WEBVTT 00:01.400 --> 00:02.390 Hello, my name is Stephanie. 00:02.390 --> 00:04.690 Welcome to another lecture of our course. 00:04.730 --> 00:10.670 In this section we are going to look at the some of the magic that occurs on the command line when we 00:10.670 --> 00:12.710 press the enter key. 00:13.220 --> 00:19.400 While we will examine several interesting and complex features of the shell, we will do it with just 00:19.400 --> 00:26.660 a one new command which is echo to display lay line of the text. 00:26.660 --> 00:28.130 So let's get started. 00:41.370 --> 00:48.840 Each time we type a command and press, the Enter Key Bash performs several substitutions upon the text 00:48.840 --> 00:51.520 before it carries out our command. 00:51.540 --> 00:57.810 So we have seen a couple of cases of how a simple character sequence, for example, these asterisks 00:57.810 --> 00:59.890 can have a lot of meaning on the shell. 00:59.910 --> 01:04.920 So the process that makes this happen is called the expansion. 01:04.920 --> 01:06.620 Actually, let me mention it here. 01:06.630 --> 01:09.630 So expansion. 01:14.280 --> 01:15.180 Expansion. 01:15.180 --> 01:23.430 So with expansion, we enter something and it is expanded into something else before the shell acts 01:23.430 --> 01:23.940 upon. 01:23.940 --> 01:31.290 So to demonstrate that what we mean by this, let's look at the echo command here. 01:31.710 --> 01:32.280 So here. 01:32.280 --> 01:33.930 So let's look at the echo command. 01:33.930 --> 01:40.500 So echo echo here is a shell builtin that performs a very simple task. 01:40.530 --> 01:44.850 It prints its text arguments on a standard output. 01:44.850 --> 01:46.140 So if you write it like that. 01:46.140 --> 01:51.840 So echo, this is a Oxley lecture. 01:52.350 --> 01:56.280 And here, as you can see here, we write it it this is Oxley lecture. 01:56.280 --> 01:58.350 So that's pretty straightforward, right? 01:58.350 --> 02:03.000 So any argument passed to Echo gets displayed. 02:03.000 --> 02:04.680 So let's try another example here. 02:04.680 --> 02:08.790 So clear echo this here asterisk. 02:08.790 --> 02:11.400 And as you can see, we've created this. 02:11.400 --> 02:12.270 So. 02:13.620 --> 02:14.520 For example. 02:14.520 --> 02:15.180 Eko. 02:16.050 --> 02:16.920 Eko. 02:18.390 --> 02:19.700 Eko, LZ. 02:21.990 --> 02:22.950 LZ. 02:23.220 --> 02:24.990 And here we can also write it like that. 02:24.990 --> 02:29.370 And as you can see here, each argument we write in Echo, we are just seeing it. 02:29.370 --> 02:30.090 So. 02:31.720 --> 02:32.560 Here. 02:34.010 --> 02:38.070 Let's write the term expansion and learn more about it. 02:38.090 --> 02:44.960 So the mechanism by which wild cards work is called the Pathname expansion. 02:45.290 --> 02:51.020 If we try some of the techniques that we employed in earlier lectures, we will see that they are really 02:51.020 --> 02:51.530 expansions. 02:51.540 --> 03:01.400 So given a home directory that looks like, for example, LZ and oops, actual CD here and here echo 03:01.700 --> 03:02.020 here. 03:02.030 --> 03:06.560 And as you can see here, we've created our like LZ here so clear. 03:06.560 --> 03:10.100 And let's echo D here and here. 03:10.100 --> 03:12.620 As you can see here, we started the arguments. 03:13.970 --> 03:14.630 So. 03:16.000 --> 03:17.530 We can also do it like that. 03:17.710 --> 03:22.210 For example, Echo is here, and as you can see here, we will print that. 03:22.990 --> 03:28.240 Uh, templates or documents that ends with s character. 03:28.240 --> 03:29.350 We can also do it like that. 03:29.740 --> 03:36.160 Echo two here, braces like that and upper, upper and here like that. 03:36.160 --> 03:42.010 And after the asterisk here and as you can see here, we printed all of that, that starts with the 03:42.010 --> 03:43.930 uppercase character. 03:45.430 --> 03:48.610 And we can also do it like that, for example, Echo. 03:49.450 --> 03:56.680 That's actually that's pretty complex and straightforward comments with with which you will learn all 03:56.680 --> 03:59.650 of the echo commands in this course. 03:59.650 --> 04:07.090 So Echo, for example, user asterisk, wildcard operator, some called asterisk, some called wildcard 04:07.120 --> 04:08.620 here share. 04:08.620 --> 04:12.040 And as you can see here, we printed our user local share. 04:12.310 --> 04:16.930 So that is called the Pathname expansion of a hidden files. 04:16.930 --> 04:21.610 So as we know, files that begin with a period, characters are hidden. 04:21.610 --> 04:30.190 So a pathname expansion also respects this behavior and expansion such as this here echo this asterisk. 04:30.220 --> 04:33.700 This will not reveal hidden files. 04:33.700 --> 04:38.380 So it might appear at first glance that we could include hidden files in an expansion, for example, 04:38.380 --> 04:44.830 like this that starts with this, uh, by starting a pattern with a leading period like this. 04:44.830 --> 04:47.960 And as you can see here, we got it. 04:47.960 --> 04:49.100 But it almost works. 04:49.100 --> 04:56.060 However, if we examine the results closely, we will see that the names from that starts with dot and 04:56.060 --> 04:56.600 double. 04:56.600 --> 05:05.300 That here will also appear in the results because these names refer to the current working directory 05:05.300 --> 05:06.710 and its parent directory. 05:06.740 --> 05:11.150 Using this pattern will include will likely produce an incorrect result. 05:11.150 --> 05:14.410 So we can see this if we try this command here. 05:14.420 --> 05:15.230 Clear. 05:15.350 --> 05:16.190 Oops, clear. 05:16.190 --> 05:21.650 And here we will list the and wildcard operator. 05:21.650 --> 05:26.300 After that we will use pipes and less here. 05:26.300 --> 05:30.800 And as you can see here, we got this our desired results here. 05:30.800 --> 05:32.600 So actually, let's end this. 05:34.040 --> 05:34.370 Oops. 05:37.710 --> 05:38.490 Here. 05:41.610 --> 05:43.720 Oh, can we change this color? 05:43.740 --> 05:47.730 I didn't realize that we can change the color of this. 05:50.240 --> 05:51.020 Here. 05:52.750 --> 05:53.200 Yeah. 05:53.200 --> 05:53.920 Let's. 05:54.840 --> 05:55.250 Quit. 05:55.440 --> 05:57.020 So whatever here. 05:57.030 --> 06:02.190 Now we're going to use this echo and echo dot. 06:02.950 --> 06:04.120 Braces. 06:06.150 --> 06:07.470 And here asterisk. 06:07.500 --> 06:10.890 And as you can see here, the event not found. 06:10.920 --> 06:12.530 We got an error here. 06:12.540 --> 06:17.340 So this pattern here, echo and as you can see here, this. 06:18.680 --> 06:27.920 So this pattern expands into every file name that begins with only one, followed by another characters. 06:27.920 --> 06:30.800 So this will work correctly with most hidden files. 06:30.800 --> 06:36.710 So it will it will not include file names with multiple leading periods and the LS command. 06:36.710 --> 06:40.550 With this a option uppercase. 06:40.550 --> 06:45.320 A option will print this to print that. 06:46.680 --> 06:47.310 Uh, so. 06:48.940 --> 06:49.880 And we will. 06:49.900 --> 06:54.460 And as you can see, we got an correct listing of a hidden files. 06:54.460 --> 06:56.110 So I'm waiting you in next lecture.