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[Intro Music]

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I have just demonstrated to you how

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you could change your permissions

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for a specific file. You are able

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to assign specific permissions, to

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add permissions, or to remove

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permissions. And for that, you need

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to use command 'chmod'. Please

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know that if you want to modify

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permissions for entire directory,

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you need to use additional option

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'-R'. Great. Now, let's

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create a sample script, and make

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the script executable script. And

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actually, we will create simply

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file, and you are not able to

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execute any file in the new system.

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You need to make this file

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executable first. And let's try to

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do this here in this lecture. Let's

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clear terminal, and here let me type

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the following command, 'touch

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script.sh'. Notice that I have just

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added the extension 'sh', that stands

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for Shell. And the reason for that

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is that I am going now to create

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executable script, and this script

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will be executed by a specific

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process. And that process will be

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bash shell. And that's why if

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you're going to create executable

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scripts that will be executed in

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Shell, you should add extension 'sh'.

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Of course, you could go on

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without any extension; and in such

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way you will be able to execute the

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file as well. But it's a good

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practice to add extension. All

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right, let's create a new file

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'script.sh'. Let's list files and

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folders here. Let me actually

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remove 'new-file.txt'. I don't

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need it anymore. And now I see

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script.sh file here. And notice

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permissions for this file. It is

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readable, writeable, but not

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executable by owner; readable,

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writeable, and not executable by any

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other users in the same group

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'bogdan'; and only readable by

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all remaining users in all other

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groups. Could you quickly tell me

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decimal representation of those permissions?

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[Clock Ticking]

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This section stands

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for 4+2, 6; this 4

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+2, also 6; and here it will be

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4. So, resulting permission is

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664. Great. Now let's make this

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file executable. And I want to make

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it executable only by owner, this

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user, 'bogdan'. And I will modify

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only this section. And for that I

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could use either decimal

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representation of the resulting

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permission, or I could add only

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execution permission for user. And

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for that I'll use 'chmod' command.

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And here I'll type 'u', stands for

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user; next '+', I'm adding

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permission; and here will be

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execution permission 'x'; and here

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will be name of the file, 'script.sh'.

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Let's run it, and let's verify

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permissions now. And you'll see

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that now this file script.sh is

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marked in green color. And now it is

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executable by user - read, write and

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execute, 'rwx'. And now let's open this

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file, 'sh' file in Nano Editor; and

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let's add some shell commands there.

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'nano script.sh'. And first what you

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need to do here in this file is to

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add reference to a specific

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executable file that will run this

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file, this script. And I'm going to

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run this script using bash shell

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process. And for that you need to

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use following line. '#', next

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'!', and here will be

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path to corresponding executable

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that is supposed to run this shell

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script, and path is following '/bin

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/bash'. Actually, you could

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find the full path to bash shell if

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you type 'which bash' in terminal.

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Actually, let me quickly do that.

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Let's exit without saving. And here

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type 'which bash', and here in the

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system I see that bash executable

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file is located in '/usr/bin/bash'.

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But let me actually have a look at

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contents of the 'bin' folder, 'ls

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-l'; and you'll see that this

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folder is actually linked to '/usr/

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bin'. We have talked about links

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before. And that means that I'm

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able to use either this path as

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reference to the location of the

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bash script, or simply '/bin/bash'

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because if I enter '/bin/bash', it

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will point to 'usr/bin/bash'. All

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right, it sounds a bit complicated,

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but in fact it is very simple.

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Let's go back to editing of the

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file, 'nano script.sh'. And here I'll

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type same line, '!

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/bin/bash' like so. And

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it tells system that this

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executable file 'bash' will be used

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for execution of the script. Great. And here

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let's simply type 'echo', and here in

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double quotes, "Hello from the

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custom script", like so. Let's now

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save contents of this file, like

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so. Yes, Enter. And now let's try

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to execute this file. And if you

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want to execute a specific script,

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you need to enter simply absolute

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or relative path to this script. In

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this case, this script is located

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here in home directory for this

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user. It is actually current folder

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represented by '.' or by '~' sign. It

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is home directory for this user, or

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absolute path is '/home/

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bogdan/script.sh'. And

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actually, you are able to use any

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of those variants. Any will work.

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Let's go try to use this

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absolute path, and simply press

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Enter. And I see, 'Hello from the

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custom script'. And that means that

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bash shell has executed this

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script.sh file. You don't need to

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enter any arguments or options or

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any other commands, simply path to

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corresponding executable script.

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That's it. Now let's try to use

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relative path and simply type

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'./script.sh', and I see same

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result, 'Hello from the custom

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script'. Let's try to use reference

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to home directory, '~/

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script.sh'. And I see same result

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again. But if I enter simply

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script.sh, I'll get 'command not

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found'. And now question to you, why

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I get this error when I entered

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this command without full path to

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it? Answer is very simple. At the

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beginning of this course, I have

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explained to you what is the PATH

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variable, and how actually Linux

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shell understands that you want to

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enter a specific command. And if I

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enter 'echo $PATH', I will

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see a set of different paths that

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are concatenated using a colon.

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For example, here is location of

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some executable files, '/usr/local/sbin',

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next one, next one, and so on.

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And now this script.sh is located

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simply in '/home/bodgan'.

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And this path is not in this list,

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that's why shell is not able to

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recognize that I want to run some

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script named script.sh. If you want

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to be able to run some scripts in

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such way without full path, you

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need to add the folder name where

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the script is located to your PATH.

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Simply concatenate to existing

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PATH. But it's not a good practice

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to add home directory to PATH. It's

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a good practice to create 'bin'

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folder in home directory for your

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user and place all executable

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scripts there. But let's talk about

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it in the next lecture. I will show

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you how to do that, and how to

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modify path, and next after this

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action you will be able to execute

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script like this anywhere in any

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folder. I will see you in the next

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lecture guys. Bye-Bye.

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[no audio]