Article 6QXMY unique sorted search from text file

unique sorted search from text file

by
MakeTopSite
from LinuxQuestions.org on (#6QXMY)
Code:$ cat file.txt
word4 word2
word4 word2
word3 word1
word1 word3
$How can I please get this output from file.txt ?
Code:word1
word2
word3
word4
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