awk -F: '{print $4}'

• awk - this is the interpreter for the AWK Programming Language. The AWK language is useful for manipulation of data files,
  text retrieval and processing


• -F <value> - tells awk what field separator to use. In your case, -F: means that the separator is : (colon).


• '{print $4}' means print the fourth field (the fields being separated by :).

Example:

Let's say that there's a file called test, and it contains the following:

Hello:my:name:is:Alaa

If we execute the command awk -F: '{print $4}' test, the output will be:

is

Because is is the fourth field.

      field1   field3  field5

       -----    ----    ----

       |   |    |  |    |  |

       Hello:my:name:is:Alaa

             ||      ||

             --      --

           field2  field4