To Join/Merge Multiple Files into One with a Command from Terminal Simply Execute:
su -
cd path/To/YourArchive
cat * > yourUnifiedFile.xxx
Example
Suppose that you have a Directory with Path “/home/myself/multiarchive”:
cd /home/myself/multiarchive
Containing the following Files:
myFile.rar.1
myFile.rar.2
myFile.rar.3
To Join them into One perform:
cat * > myFile.rar
.