remove duplicate lines in linux

Always starting with sort, then uniq command. 

Attention: uniq -d to only print duplicate lines, and uniq -u to only print unique lines

Given data.txt
79417701
79417701
79417701
88341001
88341001
88341001
88341001

cat data.txt | sort | uniq -d to print
79417701
88341001


cat data.txt | sort | uniq -u to print
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