Remove Duplicate Text Lines

1. Open terminal and go to the folder of the file
cd /path_to_the_file
2. Remove dublicates (e.g from file1.txt)
sort file1.txt | uniq > file2.txt

http://www.cyberciti.biz/faq/unix-linux-shell-removing-duplicate-lines/

“A.. You need to use shell pipes along with following two utilities:

a] sort command – sort lines of text files

b] uniq command – report or omit repeated lines
Removing Duplicate Lines With Sort, Uniq and Shell Pipes

Use the following syntax:
sort {file-name} | uniq -u
sort file.log | uniq -u

Here is a sample test file called garbage.txt:
this is a test
food that are killing you
wings of fire
we hope that the labor spent in creating this software
this is a test
unix ips as well as enjoy our blog

Type the following command to get rid of all duplicate lines:
$ sort garbage.txt | uniq -u

Sample output:
food that are killing you
unix ips as well as enjoy our blog
we hope that the labor spent in creating this software
wings of fire

Where,
-u : check for strict ordering, remove all duplicate lines.