RAR  is a file format designed to archive files with compression

UNRAR is a used extract files from rar archive data

How to install rar and unrar commands?

Option : 1

32 Bit:

http://pkgs.repoforge.org/rpmforge-release/rpmforge-release-0.5.3-1.el6.rf.i686.rpm

64 Bit:
 
http://pkgs.repoforge.org/rpmforge-release/rpmforge-release-0.5.3-1.el6.rf.x86_64.rpm

Install the file and execute yum command to install these commands
 
# rpm –ivh rpmforge-release-0.5.3-1.el6.rf.x86_64.rpm

#yum install rar unrar
...
--> Running transaction check
---> Package rar.x86_64 0:3.8.0-1.el6.rf will be installed
---> Package unrar.x86_64 0:5.0.3-1.el6.rf will be installed
...
Installed:
  rar.x86_64 0:3.8.0-1.el6.rf           unrar.x86_64 0:5.0.3-1.el6.rf               

Option 2:

Would you wish to install by RPM file, download the packages with any version from the below URL,
 
http://pkgs.repoforge.org/unrar/
http://pkgs.repoforge.org/rar/

Install rar (or) unrar using below command,
 
rpm  [ install-options ]

For example:
 
# rpm -ivh unrar-3.6.2-1.el2.rf.i386.rpm

-i => Install package
-v => shows verbose information probably progress messages will be displayed.
-h => unpacked the package archive file, if you will use with -v option

Install rar and unrar in Ubuntu / Debian ?
 
# sudo apt-get update
# sudo apt-get install rar

Ubuntu does not find the packages, You need to enable multiverse repositories.
To enable multiverse, run the command in root privilege
 
#sudo software-properties-gtk

On Ubuntu software menu => Software restructed by copyright or legal issue(multiverse)
There you'll need to make sure it is selected.

Then, try  to execute the same commands again.

How to use rar and unrar commands?
unrar usage:

  e      Extract files to current directory.

   l      List out archive content.

   x      Extract files.

rar usage :

   a      Add files to archive.

   d       Delete files from archive.

   r       Repair archive

   u      Update files in archive

rar a file :
 
# rar  a  myfile.rar   MYFILE/

RAR 3.80   Copyright (c) 1993-2008 Alexander Roshal   16 Sep 2008
Shareware version         Type RAR -? for help

Evaluation copy. Please register.
Creating archive myfile.rar
Adding    MYFILE/MANIFEST.MF                                          OK
Adding    MYFILE/13NU.SF                                              OK
Adding    MYFILE/13NU.RSA                                             OK
Done

do you want to update existing rar file :
 
# rar u myfile.rar MYFILE
RAR 3.80   Copyright (c) 1993-2008 Alexander Roshal   16 Sep 2008
Shareware version         Type RAR -? for help
Evaluation copy. Please register.
Updating archive myfile.rar
Adding    MYFILE                                                      OK
Done

rar file with password :
 
# rar a –pmyfile  myfile.rar MYFILE/

List out archive file:
 
# unrar l myfile.rar
UNRAR 5.00 beta 3 freeware      Copyright (c) 1993-2013 Alexander Roshal
Archive: myfile.rar
Details: RAR 4

 Attributes      Size    Date   Time   Name
----------- ---------  -------- -----  ----
*-rw-r--r--      1221  06-08-13 06:59  MYFILE\MANIFEST.MF
*-rw-r--r--      1383  06-08-13 06:59  MYFILE\13NU.SF
*-rw-r--r--      6951  06-08-13 06:59  MYFILE\13NU.RSA
 drwxr-xr-x         0  14-06-14 14:52  MYFILE      
----------- ---------  -------- -----  ----
                 9555                  4

Extract the archive file:
 
# unrar x myfile.rar
UNRAR 5.00 beta 3 freeware      Copyright (c) 1993-2013 Alexander Roshal
Extracting from myfile.rar
Enter password (will not be echoed) for MYFILE\MANIFEST.MF:  (give password)
Extracting  MYFILE\MANIFEST.MF                                        OK
MYFILE\13NU.SF - use current password ? [Y]es, [N]o, [A]ll A

Extracting  MYFILE\13NU.SF                                             OK
Extracting  MYFILE\13NU.RSA                                           OK
Creating    MYFILE                                                             OK
All OK

Error :

If you may get an error while install rpm?  You'll probably get an error like this:
 
# rpm -ivh unrar-3.6.2-1.el2.rf.i386.rpm

error: Failed dependencies:
    libstdc++-libc6.2-2.so.3 is needed by unrar-3.6.2-1.el2.rf.i386

# yum install libstdc++-libc6.2-2.so.3

Once installed support packages then try to install again,