1 00:00:03,240 --> 00:00:10,050 Welcome to this exercise walk through now the script you're going to write today is very closely based 2 00:00:10,050 --> 00:00:11,910 on the previous script you wrote. 3 00:00:12,090 --> 00:00:16,760 As a matter of fact we don't have to do any new coding if we don't want to. 4 00:00:16,830 --> 00:00:23,290 You can simply update that existing script to conform to the new requirements that you have now. 5 00:00:23,460 --> 00:00:29,010 And speaking of those new requirements the helpdesk in our scenario has been using your script and they 6 00:00:29,010 --> 00:00:33,110 notice that there are some extra output that they don't need that they don't care to see. 7 00:00:33,110 --> 00:00:34,860 It really doesn't make any sense to them. 8 00:00:35,010 --> 00:00:37,950 So they want you to make that output disappear. 9 00:00:38,070 --> 00:00:41,550 And of course you know that output comes from the password command. 10 00:00:41,750 --> 00:00:42,690 Ss. 11 00:00:43,050 --> 00:00:49,350 And that you're going to have to use IO redirection to redirect that output to the null device. 12 00:00:49,430 --> 00:00:54,690 And so you start to think about what else you can do to this script with IO redirection and you come 13 00:00:54,690 --> 00:01:01,080 up with that you could actually conform to standard conventions standard Linux programming conventions 14 00:01:01,410 --> 00:01:05,880 by redirecting error messages to standard error and so on. 15 00:01:05,880 --> 00:01:11,700 So with that in mind let's look at just a couple of changes that we're going to make with this script. 16 00:01:11,910 --> 00:01:18,990 So we're going to change the name of the script from add new local user to add newer local user. 17 00:01:18,990 --> 00:01:23,640 Now in the real world I wouldn't necessarily change the name I would just make these couple of updates 18 00:01:23,640 --> 00:01:28,190 to that script in place of course tested first and then put it in for action. 19 00:01:28,200 --> 00:01:33,480 However just for the sake of distinguishing what exercise in what script you're working on if you need 20 00:01:33,480 --> 00:01:34,580 help and so on. 21 00:01:34,740 --> 00:01:40,590 I'm just going to use a new name here so that we just get a unique script for each exercise that we're 22 00:01:40,590 --> 00:01:41,360 working on. 23 00:01:41,550 --> 00:01:45,200 So again in the real world you can keep the same name if you'd like. 24 00:01:45,210 --> 00:01:49,290 Now really all the other requirements are still in play like you want to make sure that the script is 25 00:01:49,290 --> 00:01:54,690 run with super user privileges but the only difference there is that when you display some help or an 26 00:01:54,690 --> 00:02:00,930 error message when they don't then what you want to do is send that output to standard error instead 27 00:02:00,930 --> 00:02:03,110 of standard output like we've been doing. 28 00:02:03,360 --> 00:02:08,100 And that's going to be the same thing for all the error statuses that we're going to display in our 29 00:02:08,100 --> 00:02:11,970 scripts so that's really the main thing that we're going to be changing here. 30 00:02:12,000 --> 00:02:17,190 So here I am on my local system with my terminal open and I'm going to navigate to the class folder 31 00:02:19,280 --> 00:02:23,960 from where I'm going to navigate to the vagrant project that we're using for this set of scripts and 32 00:02:23,960 --> 00:02:25,900 that's local users. 33 00:02:26,090 --> 00:02:30,050 And then I'm going to bring this virtual machine up and then connect to it. 34 00:02:34,590 --> 00:02:41,510 Now I'm going to move into the shared folder of forward slash vagrant and then here I'm actually going 35 00:02:41,510 --> 00:02:48,410 to copy the previous script we used and just copy it to this new name that we're going to work on today. 36 00:02:50,830 --> 00:02:55,660 Of course you can write this entire script from scratch again if you would like just to give yourself 37 00:02:55,660 --> 00:02:56,860 some extra practice. 38 00:02:57,000 --> 00:03:01,540 But here for the walk through I'm just going to show you a couple of changes that you need to make from 39 00:03:01,540 --> 00:03:06,650 the previous script in order to conform to these new requirements that we've come up with here. 40 00:03:10,180 --> 00:03:14,770 So what I'm going to do is just start with the very top of the script and work my way down looking for 41 00:03:14,800 --> 00:03:17,020 any changes that I need to make. 42 00:03:17,020 --> 00:03:22,200 So here I see an exit status of one and an echo statement previously before. 43 00:03:22,210 --> 00:03:25,850 So that's really our error message when we're exiting with a 1. 44 00:03:26,050 --> 00:03:32,390 So what we need to do is send this output from the echo command to standard air right now by default 45 00:03:32,470 --> 00:03:35,750 it's going to be displayed to standard output. 46 00:03:35,910 --> 00:03:41,000 And so we can do this with a greater than symbol and ampersand and 2. 47 00:03:41,080 --> 00:03:45,680 Now realize here that the greater than symbol assumes standard output. 48 00:03:45,880 --> 00:03:52,420 So it's also the same as this if we want to be explicit and specify how far the descriptor one for standard 49 00:03:52,420 --> 00:03:53,120 output. 50 00:03:53,320 --> 00:03:54,070 I'm not going to do that. 51 00:03:54,070 --> 00:03:59,270 I'm just going to delete that and then use this syntax The greater than ampersand too. 52 00:03:59,320 --> 00:04:06,100 And of course as you know in ampersand right after a redirection operator implies that you're using 53 00:04:06,100 --> 00:04:08,380 a file descriptor instead of a file name. 54 00:04:08,380 --> 00:04:12,520 So again file descriptor 2 is associated with standard air. 55 00:04:12,670 --> 00:04:18,380 So that makes the standard output here the Echo would generate be displayed on standard air. 56 00:04:18,600 --> 00:04:20,900 Going to keep working my way down here. 57 00:04:21,010 --> 00:04:25,420 Here I come to another exit statement here and I'm just going to do the same thing. 58 00:04:25,420 --> 00:04:28,290 We're just going to send all this output to standard error 59 00:04:31,400 --> 00:04:35,690 window redraw the screen with the cursor at the top and then just keep on working down here. 60 00:04:36,540 --> 00:04:40,410 So assigning variables is not going to cause any output. 61 00:04:40,410 --> 00:04:46,480 The shift command won't either the output of this command is stored in a variable so it's not getting 62 00:04:46,480 --> 00:04:47,880 displayed anywhere. 63 00:04:48,220 --> 00:04:52,450 OK this is a command that could possibly generate output. 64 00:04:52,460 --> 00:04:59,140 Now let me go down the script a little bit here you can see that we're actually checking for its exit 65 00:04:59,140 --> 00:05:00,460 status down here. 66 00:05:00,580 --> 00:05:05,190 So we don't necessarily need to see the output generated by this command. 67 00:05:05,200 --> 00:05:08,550 So actually what I'm going to do here is ignore all the output. 68 00:05:08,560 --> 00:05:12,920 I don't need to see the standard output or the standard error from this command. 69 00:05:14,580 --> 00:05:20,940 So to redirect both standard output and standard error will use ampersand greater than sign and then 70 00:05:20,940 --> 00:05:26,000 we're going to send that to the dev null device and that's just going to throw away anything and it 71 00:05:26,000 --> 00:05:32,320 gets so all the output generated by this command will not be displayed to the user running the script. 72 00:05:32,500 --> 00:05:37,840 Again we come to another exit statement and that means this echo command right above it is going to 73 00:05:37,840 --> 00:05:46,520 be an error message so we're going to send this to standard air. 74 00:05:46,520 --> 00:05:50,580 OK so this password command we know generates some output. 75 00:05:50,720 --> 00:05:56,810 So what we want to do is you know send that output to dev null so the user doesn't see this output. 76 00:05:56,810 --> 00:06:02,360 So again we're going to use ampersand greater than and send that to the dev null device. 77 00:06:02,420 --> 00:06:07,280 We're doing a check for an exit status of the password command and then we're going to display an error 78 00:06:07,280 --> 00:06:08,390 if we get an error. 79 00:06:08,480 --> 00:06:15,980 So that means this is an error message and needs to be displayed on standard air. 80 00:06:15,980 --> 00:06:18,830 Now we have a another password command again. 81 00:06:18,920 --> 00:06:24,400 The helpdesk users don't want to see these messages so we're just going to send all that output to dev 82 00:06:24,400 --> 00:06:29,770 null. 83 00:06:29,930 --> 00:06:36,950 Since we haven't generated any output in our script here there's no need for a blank line to separate 84 00:06:37,010 --> 00:06:41,920 the information that we're going to display for the user between the output of the previous commands. 85 00:06:41,930 --> 00:06:48,350 So I'm just going to get rid of this echo statement and then the rest of our script here generates the 86 00:06:48,350 --> 00:06:50,780 output that we want the user to see. 87 00:06:50,780 --> 00:06:55,520 So let's go ahead and Saveur changes and then we'll check the permissions on the script. 88 00:06:55,520 --> 00:07:01,190 Now when you copy a script it gets the same permissions as the script it was copied from but we'll go 89 00:07:01,190 --> 00:07:04,580 ahead and check the permissions here just to be thorough. 90 00:07:06,260 --> 00:07:07,820 Hey it's 755. 91 00:07:07,820 --> 00:07:08,620 So that looks good. 92 00:07:08,620 --> 00:07:10,090 You can see the x's there. 93 00:07:10,280 --> 00:07:14,840 And all three sets of permissions so anyone can execute the script. 94 00:07:15,550 --> 00:07:19,330 Now obviously if they don't run it to privileges they're going to get an error message. 95 00:07:19,370 --> 00:07:21,680 But again the executable bit is there. 96 00:07:22,070 --> 00:07:27,790 If you created this script from scratch then you're going to need a chmod 755 your script. 97 00:07:27,860 --> 00:07:33,500 So now that we have our changes in place or a new script written let's go ahead and test it. 98 00:07:33,500 --> 00:07:40,250 So we're going to let's add a new user here and we'll just call this username Turing and the comment 99 00:07:40,250 --> 00:07:48,060 will be Alan Turing and hit enter So now you can see that the only thing is displayed is the username 100 00:07:48,090 --> 00:07:51,350 the password and the host that this user was created on. 101 00:07:51,360 --> 00:07:55,010 None of that extra output from the password commands were displayed on the screen. 102 00:07:55,050 --> 00:07:57,680 And this is exactly what we're looking for. 103 00:07:57,900 --> 00:08:03,330 So going to go ahead and create our other users here we have was 104 00:08:06,830 --> 00:08:13,010 again the display is just the information that is needed by the people running the command will create 105 00:08:13,010 --> 00:08:14,180 another user here. 106 00:08:14,210 --> 00:08:18,210 Call this more for Gordon Moore. 107 00:08:18,320 --> 00:08:20,160 Kate we've created three accounts. 108 00:08:20,360 --> 00:08:26,330 Now let's go ahead and see if those accounts were added to the ETSI password file. 109 00:08:26,360 --> 00:08:31,700 We can do that by just telling the ANSI password file are actually going to do a dash 3 for the last 110 00:08:31,730 --> 00:08:34,190 three lines of the ETSI password file. 111 00:08:34,400 --> 00:08:34,610 OK. 112 00:08:34,610 --> 00:08:35,580 There you can see our users. 113 00:08:35,580 --> 00:08:37,850 Turing was and more. 114 00:08:37,850 --> 00:08:43,010 Now I'm just going to switch to an account to be thorough here to make sure that it still forces the 115 00:08:43,010 --> 00:08:46,830 password expiration and prompts us for a new password on log in. 116 00:08:47,060 --> 00:08:52,290 As a matter of fact before I do this I need to go back up here and actually copy the password 117 00:08:58,010 --> 00:09:01,500 and asking for a current password and then a new password 118 00:09:09,000 --> 00:09:10,540 OK that looks like it worked. 119 00:09:10,540 --> 00:09:16,960 And we're all done with this user so we'll just hit exit here and return to our normal vagrant user. 120 00:09:16,960 --> 00:09:21,940 So the core functionality of our script is still in place it creates users that expire passwords and 121 00:09:21,940 --> 00:09:22,750 so on. 122 00:09:22,750 --> 00:09:26,550 So what we want to do is actually test our new functionality. 123 00:09:26,980 --> 00:09:33,010 So one way to do that is to make our script generate an air and we can do that by not running it with 124 00:09:33,070 --> 00:09:34,500 super user privileges. 125 00:09:36,690 --> 00:09:38,730 Hey we get a message on our screen. 126 00:09:38,860 --> 00:09:43,510 Of course you can't tell if that message is standard input or standard output but we'll get to that 127 00:09:43,510 --> 00:09:44,660 in just a second. 128 00:09:44,800 --> 00:09:46,630 It prints a message to our screen. 129 00:09:46,630 --> 00:09:49,150 Now let's check the exit status of the command. 130 00:09:51,750 --> 00:09:53,930 Sure enough it's an exit status of one. 131 00:09:54,090 --> 00:09:56,460 Which is exactly what we want. 132 00:09:56,490 --> 00:10:01,890 Now let's do the same thing again but this time let's redirect the standard output and standard error 133 00:10:01,890 --> 00:10:05,870 to different places and then check those to see what is going where. 134 00:10:05,940 --> 00:10:11,520 Now because by default standard output and standard error are both displayed to our screen we can't 135 00:10:11,520 --> 00:10:16,450 necessarily tell what standard output or standard error just by looking. 136 00:10:16,800 --> 00:10:22,600 So if we're going to do is redirect standard output to a file called STV out we can name that anything. 137 00:10:22,600 --> 00:10:25,740 I'm just going to use the kind of standard abbreviation here. 138 00:10:25,740 --> 00:10:28,130 Again standard error is going to go to a file. 139 00:10:28,140 --> 00:10:30,040 I'm just going to name SDD. 140 00:10:30,090 --> 00:10:33,600 E r r again you can name it any file name you want. 141 00:10:33,600 --> 00:10:36,710 So all the output either goes to standard out or standard error. 142 00:10:36,870 --> 00:10:39,560 So let's examine the standard elf file. 143 00:10:40,050 --> 00:10:41,960 And there's nothing in that file. 144 00:10:42,240 --> 00:10:46,720 And if we look at standard air then our error messages in that file. 145 00:10:46,800 --> 00:10:52,380 So we know that the echo statement is displaying its output to standard error and that's exactly what 146 00:10:52,380 --> 00:10:53,420 we want. 147 00:10:53,430 --> 00:10:56,100 So let's go ahead and remove these files. 148 00:10:57,200 --> 00:11:00,820 Let's test for another error condition that our script checks for. 149 00:11:01,040 --> 00:11:06,460 We'll actually run the script here but we won't supply any arguments so will hit enter. 150 00:11:06,680 --> 00:11:11,260 And sure enough we get an exit status here of one. 151 00:11:11,450 --> 00:11:13,550 And now let's run the same kind of test. 152 00:11:13,550 --> 00:11:19,950 We'll just send the standard output to standard out and the standard air to a standard error file. 153 00:11:20,030 --> 00:11:22,660 We'll look to see if it generated in the standard output. 154 00:11:22,670 --> 00:11:23,950 It did not. 155 00:11:23,960 --> 00:11:30,500 So all the error messages went to standard error and that's exactly what we want our script to do. 156 00:11:30,610 --> 00:11:32,330 We'll go ahead and clean up here. 157 00:11:34,180 --> 00:11:34,410 All right. 158 00:11:34,420 --> 00:11:39,820 Now that brings us to the end of this exercise so we've made our changes our error messages are now 159 00:11:39,820 --> 00:11:45,430 being displayed to standard air instead of standard out and all that output that was generated from 160 00:11:45,430 --> 00:11:49,120 those other commands are now hidden from the user. 161 00:11:49,150 --> 00:11:53,730 Since I'm done for the day I'm going to exit out of the virtual machine and then go ahead and halt it.