1
00:00:00,000 --> 00:00:13,920
Now, the essence of this script is to rewrite to uppercase, so I am going to use echo hello

2
00:00:13,920 --> 00:00:25,840
pipe tr lower between square brackets, that's a typo, to upper between square brackets.

3
00:00:25,840 --> 00:00:29,680
And there you can see that it has hello in uppercase.

4
00:00:29,680 --> 00:00:35,680
But this time we don't need echo on a fixed value, but we need echo on a variable.

5
00:00:35,680 --> 00:00:45,799
So let's write a script, lab18, and in the script we start with binbash, and then if

6
00:00:45,799 --> 00:00:50,200
no argument was provided, script should print an error message.

7
00:00:50,200 --> 00:01:04,320
So I should say if minus z dollar one, then echo you have to provide at least one filename

8
00:01:04,320 --> 00:01:07,440
as argument.

9
00:01:07,440 --> 00:01:13,160
Echo exiting now, exit three.

10
00:01:13,160 --> 00:01:17,879
The number behind the exit really doesn't matter, it has an internal meaning only, and

11
00:01:17,879 --> 00:01:20,440
I'm using fi to close it.

12
00:01:20,440 --> 00:01:27,160
Then I'm using for i in dollar at, I like dollar at because it refers to all of the

13
00:01:27,160 --> 00:01:28,160
arguments.

14
00:01:28,160 --> 00:01:30,040
Do, and what are we going to do?

15
00:01:30,040 --> 00:01:37,559
Well, we are going to do env, dollar i, to, yeah, to what?

16
00:01:37,559 --> 00:01:51,480
Well, to dollar parentheses, echo, dollar i, pipe, tr, lower, upper.

17
00:01:51,480 --> 00:01:53,559
Now what is going on here?

18
00:01:53,559 --> 00:02:00,279
Well, what is going on is that we are moving the current element in dollar at.

19
00:02:00,279 --> 00:02:04,839
Let's say that dollar at currently has the value of file one.

20
00:02:04,839 --> 00:02:09,440
Then env is going to move the current element, so the first part is easy.

21
00:02:09,440 --> 00:02:12,720
Dollar i is just a current value, file one.

22
00:02:12,720 --> 00:02:19,240
Then the construction with the echo and the parentheses is what we call command substitution.

23
00:02:19,240 --> 00:02:24,880
So the second argument to env is the result of the command substitution.

24
00:02:24,880 --> 00:02:26,880
And what is the command substitution doing?

25
00:02:26,880 --> 00:02:32,440
Well, it's taking the current value of dollar i, and it's rewriting that from lowercase

26
00:02:32,440 --> 00:02:35,639
to uppercase, and that should be doing it.

27
00:02:35,639 --> 00:02:43,520
So I'm using touch file, file one dot dot nine to create a range of files, chmod plus

28
00:02:43,520 --> 00:02:53,199
x on lab 18, and let's run lab 18 on file one, two, nine.

29
00:02:53,199 --> 00:02:55,039
That should be doing all right.

30
00:02:55,039 --> 00:02:56,039
And now what is the result?

31
00:02:56,039 --> 00:03:01,520
Well, as you can see, the result is that it has written all these files to uppercase.

32
00:03:01,520 --> 00:03:05,639
So something like this is what I had in mind for the solution for this lab.