Useful Examples and snippets
============================

Important commands

* ``head -n 1`` to get the first token in a string
* ``tail -n 1`` to get the last token in a string
* ``wc -l`` count the number of files in a file or a stream
* ``wc -w`` count the number of words (tokens) in a file or a stream
* ``tr " " "\n"`` replace spaces with new lines in a string or stream
* ``tr "," "\n"`` replace commas with newlines in a string or stream

Capture Earlier or latest Files, or directories

.. code-block:: bash

    latest_node=$(ls /lib/modules -At | head -n 1)

    earliest_node=$(ls /lib/modules -At | tail -n 1)

    echo "python javascript C++" | tr " " "\n" | head -n 1  # get the first token, python
    echo "python javascript C++" | tr " " "\n" | tail -n 1  # get the last token, C++



Redirection and useful pipelines

.. code-block:: bash

    # redirect errors and warnings to the null device
    sudo apt update 2> /dev/null

    # count the linux packages in an upgrade
    linux_packages=$(apt list --upgradable 2>/dev/null  | grep -e "^linux-.*" | wc -l)



Modules installation with Kernel Upgrades

.. code-block:: bash

    sudo apt update > /dev/null # Get Available Upgrades from the ubuntu repo
    linux_packages=$(apt list --upgradable 2>/dev/null  | grep -e "^linux-.*" | wc -l) # count the linux packages
    if [[ $linux_packages -gt 0 ]] ; then kernel_update=1; fi  # Set the Kernel upgrade flag if needed
    sudo apt upgrade 2>/dev/null # promt user and confirm upgrade
    sudo apt-get -y autoremove # remove the previous kernel if needed
    if [[ $? -eq 0 && $kernel_update ]]; then echo "Run wifi script"; fi # Execute Wifi driver script if needed