unix-pipeline-solutions.md

Unix Pipeline Solutions

Here are some solutions to the Unix pipeline exercise. These are not the only solutions. You might have found others that work just as well. There are often several ways to obtain the same result by chaining different Unix programs into different pipelines.

• Count the number of lines and characters in the text

  Solution:

  $> cat rainbow.txt | wc -l
  50
  $> cat rainbow.txt | wc -m
  1284

  Solution counting the number of characters excluding new lines:

  $> cat rainbow.txt | fold -w 1 | wc -l
  1242

• Print the lines of the text containing the word rainbow

  Solution:

  $> cat rainbow.txt | grep rainbow
  Somewhere over the rainbow
  Somewhere over the rainbow
  Somewhere over the rainbow
  The colors of the rainbow so pretty in the sky
  Oh, somewhere over the rainbow

  💎 Note that this looks for occurrences of the work "rainbow" exactly like this, in lowercase. If you wanted to make a case-insensitive search, you would use the grep command's -i or --ignore-case option.

• Do the same but without any duplicates

  Solution:

  $> cat rainbow.txt | grep rainbow | sort | uniq
  Oh, somewhere over the rainbow
  Somewhere over the rainbow
  The colors of the rainbow so pretty in the sky

• Print the second word of each line in the text

  Solution:

  $> cat rainbow.txt | cut -d ' ' -f 2
  over
  up
  the
  in
  
  over
  fly
  ...

• Compress the text and save it to rainbow.txt.gz

  Solution:

  $> cat rainbow.txt | gzip -c > rainbow.txt.gz

• Count the number of times the letter e is used (case-insensitive)

  $> cat rainbow.txt | fold -w 1 | grep -i e | wc -l
  131

• Count the number of times the word the is used (case-insensitive)

  $> cat rainbow.txt | tr '[:upper:]' '[:lower:]' | tr -s '[[:punct:][:space:]]' '\n' | grep -i '^the$' | wc -l

  💎 Instead of using a regular expression (^the$) with grep, you could also use its -w (word regexp) option which does the same thing in this case: grep -i -w the.

• 👾 Answer the question: what are the five most used words in the text (case-insensitive) and how many times are they used?

  Solution:

  cat rainbow.txt | tr '[:upper:]' '[:lower:]' | tr -s '[[:punct:][:space:]]' '\n' | sort | uniq -c | sort -r | head -n 5

  💎 By luck, simply sorting alphabetically works because the numbers are correctly aligned. But if you want a more robust solution, you can add the -b or --ignore-leading-blanks option and the -n or --numeric-sort option to the sort command: sort -bnr.