hpr-knowledge-base/hpr_transcripts/hpr0045.txt

Episode: 45
Title: HPR0045: Shell Scripting
Source: https://hub.hackerpublicradio.org/ccdn.php?filename=/eps/hpr0045/hpr0045.mp3
Transcribed: 2025-10-07 10:41:18

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Hello and welcome to episode 45 of Hacker Public Radio.
Today I'm your host, Doss Man, and today we're going to talk about shell scripting.
So what exactly is shell scripting versus other programming languages?
Basically, shell scripting is just a quick and easy way of stringing together several
different commands that already do the work you need to do, but you just need to automate
that.
And there's a lot of different ways to use shell scripts and whatnot.
There's a lot of different shells.
Now what other kind of examples might there be or what would make us different from
other programming?
Something like say, Perl would be probably a little bit better solution for a lot of things,
but for whatever reason, if you already know shell scripting, there's nothing wrong with
using that as opposed to Perl.
Perl is a little bit more programming, shell scripting or shells, corn shell, born-again
shell, bash shell, sea shell, all those.
There were their own unique syntax, basic looping capability, variables, and whatnot.
So they provide some basic programming functionality for the typical Unix Administrator or anyone
else, per se.
So I guess we'll jump into what really is the written butter of shell scripting.
But a lot of that is basically mostly using other commands.
You're just manipulating other commands to do your bidding in an automated fashion.
Other commands, mostly like the Unix Utilities, like Cat, Soar, Grip, Head and Tail.
You're basically saying you need to analyze some log files automatically and send yourself
a notification.
Well, you know, you just use Grip to extract out, you know, look for certain strings,
like saying you're a sys log.
And then if there is a match found, you can use, you know, like mail X or mail or some
dogmaically send yourself an email to your cellphone or whatever when there's a problem found.
So of course, really what you're learning is the syntax of all these external commands
that you're using for the shell script and then just, you know, learning how to string
them together through the use of the shell.
There's also a bit more complicated shell or not shell, but Unix Command, like said
in Ock.
I wouldn't exactly call this complicated, but there's a lot of functionality in those
two commands right there that you can do.
And it's kind of funny to see over and over new programming languages, we implement with
these two commands had, you know, years ago.
So you know, there's a lot that you can do.
You can pretty much do anything that you would normally do in Perl and a shell script.
But the, it may not be quite as efficient because the way you have to interact with the
commands, you know, but said in Ock, give you a lot of ability there, like, uh, Ock typically
I'll use that for extracting columns, like say you have some output and you need to separate
based on, you know, a common delimiter, you can use an Ock with a dash f flag and then
a comma and it'll separate.
And then, uh, then I, you know, do a print and a dollar sign, uh, three to get the third
column separated by semicolon or colon, comma, I said.
And, uh, so, you know, you can cut up your data in certain ways.
Ock, you could actually do in your entire script probably and said just said or just Ock.
They're a very full featured, uh, programs, but I only use a very tiny subset of their
features typically said is really good for, uh, of course, said is the stream editor basically
it's just a line at a time editor and you perform functions based on a line, uh, a, you
know, based on a single, you know, field per se.
And so you could, uh, a lot of times I'll do like a, uh, substitution and that's real
handy way of basically match the string and then change it to this other string or also
another way you could use that, uh, I use that a lot to just blank out a certain portion
of the string that I don't want.
Um, so if this, if this, you know, find the string and just remove it from my, my input
line, uh, Ock, again, looks at the whole document and sort of works on columns, although
that it's not the only thing it does.
But, uh, now there, there's a lot there, um, now also a lot of what people probably use
and what I use are third party tools, uh, that are not, I wouldn't say classic Unix tools
but these days pretty much are like, say, W get, um, I'll use that a lot to retrieve things
for myself and, uh, do that in an automated fashion like all, uh, one script that I use
that's, uh, fairly, got to be fairly large for a radio station and I, it automatically
checks the latest gas prices from gasbuddy.com and, uh, what it does, it loads the front page
with W get, I pull it down and then I use said and Ock and other various utilities to carve
out the, uh, names, the URLs for the image files that I have currently contained in the
current gas prices and then I'll, uh, parse through and use W get again to download those
image files, um, individually from the site and then I'll pipe them through, uh, image
magic and then, uh, go CR, uh, uh, good new, uh, OCR program and extract the, uh, text
data per se that that image contains, um, and then, uh, at last lay, I feed that into
festival, um, and without, before going into festival, I actually will feed it through
ECA Sam, which is a command line, sound board, uh, sound program that you can, uh, change
the bit rate, change, uh, you know, quality or whatnot or me. And the reason I do that
is I make it match, uh, the same characteristics as a piece of background music and then merge
them together and of course you have to cut the background music off at a certain length
so you don't have, you know, like your, your 45 second gas report and then another minute
of music running in the background. So, so you can do quite a bit, uh, with shell scripts,
whatnot and, you know, someone, it might be better to, to do this in parole, it might be
more efficient possibly but, uh, it, at the moment I've gotten to be, uh, probably too good.
I don't want to say that I'm too good at shell scripting but I've gotten good enough,
I can do everything I want to do with it. I'm really not a programmer but I do enjoy being
able to automate things and whatnot. So, uh, there's, uh, you know, I've gotten good enough that
I can do anything that I want to do with, with, with, uh, shell scripting, uh, compared to any other
type of, uh, typical scripting language like parole or, uh, Python or something, you know. So,
until I find he had an even bigger project that I want to do, uh, uh, you know, I, not to say
I don't know anything about parole but, uh, I, I, I have to, I enjoy just being able to sit down
and get results right away and basically I'm impatient and since I, uh, I know enough parole to,
uh, fix other people's scripts and stuff, uh, make them do my bidding, uh, but I, uh, if I'm writing
something from scratch, I usually start with shell script. Um, so anyway, um, yeah, I mean,
and the other thing is, you know, I really don't like re-inventing the wheel. Uh, if there's a,
a binary program that does what I want to do and I just need to automate it, fine. Um, I, I just
use a shell script to, uh, you know, someone else has already done the hard work of writing the
program that does something like, you know, like the Aircrack suite and then all I want to do is just
automate it, you know, so, um, all right, uh, I guess an actual kind of move into some places
shell scripts are commonly used, um, and that you might encounter them, uh, you know, like,
configure scripts. If you, uh, build a compile open source software, uh, that's all, uh, you know,
shell scripting and, uh, you know, custom tools. If, if, you know, if you're a unique sad man,
you're always doing something. It may not be, a lot of people probably are a bit more advanced
in using parole or something, but, you know, shell script, uh, quick and dirty is a,
easy way to solve a lot of problems, you know, um, there's also, uh, probably places that a
shell script shouldn't shouldn't even be used. Uh, one place, be like Apache CGI's, um, you know,
that's, uh, pretty dangerous to use a shell script in a CGI, uh, because if something breaks in
your script, you're actually left with a real shell there, and that's one reason probably why
parole is traditionally used in that environment, although PHP is taken over that role now, but,
um, you know, a parole script, uh, if it breaks and it dumps out, it's just a parole interpreter.
There's no shell there. So you can do CGI's in shell, and I'll, I'll
will admit that I've done that from time to time, uh, the quick and dirty way to get something done,
but I would not leave that in a production environment or something. That's not a good,
good place for, for a shell script for that reason. So, um, yeah, uh, I guess that's, uh,
about all I had to talk about today. Um, hope, uh, this was informative for, for someone that's
not familiar, per se, with shell scripting, uh, hope you have a good day. Enjoy it. And talk to you later.
Thank you for listening to Hack with Public Radio.
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