hpr-knowledge-base/hpr_transcripts/hpr0562.txt

Episode: 562
Title: HPR0562: Introduction to bash scripting
Source: https://hub.hackerpublicradio.org/ccdn.php?filename=/eps/hpr0562/hpr0562.mp3
Transcribed: 2025-10-07 23:06:57

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Hello everybody, my name is Ken Fallon and this is the first in a new bash scripting tutorial
series on Harker Public Radio.
This is a series of bash scripting for Linux, Unix and Windows systems.
First of all, let's cover what bash is.
From Wikipedia, bash is a free software, Unix, Shell, written for the GNU project.
This name is an acronym, which stands for the Born Again Shell, and the name is upon
on the name Born Shell, which was an early and important Unix shell, written by Stephen
Born, and distributed in version 7 of Unix in around 1978.
And the common Christian concept of Born Again, bash was created in 1987 by Brian Fox
and in 1990, Chet, Rami became the primary maintainer.
That's all very well and good, but it doesn't actually explain a lot what the bash shell
is.
It's actually the command line for Linux, so if you're coming from Windows, it's kind
of like the dust prompt, now you might be tempted to say how 1980's, but as any system
admin, even those coming from Windows, will know the command line is very, very powerful.
You'll also hear the command line referred to as the CLI, but what about the graphical
user interface?
Now this is fine as a means of interacting with an application, but it's very difficult
to automate stuff, and more importantly, it's very inconsistent.
Now what I mean by that is over time, over languages and over desktop environments.
So taking as an example, you want to explain to somebody over the phone how you might print
Microsoft Word, so you say go to file and print and then press OK, and they are very confused.
And after about an hour you realize that they're using Word 2007, and there is no file
menu.
It is just a menu bar.
If you think these problems are limited to Windows, you'd be wrong.
For example, since the initial iteration of Ubuntu, there has been at least three different
names and locations where you would install Add and Move software.
During the entire time, the command line way of doing things of installing software has
remained the same.
Now let's take into account different languages, different test up environments, going from
KDE to GNOME to XFCE, and it makes the issue worse.
The command line is the least common denominator, and this is why many people on forums tend
to have command line solutions, which if not exactly the same on your system will often
be close enough to get you started.
The fact is that all GUIs call lower level system calls anyway.
On the command line, these calls probably have a richer or the more complicated set of
options.
OK.
So that's bash.
Now let's move on to what scripting is.
The most common use scripting is to automate a task, that is big or boring or repetitive
or all three.
A script can be as simple as a file containing one or more commands that you type a lot,
but it also can be a complex thousand line program.
That accepts arguments, that has config files, that use procedures, functions, yad yad yad
yad.
On this series, we're going to try and take you from the complete novice to give you a
good understanding of bash scripting in particular, but also programming in general.
Now if at any time there is anything in this series that you don't understand or that
I have assumed that you know about, please send an email to kenatkenfallon.com.
So what's the difference between a bash script and a real program?
Now the traditional answer to that one is that a script is interpreted while a program
is compiled.
Now that might not make a lot of sense right now.
So let me go on to explain a little bit.
Start off as a file or many files, which is a human readable ish script.
This is called source code because it's the source of the end program that you're trying
to get to.
Now there are many programming languages just like there are many oral or verbal languages.
And as with verbal communication, languages, computer languages have different words and
different grammar.
And you can use a different computer language to ask the computer to do the same thing.
The traditional example is the hello world program.
And that's a simple program that prints hello world on the screen.
I'll put a link into the show notes with a site with examples of hello world programs
written in different computer languages.
However, regardless of how computer programming language you use, at the end of the day all
computer programs are broken down into a series of ones and zeros that the computer understands.
The difference between a compiled program and a script is the point at which the conversion
from this higher level for one of the better word English is done into the ones and zeros
that the computer understands.
In a compiled program like C, every time you make a change to the line in the source code
you need to recompile the program.
This takes the source code, which is a series of commands, and translates them into a
raw byte code that the computer processor understands.
If you're running the same program on two different processors, you need to compile it
for both processors.
Now you can do this.
You can, that's called cross-compiling if you compile it on one processor with the instruction
sets needed for another one.
That's where architectures come into their own.
So you have the i3 at 6 architecture and the AMD 64 architecture.
You also have the SPARC and various different other power PC architectures.
If you wanted to run the same program on all these, you would need to recompile it for
the different architectures.
Now in an interpreted language or scripting language, the source code is translated into
byte code each time that the program is run.
The advantage is that you don't need to recompile for the different processors.
The disadvantage is that it will be slower because every instruction has to be converted
into byte code on the fly.
So the question is, why are we doing a bash scripting tutorial?
And the reason is that bash scripts have all the functionality of procedural languages,
like C or whatever.
So it has powerful features, but its system calls are other bash programs.
And if you get to know the other programs on the command line, you can include its features
and functions into your script.
So as you get better with the command line, you also get better with scripting.
So it's a win-win situation.
Okay, this episode is getting a bit long, so I want to make a start today.
And before we start, you're going to need a text editor.
Which one you use is up to you.
Even though this is about the command line, there's absolutely no reason why you can't
use a GUI text editor.
For example, Kate or G-Edit, or if you're on Windows, no pad++.
If you prefer, there's also text editors that work in the console, like Vim or Joe or
Nano.
One thing to look for in a editor is code highlighting.
That's where the words, which are the commands, that have a special meaning are highlighted
in a different color or font or in some way distinguished.
Although you probably want to start with an easier editor, I suggest you get to grips
with basic editing in VI or VIM.
Because this tends to get installed on most Unix and Linux systems.
And there is also a version for Windows, whereas EMAX isn't.
Once you're comfortable with your text editor, you also now need a way to get to the
bash console.
And depending on your desktop environment, this may be listed as something else.
My console of choice is called console, that's K-O-N-S-O-L-E.
But just like VI, the external is probably installed on any Unix or Linux system.
That has a GUI.
So let's use that one if you can't find a console on your system.
If you can, then use it.
You can usually start external by holding down the Alt key and pressing F2.
This will usually bring up a dialog box.
And you can type in the words X-Term in lowercase letters and press Center.
If a Windows opens, you're in business.
On Windows, you can also enjoy the joys of bash.
By probably the easiest way is to install the SIGWIN program.
And there will be a link in the show notes as to how to do that.
And on Windows, I suggest using the no pad++.
And links for all of this stuff will be in the show notes.
So now you have a window open, which will be black background or white text or white background
which black text doesn't really matter.
What you're probably looking at now is what's called the command prompt or the bash prompt
or the shell or the terminal or the dustbox or the console, all depending on what you do.
There's probably a flashing cursor and that is the command prompt.
It's named the prompt because it's prompting you to enter a command by flashing the cursor.
So press Center a few times and you should see the same line repeat each time you do.
The makeup of a command prompt differs from system to system.
But a common prompt is made up of the user name.
That's the user that's logged in, for example you, the at separator, the host name, that's
the name of the computer you logged into, a colon separator, the path, now that's the
location in the file system where you are.
This might be the tilde, which is in the top left hand corner of most keyboards.
It's a bit like an s rotated 90 degrees, a merge.
This is the bash shortcut and it means your home directory.
A tilde by itself is the home directory of the logged on user, namely you, and a tilde
joe means the home directory of the user joe.
And just finishing off the prompt is the dollar sign.
This means a non-rush user is logged in.
If you see an octop which is the tic-tac-toe and the incorrectly termed pound sign, it
means the root is logged on and then of course you have a space.
Everything you type after that will be considered by bash to be a command and will be treason
as such when you press the enter key.
Now, let's get on to our first bash program and following the tradition where write and
a low world program.
I want you to type these commands into the terminal.
First of all, listen to an explanation before you go hit enter.
This is a very good place for a warning.
Bash is very powerful and there's absolutely no hand-holding.
If you type a command on the computer, it's not going to ask you, sure, it's just going
to do it and sometimes you won't be even given any visible feedback that is doing anything.
If you enter the command to delete all my files and press enter, it's just going to go
delete them.
There's going to be no confirmation, there's no recycling, there is no way to recover
them.
They're gone, gone forever.
So make sure you know what you're doing before you type anything into the console.
And you also don't be accepting blindly commands from forums on the internet.
I'm going to show you later on how to get help and to check what those commands are before
you run them.
So open up your text editor.
Actually, you don't need a text editor, we're going to be entering these commands directly
onto the command line.
And we're going to create a file which you can later open up in a text editor.
But for now, we're going to do everything from the command line, including putting everything
into a text file.
So the first command we're going to do is write the location of the bash interpreter into
the text file.
And this will tell bash itself what program is running.
Bash is very friendly and that you can run other programs within it just simply by changing
the first line.
And then you can write it in another dialect.
So thinking French instead of English, although it's also going to be English.
But anyway, I digress.
The second command will actually print the greeting on the screen.
Don't worry if you don't fully understand everything yet.
We're going to cover everything here in later episodes.
Now, the first thing you need to type, everything we're going to be typing, by the way, is
all lowercase.
Unix and bash are case sensitive.
So capital H-E-L-L-O is different from lowercase H-E-L-L-O.
And lowercase H, uppercase E, lowercase L, uppercase L are also different.
So you've got to be careful about that.
Which is why things generally tend to be done in lowercase.
Okay.
I'll not command.
So you type the command echo, space, single quote, the octetorb character, exclamation
mark, forward slash, bin, forward slash, bash, another single quote, the greater than
sign, hello, dot, and then bash, and press enter.
Then the next line type, echo, space, double quotes, echo again, space, hello, space,
world, double quotes.
And then the greater than sign, the greater than sign again, and then hello, dot, bash.
Has entered the commands into the hello dot text file.
Now we need to make the text file executable.
Under bash and under unix, a file name can be have any extension.
There are special permissions assigned to the file, which states whether it's going
to be executable or not.
It can't run a program unless that flag is turned on.
And in order to do that, we need to use a bash program called chmod, which means change,
change modular, something, I looked it up in the show notes.
So it's change mod, space, the plus sign, lowcase x, space, hello, dot, bash.
And that is enough to make the program executable.
And now what we can do is type the dot forward slash hello, dot, bash.
And you should see hello world.
Congratulations, you've written your first bash program.
And now if you want to finish, only need to do is type exist, close the terminal and
you're done.
Well, that's it for the first episode.
I hope you could follow along.
If you have any feedback, good or bad, you can send it to feedback at kenfallon.com.
And you can join me next time as we go through some basic bash commands.
A lot of these we'll use in scripts later in other episodes.
Thank you for listening to AcrofovaGradio, HPR is sponsored by Carol.net, so head on over
to C-A-R-O dot anything for all of us here.
Thank you for listening to AcrofovaGradio.