Here are some useful examples of rar and unrar usage under Linux shell. 

To create a rar archive archive.rar containing directory called folder_to_be_rared, use the following command:

rar a archive.rar folder_to_be_rared/

To create a rar archive archive.rar containing files file1.dat, file2.dat, file3.dat, use:

rar a archive.rar file1.dat file2.dat file3.dat

or, more general:

rar a archive.rar file?.dat

or 

rar a archive.rar . 

To create a password protected rar archive archive.rar with password set to password, use:

rar a -ppassword archive.rar folder_to_be_rared/ 

To create a password protected rar archive archive.rar with password set to password, where even file lists are encrypted, use:

rar a -hppassword archive.rar folder_to_be_rared/ 

To create a rar archive that splits the file/files into multiple parts of equal size, use:

rar a -v50M -R archive.rar folder_to_be_rared/

-v50M : determine the size of each file in split archive, in this example you get files with size 50MB (if you wanted files of 512kB size you would write -v512k)

To create a rar archive with a specified compression level (0-5):

rar a -m0 archive.rar folder_to_be_rared/

-m0 : use a compression level of 0 (store only)
This will save a significant amount of time and processing power for you and other users on your server. 
-m3: this is the default compression level

To create a rar archive with files of 200MB and with some other compression settings (got this from a scener)

rar a filename.rar -r -m0 -vn -md4096 -ep1 -v200000000b $DIR

-r : Recurse subdirectories.
-m0 : compression level (0-store / 3-default / 5-best)
-vn: Use the old style volume naming scheme, where the first volume file in a multi-volume set has the extension .rar, following volumes are numbered from .r00 to .r99.
-md4096 : dictionary size in Kb (64,128,256,512,1024,2048,4097  or a,b,c,d,e,f,g)
-ep1:  Exclude base dir from names
-v200000000b : split rar files in 200000000b (200mb) files

To extract rar archive archive.rar, use:

unrar e archive.rar 

This will uncompress the archive in the current directory, without creating a new folder. If you want to uncompress the archive with a full path, use the option x:

unrar x archive.rar 

To find and extract all rar archives in . path and redirect outputs to unrar.log log file, use:

find . -name '*.rar' -print0 | xargs -I{} -0 -n 1 unrar e -y '{}' >unrar.log 2>&1

You can read the manual for more options:

man rar

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