Bash closing session

  1. Are there any questions on the materials you just watched?
  2. Let’s go together through the challenges, do some exercises, and debug problems.

Click on a triangle to expand a question:

Question 33 File permissions (no need to type any answer)
 
Question 34

In the molecules directory (download link mentioned here), create a shell script called scan.sh containing the following:

#!/bin/bash
head -n $2 $1
tail -n $3 $1

While you are in that current directory, you type the following command (with space between two 1s):

./scan.sh  '*.pdb'  1  1

What output would you expect to see?

 
Question 35 
The Tao that is seen
Is not the true Tao, until
You bring fresh toner.
With searching comes loss
and the presence of absence:
"My Thesis" not found.
Yesterday it worked.
Today it is not working.
Software is like that.

From the above text, contained in the file haiku.txt, which command would result in the following output:

and the presence of absence
 
Question 36 The -v flag to grep inverts pattern matching, so that only lines that do not match the pattern are printed. Given that, which of the following commands will find all files in /data whose names end in ose.dat (e.g., sucrose.dat or maltose.dat), but whose names do not contain the word temp?
 
Question 37 Write a one-line command that will search for a string in all files in the current directory and all its subdirectories, and will hide errors (e.g. due to permissions).
 
Question 38 Play with command substitution using both $(...) and `...` syntax. (no need to type any answer)
 
Question 39a Write a script that takes an English-language file and print the list of its 100 most common words, along with the word count. Hint: use the workflow from the text manipulation video. Finally, convert this script into a bash function. (no need to type any answer)
 
Question 39b

Write a function countFiles() to count files in all directories passed to it as arguments (need to loop through all arguments). At the beginning add the check:

    if [ $# -eq 0 ]; then
        echo "No arguments given. Usage: countfiles dir1 dir2 ..."
        return 1
    fi
 
Question 40

Write a function archive() to replace directories with their gzipped archives.

$ ls -F
chapter1/  chapter2/  notes/
$ archive chapter* notes/
$ ls
chapter1.tar.gz  chapter2.tar.gz  notes.tar.gz

(no need to type any answer)

 
Question 41a Write a one-line command that finds 5 largest files in the current directory and prints only their names and file sizes in the human-readable format (indicating bytes, kB, MB, GB, …) in the decreasing file-size order. Hint: use find, xargs, and awk.
 
Question 41b Let’s discuss incorporating scripts from other languages into bash, as suggested in this Python example.
 
Question 42

Let’s study together these commands:

$ source ~/projects/def-sponsor00/shared/fzf/.fzf.bash
$ kill -9 `/bin/ps aux | fzf | awk '{print $2}'`
 
Question 43 Are there questions on any of the topics that we covered today? You can type your question into the chat or ask via audio (unmute), or raise your hand in Zoom.