1 00:00:01,520 --> 00:00:06,620 In this lecture we are going to learn about readed action and piping. 2 00:00:07,140 --> 00:00:14,530 Before we do that we need to know that every program we run on the command line has three data streams. 3 00:00:15,640 --> 00:00:20,740 It has some that input which represents the data provided to program. 4 00:00:20,830 --> 00:00:24,870 The stream is represented by number 0. 5 00:00:24,880 --> 00:00:32,470 Then we have standard output which is very present in Dubai number one and it is basically what program 6 00:00:32,500 --> 00:00:38,990 brings to us stream is standard and are represented by number two. 7 00:00:39,090 --> 00:00:48,220 And it means a lot of messages de-program brains how to imagine those streams in more graphical way. 8 00:00:48,240 --> 00:00:55,320 Here we see that the standard input stream provides some data into a program then the program for example 9 00:00:55,320 --> 00:00:58,970 cat ping or US processes data. 10 00:00:59,100 --> 00:01:07,310 And if there is no problem with processing data program provides output on standard outputs in other 11 00:01:07,310 --> 00:01:14,190 device if program has some issue with processing input data it will provide output into standard error 12 00:01:14,220 --> 00:01:15,950 string. 13 00:01:16,530 --> 00:01:22,180 Now let's Jeg how detection works and we can check it on some examples. 14 00:01:23,560 --> 00:01:30,400 We have here output of cat command which will basically display content of file 1.0 text. 15 00:01:30,400 --> 00:01:38,980 So how we do the actual early detection we are using symbol greater than by specifying greater and symbol 16 00:01:39,190 --> 00:01:43,180 we can detect output of cut command somewhere else. 17 00:01:43,180 --> 00:01:52,180 In our case the file output from code that text but the stream is directed to that output from Cat file. 18 00:01:52,240 --> 00:01:57,040 It is standard output or standard error or both of them. 19 00:01:57,050 --> 00:02:02,290 Firstly Let's check another example because it is important. 20 00:02:02,380 --> 00:02:06,610 Now if I tell you that both commands do the same. 21 00:02:06,610 --> 00:02:11,280 Can you tell me what stream is re-elected in the first example. 22 00:02:12,200 --> 00:02:18,850 It is standard output views before a greater than symbol number of specific string. 23 00:02:18,930 --> 00:02:24,330 We are basically telling that direct output from that stream to somebody else. 24 00:02:24,680 --> 00:02:29,490 And because in most cases it is redirected on a standard output. 25 00:02:29,510 --> 00:02:37,120 You don't need to specify number one before a greater than symbol and it will do the same job for you. 26 00:02:37,640 --> 00:02:45,570 Similarly if you want to redirect only standart at overstrain to some file we are using number two before 27 00:02:45,580 --> 00:02:47,620 a greater than symbol. 28 00:02:47,750 --> 00:02:56,380 We can also redirect both standard output and error streams to different files if you want to read it 29 00:02:56,390 --> 00:02:59,970 at both standard and stream to same file. 30 00:02:59,990 --> 00:03:06,730 We can do it easily by prepending ampersands and more before a greater than symbol. 31 00:03:06,950 --> 00:03:13,850 In some cases we maybe want to read it as standard or stream to standard output stream and we can do 32 00:03:13,850 --> 00:03:19,950 that using two greater than ampersands one in this example. 33 00:03:19,970 --> 00:03:27,500 We are directing Stamm that output stream to file output from Qadar text and we also are directing standard 34 00:03:27,590 --> 00:03:34,300 arrow stream to standard output stream which is is to the file output from Cadoudal text. 35 00:03:34,520 --> 00:03:45,800 So that means that stream is directed also to that file output from cat got text when we are using gaitered 36 00:03:45,800 --> 00:03:52,690 and symbol one had a direct link to a file we always sort of writing Godet file if that file does not 37 00:03:52,750 --> 00:04:01,180 exist it will be created in some cases you might want to rather add some lines to a file instead of 38 00:04:01,180 --> 00:04:02,720 completely rewrite it. 39 00:04:02,770 --> 00:04:07,390 So for that you can use double grade then symbol. 40 00:04:07,840 --> 00:04:13,130 We can also use redirection to provide the data to standard input. 41 00:04:13,150 --> 00:04:21,100 Here we have examples of wc command which takes one argument Feitel dot text if you want to provide 42 00:04:21,100 --> 00:04:23,640 file that text as a standard import. 43 00:04:23,800 --> 00:04:26,690 We are using less than symbol. 44 00:04:26,830 --> 00:04:31,280 So what is the difference between those two examples provided out. 45 00:04:31,290 --> 00:04:39,590 What is the difference as of when we do that actually using less than symbol data are sent anonymously. 46 00:04:39,610 --> 00:04:44,770 So we see only how many lines that file contains. 47 00:04:44,780 --> 00:04:50,440 Now let's talk also about piping of what piping does is simple. 48 00:04:50,520 --> 00:04:55,240 It is sending data from one program to another. 49 00:04:55,320 --> 00:05:02,970 For example here we are sending output of the command to command that Brucey which will then print the 50 00:05:02,970 --> 00:05:05,960 same output as using readied action. 51 00:05:06,330 --> 00:05:12,360 But if you want to see the real power of piping look at the following example. 52 00:05:12,470 --> 00:05:19,530 Here we have output of the command which you send to the program with parameter 5. 53 00:05:19,560 --> 00:05:23,580 That means only first five lines will be printed. 54 00:05:23,580 --> 00:05:32,250 Then this output of five lines is sent to program tail with parameter Swee which means only last sorry 55 00:05:32,340 --> 00:05:37,530 lines of previous output are printed and then does. 56 00:05:37,570 --> 00:05:44,490 So the lines output is sent to that Brucey command which will print number of lines. 57 00:05:44,580 --> 00:05:49,980 In our case number Sorry So enough already. 58 00:05:50,090 --> 00:05:52,890 Let's see this bad boy in action.