1
00:00:06,559 --> 00:00:10,130
The next feature of the bash shell
that you really should understand is the variable.

2
00:00:11,150 --> 00:00:14,449
A variable is a label to
which a dynamic value can be assigned.

3
00:00:15,490 --> 00:00:19,539
Variables are convenient for scripting,
and you define the variable

4
00:00:19,539 --> 00:00:23,589
once and use in a
flexible way in different environments.

5
00:00:24,410 --> 00:00:30,186
What's the idea behind that? Well, if you create
a script, you don't want hard coded values, you

6
00:00:30,186 --> 00:00:35,963
want values to be defined in a variable, and
the script will pick up the value from the

7
00:00:35,963 --> 00:00:41,740
variable whenever it is running. And that is
a nice way of making your scripts flexible.

8
00:00:42,259 --> 00:00:47,155
But for now, let's not talk about scripts,
let's talk about system variables. They contain default

9
00:00:47,155 --> 00:00:52,049
settings that are used by Linux and there's
a couple of them that are quite convenient.

10
00:00:52,549 --> 00:00:56,060
Like the path variable, which
contains a list of directories

11
00:00:56,060 --> 00:00:59,570
that I search for
binaries while executing a command.

12
00:01:00,729 --> 00:01:04,390
I am writing $path, by the
way, because if you want to get

13
00:01:04,390 --> 00:01:08,049
the value of a variable, you
put a dollar in front of it.

14
00:01:09,150 --> 00:01:13,049
Another variable is dollar shell. Dollar shell
is the current shell that is used.

15
00:01:14,109 --> 00:01:17,689
Environment variables can be
set for application use.

16
00:01:18,489 --> 00:01:22,009
You use varname is
value to define your variable,

17
00:01:22,009 --> 00:01:25,530
and then you can
use echo$varname to read.

18
00:01:26,409 --> 00:01:31,629
Now, by default, variables are only known to the
current shell. If you want to define a variable that

19
00:01:31,629 --> 00:01:36,849
is known in subshells as well, you need to
use export in front of it. Let me show you.

20
00:01:37,930 --> 00:01:42,250
Let's start with env. Env is
for env environment and that is

21
00:01:42,250 --> 00:01:46,569
showing the environment variables that
are in use by my system.

22
00:01:47,230 --> 00:01:53,805
So echo dollar user, for instance, is giving my current
user ID that student or echo dollar path, which is

23
00:01:53,805 --> 00:02:00,379
giving a list of directories where the bash shell is
checking for program files. When I run a program file.

24
00:02:00,939 --> 00:02:05,840
Did I say the bash shell? Is that so? Well,
let's use echo dollar shell. Yeah, it's the bash shell.

25
00:02:06,680 --> 00:02:12,534
Now, variables are used as system variables
and these are convenient. You can set them

26
00:02:12,534 --> 00:02:18,389
yourself as well. Let's use color is
red. That's how you define a variable.

27
00:02:18,789 --> 00:02:25,110
Next, if I want to refer to the variable echo
dollar color and there we can see the current value.

28
00:02:25,969 --> 00:02:32,365
Now if I start a subshell, what is a subshell?
Well, that's a process that started from the current environment.

29
00:02:32,365 --> 00:02:38,759
I'm going to run bash as subshell and then I'm
using echo dollar color and I don't see it anymore.

30
00:02:39,259 --> 00:02:44,394
Let's get out of the subshell to
the parent shell and let's define the variable

31
00:02:44,394 --> 00:02:49,529
in a way that it also exists
in the subshell. So export color is red.

32
00:02:50,139 --> 00:02:54,000
And now I'm starting my subshell
again in echo dollar color and

33
00:02:54,000 --> 00:02:57,860
there we can see that
it does exist in the subshell.

34
00:02:58,740 --> 00:03:04,094
Now, setting variables yourself is not so useful
if you're not going to use them. This particularly

35
00:03:04,094 --> 00:03:09,449
makes sense when you are going to work
with Bash shell scripts to automate tasks on Linux.