How use Uniq Command in Linux

Uniq command is mostly used in combination with sort command, as uniq
removes duplicates only from a sorted file. i.e In order for uniq to work, all
the duplicate entries should be in the adjacent lines. Following are some
common examples.

1. When you have an employee file with duplicate entries, you can do the
following to remove duplicates.
$ sort namesd.txt | uniq
$ sort –u namesd.txt

2. If you want to know how many lines are duplicates, do the following. The
first field in the following examples indicates how many duplicates where
found for that particular line. So, in this example the lines beginning with
Alex and Emma were found twice in the namesd.txt file.
$ sort namesd.txt | uniq –c
2
2
1
1
1
Alex Jason:200:Sales
Emma Thomas:100:Marketing
Madison Randy:300:Product Development
Nisha Singh:500:Sales
Sanjay Gupta:400:Support
3. The following displays only the entries that are duplicates.
$ sort namesd.txt | uniq –cd
2 Alex Jason:200:Sales
2 Emma Thomas:100:Marketing