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In this movie we're going to learn how to customize the Unix command prompt. And we talked about long time ago the prompt is this bit of text right here that occurs before every line, right, to prompt you to enter something. I don't know why, but it's very, very satisfying to customize that to something that you like. Maybe it's because it's the part of Unix that you see most often, but it's really useful to be able to customize that and make it look exactly the way that you want. The way that we're going to do that is with a shell variable. And we saw shell variables in the last movie. The shell variable we want here is PS1. That's for the main command prompt.
There's also a PS2, 3 and 4. those are for other prompts that occur in other contexts and we don't need to worry about those. PS1 is the one we want. PS1= and then we can make it equal to whatever we want, so -->. It's always a good idea to put a space after it just so that it separates the prompt from what you're about to type. Notice the space that it gave me. We could try it without the space and see the difference. See now when I type it's right up against that. So if you like that, you certainly can do it. I prefer to have the space there. So that's it. You can see that it took effect right- away but like the shell variables that we were setting before, if we close this window and log out, it won't be set anymore.
In order to have shell variables set so that they're there all the time, we need to put those in either our .bash_profile or our .bashrc file. If we define them there, then as soon as we log in, then our prompt will be defined the way we want it. So we're going to do that. We're going to move it over there, but this is a great way to play with it. Just play with it here, get it to something that you like, and then we'll move over to .bashrc and we'll actually plug it in there permanently. So let's try a few more. You can have it be whatever you want. You're going to be What now?, space, and that's what you'll get every time, or you can have it just be something like your username, all right. kevin.
Now that's the string kevin. That's not my username kevin. In order to get the username I have to use some special formatting codes. \u will be for my username, so that's my actual username. The other one was just a string of characters. It could have just as easily been bob. It wouldn't have mattered. \u is actually pulling my username from Unix. Let's look at what these other formatting codes are so that you'll be able to use them when customizing your prompt. So as we just saw there's u for username. We also can use a lowercase s for the current shell that we're in. bash in this case.
There's lower case w and upper W which will show the working directory. The difference is that w shows you the full path to get to the working directory whereas capital W just shows you essentially the name of the folder that you're in, just that current directory only. w is the same thing as if you typed pwd. Then there's \d which will show you the date. There's \D which allows you to then provide curly braces with a format, a string from time format. You can look up with those formatting codes or other places. I've just given you a real simple one to show you the year, the month, and the day.
Then we have four different ones that'll show the time, depending on the format you want. There's capital A, lowercase t, there's the at sign, and then there's the capital T. There's capital H for hostname, lowercase h for just the first part of the hostname. There's exclamation point which will be the history number of this command. If you use your history a lot, that might be useful. And then there's the special dollar sign. If you're logged in as root, that will then display a pound sign; otherwise it's going to display a dollar sign . So essentially it gives you a nice visual cue for whether or not you're logged in as root at the moment.
And then \\ would be a literal backslash, if you want to use the actual backslash character instead of using it for one of these formatting codes. So before we launch into a lot of these let me just show you what the Mac default. The Mac default is the \h:\W \u$, space, and then we close the quotes. So that's the default setting. If you decide oh, you know what, I liked most of that. I just wish it didn't show me the hostname at the beginning. Well then, no problem. You can take that out. Let's try some other ones.
So let's say we have t that'll show us the time. We have capital T was another one, shows the time. Capital A. We have a at sign that we can plug in there. So you see the different versions the time that it'll give you. Let's do a lowercase d for the date. If we want capital D then we need to provide some formatting as well. Capital D and then inside the curly braces we'll use %Y-%m-%d. The percents are the special characters.
These dashes could just as easily be swapped in with something like this if you like that better. So let's just do the dashed version for now. There we go. And you can combine these of course. So if you want that, then you also wanted to have a space followed by a slash. Let's pick the at sign. there you go. So now you get the date and time. Now I just want to show you the difference between the w version. Go up here and let's pick out w, lowercase w. Notice that in my current directory it's just the tilde. If I switch into the unix_files directory into test1, now I get that full path, right? Exactly the same thing as if I did pwd, except it abbreviates it for the fact that I am in my user directory.
So it tries to shorten it when it can, but it does still show me the full path. If I instead put the prompt with a capital W, then now I get just the current directory that I am in. As I move backwards I see just the current directory. So again, you can customize it to be absolutely anything you want. This is actually one of the ones that I find to be most useful. So I am just going to copy that using Command+C and then I will back up into my user directory, nano .bashrc, and then we'll just put that in there. Let's drop it right below all the exports we do here.
We'll do export PS1. Now remember export we need to do to make sure that it's available all the time, so go ahead and make sure you add that. export PS1 and then whatever prompt you decided you liked. Ctrl+X. save it, and then just to make sure that it takes effect, you want to say source .bashrc and that'll read that file then. So now that's my prompt and as I move around we'll just see the current directory that I am in. unix_files. That's the file we'll see. So on your own, play around with those different format codes, come up with a prompt that works well for you, and then put that in your .bashrc file.
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