za /usr/share/man/man1/7za.1.gz

If you don’t have 7za command, install p7zip package as shown below.
Install p7zip to unzip *.7z files on Fedora

# yum install p7zip

Install p7zip to unzip *.7z files on Debian and Ubuntu

$ sudo apt-get install p7zip

Uncompressing a *.7z 7zip files in Linux using 7za

$ 7za e myfiles.7z 

7-Zip (A) 9.04 beta  Copyright (c) 1999-2009 Igor Pavlov  2009-05-30
p7zip Version 9.04 (locale=C,Utf16=off,HugeFiles=on,1 CPU)

Processing archive: ../../myfiles.7z

Extracting  myfiles/test1
Extracting  myfiles/test2
Extracting  myfiles/test
Extracting  myfiles

Everything is Ok

Folders: 1
Files: 3
Size:       7880
Compressed: 404

7za – command namee – specifies the 7z to be extractedmyfiles.7z – is the file that is to be extracted
Creating a 7zip compression file in Linux

$ 7za a myfiles.7z myfiles/

7-Zip (A) 9.04 beta  Copyright (c) 1999-2009 Igor Pavlov  2009-05-30
p7zip Version 9.04 (locale=C,Utf16=off,HugeFiles=on,1 CPU)
Scanning

Creating archive myfiles.7z

Compressing  myfiles/test1
Compressing  myfiles/test2      

Everything is Ok

Files and sub directories of myfiles/ will be added to the myfiles.7z.
a – add to archivefile.7z – archive file to which these files and dir from dir1 will be added to.