uniq:tldr:21d52

This command performs a series of operations on the contents of the file specified by the variable ${filename}.

1. sort ${filename}: This command sorts the lines in the file in ascending order. The ${filename} variable represents the name of the file.

2. uniq -c: This command eliminates adjacent duplicates and displays only unique lines. The -c option also reports the number of occurrences of each unique line.

3. sort -nr: This final command sorts the lines again, but this time in descending order (-r option) based on the count of occurrences (-n option), which was added by the previous uniq -c command.

In summary, this command sorts the lines in the file, removes duplicate lines, and then sorts the unique lines in descending order of their occurrence count.