hpr-knowledge-base/hpr_transcripts/hpr1213.txt

Episode: 1213
Title: HPR1213: LiTS 026: units
Source: https://hub.hackerpublicradio.org/ccdn.php?filename=/eps/hpr1213/hpr1213.mp3
Transcribed: 2025-10-17 21:44:29

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Welcome to Linux in the Shell Episode 26, the UNIS command.
My name is Dan Waschko, as always I am your host.
I'd like to thank Hacker Public Radio for hosting the website and the audio files and
being an all-around wonderful community.
So consider contributing to Hacker Public Radio or at the very least head on over there
to see the other exciting shows that are available at hackerpublicradio.org.
Last episode I talked about some mathematics in the command line and focused on the BC
command.
And I ended with talking about some unit conversions.
Well, this episode, I'm going to talk about a tool that makes it really easy to do unit
conversions without having to know the functions or equations behind converting between
units.
And that is the units command.
Take the BC command, if you execute the units, units, not units, units command, you end
up in an interactive shell.
So what you can do at this point is begin converting units.
Now I want to warn you about a couple of things.
First, chances are units is not installed by default.
Just head on over to your package manager, look for the command units, sort of software
units, UNITS, it's plural.
I found it in Arches in the main repository, is Pacman-CapitalS, units, install it right
away.
Secondly, units at first glance is really simple, but can get complex and frustrating
really fast.
Well, let's step back a second.
When you fire up the units command, you're going to be presented with an interactive
shell.
That shows you some information about units like BC did.
It shows you the, some of the conversions available to it, the metrics behind it, conversion
exchange rates from, and it gives you a date, mine says 2012, dash 10, dash 24, so that's
October 24, 2012.
It'll also tell you the number of unit conversions available, mine says 2500, 65 units, 85
prefixes, and 66 nonlinear units.
That's just some basic information, probably won't mean much to you, but that's just there
for your information.
Then you're presented with the first prompt, it says you have colon.
Now that's where you enter the units that you have, and for example, let's say 300 feet.
If we enter in 300 feet and hit the enter button, it's then going to present you with
the next prompt, it says you want.
Now you enter some unit that you want to convert 300 feet into, I'll say inches.
So when I hit 300 feet, converting to inches, I get the return value of 3600 or 3600 inches.
That's not all I get.
I get an asterisk that says 3600, and I get a, a next one, another one has a forward slash
that gives me another value.
Another value is 0.0002777777778.
What does that mean?
Well, the first value, obviously, is the conversion that I wanted, 3600 inches or 3600 inches.
The second value is the inversion of that conversion.
So that's basically red.
There are 0.0002777777778 inches in 300 feet.
It's just a conversion, quite simple.
Pretty elegant, pretty nifty to have if you wanted that information.
Maybe you didn't, but you got it anyway.
So you're saying to yourself right now, this is great.
I can be converting right and left between everything I want.
I don't have to fire up a calculator and start typing things in.
Remember some funky equation or a function to convert between the values that I want?
Well, yes and no.
It is great, but you have to understand that other caveat I said that it's sometimes
it's not as evident as you'd expect it to be.
Case in point, converting between temperature, Celsius and Fahrenheit.
You might think, oh, I'll just type in 10 degrees Celsius or 10 degrees, 100 degrees Celsius
and get the conversion to Fahrenheit.
No, it's not that simple because if you type in 100 degrees, you're not going to get
what you expect.
You're not going to find degrees.
Now, most versions of units will have been compiled with realign support and you will have
tab completion.
So you can type in 100 space, D-E-G and hit tab and it'll show you the possible values
available to you and you look in those values and you'll see something like D-E-G for
degree.
You'll also say D-E-G-C and D-E-G-F and you might think, oh, well, I'll type in 100.
100, D-E-G-C and hit enter and then I'll just type in D-E-G-F and I'll get 100 degrees
Celsius converted to what it is in Fahrenheit and the return value is 180.
And you'll be, whoa, no, no, no, no, wait, 100 degrees Celsius should equal to 112 degrees
Fahrenheit.
That's the temperature water boils at.
Why is that not working?
Well, that's because you have to make sure you understand the correct units and how to
input those units.
Now, for instance, what we actually received here wasn't a conversion of degrees Celsius
to Fahrenheit that you expect.
What we actually received was this.
When there is a temperature degree change of 100 degrees Celsius, that is equivalent
to a temperature change of 180 degrees Fahrenheit.
That doesn't mean 100 degrees Celsius equals 180 degrees Fahrenheit.
That just means that a temperature change of 100 degrees Celsius is equivalent to a temperature
change of 180 degrees Fahrenheit, just be aware of that.
That's kind of what that means.
What you're looking for is to convert Fahrenheit into Celsius in the Fahrenheit.
Well, that's a little different because then you have to type in temp Celsius and then
parentheses put the number 100 and then it asks you what the conversion you want is temp
Fahrenheit.
When you hit enter, you get 212.
That is not clear.
That's because it's not a what units cause a linear conversion.
It's more of a functional conversion and you have to put it in a functional notation format
like that.
There's a lot of caveats to units that will trip you up, but you can easily rectify
that by just perusing the man page or even the info page, which is really really nice,
but there's some caveats there.
A lot of the stuff that you might want to do feet to inches and just the miles, kilometers
to inches, stuff like that, pretty straightforward, but if you want to get into more esoteric
things like temperature or even converting between megabits or I'm saying megabytes, megabits
is fairly simple, but megabytes and gigabytes and gigabytes and stuff, not a straightforward.
For instance, again, talking about kilobytes, that uses a specific notation.
You look in there and if you were to say, well, if I want to convert 10 gigabytes to
kilobytes, how do I do that?
If you type in 10GIB and hit enter and hit KIB for kilobytes, it gives you the correct
value.
The odd thing about that is if you type in 10 and then GI and hit tab for completion,
it will complete and if you actually type in a capital G, you would see GI in there and
then you would think, okay, I'm going to do MI, you're not going to get the same value,
okay?
You're going to get some weird number that says 7.9577472A as opposed to 10485760, which is
what is that?
That is going to be 10485,760 kilobytes as opposed to, you know, in 10GIB, so units
has a specific notation that you need to use and you could find out a lot of this stuff
by perusing the definitions file and where is the definitions file?
Well, that's pretty simple.
You can find that quite easily, but before I tell you how to find some of this stuff out,
you might be wondering, how do I get out of units once you're in it?
That's pretty simple.
Hit the control C key, it takes you right out of units.
Very simple.
Now, to find the definitions list or units, definitions.units is what the name of it is.
You just type in units and then the switch, dash capital V for a version information and
it's going to tell you the version of units, whether it was compiled with re-line, it's
going to tell you what locale support it's been compiled with or what it's using, and
then it's going to tell you the units database, which will probably be in slash user slash
share slash units and be called slash definitions.units.
If you use less or more whatever page you like to use and open that file up and start
looking in there, you'll see all the different units available and a lot of really good information
about how those units are defined.
It's really, really good something excellent to read.
If you're not sure what a unit is, looking there and it'll tell you exactly what it is,
but it's really, it's really great.
Now, there's some other switches that we can talk about here for units.units itself has
a quiet mode and what quiet does is that's the dash q or dash dash quiet.
What quiet will do is it will bring you up and suppress the prompting of the interactive
tool.
You won't see that initial information and you will not see that you have colon and you
want prompts.
You'll just type in whatever you want.
Compact suppresses the printing of the asterisk and the slash forward slash, but it'll still
show you those both of those values.
The dash L or dash dash one line will show you the first line of the output, but it'll
suppress the inversion of the conversion.
Now, sometimes a lot of those are handy for a cover that in a second, but those three
values are all combined in the dash T or dash dash Terse option, which combines quiet,
compact and one line all at once.
That might be the most handy for when you want to use units without an interactive mode.
That's just by typing units and then if you want to do any switches and then followed
by in double quotes, what you have, like for instance we talked to 15 feet, you type
in 15 space feet, double quotes, closes it, and then space and what you want and then
inches.
And that'll convert 15 feet into 180 inches.
And if you didn't supply any switches, you're going to get the output just like if you were
an interactive mode, except it's going to show you currency exchange rates from line and
then it's going to show you the asterisk 180.
And then the next line, the forward slash 0.0055555556, which is the inversion conversion
maybe.
So that's interactive or you don't have to go into interactive mode right there.
Now, if you were to use the dash T option there, the units dash T, double quotes 15 feet,
close the double quotes and then space inches, all you're going to get back is the value
of 180 right there.
Now you might want to use units with the dash V or dash dash for both mode, which is kind
of nice because if we did that same conversion with the dash V instead of it just saying 180,
it would produce the output 15 feet equals 180 inches.
So it provides a little more robustity to the output, which can be quite nice.
Now, units is a monster of a program and has just like BC, an incredible amount of functionality.
If you really want to delve into the units command, head on into the man page and the info
pages thoroughly explains all this stuff.
If you just want to do a simple conversions, you know, you can do that based upon the information
I provided you here.
But to get involved in more of the esoteric to the units command and the switches and
what you can and cannot do, well, I'll say what you can do because there's not a lot
you cannot do in the units.
You really need to read the man page in this far more detailed cover than in here.
If you're scientifically minded and mathematically minded in that way to get the conversions
and functions that you can do with units.
This has been episode 26 of Linux in the Shell.
My name is Dan Washco and I thank you for listening.
Join us again for some more Linux in the Shell goodness.
And make sure you head on over to the website if you have not already to read the right
up and watch the video of this command.
That's Linux in the Shell.org.
Thank you and have a great day.
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