WEBVTT 1 00:00:00.040 --> 00:00:02.399 All right, get ready to dive into the world to 2 00:00:02.480 --> 00:00:05.200 the Linux command line. Yeah, we're going to turn you 3 00:00:05.240 --> 00:00:09.480 into a command line ninja with this twenty twenty one 4 00:00:09.800 --> 00:00:13.839 edition of the Linux command Line and Shell Scripting Bible. 5 00:00:14.480 --> 00:00:16.480 This book, oh wow, the Bible. 6 00:00:16.559 --> 00:00:17.559 Huh, it's a big one. 7 00:00:17.679 --> 00:00:18.000 Yeah. 8 00:00:18.039 --> 00:00:21.399 We've got basic commands, advanced commands. Yeah, we're going to 9 00:00:21.399 --> 00:00:25.480 get into managing files and directories, understanding how the shell 10 00:00:25.559 --> 00:00:29.359 actually works, working with data, and then even getting into 11 00:00:29.399 --> 00:00:30.600 the scripting side of things. 12 00:00:30.800 --> 00:00:31.960 Yeah, this is going to be fun. 13 00:00:32.079 --> 00:00:34.920 So you navigate the file system like a pro, write 14 00:00:35.000 --> 00:00:36.119 some really cool scripts. 15 00:00:37.479 --> 00:00:39.840 I think a good place to start would be just 16 00:00:39.880 --> 00:00:42.159 talking about the different ways that you can even access 17 00:00:42.240 --> 00:00:43.119 the command line. 18 00:00:43.240 --> 00:00:46.000 Okay, yeah, that's a good point. So you've got like 19 00:00:46.320 --> 00:00:51.159 virtual consoles, graphical terminal emulators. That's just like a fancy 20 00:00:51.200 --> 00:00:52.359 way of saying the same thing. 21 00:00:52.560 --> 00:00:55.399 Well, I would say it's important to know the difference 22 00:00:55.759 --> 00:00:58.560 because it affects how you interact with the system. So 23 00:00:58.679 --> 00:01:01.520 when you think about virtual consoles, you want to think 24 00:01:01.560 --> 00:01:05.000 about it's like a direct connection to your system's heart. 25 00:01:05.439 --> 00:01:08.439 It runs right on the system memory. Oh, so it 26 00:01:08.439 --> 00:01:12.760 gives you that old school no frills command line experience. Now, 27 00:01:12.879 --> 00:01:16.719 terminal emulators are like command line windows within your graphical 28 00:01:16.760 --> 00:01:20.560 desktop environment. Okay, they're going to give you more flexibility 29 00:01:20.560 --> 00:01:23.319 and features, but they do have a little bit of 30 00:01:23.359 --> 00:01:24.560 a performance trade off. 31 00:01:25.280 --> 00:01:27.799 Yeah, I guess that makes sense. It has to run 32 00:01:27.840 --> 00:01:31.439 inside of the graphical environment. Okay, So choosing between those 33 00:01:31.439 --> 00:01:33.120 two is like choosing if you're going to be a 34 00:01:33.120 --> 00:01:35.879 survivalist or if you want like the modern conveniences of 35 00:01:35.879 --> 00:01:40.200 the graphical environment. But in both cases you're still using 36 00:01:40.200 --> 00:01:42.560 that command line. So now that we're in the command line, 37 00:01:43.239 --> 00:01:45.120 how do you find your way around? It's not like 38 00:01:45.599 --> 00:01:47.920 Windows with folders and icons and all of that. 39 00:01:47.920 --> 00:01:51.359 That's right. So we've got the Linux file structure. It 40 00:01:51.640 --> 00:01:53.840 is quite a bit different from what you might be 41 00:01:54.040 --> 00:01:58.200 used to, but once you grasp it, it's pretty logical 42 00:01:58.319 --> 00:02:01.560 actually and efficient. Fit like a tree with the root 43 00:02:01.599 --> 00:02:04.840 directory as the trunk. Everything kind of branches out from there. 44 00:02:05.000 --> 00:02:05.439 I see. 45 00:02:05.480 --> 00:02:08.759 And then here's where it gets interesting. Mount points Okay, 46 00:02:08.759 --> 00:02:10.560 you know those are those connectors that let you attach 47 00:02:10.599 --> 00:02:14.719 additional storage devices like hard drives USB drives, Yeah, and 48 00:02:14.759 --> 00:02:17.560 make them appear as part of this unified tree structure. 49 00:02:17.680 --> 00:02:20.560 So no matter where I plug a new device in, 50 00:02:20.960 --> 00:02:22.000 it's going to show. 51 00:02:21.879 --> 00:02:23.439 Up in that one seamlessly integrated. 52 00:02:23.479 --> 00:02:27.400 Okay, it's pretty cool. But with all those directories and files, 53 00:02:27.800 --> 00:02:29.560 how do you it can get. 54 00:02:29.439 --> 00:02:32.759 A little bit daunting. Yeah, especially with those really long 55 00:02:32.800 --> 00:02:34.120 file names that Lennox. 56 00:02:33.840 --> 00:02:36.039 Is known for. Right, yeah, yeah, exactly, exactly. 57 00:02:36.159 --> 00:02:40.199 Yeah. So you've got a master tab completion. Okay, that's 58 00:02:40.240 --> 00:02:43.159 your first step towards being a command line ninja. Right, 59 00:02:43.319 --> 00:02:46.199 just start typing a command or file name, hit the 60 00:02:46.240 --> 00:02:49.280 tab key, and then the shell will just magically complete 61 00:02:49.319 --> 00:02:51.199 it for you. It's going to give you suggestions. It 62 00:02:51.240 --> 00:02:52.520 is a real time saver, right. 63 00:02:52.479 --> 00:02:56.199 Find me up for that. So I've got tab completion. 64 00:02:56.439 --> 00:02:57.360 What other tips? 65 00:02:57.759 --> 00:02:59.879 Okay? So another tip is to look out for those 66 00:03:00.039 --> 00:03:00.840 hidden files. 67 00:03:01.000 --> 00:03:01.240 Okay. 68 00:03:01.319 --> 00:03:05.240 They start with a period, and they're normally invisible, right okay, 69 00:03:05.479 --> 00:03:09.000 and they often contain some pretty important configuration settings or 70 00:03:09.080 --> 00:03:12.199 system data. So if you ever need to delve into 71 00:03:12.280 --> 00:03:15.919 that hidden world, the LSA command is your go to. 72 00:03:16.439 --> 00:03:19.080 It's like putting on X ray vision for the file system. 73 00:03:19.159 --> 00:03:21.080 Oh okay, So I need to be careful not to 74 00:03:21.159 --> 00:03:24.879 delete anything that I can't see them. If it's important, you. 75 00:03:24.879 --> 00:03:26.639 Don't want to accidentally delete something important? 76 00:03:26.800 --> 00:03:31.120 Yeah, yeah, okay, Now let's get into actually managing these files, right, 77 00:03:31.240 --> 00:03:33.400 I mean, what good is a command line if you 78 00:03:33.479 --> 00:03:36.479 can't move, copy, delete these files? 79 00:03:36.800 --> 00:03:40.639 Absolutely, So this book it dives into those essential commands 80 00:03:40.919 --> 00:03:44.520 CEE for copying, m V for moving or renaming, and 81 00:03:44.599 --> 00:03:47.960 then of course we've got the infamous RMM for deleting. Yeah, 82 00:03:48.039 --> 00:03:50.919 but before you go on a deleting spree, we've got 83 00:03:51.000 --> 00:03:51.800 to talk about. 84 00:03:51.560 --> 00:03:53.759 In noodes innodess a little technical. 85 00:03:53.879 --> 00:03:56.479 Yeah, they are a little technical, but they're also very cool. 86 00:03:56.800 --> 00:04:00.400 They're like unique fingerprints for each file. So even if 87 00:04:00.439 --> 00:04:03.039 you change a file's name or move it, it's in 88 00:04:03.159 --> 00:04:04.400 a number stays the same. 89 00:04:04.599 --> 00:04:07.000 So it's not just about the name, that's right, it's 90 00:04:07.039 --> 00:04:10.319 an underlying identifier. Okay, So imagine if you need to 91 00:04:10.319 --> 00:04:13.319 find a file that's been moved or renamed. In odes 92 00:04:13.360 --> 00:04:15.759 are your secret weapon. I see, Yeah, you can find 93 00:04:15.759 --> 00:04:17.399 that file no matter where it is. Wow. 94 00:04:17.560 --> 00:04:21.399 Okay, yeah, Now what about dealing with the output of commands? 95 00:04:22.079 --> 00:04:24.439 Sometimes you get this massive wall. 96 00:04:24.240 --> 00:04:26.199 Of text that's right scrolling by. 97 00:04:26.480 --> 00:04:28.560 Is there a way to kind of capture that information? 98 00:04:28.800 --> 00:04:32.040 Yes, So that's where we've got output redirection. Okay, this 99 00:04:32.120 --> 00:04:34.480 is one of those aha moments. Once you learn how 100 00:04:34.480 --> 00:04:37.759 to use it. The symbol is your friend here. Okay, 101 00:04:38.199 --> 00:04:41.639 you can readirect the output of a command to a file, 102 00:04:41.759 --> 00:04:44.279 so instead of seeing it on the screen, you can 103 00:04:44.480 --> 00:04:47.160 capture it, put it in a file, and use it 104 00:04:47.279 --> 00:04:51.399 later for analysis or reference. Oh that's so useful. Yeah, 105 00:04:51.519 --> 00:04:53.160 instead of it just flying by on the screen. 106 00:04:53.240 --> 00:04:54.360 Yeah, just capture it. 107 00:04:54.279 --> 00:04:55.680 You can actually. Yeah, okay, brilliant. 108 00:04:55.759 --> 00:04:56.720 Yeah, it's a good one. 109 00:04:56.839 --> 00:05:00.639 Now we keep hearing the word shell. Exactly is a shell? 110 00:05:00.879 --> 00:05:02.160 Ah? Yes, the shell? 111 00:05:02.240 --> 00:05:03.399 And why should I care about it? 112 00:05:03.399 --> 00:05:05.879 The shell? So think about this. This is your command 113 00:05:05.879 --> 00:05:09.480 line interpreter, the bridge between you and the Linux kernel, 114 00:05:10.000 --> 00:05:12.759 which is the heart of the operating system. Right, So 115 00:05:12.839 --> 00:05:15.600 it's taking your commands, figuring out what you mean, and 116 00:05:15.680 --> 00:05:18.240 then it instructs the kernel to make it happen. 117 00:05:18.439 --> 00:05:18.759 Gotcha. 118 00:05:18.879 --> 00:05:21.199 And there's not just one shell. There's several. 119 00:05:21.360 --> 00:05:23.839 Oh interesting, So I don't have to just use one shell. 120 00:05:24.000 --> 00:05:27.639 No, And this book delves into the different types of shells, 121 00:05:27.720 --> 00:05:30.800 like the very popular beast shell off in the default, 122 00:05:31.399 --> 00:05:35.040 and then you have alternatives like TS and DASH. 123 00:05:35.079 --> 00:05:38.079 Wow. Okay, so there's each one has its choices. 124 00:05:38.199 --> 00:05:42.000 Yeah, they each have their own personality, their own quirks strengths. 125 00:05:42.079 --> 00:05:44.279 So it's like choosing your weapon, choosing your. 126 00:05:44.519 --> 00:05:47.519 Exactly which one fits your style and needs. 127 00:05:47.800 --> 00:05:51.560 Now, every time I hit enter, it creates a child process. 128 00:05:51.839 --> 00:05:54.639 That's right, a child process to handle that command. 129 00:05:54.759 --> 00:05:56.839 So there's a whole family going on every time I 130 00:05:56.920 --> 00:05:57.360 hit a key. 131 00:05:57.720 --> 00:06:00.360 It's like a parent shell gives both to it childs 132 00:06:00.360 --> 00:06:02.079 shell to kind of carry out your instructions. 133 00:06:02.319 --> 00:06:05.480 I see. Okay. And then they also mentioned subshells are 134 00:06:05.519 --> 00:06:08.399 subshells like the rebellious teenager of the shell world. 135 00:06:08.680 --> 00:06:09.079 Huh. 136 00:06:09.120 --> 00:06:09.560 I like that. 137 00:06:10.399 --> 00:06:15.120 Yeah, kind of subshells are temporary shells created within your 138 00:06:15.160 --> 00:06:18.720 main shell. Okay, So think of it as a sandbox 139 00:06:19.160 --> 00:06:22.759 where you can play around commands and environment variables without 140 00:06:22.759 --> 00:06:24.399 really affecting your main shell. 141 00:06:24.560 --> 00:06:26.519 So if I mess up in the subshell, it doesn't 142 00:06:26.519 --> 00:06:28.160 blow up my main shell exactly. 143 00:06:28.240 --> 00:06:30.160 That's the beauty of it. What happens in the subshell 144 00:06:30.240 --> 00:06:31.279 stays in the subshell. 145 00:06:31.439 --> 00:06:33.360 Okay, I like that. Yeah, all right, now let's talk 146 00:06:33.360 --> 00:06:34.639 about environment variables. 147 00:06:34.879 --> 00:06:35.199 Hmmm. 148 00:06:36.480 --> 00:06:37.959 That sounds a little bit intimidating. 149 00:06:38.079 --> 00:06:40.279 I know, I know they can be. Yeah, but think 150 00:06:40.279 --> 00:06:45.079 about like this. They're the settings that control how your 151 00:06:45.279 --> 00:06:48.759 shell and other programs behave. So it's like a behind 152 00:06:48.800 --> 00:06:50.720 the scenes control panel for your system. 153 00:06:50.920 --> 00:06:51.399 I see. 154 00:06:51.519 --> 00:06:56.319 Now you have global environment variables those apply system wide, okay, 155 00:06:56.399 --> 00:06:59.240 and then you have local ones, which are specific to 156 00:06:59.399 --> 00:07:00.920 your current shell session. 157 00:07:01.120 --> 00:07:04.000 So global or like the laws of the Lenox universe, 158 00:07:04.480 --> 00:07:06.600 and local are like my own personal preference. 159 00:07:06.720 --> 00:07:08.839 There you go. Okay, that's a great way to put it. 160 00:07:08.920 --> 00:07:17.439 Now. The book mentions these VIP environment variables. Yes, like path, home, shell, term. 161 00:07:18.120 --> 00:07:18.720 It's a path. 162 00:07:18.839 --> 00:07:19.600 Yeah, where are those? 163 00:07:19.680 --> 00:07:22.639 So? Path that tells the shell where to look for 164 00:07:22.759 --> 00:07:26.360 executable commands. Okay, so it's like a roadmap guiding the 165 00:07:26.360 --> 00:07:27.800 shell to find those tools. 166 00:07:27.920 --> 00:07:28.240 Gotcha. 167 00:07:28.360 --> 00:07:32.560 And then home that points to your home directory, your 168 00:07:32.600 --> 00:07:37.519 personal space within that file system. Shell specifies which shell 169 00:07:37.639 --> 00:07:41.279 you're using, and then term defines your terminal type okay, 170 00:07:41.319 --> 00:07:44.680 so that programs understand how to display information properly. 171 00:07:44.800 --> 00:07:46.920 So these variables are kind of like setting the stage 172 00:07:46.920 --> 00:07:47.920 for how everything's going to do. 173 00:07:48.040 --> 00:07:50.120 That's right, how everything is going to run okay. Yeah, 174 00:07:50.279 --> 00:07:55.000 and then you've got commands like set envy and print him. 175 00:07:55.040 --> 00:07:57.000 Those are going to be your tools for viewing and 176 00:07:57.120 --> 00:08:00.079 manipulating these environment variables. 177 00:08:00.120 --> 00:08:04.319 So we can actually modify these settings totally customize our environments. Yep. 178 00:08:04.680 --> 00:08:06.480 All right, Now we need to talk about these shell 179 00:08:06.560 --> 00:08:09.319 startup files okay, before we get too far into the 180 00:08:09.800 --> 00:08:10.600 scripting side. 181 00:08:10.720 --> 00:08:13.720 Right, So these are those secret ingredients that make your 182 00:08:13.800 --> 00:08:19.519 shell experience really personalized. Okay, So shell startup files like 183 00:08:19.639 --> 00:08:24.160 et cetera profile, dot bash profile, dot bash rc. There're 184 00:08:24.240 --> 00:08:26.600 scripts that run every time you log in or start 185 00:08:26.639 --> 00:08:27.560 a new shell session. 186 00:08:27.639 --> 00:08:29.199 So it's like a set of instructions for how the 187 00:08:29.199 --> 00:08:29.759 shell's going. 188 00:08:29.680 --> 00:08:31.480 To exactly how it's going to set up. Okay, you 189 00:08:31.480 --> 00:08:35.320 know you can customize your command prompt, set environment variables, 190 00:08:35.320 --> 00:08:38.360 define aliases for those frequently used commands. Wow. 191 00:08:38.399 --> 00:08:40.720 So it's like my own little personal exactly. It's like 192 00:08:40.759 --> 00:08:41.559 your assistant. 193 00:08:41.600 --> 00:08:43.840 It's like having a personal assistant just for your shell, 194 00:08:44.080 --> 00:08:46.000 taking care of all the yeah, taking care of all 195 00:08:46.000 --> 00:08:48.440 the tedious stuff so you can focus on the fun stuff. 196 00:08:48.639 --> 00:08:51.159 Okay, So now we've got our environments set up, it's 197 00:08:51.200 --> 00:08:52.720 time to write a shell script. 198 00:08:52.799 --> 00:08:53.799 All right? Are you ready? 199 00:08:53.879 --> 00:08:57.360 Yeah? How do we bring these shell scripts to life? 200 00:08:57.399 --> 00:08:59.960 All right? So first thing you want to do is 201 00:09:00.120 --> 00:09:03.080 you want to create a simple text file. Okay, you're 202 00:09:03.080 --> 00:09:06.639 going to write your commands in plain text, just like 203 00:09:06.679 --> 00:09:08.879 you would type them at the command line, right, and 204 00:09:08.919 --> 00:09:11.799 then you need to make that script executable using the 205 00:09:11.879 --> 00:09:12.639 chron command. 206 00:09:13.080 --> 00:09:15.159 So we're giving it permission to do its things. 207 00:09:15.200 --> 00:09:18.039 Exactly, you're giving it permission to do its thing. You're 208 00:09:18.120 --> 00:09:20.840 changing the file permissions and telling the system, hey, this 209 00:09:20.879 --> 00:09:23.320 is a program. This can be executed. 210 00:09:23.519 --> 00:09:26.759 Gotcha. So what kind of commands can we put inside 211 00:09:26.799 --> 00:09:27.559 of these scripts? 212 00:09:27.679 --> 00:09:31.159 So you've got the Echo command. That's your basic communication tool. 213 00:09:31.399 --> 00:09:31.799 Okay. 214 00:09:31.919 --> 00:09:34.639 You can display messages on the screen, so it's good 215 00:09:34.639 --> 00:09:38.159 for providing feedback or debugging your script. 216 00:09:38.480 --> 00:09:41.960 So if I wanted to say Hello World, I could 217 00:09:41.960 --> 00:09:42.759 do that with Echo. 218 00:09:42.960 --> 00:09:44.399 You got it. Echo is your friend? 219 00:09:44.679 --> 00:09:47.799 All right? What about making these scripts a little more dynamic, 220 00:09:48.120 --> 00:09:49.679 like working with data? 221 00:09:49.720 --> 00:09:51.840 Ah? Okay, so we're going to bring in variables. 222 00:09:51.919 --> 00:09:52.159 Okay. 223 00:09:52.279 --> 00:09:56.639 Variables are like containers that hold data within your script. 224 00:09:56.840 --> 00:10:00.919 So think of them as like labeled boxes store information 225 00:10:01.679 --> 00:10:05.480 and then refer to that information by that label or 226 00:10:05.679 --> 00:10:06.559 variable name. 227 00:10:06.720 --> 00:10:08.039 So it's like giving the script a memory. 228 00:10:08.080 --> 00:10:10.480 Then you got it. You're giving it a memory. And 229 00:10:10.840 --> 00:10:15.919 this book shows you how to assign values to those variables, 230 00:10:16.440 --> 00:10:19.799 and then use those values within your script. It even 231 00:10:19.840 --> 00:10:22.240 shows you how to capture the output of a command 232 00:10:22.799 --> 00:10:24.200 and store that in a variable. 233 00:10:24.320 --> 00:10:27.039 Really yeah, so I could run a command and then 234 00:10:27.240 --> 00:10:29.679 take that output and use it somewhere else. 235 00:10:29.519 --> 00:10:31.240 And feed it into your script. Yeah. 236 00:10:31.279 --> 00:10:31.960 That's awesome. 237 00:10:32.159 --> 00:10:33.039 Yeah, that's a good one. 238 00:10:33.080 --> 00:10:33.919 So how do you do that? 239 00:10:34.519 --> 00:10:36.679 So there's a couple of ways to do it. One 240 00:10:36.720 --> 00:10:39.519 is using backticks. That's the older syntax okay, and then 241 00:10:39.519 --> 00:10:42.000 you've got the newer syntax for command substitution. 242 00:10:42.159 --> 00:10:42.480 Okay. 243 00:10:42.639 --> 00:10:46.080 Both achieve the same goal. They're capturing the output of 244 00:10:46.080 --> 00:10:49.320 that command to data stream and then you can feed 245 00:10:49.360 --> 00:10:50.919 that into your script, so I. 246 00:10:50.919 --> 00:10:54.360 Can build mini pipelines right inside my script. That's right. Wow, yeah, 247 00:10:54.360 --> 00:10:56.159 pretty cool? Right, this is really cool. Yeah. 248 00:10:56.200 --> 00:10:59.159 So we've covered the foundations of shell scripting here, but 249 00:10:59.240 --> 00:11:00.960 there's so much more to explore. 250 00:11:01.240 --> 00:11:02.919 I'm ready. What's coming up next? 251 00:11:03.000 --> 00:11:05.679 Okay? Well, next we're going to dive into more advanced 252 00:11:05.720 --> 00:11:09.799 scripting techniques like conditional statements and loops. Those allow your 253 00:11:09.840 --> 00:11:12.279 scripts to make decisions and repeat actions. 254 00:11:12.440 --> 00:11:14.639 Okay, cool, let's get into it all right, So. 255 00:11:14.679 --> 00:11:17.399 Are you ready to go beyond those scripting basics and 256 00:11:17.440 --> 00:11:19.039 give those scripts some intelligence. 257 00:11:19.120 --> 00:11:19.559 I'm ready. 258 00:11:19.559 --> 00:11:22.360 How do we do that with conditional statements and loops? 259 00:11:22.720 --> 00:11:24.399 Ooh that sounds interesting. 260 00:11:24.559 --> 00:11:27.120 Yeah, they're really cool. It's like adding a brain to 261 00:11:27.200 --> 00:11:30.159 your script so they can adapt to different situations and 262 00:11:30.279 --> 00:11:33.360 automate those tedious, repetitive tasks. Right. 263 00:11:33.399 --> 00:11:36.000 Oh yeah, yeah, okay, so let's start with conditional statements. 264 00:11:36.320 --> 00:11:38.399 How do those work? It kind of sounds like teaching 265 00:11:38.399 --> 00:11:39.240 the script to think. 266 00:11:39.399 --> 00:11:42.320 Yeah, it's kind of like that the if then statement. Okay, 267 00:11:42.360 --> 00:11:45.440 it's your building block for decision making. You know. Think 268 00:11:45.480 --> 00:11:49.480 of it like a gatekeeper evaluating a condition and only 269 00:11:49.559 --> 00:11:52.159 letting those commands through if the condition is true. 270 00:11:52.480 --> 00:11:55.440 So it's like saying, hey, script, if this is true, 271 00:11:55.480 --> 00:11:58.639 then do that. If not, skip it, that's right. Okay, 272 00:11:59.120 --> 00:12:01.159 what kind of condition can we actually put in there? 273 00:12:01.200 --> 00:12:04.480 Well? Remember those exit status codes. You know, the command 274 00:12:04.679 --> 00:12:07.399 typically exists with the status of zero if it's successful, 275 00:12:07.879 --> 00:12:11.159 or a non zero status if there's an error. Right, right, Well, 276 00:12:11.159 --> 00:12:13.840 conditional statements use those statuses to make decisions. 277 00:12:13.960 --> 00:12:16.759 Oh okay, so the command is actually reporting back to 278 00:12:16.759 --> 00:12:19.159 the script saying hey I did it, or hey I 279 00:12:19.200 --> 00:12:21.600 had a problem that's right. You decide what to do 280 00:12:21.679 --> 00:12:22.639 next exactly. 281 00:12:22.679 --> 00:12:26.240 So in an if then statement, if that preceding command 282 00:12:26.360 --> 00:12:29.639 exits with a zero, the commands in the then block 283 00:12:30.039 --> 00:12:32.440 get executed. Otherwise they get skipped. 284 00:12:32.519 --> 00:12:34.559 Okay, So what if you want to have an alternative 285 00:12:34.679 --> 00:12:37.799 like run these commands if it's true, but if not, 286 00:12:38.039 --> 00:12:38.960 then do something else. 287 00:12:39.159 --> 00:12:40.639 Ah, so you want a backup plan? 288 00:12:40.799 --> 00:12:41.440 Yeah, exactly. 289 00:12:41.440 --> 00:12:44.200 Well that's where if then else comes in. It's giving 290 00:12:44.240 --> 00:12:47.519 your scripts two possible paths. Okay, one for when the 291 00:12:47.519 --> 00:12:49.679 condition is true and one for when it's false. 292 00:12:50.120 --> 00:12:52.639 I like having options. You got it now. I also 293 00:12:52.679 --> 00:12:59.360 see nested if statements. Yes, are those like nsted if statements? 294 00:12:59.440 --> 00:13:03.720 Those rush yes exactly, like those Russian nesting dolls with 295 00:13:03.840 --> 00:13:07.039 one if statement inside of another. Okay, So that allows 296 00:13:07.120 --> 00:13:11.240 you to create more complex decision making logic. You know, 297 00:13:11.320 --> 00:13:13.679 it's like creating a multi level decision tree. 298 00:13:13.759 --> 00:13:16.799 So it's like adding layers of intelligence to that script. 299 00:13:16.960 --> 00:13:17.399 That's right. 300 00:13:17.440 --> 00:13:19.840 It can evaluate more sophisticated scenarios. 301 00:13:19.919 --> 00:13:20.440 Exactly. 302 00:13:20.799 --> 00:13:23.279 Wow. Okay, now we need to talk about loops. 303 00:13:23.759 --> 00:13:27.519 Okay, So loops for those repetitive tasks exactly. Loops are 304 00:13:27.600 --> 00:13:31.039 the workhorses of automation. Okay, the book covers several types 305 00:13:31.080 --> 00:13:32.960 of loops, for loops and wild loops. 306 00:13:33.200 --> 00:13:35.960 You know, imagine if you had to process one hundred files, 307 00:13:36.080 --> 00:13:39.519 or maybe you're waiting for a specific condition to change. Yeah, 308 00:13:40.120 --> 00:13:43.399 you know loops. Let you handle those situations without writing 309 00:13:43.399 --> 00:13:45.159 the same commands over and over again. 310 00:13:45.399 --> 00:13:47.480 Okay, yeah, I can see where that would get really tedious. 311 00:13:47.559 --> 00:13:48.759 Yeah, I would get really tedious. 312 00:13:48.799 --> 00:13:50.159 Okay, let's start with the four loop. 313 00:13:50.440 --> 00:13:51.480 All right. So the four loop. 314 00:13:51.639 --> 00:13:52.440 How does that one work? 315 00:13:52.639 --> 00:13:56.320 It's design to iterate through a list of values, okay, 316 00:13:56.399 --> 00:13:59.320 and execute a set of commands for each value. It's 317 00:13:59.320 --> 00:14:02.480 like a processing You take each item from that list, 318 00:14:02.720 --> 00:14:05.480 you run it through the same set of instructions. 319 00:14:05.759 --> 00:14:07.480 Gotcha. So if I had a list of file names, 320 00:14:07.519 --> 00:14:10.000 I could run the same action on all those files exactly. 321 00:14:10.120 --> 00:14:12.399 That's pretty cool. What about the wile loop? 322 00:14:12.440 --> 00:14:13.559 All right? So the wile loop? 323 00:14:13.559 --> 00:14:14.480 Why would I use that one? 324 00:14:14.559 --> 00:14:18.320 So the wile loop is like this persistent little engine. Okay, 325 00:14:18.399 --> 00:14:23.320 It keeps running as long as a specific condition remains true. Okay, 326 00:14:23.600 --> 00:14:26.399 So it's perfect for situations where you don't know in 327 00:14:26.519 --> 00:14:29.440 advance how many times you need to repeat those commands. 328 00:14:29.879 --> 00:14:33.600 So imagine you're monitoring a system log file okay, and 329 00:14:33.639 --> 00:14:38.000 you're waiting for a specific error message to appear. Yeah, 330 00:14:38.120 --> 00:14:41.600 a while loop can keep checking that file, oh okay 331 00:14:41.720 --> 00:14:43.000 until that message pops out. 332 00:14:43.080 --> 00:14:45.320 Yeah, so it's just constantly checking and checking. 333 00:14:45.120 --> 00:14:47.639 Until exactly continually monitoring. 334 00:14:47.759 --> 00:14:50.399 Okay. What if I need to bail out of a 335 00:14:50.440 --> 00:14:51.120 loop early? 336 00:14:51.720 --> 00:14:55.200 Ah, well, we've got the brake command for that. 337 00:14:55.639 --> 00:14:55.879 Okay. 338 00:14:55.919 --> 00:14:59.120 You know, that's your emergency exit for loops. So if 339 00:14:59.159 --> 00:15:02.759 a certain condition is met within that loop, yeah, break, 340 00:15:03.000 --> 00:15:06.720 we'll stop it right there, preventing any further iteration, like. 341 00:15:06.679 --> 00:15:08.159 The loop stopping Superhero. 342 00:15:08.279 --> 00:15:11.200 That's right, that's right. So what about skipping over certain 343 00:15:11.240 --> 00:15:12.320 iterations of a loop? 344 00:15:12.399 --> 00:15:14.399 Oh? Yeah? What if I want to just process certain 345 00:15:14.440 --> 00:15:17.039 files like that meet certain criteria. 346 00:15:16.639 --> 00:15:19.360 Well, for that, you have the continued command OKA that 347 00:15:19.480 --> 00:15:22.480 lets you jump to the next iteration of the loop 348 00:15:22.799 --> 00:15:24.919 without executing those remaining commands. 349 00:15:25.000 --> 00:15:26.720 It's like, nope, not that one, move on to the 350 00:15:26.759 --> 00:15:30.720 next exactly exactly. Okay. These loop control commands are really cool. 351 00:15:31.080 --> 00:15:34.039 So I've got conditional statements for decision making, we've got 352 00:15:34.080 --> 00:15:37.879 loops for repeating actions. What else can we do to 353 00:15:37.919 --> 00:15:40.480 make our scripts a little more interactive and powerful. 354 00:15:40.639 --> 00:15:43.960 Well, how about giving them the ability to take constructions 355 00:15:44.080 --> 00:15:47.039 directly from the user? Oh okay, you know with command 356 00:15:47.039 --> 00:15:47.759 line parameters. 357 00:15:47.799 --> 00:15:50.399 Okay, so like giving it instructions or settings when I 358 00:15:50.519 --> 00:15:51.080 start the. 359 00:15:51.000 --> 00:15:55.039 Script exactly exactly. You know, you pass information to the 360 00:15:55.080 --> 00:15:58.360 script when you run it, customize its behavior on the fly. 361 00:15:58.720 --> 00:15:59.080 Okay. 362 00:15:59.159 --> 00:16:03.480 Within the script, you access those parameters using special variables 363 00:16:03.519 --> 00:16:06.120 like one dollar, two dollars, and so on. One dollars 364 00:16:06.159 --> 00:16:08.759 is the first parameter, two dollars is the second. 365 00:16:08.879 --> 00:16:11.840 Okay, that's pretty straightforward. What if I've got a script 366 00:16:11.879 --> 00:16:14.399 that takes a bunch of parameters, Well, you know, the. 367 00:16:14.320 --> 00:16:17.559 Book explains special variables like hashtag that gives you the 368 00:16:17.600 --> 00:16:20.480 total number of parameters past ok and then you have 369 00:16:20.799 --> 00:16:22.840 at which lets you access all of them as a 370 00:16:22.840 --> 00:16:23.480 single unit. 371 00:16:23.759 --> 00:16:24.080 Gotcha. 372 00:16:24.200 --> 00:16:27.559 And then there's even a clever trick to access the 373 00:16:27.679 --> 00:16:29.799 very last parameter using ash. 374 00:16:29.960 --> 00:16:30.960 Wow. It's pretty handy. 375 00:16:31.039 --> 00:16:33.720 Yeah, it's pretty handy. So how about those single letter 376 00:16:33.720 --> 00:16:38.080 command line options, right, you know, like L for the long. 377 00:16:37.879 --> 00:16:39.960 Listing with l's Yeah, yeah, exactly. 378 00:16:40.000 --> 00:16:41.360 You can use those in your scripts too. 379 00:16:41.559 --> 00:16:41.879 Really. 380 00:16:42.039 --> 00:16:45.519 Yeah, So the book outlines three ways to handle those options, okay, 381 00:16:45.639 --> 00:16:48.399 so you can process them directly as parameters. You can 382 00:16:48.519 --> 00:16:52.879 use if statements to check for specific options, or the 383 00:16:52.919 --> 00:16:56.200 most elegant approach is to use the get tops command 384 00:16:56.320 --> 00:16:58.720 get tops get tops. You know that's your built in 385 00:16:59.000 --> 00:17:00.279 option parsing wizard. 386 00:17:00.639 --> 00:17:01.120 Oh wow. 387 00:17:01.279 --> 00:17:04.200 It handles both short and long options, whether they have 388 00:17:04.240 --> 00:17:05.519 associated values or not. 389 00:17:05.799 --> 00:17:06.079 Wow. 390 00:17:06.440 --> 00:17:08.880 And you can even specify which options are expected. 391 00:17:09.119 --> 00:17:11.839 So it's kind of streamlining all that option handling exactly. 392 00:17:11.880 --> 00:17:13.759 It streamlines it and makes it more robust. 393 00:17:13.920 --> 00:17:17.880 Okay, very cool. So we've got conditional statements, loops, we've 394 00:17:17.920 --> 00:17:21.359 got these command line parameters and options. Anything else we 395 00:17:21.400 --> 00:17:22.079 can do well. 396 00:17:22.240 --> 00:17:25.440 One of the most powerful techniques is to encapsulate those 397 00:17:25.759 --> 00:17:29.160 reusable code blocks into functions. 398 00:17:29.200 --> 00:17:31.839 Functions okay, yeah, functions in programming. 399 00:17:31.960 --> 00:17:34.000 Yeah, just like in programming. They are like mini scripts 400 00:17:34.000 --> 00:17:37.559 within your main script. They help you avoid repetition and 401 00:17:37.640 --> 00:17:41.079