Answer by Kamil Maciorowski for Linux, How to cleanup random duplicates?

<b.txt uniq

The uniq utility shall read an input file comparing adjacent lines, and write one copy of each input line on the output. The second and succeeding copies of repeated adjacent input lines shall not be written. The trailing <newline> of each line in the input shall be ignored when doing comparisons.

Repeated lines in the input shall not be detected if they are not adjacent.

^(source)