1 00:00:01,360 --> 00:00:07,800 Last option or how to assign a value to a variable is by using command substitution. 2 00:00:07,800 --> 00:00:14,280 Here we are storing output of system command into variable and we have to raise how to do that. 3 00:00:14,290 --> 00:00:20,350 First one is by using a dollar sign and command enclosed in brackets. 4 00:00:20,350 --> 00:00:26,370 Second one is to enclose system command into Bedworth apostrophes. 5 00:00:26,380 --> 00:00:29,880 Now let's write some script to practice this option. 6 00:00:33,600 --> 00:00:39,840 I will create a script called command SOP's that as I age 7 00:00:45,210 --> 00:00:48,020 on the first line start to beat shoving 8 00:00:50,590 --> 00:00:54,010 bin bash. 9 00:00:54,550 --> 00:00:58,600 Well that's great variable called current directory 10 00:01:01,080 --> 00:01:02,390 and assigned to it. 11 00:01:02,430 --> 00:01:05,060 Output of BW D. 12 00:01:05,110 --> 00:01:05,790 C'mon 13 00:01:09,210 --> 00:01:11,630 on the next line we can print 14 00:01:15,500 --> 00:01:16,740 script is 15 00:01:20,230 --> 00:01:25,290 I'm from do our sign current directory 16 00:01:32,300 --> 00:01:43,590 now save the file and video editor you need to change is a good promotion. 17 00:01:44,140 --> 00:01:45,490 And now we can get on descript 18 00:01:49,220 --> 00:01:50,170 and it works it out. 19 00:01:50,170 --> 00:01:57,550 Script is where I'm from and the location from which the script was set I'm. 20 00:01:57,850 --> 00:02:01,850 Now let's change the script a little bit. 21 00:02:02,010 --> 00:02:12,760 We will get rid of parents issues and instead we will use Beckford apostrophe's which is another option 22 00:02:13,030 --> 00:02:18,980 to save Gaumont output to a variable saving defile 23 00:02:23,780 --> 00:02:24,580 and that AMIN 24 00:02:27,880 --> 00:02:32,700 Yes the result is same as in previous example. 25 00:02:32,760 --> 00:02:33,230 Great. 26 00:02:35,030 --> 00:02:41,120 The great command substitution example from the real world can be time measurement. 27 00:02:41,150 --> 00:02:46,830 Sometimes my want to know how much time is taken by some section of commands. 28 00:02:46,970 --> 00:02:49,860 So let's make such a script. 29 00:02:50,570 --> 00:03:03,650 Starting with siobhán bin bash then we can for better readability type command start time measurement 30 00:03:08,630 --> 00:03:10,690 from here. 31 00:03:11,600 --> 00:03:16,010 Now this will store Unix time into variable standard. 32 00:03:16,550 --> 00:03:24,630 And of course we need to use command substitution here by opening bus percentage as to date command 33 00:03:25,270 --> 00:03:29,380 we are converting date into a unique Styne. 34 00:03:29,630 --> 00:03:37,280 If you don't know what Unix time is it is a system for describing a point in time defined as the numbers 35 00:03:37,280 --> 00:03:42,750 of seconds that have elapsed since first January 1970. 36 00:03:43,250 --> 00:03:48,410 What is most important here that is represented by one number. 37 00:03:48,500 --> 00:03:57,760 So we can easily do difference between two unique stion we can again start output of P.W. the command 38 00:03:58,000 --> 00:04:08,460 into a variable called current directory. 39 00:04:09,540 --> 00:04:17,800 But because this command won't take much time we can use command sleep which will make sure that program 40 00:04:17,880 --> 00:04:21,440 will be paused for specific time of seconds. 41 00:04:21,510 --> 00:04:24,640 In our case two seconds. 42 00:04:25,620 --> 00:04:31,780 Now we can create a variable called end and start next time. 43 00:04:31,820 --> 00:04:32,550 And also 44 00:04:42,220 --> 00:04:49,470 now but stype some command and time measurement 45 00:04:54,330 --> 00:04:59,140 that's also great variable cost difference and store in it. 46 00:04:59,150 --> 00:05:05,470 The difference between end and start don't pay much attention on how to do. 47 00:05:05,640 --> 00:05:06,980 With variables. 48 00:05:07,300 --> 00:05:13,410 Just do the same as me will cover of met in bash in another section. 49 00:05:20,580 --> 00:05:29,650 Pay attention to that spaces between parentheses and variables. 50 00:05:29,770 --> 00:05:34,690 Now we can write time elapsed 51 00:05:39,680 --> 00:05:44,370 and print the output the value of different rebel 52 00:05:50,070 --> 00:05:51,900 so scrip is dumb. 53 00:05:51,970 --> 00:05:53,060 We can save it. 54 00:05:56,620 --> 00:05:57,310 And we can 55 00:06:03,000 --> 00:06:06,340 is good permission for that file. 56 00:06:10,540 --> 00:06:11,160 And Danny 57 00:06:16,760 --> 00:06:21,000 great we can see time lapse 2 seconds. 58 00:06:21,230 --> 00:06:22,570 Amazing. 59 00:06:23,120 --> 00:06:29,450 In the same way you can easily measure how much time does it take to copy all files of some directory 60 00:06:29,720 --> 00:06:31,490 into another location. 61 00:06:31,700 --> 00:06:38,630 You would just replace the sleep command we have just used as example with command for copying files.