Demo: Creating & Executing a Bash Script


This file is written as instructions for an instructor-led demo. As a student you probably can work through this file on your own, but it does a few things that we haven’t learned or practiced yet. You very possibly could get stuck and will not receive guidance on moving through any issues you encounter. That being said, you can attempt this demo and work through the issues you encounter as practice for attempting to learn on your own and troubleshooting issues as they arise.

In this Demo your instructor will show you how to create and execute a bash script, how to add to the $PATH Shell Variable, and how to create a SymLink. This demo will also give a sneak peek into creating directories and files from the Bash shell.

Create Directory & File

  • mkdir /home/student/bin
  • touch /home/student/bin/whattimeisit

Add the following text into the file. You may find nano to be useful, but feel free to edit the file however you want.


echo "Hello Paul..."
echo "It is currently $(date)"
echo "Have a nice day!"

Execute the file using the Bash command

  • run the file: bash /home/student/bin/whattimeisit

Make the file executable & execute in new ways

  • make the file executable: chmod +x /home/student/bin/whattimeisit
  • run the file: /home/student/bin/whattimeisit
    • or: ./bin/whattimeisit
    • or: bash /home/student/bin/whattimeisit

Adding /home/student/bin to $PATH

  • what is the shells $PATH: echo $PATH
  • update the PATH variable with our personal bin: PATH=$PATH:/home/student/bin
  • check $PATH for the new information: echo $PATH

Execute the program directly from $PATH

  • whattimeisit

Rename file

  • what if I want to change the name of my program?
    • mv /home/student/bin/whattimeisit /home/student/bin/when

Run same program with new name

  • when
  • can you run the old name? whattimeisit
  • can you run it directly with bash? bash /home/student/bin/when
    • can you run it the other ways we tried above?

How can we view the absolute path of the when program?

  • what happens if we: which when

Does the when program have a man page?

  • what happens if we: man when

Where is python?

  • python comes standard as a part of most Linux distros
  • which python –> so where is it?
  • which python3 –> here it is (python 2 is dead and has been fully replaced by python3) –> older versions of Ubuntu did have python which defaulted to Python2 & also had a version of Python3 installed.

Manually search for python3 in /usr/bin

  • ls /usr/bin
    • python should be here, manually search for it
      • why is python3 blue?
      • why is there a python3.8 that is green?
        • when we made our Bash script executable it turned green
        • are all executables green?

Take a deeper look at the file metadata

  • could do it manually with ls -l /usr/bin, but that would take a while

  • let’s use grep to search for the output we want instead: ls -l /usr/bin | grep python3

ls -l /usr/bin | grep python3

What is python3 -> python3.8 representing? It looks like python3 is a shortcut to python3.8!

  • what is a Symlink?
    • it really is just a shortcut
    • soft link
    • both python3 and python3.8 should execute the same program
      • Enter python3 --version & python3.8 --version
        • same program!

Change name back to whattimeisit

  • mv /home/student/bin/when /home/student/bin/whattimeisit
  • ln -s /home/student/bin/whattimeisit /home/student/bin/when
  • look at the contents of the /home/student/bin directory: ls -l /home/student/bin

How can we run the program?

  • whattimeisit
  • when

This explains what Python3 is in /usr/bin – just a symlink pointing at the actual python3.8 interpreter!


In Ubuntu the color scheme of STDOUT is helpful. Green files are executable, light blue files are SymLinks, dark blue files are directories, white files are standard files. Not all terminal emulators support color, but it is quite useful when it is around.