1 00:00:02,980 --> 00:00:09,800 In this lesson you'll learn how to process command line options using the shell built in getups if you 2 00:00:09,800 --> 00:00:13,310 want your shell scripts to behave like other Linux executables. 3 00:00:13,310 --> 00:00:19,490 You're going to want to allow users to specify options that change the behavior of your scripts. 4 00:00:19,490 --> 00:00:24,980 For example you might want to give the user of both option where the user sees a lot of output from 5 00:00:24,980 --> 00:00:25,750 your script. 6 00:00:25,910 --> 00:00:31,430 Or maybe you want to give them a quiet option where your script does its work silently and then only 7 00:00:31,430 --> 00:00:33,700 reports if it has an error. 8 00:00:33,740 --> 00:00:39,620 Probably one of the first commands you learn how to use on a Linux system was less right after learning 9 00:00:39,620 --> 00:00:47,420 that ls lists files you probably learned about the dash l option which makes LS list files in a long 10 00:00:47,480 --> 00:00:53,870 listing format giving you more information using get ups helps you not only provide such functionality 11 00:00:53,870 --> 00:00:58,770 in your scripts but also helps you to conform to Linux programming conventions. 12 00:00:58,850 --> 00:01:03,560 Knowing what you've learned so far you could use an if statement or a case statement to check for individual 13 00:01:03,560 --> 00:01:06,810 options like Dasch L or dash A. 14 00:01:07,010 --> 00:01:12,550 However if you want to allow the user to combine those short options together so that Dasch L-Space 15 00:01:12,560 --> 00:01:17,850 Dasch a performs exactly like a dash L.A. or dash a. 16 00:01:18,170 --> 00:01:21,290 Doing that with a simple case statement is actually kind of hard. 17 00:01:21,440 --> 00:01:26,160 And get UPS handles this and other little gotchas when working with options. 18 00:01:26,270 --> 00:01:29,660 And that's one of the reasons why we're going to use it here today. 19 00:01:29,990 --> 00:01:31,190 OK let's get to it. 20 00:01:31,190 --> 00:01:37,640 I've got a terminal open on my local machine and I'm going to go into our class folder of shell class 21 00:01:38,000 --> 00:01:43,670 and then we're still working on the local users vagrant project and I'm going to bring up the system 22 00:01:43,670 --> 00:01:52,190 with vigor and up. 23 00:01:52,340 --> 00:01:56,200 Hey let's move into our shared folder of forward slash vagrant. 24 00:01:56,430 --> 00:02:01,880 Now first off getups is a shell built in and we can tell this by running the type command against it 25 00:02:01,880 --> 00:02:06,080 will do type Desch a g e t o p t s. 26 00:02:06,090 --> 00:02:09,060 And sure enough it is a shell built in. 27 00:02:09,270 --> 00:02:14,520 As you already know I recommend using shell built ins whenever possible because it makes your script 28 00:02:14,580 --> 00:02:15,800 more portable. 29 00:02:15,810 --> 00:02:19,040 That's one of the reasons why we're going to be using get ops. 30 00:02:19,050 --> 00:02:25,890 There is a very similar command called Get Opt. that singular that you might see in some older scripts. 31 00:02:25,890 --> 00:02:31,440 Get up is an executable on the file system so it will do type Desch a get up and sure enough that is 32 00:02:31,440 --> 00:02:33,810 located on this particular system in user bin. 33 00:02:33,810 --> 00:02:35,790 Get up Get up. 34 00:02:35,820 --> 00:02:42,030 Is very similar to get ups but it has its limitations in its own set of unique quirks. 35 00:02:42,030 --> 00:02:47,010 If you're interested in learning more about it or you end up having to dive into the details of it at 36 00:02:47,010 --> 00:02:53,340 some point because you run across a script that has to get up in it then just read the man page on get 37 00:02:53,340 --> 00:02:55,560 up and you'll be well on your way. 38 00:02:55,560 --> 00:02:59,560 Now let's get some help on the get UPS built in function here. 39 00:02:59,610 --> 00:03:02,290 So do help get ops. 40 00:03:02,340 --> 00:03:07,950 Actually let me pipe that to less so we can actually read what it says here on the screen and its usage 41 00:03:07,950 --> 00:03:08,250 is. 42 00:03:08,250 --> 00:03:11,010 Get ups Opt. string name. 43 00:03:11,100 --> 00:03:16,700 And as we know anything in brackets is optional so you have an optional argument there on the end. 44 00:03:17,460 --> 00:03:22,590 Now instead of me reading this entire Help section to you just let me quickly summarize it and we'll 45 00:03:22,590 --> 00:03:24,420 start using it right away. 46 00:03:24,540 --> 00:03:29,070 So the Opt. string is something that you are going to provide. 47 00:03:29,070 --> 00:03:33,420 These are the options that your script is going to recognize and accept. 48 00:03:33,420 --> 00:03:36,640 It's just a series of letters that are going to be your options. 49 00:03:36,810 --> 00:03:41,630 If you want to make an option mandatory then follow that letter option with a colon. 50 00:03:41,670 --> 00:03:44,010 Next you're going to provide a name. 51 00:03:44,040 --> 00:03:48,220 It's a variable that's going to get populated with an option. 52 00:03:48,240 --> 00:03:53,430 That way you can do something based on that option because you have no idea what a user is going to 53 00:03:53,430 --> 00:03:56,750 do and how many options they may try to supply. 54 00:03:56,970 --> 00:04:04,700 You'll need to use get ups in a while loop get ops returns 0 as long as it finds an option to process. 55 00:04:04,830 --> 00:04:09,630 Otherwise it returns one which will cause the while loop to exit. 56 00:04:09,630 --> 00:04:14,350 Finally get ups parses positional parameters by default but you can make it parse. 57 00:04:14,360 --> 00:04:18,950 Something else entirely by providing it with an argument at the end. 58 00:04:19,170 --> 00:04:26,010 All right so let's write a script that uses get ups. 59 00:04:26,130 --> 00:04:39,410 Let's make this script generate a password. 60 00:04:39,410 --> 00:04:42,930 Let's also give the users some control over what happens here with a script. 61 00:04:42,950 --> 00:04:50,060 We'll let them specify a password length with a dash l option and whether or not to use a special character 62 00:04:50,330 --> 00:04:52,120 with the dash s option 63 00:05:06,850 --> 00:05:12,730 and let's let them control the verbosity or level of output that is going to be displayed to the screen. 64 00:05:18,950 --> 00:05:22,540 Because a user can optionally specify a password length. 65 00:05:22,550 --> 00:05:25,270 Let's go ahead and set a default value for that 66 00:05:30,790 --> 00:05:39,640 will use the variable length and we'll send it to 48 characters long this default value will be overridden 67 00:05:39,640 --> 00:05:41,500 with whatever the user provides. 68 00:05:41,530 --> 00:05:47,800 If they decide to specify a password length with the dash l option which we're going to account for 69 00:05:47,800 --> 00:05:48,950 in just a second. 70 00:05:49,340 --> 00:05:55,600 Now what we're going to do is use a while loop in conjunction with the get ups command in the while 71 00:05:55,600 --> 00:06:00,180 loop we're going to use a case statement to do something based on the option provided. 72 00:06:00,220 --> 00:06:06,420 This is the structure you're going to see and use when processing command line options. 73 00:06:06,470 --> 00:06:09,630 All right I'll just start the while command here will do while yet. 74 00:06:09,640 --> 00:06:12,010 Ops This is our OP string. 75 00:06:14,140 --> 00:06:17,500 And this is our variable name. 76 00:06:17,530 --> 00:06:18,960 Now remember we have to tell. 77 00:06:18,960 --> 00:06:22,000 Get ups what options are valid here. 78 00:06:22,000 --> 00:06:27,970 We're going to allow the dash via option the dash l option and the dash s option. 79 00:06:27,970 --> 00:06:33,190 That's why we have the characters Violette's and the OP string if you want to make an option have a 80 00:06:33,190 --> 00:06:41,950 mandatory value although that option with a colon by using the L colon as we are saying that the dash 81 00:06:41,980 --> 00:06:46,460 l option must be followed with an argument of its own for this script. 82 00:06:46,480 --> 00:06:50,380 We want the user to supply a link to the dash l option. 83 00:06:56,650 --> 00:07:00,120 Now we're going to use a case statement to process our options. 84 00:07:26,020 --> 00:07:33,490 When an option requires an argument getups places that argument into the shell variable opt ARG here 85 00:07:33,490 --> 00:07:37,430 were signing that arguments value to the link variable. 86 00:07:37,600 --> 00:07:44,490 If the user were to execute our script with Dash L4 then four will be assigned to opt Argin here. 87 00:07:44,500 --> 00:07:50,100 We're assigning that value of 4 into the length the variable that we'll be using later on in the script. 88 00:08:20,950 --> 00:08:26,000 By the way you could have used an asterisk as the catchall pattern in the case statement but get obs 89 00:08:26,030 --> 00:08:29,610 is giving us a single character option at a time. 90 00:08:29,630 --> 00:08:34,280 So I decided to use the pattern for a single character which is the question mark. 91 00:08:34,460 --> 00:08:36,270 We'll come back to this section in the second. 92 00:08:36,290 --> 00:08:39,760 But first let's see what we have so far. 93 00:08:47,680 --> 00:08:51,370 OK that's dash V for the verbose option and that seems to work. 94 00:08:51,700 --> 00:08:55,500 That just doesn't display any output because we didn't tell it to. 95 00:08:55,570 --> 00:09:00,120 Let's see what happens when we run it with Dash L we get an error. 96 00:09:00,130 --> 00:09:06,460 So get ups is taking care of this situation for us it's saying hey this option requires an argument. 97 00:09:06,610 --> 00:09:10,370 So we'll go ahead and give it an argument and that looks good. 98 00:09:10,370 --> 00:09:13,060 Again we didn't print anything or do anything in that case statement. 99 00:09:13,060 --> 00:09:15,630 So this is expected behavior at this point. 100 00:09:15,670 --> 00:09:18,600 So let's do this given an option that is invalid. 101 00:09:18,610 --> 00:09:22,870 So we'll get that here and it says illegal option X.. 102 00:09:23,080 --> 00:09:25,000 OK so this is a good basis for our scrip. 103 00:09:25,000 --> 00:09:27,530 Now let's jump back in and continue building this out. 104 00:09:28,600 --> 00:09:34,870 Instead of echoing in valid option to the screen and exit teaching I want to teach the user how to use 105 00:09:34,870 --> 00:09:35,950 this script. 106 00:09:35,950 --> 00:09:39,270 In theory I could place that code right in the case statement. 107 00:09:39,280 --> 00:09:44,030 However I think it's going to be several lines long so I'm going to put it into a function. 108 00:09:44,050 --> 00:09:46,830 This makes the case statement easier to read. 109 00:09:46,870 --> 00:09:51,930 Again this is a pure judgment call you can do this without a function if you want to. 110 00:09:51,940 --> 00:09:54,310 So here I'm going to do this. 111 00:09:54,310 --> 00:10:00,800 I'm going to get rid of this and instead I'm going to say usage. 112 00:10:00,860 --> 00:10:05,080 Now we have to go back to the top of our script and define this usage function. 113 00:10:05,120 --> 00:10:09,610 Again it's a best practice to place all your functions at the very top of your script. 114 00:10:09,710 --> 00:10:18,720 So I go up here and I will say usage will do this here. 115 00:11:22,690 --> 00:11:29,140 So here we have a function that displays the usage we're modeling our usage here after man pages and 116 00:11:29,140 --> 00:11:30,830 the help built in command. 117 00:11:30,940 --> 00:11:34,870 We're putting optional options within brackets and so on and so forth. 118 00:11:34,870 --> 00:11:39,590 We're giving some information about what those options are and then we're going to exit the script with 119 00:11:39,590 --> 00:11:44,680 the next status of one because if they've ended up here that means they've used an invalid option or 120 00:11:44,680 --> 00:11:45,920 something like that. 121 00:11:45,940 --> 00:11:49,210 So we're going to exit with a non zero exit status. 122 00:11:49,240 --> 00:11:50,920 So let's try this out. 123 00:11:53,880 --> 00:12:02,040 Our user demo 11 dash X and it says a legal option X that's coming from get ups and then what has happened 124 00:12:02,040 --> 00:12:08,640 is our catchall of the question mark in our case statement has been executed or that has been matched 125 00:12:08,910 --> 00:12:14,700 and the code underneath it which is usage causes us to execute the code in the usage function that we 126 00:12:14,700 --> 00:12:17,690 declared and then we get this information to our screen. 127 00:12:17,730 --> 00:12:22,680 Now our exit status should be one because that is what's going on in that function. 128 00:12:22,680 --> 00:12:30,660 So let's just check it real quick and sure enough the exit status is one. 129 00:12:30,840 --> 00:12:35,810 If we're in verbose mode we want to tell the user everything that is happening in the script. 130 00:12:36,030 --> 00:12:37,610 So let's do a little check. 131 00:12:37,620 --> 00:12:45,850 Let's go down here after the case statement and the while loop and we'll do this 132 00:13:03,670 --> 00:13:05,350 so this is the type of check we need. 133 00:13:05,350 --> 00:13:10,810 But if we need to check the verbose variable every time we want to display something to the screen that 134 00:13:10,810 --> 00:13:14,740 is going to be a lot of duplicated code and repeated work. 135 00:13:14,950 --> 00:13:18,190 So in the spirit of keeping things dry don't repeat yourself. 136 00:13:18,340 --> 00:13:24,760 We're going to move this check into a function so I'll just actually delete this and move it back up 137 00:13:24,760 --> 00:13:25,840 to the top here. 138 00:13:31,020 --> 00:13:34,570 So what we'll do is call log. 139 00:13:34,620 --> 00:13:39,000 Now I'm not the biggest fan of that name because we're not actually going to write anything to a log 140 00:13:39,000 --> 00:13:44,820 file and this particular script but it works for demonstration purposes here gives you an idea of what 141 00:13:44,820 --> 00:13:47,270 is happening or what this function does. 142 00:13:47,280 --> 00:13:54,990 Now perhaps we could have named this function something like local echo or display or say or probably 143 00:13:54,990 --> 00:14:00,690 something that I like better or something more verbose like send to standard out or something else that 144 00:14:00,690 --> 00:14:01,400 you dream up. 145 00:14:01,410 --> 00:14:03,860 Anyway I'm going to go with log here for now. 146 00:14:03,860 --> 00:14:05,730 It's going to work for our purposes. 147 00:14:05,760 --> 00:14:12,880 So what are we going to do is have a local variable called message and we're going to assign that any 148 00:14:12,880 --> 00:14:16,090 anything that has been passed into this function. 149 00:14:17,650 --> 00:14:19,560 Now we'll just do our check here. 150 00:14:20,380 --> 00:14:24,860 If verbose is true then we'll echo whatever that message is to the screen. 151 00:14:33,660 --> 00:14:33,910 OK. 152 00:14:33,920 --> 00:14:35,850 And that wraps up our little function. 153 00:14:36,050 --> 00:14:38,950 So now that we have a function we need to call it instead. 154 00:14:38,990 --> 00:14:42,300 So we'll go down to the bottom of our script here. 155 00:14:43,230 --> 00:14:50,510 And instead of doing an echo we'll do log generating a password. 156 00:14:50,580 --> 00:14:56,190 Also we can replace the echo command with the log function for the initial verbose message above. 157 00:14:56,190 --> 00:14:57,900 So we have echo here. 158 00:14:58,020 --> 00:15:02,680 So all we can do the same thing or just log here to be consistent. 159 00:15:02,740 --> 00:15:08,480 Kate let's see if this works so we'll do our script name here and we'll do a dash of the option. 160 00:15:08,780 --> 00:15:14,110 Hey sure enough verbose mode gets printed to the screen generating a password also gets displayed to 161 00:15:14,110 --> 00:15:14,890 the screen. 162 00:15:14,890 --> 00:15:18,070 Well let's see what happens if we don't use for bus mode. 163 00:15:18,490 --> 00:15:18,780 OK. 164 00:15:18,790 --> 00:15:24,580 Nothing gets echoed to the screen even though we had that log that says generating a password. 165 00:15:24,700 --> 00:15:27,760 Well that log function checked a verbose mode was set and it wasn't. 166 00:15:27,760 --> 00:15:32,600 So it did not display it to the screen so this is doing exactly what we wanted to do. 167 00:15:35,730 --> 00:15:37,860 So now it's actually generate a password. 168 00:16:03,080 --> 00:16:06,860 I just stole that little line of code from one of our earlier lessons. 169 00:16:06,890 --> 00:16:11,900 The main thing to point out here is that we're using the variable length we set the default value to 170 00:16:11,900 --> 00:16:17,070 be 48 but a user can change that with a dash l option. 171 00:16:17,070 --> 00:16:22,500 Now let's see if we need to append a special character to the password or not and we can do a simple 172 00:16:22,500 --> 00:16:24,240 check with an if statement. 173 00:17:32,360 --> 00:17:38,800 Again the couple of lines of code here that do the actual work were covered in an earlier lesson. 174 00:17:39,200 --> 00:17:41,930 Let's tell the user that we're done and then just give them the password 175 00:18:05,520 --> 00:18:10,840 and wanted to point out that the reason I'm using the echo statement directly to display the password 176 00:18:10,840 --> 00:18:16,600 is that I want to display that password no matter if the verbose mode is on or not. 177 00:18:16,840 --> 00:18:19,620 So let's check our work at the command line here. 178 00:18:22,120 --> 00:18:27,540 OK we get a random password that's 48 characters in length by default so that looks good. 179 00:18:27,540 --> 00:18:34,560 Let's append the dash s and sure enough you can see that a special character is appended to the end. 180 00:18:34,560 --> 00:18:39,320 Let's do this with verbose mode. 181 00:18:39,460 --> 00:18:44,720 Sure enough now it says verbose mode is on regenerating a password we're selecting a random character. 182 00:18:44,830 --> 00:18:51,130 We're all done and here's your password so that's very very wordy or very verbose so obviously the verbose 183 00:18:51,190 --> 00:18:52,640 mode is doing its job. 184 00:18:52,960 --> 00:18:58,830 Now by the way something that get ups handles for us here is a convention where you can not only do 185 00:18:58,830 --> 00:19:07,630 s v but you can do Dasch the S which is the same as dash of the dash s or dash dash V. 186 00:19:07,960 --> 00:19:15,760 OK now let's try specifying a length so we'll do dash l dash 8 and sure enough we get a password that 187 00:19:15,760 --> 00:19:22,840 has eight characters in it and lets also combine this with a dash s option to append a special character. 188 00:19:22,870 --> 00:19:27,400 All right so we have a password that's 8 in length plus one plus a special character. 189 00:19:27,400 --> 00:19:32,200 Again we could go back and really revise the script and get specific and really make sure that if we're 190 00:19:32,200 --> 00:19:38,230 adding a special character that we chop off a character from the password before it is actually truly 191 00:19:38,230 --> 00:19:39,410 eight characters. 192 00:19:39,430 --> 00:19:44,590 Again I'm of the mind that this probably is close enough this gets us like 90 percent of the way there 193 00:19:44,860 --> 00:19:50,430 without going in and doing some even more complex work that in the end probably truly doesn't matter. 194 00:19:50,500 --> 00:19:52,900 For our practical use case here. 195 00:19:53,300 --> 00:19:59,500 OK so at this point we could really stop here because our script does exactly what we want it to do. 196 00:19:59,530 --> 00:20:04,990 However I want to show you how to handle additional command line arguments beyond the options that you 197 00:20:04,990 --> 00:20:12,010 are taking care of with get ops in order to do that we need to talk about arithmetic expansion and arithmetic 198 00:20:12,010 --> 00:20:12,990 evaluation.