1
00:00:00,000 --> 00:00:04,300
[Intro Music]

2
00:00:04,350 --> 00:00:06,780
We have just tried to send the data

3
00:00:06,780 --> 00:00:09,360
from STDOUT and STDERR to

4
00:00:09,390 --> 00:00:11,370
different files; and it was

5
00:00:11,370 --> 00:00:13,110
successful. We have written

6
00:00:13,110 --> 00:00:14,550
different streams to different

7
00:00:14,550 --> 00:00:17,040
files. And actually we have tried

8
00:00:17,070 --> 00:00:19,440
this part. There were two different

9
00:00:19,470 --> 00:00:21,840
data streams STDOUT and STDERR,

10
00:00:21,840 --> 00:00:24,630
and two different files. But what

11
00:00:24,660 --> 00:00:27,300
if we want to send the data from

12
00:00:27,330 --> 00:00:30,540
STDOUT data stream to STDIN of

13
00:00:30,600 --> 00:00:34,740
other process. Let's try it using the

14
00:00:34,740 --> 00:00:36,720
same approach as we used in

15
00:00:36,720 --> 00:00:38,640
previous lectures. Let's go to the

16
00:00:38,640 --> 00:00:40,830
terminal and let's suppose that we

17
00:00:40,830 --> 00:00:43,560
want to redirect STDOUT of 'ls'

18
00:00:43,560 --> 00:00:46,560
command to STDIN of 'cat' command.

19
00:00:47,310 --> 00:00:49,080
Let's try approach that we have

20
00:00:49,080 --> 00:00:52,350
used with files, 'ls', then comes

21
00:00:52,380 --> 00:00:54,390
greater than, '>' operator that will

22
00:00:54,420 --> 00:00:57,450
redirect actually STDOUT of 'ls'

23
00:00:57,450 --> 00:00:59,970
command; and let's here write 'cat'

24
00:00:59,970 --> 00:01:03,030
command, and let's press Enter, and I

25
00:01:03,030 --> 00:01:06,269
see actually nothing. I could try

26
00:01:06,480 --> 00:01:09,630
here add '1' because '1' is ID of

27
00:01:09,630 --> 00:01:12,360
STDOUT, and press Enter, and again

28
00:01:12,360 --> 00:01:14,730
nothing. And that means that with

29
00:01:14,730 --> 00:01:17,070
this '>' operator, you are not

30
00:01:17,100 --> 00:01:20,520
able to redirect data from STDOUT

31
00:01:20,550 --> 00:01:24,690
or STDERR to STDIN of other process.

32
00:01:25,140 --> 00:01:26,490
That's why here we see nothing.

33
00:01:27,420 --> 00:01:29,250
If you want to do so, you need to

34
00:01:29,250 --> 00:01:32,100
use other operator called pipe, '|', and

35
00:01:32,100 --> 00:01:34,710
approach that is called Piping. With

36
00:01:34,710 --> 00:01:37,996
piping you could send data from STDOUT

37
00:01:37,996 --> 00:01:40,770
of one process to STDIN of

38
00:01:40,800 --> 00:01:43,410
other process. Next, you are also

39
00:01:43,410 --> 00:01:46,020
able to send STDOUT data flow from

40
00:01:46,020 --> 00:01:48,450
this process to another STDIN

41
00:01:48,480 --> 00:01:51,270
of other process, and so on. You could

42
00:01:51,300 --> 00:01:53,550
pipe different processes one after

43
00:01:53,550 --> 00:01:57,110
previous. But please notice that STDERR

44
00:01:57,110 --> 00:02:00,360
data stream is not piped, and

45
00:02:00,360 --> 00:02:02,370
you are able to write it to the

46
00:02:02,370 --> 00:02:04,290
file same as we did in previous

47
00:02:04,290 --> 00:02:07,140
examples, or you could still bring

48
00:02:07,140 --> 00:02:09,030
it to the terminal, that is actually

49
00:02:09,030 --> 00:02:11,880
a default action. All right, let's

50
00:02:11,880 --> 00:02:13,919
try to use piping here in this

51
00:02:13,919 --> 00:02:16,740
example with 'ls' and 'cat' processes;

52
00:02:17,160 --> 00:02:20,520
and for that I'll type 'ls', then pipe, '|'

53
00:02:20,670 --> 00:02:22,920
this vertical line, and here will be

54
00:02:22,920 --> 00:02:26,460
'cat' like so. Press Enter, and now I

55
00:02:26,460 --> 00:02:28,380
see a list of files and folders.

56
00:02:28,860 --> 00:02:31,290
And that means that now STDOUT

57
00:02:31,440 --> 00:02:35,370
from 'ls' process was sent to STDIN

58
00:02:35,490 --> 00:02:39,780
of 'cat' process. Alright, but let me

59
00:02:39,780 --> 00:02:41,820
demonstrate to you that pipe does not

60
00:02:41,850 --> 00:02:44,310
send STDERR data stream. For

61
00:02:44,310 --> 00:02:46,590
that I could use here 'cat' command

62
00:02:46,620 --> 00:02:50,040
with some missing file, 'missing-file

63
00:02:50,160 --> 00:02:52,350
.txt', like so; and then let's

64
00:02:52,350 --> 00:02:54,270
suppose that I want to pipe result

65
00:02:54,270 --> 00:02:56,340
of this command to another 'cat'

66
00:02:56,340 --> 00:02:59,370
process, press Enter, and I see

67
00:02:59,400 --> 00:03:00,960
error directly here in the

68
00:03:00,960 --> 00:03:04,079
terminal. And that means that STDERR

69
00:03:04,079 --> 00:03:06,570
data stream was not sent to

70
00:03:06,630 --> 00:03:09,480
another process. Alright, that's

71
00:03:09,480 --> 00:03:11,160
how you could pipe different

72
00:03:11,160 --> 00:03:13,320
processes together. For example, let

73
00:03:13,320 --> 00:03:16,830
me pipe another process 'echo'; and by

74
00:03:16,830 --> 00:03:18,300
default this command will simply

75
00:03:18,300 --> 00:03:20,610
print some text to the terminal and

76
00:03:20,610 --> 00:03:22,410
this text will be supplied here as

77
00:03:22,410 --> 00:03:24,630
argument. Let's type "Hello World".

78
00:03:25,440 --> 00:03:27,630
And if I press Enter now I see

79
00:03:27,690 --> 00:03:30,630
output from STDOUT data stream, and

80
00:03:30,630 --> 00:03:32,550
it prints "Hello world". Now let's

81
00:03:32,550 --> 00:03:33,960
suppose that I want to send the

82
00:03:33,960 --> 00:03:37,770
result of this operation to another

83
00:03:37,920 --> 00:03:40,050
command; and let's use here again

84
00:03:40,050 --> 00:03:42,450
'cat'; and let's suppose that I want

85
00:03:42,450 --> 00:03:45,300
to write result of 'cat' operation

86
00:03:45,330 --> 00:03:48,540
from STDOUT to file; and here I

87
00:03:48,540 --> 00:03:50,190
could use the following syntax

88
00:03:50,490 --> 00:03:52,740
'>'; and here will

89
00:03:52,740 --> 00:03:55,989
be 'hello.txt'. Again here following

90
00:03:55,989 --> 00:03:58,830
will happen, STDOUT data stream of

91
00:03:58,860 --> 00:04:02,559
this process will send data to STDIN

92
00:04:02,559 --> 00:04:06,270
of 'cat' process, and STDOUT of

93
00:04:06,270 --> 00:04:09,570
'cat' process will be stored in the

94
00:04:09,570 --> 00:04:12,750
file hello.txt. If this file is

95
00:04:12,750 --> 00:04:14,190
absent, it will be created.

96
00:04:14,640 --> 00:04:17,610
Alright, let's try that. Enter. I see

97
00:04:17,610 --> 00:04:19,920
nothing here in the terminal. But

98
00:04:19,950 --> 00:04:21,990
if I list the contents of file

99
00:04:22,019 --> 00:04:24,540
hello.txt, I see "Hello world".

100
00:04:25,290 --> 00:04:27,029
That's how it works, and that's how

101
00:04:27,029 --> 00:04:29,880
you're able to combine pipe, '|' operator

102
00:04:30,030 --> 00:04:32,190
and redirect, '>' operator. Please note

103
00:04:32,190 --> 00:04:34,320
again that redirect, '>' operator will

104
00:04:34,320 --> 00:04:36,450
write contents only to file, it is

105
00:04:36,450 --> 00:04:39,306
not capable of sending data to STDIN

106
00:04:39,306 --> 00:04:41,730
of other processes. For that you

107
00:04:41,730 --> 00:04:44,460
need to use pipe, '|' operator. Alright,

108
00:04:44,610 --> 00:04:45,840
that's all for this lecture and

109
00:04:45,840 --> 00:04:47,520
next let me summarize what we have

110
00:04:47,520 --> 00:04:48,930
discussed over the course of the

111
00:04:48,930 --> 00:04:51,400
previous lectures. I'll see you next. Bye-Bye.

112
00:04:51,400 --> 00:04:54,300
[no audio]