Demo

Demo: Creating & Executing a Bash Script

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.

#!/bin/bash

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

Symlink

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

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!

Edit our Bash script to be executable with a SymLink

Change name back to whattimeisit

• mv /home/student/bin/when /home/student/bin/whattimeisit

Create a SymLink pointing to whattimeisit named when

• 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!