I believe that there will be a day on which I dive into LInux. When I do, I think this post will be helpful.
From: Jason Cannon
<support at linuxtrainingacademy dot com>
Sent: Thursday, March 24, 2022 7:00 AM
To: Me
Subject: Here's a quick, but valuable, shell scripting
lesson.
Hello!
In this email I'm going to teach you a quick, but valuable lesson on shell
scripting.
First off, a shell script is simply a file that contains a series of Linux
commands and shell statements. When a shell script is executed, it in turn
executes the commands listed in the script. It starts at the top and executes
the commands on each line, one line a time, until the end of the file.
By the way, the script's filename doesn't matter. You may be used to a
different operating system where files have to have a specific file extension
before they will be treated as an executable. (I'm talking about ".exe"
files in Windows, for example.) That's not the case with Linux shell scripts.
By convention, shell scripts end in ".sh", but it is not a
requirement. The following are all valid shell script names:
|
·
use-the-force.sh
·
do_or_do_not_there_is_no_try
·
ThisIsSomeRescue
What IS important is
that your shell script has executable permissions. (We'll get to that in just
a second.)
If you remember the advice from my previous email, it's best to start with
the end in mind. So, the goal for this shell script is to collect and display
some basic information about a Linux system.
If you want to follow along, open up a terminal on a Linux system and create
a new file named "sysinfo.sh". If you have a favorite text editor,
use that. If you don't, I suggest that you use nano as it's simple to use and
always displays help at the bottom of the screen.
The very first line of every script you write should begin with "#!"
followed by the path to an interpreter. We're going to write a bash shell
script, so we'll use "#!/bin/bash". If you were going to write a
Python script this line would be "#!/usr/bin/python"; a ruby script
would be "#!/usr/bin/ruby" and so on.
One very common task you'll perform in your shell scripts is displaying
messages on the screen. To do this, use the echo command followed by whatever
you want to display to the screen and enclose it in quotes. Like this:
Now save your changes and exit your editor. If you're using nano type Ctrl-X
to exit, then type "Y" to save your changes, and finally press
ENTER to write the changes to your script.
The next step is to add executable permissions to your script. You do this
with the chmod command, which stands for "change mode". There are
different ways to add executable permissions to a file, but the simplest is
chmod +x FILE_NAME.
Now you're ready to execute your shell script. You do this by typing "./"
followed by the script name. In this example, you would run "./sysinfo.sh":
You'll see the text you supplied to the echo command displayed on your screen.
Now that you have a working shell script with the proper permissions, you can
continue writing your script. Let's add some commands that will display
information about the Linux system.
First, display the current date and time when this information was collected.
Next, display the hostname of the system.
Next, display the kernel release followed by the architecture. You'll need to
use the uname command to do this.
Display the disk usage in a human readable format.
Finally, end the script by letting the user know that it's done.
It's time to see what your script does! Save your changes and execute your
script.
Now you have a script that displays some basic information about the system
you're on. You could easily expand this to show information about the CPUs,
memory, networking configuration and more.
If you would like to write even more in-depth and practical scripts, reserve your seat in the upcoming shell
scripting class. Registration closes a week from Sunday and
class runs for 4 weeks. I'm limiting the number of students, so I can give
individual attention to everyone in the class.
Hope to see you there!
Jason
P.S. The shell scripting class is currently being offered at a deeply
discounted rate, so now is a great time to enroll. ;-)
|
