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In this movie, I want to show you several utility programs that Unix provides that I think can be really useful to you. We are going to look at cal and also a variation on that called ncal, which is a calendar program. bc, which is a calculator program. bc stands for bench calculator. Then we have expire, which is an expression evaluator. essentially it's a simple one line calculator. We are just evaluating a mathematical expression. And then units which allows us to do units of measure conversion. So for example, from feet to meters. Let's try all of them out.
We will just start with the simplest one, which is calendar. Just type cal and look what you got. You get the current month's calendar. That's it. That's all it does. It is very simple, shows you by default the current month's calendar. So let's type in the month 12, followed by 2020. So we are going to see what December of 2020 looks like. As an exercise, plug in your month and year that you were born and you can see what day of the week that you were born on. Now in addition we also have the ability to take a look at a full year by using the y option. So this will be the year 2000. We can see what that full-year of calendar looks like.
Now, of course, we could do the same thing for this current year as well. There we go. That's what the current year looks like and then let me just show you the variation on this, which is ncal. It has some slightly different options to it. It's actually a different program but what it mainly does is it rotates the calendar so that the days of the week run down the left side instead of running across the top. You can look at the man pages to see what's some of those additional options are. Personally, I prefer the standard cal most of the time, but I just want you to know that this is there as well. Okay, let's move on to look at the next one, which is bc for bench calculator.
If we just type bc and hit Return, it drops us into this calculator. It's a program that runs and it actually has a pretty rich programming language. So there is a lot of things that you can do in here. We are just going to use it for the most basic. I am not going to try and teach you everything there is to know about it. I just want you to know it's there and get an idea of how it works. So just 1+1 and it reports the results once we hit Return. That's what it does for us. To get out, we type quit and we exit back out again. So let's go back in there and take a look at a couple of other things about it. So let's try some expressions. 3+4 times 210.3 and there it gives us the result.
Let's try another one. 1000 divide by 9. Now wait a minute. I think about the math here for a second. That doesn't seem quite right, because 9 times 111 actually equals only 999. We are missing some decimal places here. There is an important point about this, is that the precision that it reports the results is arbitrary. We can change the precision that it reports those results and the way we do that is what scale equals and then whatever scale we want.
That's how many decimal places we are looking at. So now when we try 1009, you can use the up arrow to get there as well, just like you normally can. Now it says okay, it's actually equal to 111. and then 10 decimal places of 1s because that's the precision than I told it to report. You can change the scale to be 5 and of course it will only give you 5 back. So that's an important point, that you do have to tell it how much precision you wanted to return to you. Now again, there is lots more that you can do with the bench calculator, but at its simplest, this is what it is.
Just a calculator where you can type in expressions and they will return results and then wait for you to do another calculation. Let's quit out of that. If you really just want to calculate a really simple expression then you have expr available to you. Expr says all right, calculate the expression and I am going to just show you what won't work first. 1+1. It doesn't realize that it needs to break that up. You have to put spaces in here. Let me just show you if I try it first. It just comes back and says, oh, the value of that word, that thing, that unit is 1+1.
It returns it to you. What we need to do is put spaces, so it says, ah! I recognize. The first thing is a 1, the next thing is what you want to do to it and the next thing is the 1. That's because we are in the Unix command line and Unix is taking each one of these as arguments. Even though it's an expression when we are in bc, we don't have that Unix command line issue. But here we really need an expression to see ah, there are three arguments here. So we need those spaces. Also because we are on the command line, if we wanted to do something like multiplication, 1122 times 3344, this won't work because this has special meaning in Unix. It's a wildcard.
Remember that? So if I hit Return, comes up as oops, I don't know what do you mean. We have to escape that first. Just like we had to escape spaces in the file names, we need to escape it to let the command line know, hey, I mean the literal asterisk. I'm not using this as a wildcard. And then it works properly. Okay, so that's the things you need to know. Make sure that you put spaces there, make sure that you escape characters that the command line is going to interpret as something different. But you're going to see that's probably the simpler calculator then actually dropping into bc. bc is really designed to switch into it, to do lots of calculations over and over, to sort of leave it running while you're working at your workbench, which is why it's a bench calculator, whereas expression really just does a real simple expression evaluation.
Okay, let's look at units. units is another one that drops you into a mode. It comes up and tells me how many units it has in its library and then it asks you have what, and that you can put in a value here. Let's say I have 1 foot, all right. We are talking about a unit of measure 1 foot and what I want is meters and then it comes back and it tells me that is equal to 0.3048 meters. Then it gives me the second line here which is the reverse calculation.
That's what it would take to go the opposite way. Most times you can just ignore that. It gives it to you because there are times when the precision is actually better in that second line than it is in the first line. Most of the time you can just ignore that other line. Then it pops up and it says all right, you have what? And it asks again. So let's just try a few more. Let's say 1 inch into centimeters. 1 inch is equal to 2.54 centimeters. 5 gallons is equal to liters.
There we go and let's try 3 furlongs into miles. Let's try 72 degF, degrees Fahrenheit, followed by degrees Celsius and it turns up and tells what 72 degrees Fahrenheit is equal to in Celsius. So when we finally want to get out of this, there's no graceful way, unfortunately. We can't just type quit, which just seems a shame. Instead you would hit Ctrl+C to exit out of it, just like you would force quit a program. There is also a usage of units from the command line if we put it in quotes.
So '2 liters' into 'quarts' and that comes back and just returns it and then it comes back to the command line, more like the expression evaluator that we were just using. That's a really handy tool. It's nice to be able to just very quickly drop into units and be able to figure out the conversion that you're working with. So you have this tool available to you on your Mac all the time. Just open up Terminal, type units and voila, you can do all the conversions that you are trying to figure out. So I think all four of these utility programs can be really useful. So try and make yourself a mental note. The next time I want to do some calculations and the next time I want to do some unit conversions, to switch into Unix, and actually try them out and get used to using these.
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