sort and uniq in pipelines in Bash Scripting - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the sort command do in a pipeline?

The sort command arranges lines of text in order, usually alphabetically or numerically, making it easier to find duplicates or organize data.

beginner

What is the purpose of the uniq command in a pipeline?

The uniq command filters out repeated adjacent lines, showing only unique lines. It works best when input is sorted first.

beginner

Why do we usually use sort before uniq in pipelines?

Because uniq only removes duplicates that are next to each other, sorting first groups duplicates together so uniq can remove them properly.

intermediate

How can you count how many times each unique line appears using sort and uniq?

Use sort | uniq -c. The -c option tells uniq to prefix each unique line with the number of times it appears.

beginner

What will the command cat file.txt | sort | uniq do?

It will read the file file.txt, sort all lines alphabetically, then remove any duplicate lines, showing only unique sorted lines.

Why should you use sort before uniq in a pipeline?

A Because <code>uniq</code> sorts the lines automatically

B Because <code>sort</code> removes duplicates

C Because <code>uniq</code> only removes adjacent duplicate lines

D Because <code>sort</code> counts duplicates

uniq only removes duplicates if they are next to each other. Sorting first groups duplicates together so uniq can remove them.

What does the command sort file.txt | uniq -c do?

A Sorts lines and counts how many times each unique line appears

B Sorts lines and removes all duplicates without counting

C Counts lines without sorting

D Removes duplicates but does not sort

The -c option with uniq counts occurrences of each unique line after sorting.

What happens if you run uniq file.txt without sorting first?

A Only adjacent duplicate lines are removed

B All duplicates in the file are removed

C The file is sorted automatically

D The command will fail

uniq only removes duplicates that are next to each other, so unsorted duplicates remain.

Which command pipeline shows unique lines sorted alphabetically?

A <code>sort file.txt | uniq -c</code>

B <code>cat file.txt | uniq | sort</code>

C <code>uniq file.txt | sort</code>

D <code>cat file.txt | sort | uniq</code>

Sorting first then applying uniq ensures duplicates are removed and lines are sorted.

What does the -c option do with uniq?

A Removes all lines

B Counts occurrences of each unique line

C Sorts the lines

D Changes the case of lines

The -c option prefixes each unique line with the count of how many times it appears.

Explain why sorting is important before using uniq in a pipeline.

Think about how <code>uniq</code> works with lines next to each other.

Describe how to count the number of times each unique line appears in a text file using bash commands.

Combine sort and uniq with a special option.