BASH/C2/String-and-File-attributes/English-timed

Title of script: String and File Attributes comparison in Bash

Author: Ashwini Patil

Keywords: video tutorial, ==, !=, string compare, file attributes.

Time	Narration
00:01	Dear friends, welcome to the spoken tutorial on String and File Attributes comparison in Bash.
00:10	In this tutorial, we will learn:
00:13	* String comparison and File attributes comparison.
00:18	We will do this using a few examples.
00:22	For this tutorial, I am using:
00:25	* Ubuntu Linux 12.04 Operating System and
00:30	* GNU BASH version 4.1.10
00:34	Please note, GNU Bash version 4 or above is recommended to practice this tutorial.
00:42	Let us start with an introduction.
00:45	There are two ways to compare a string in Bash.
00:49	1) First: using == (equal to equal to) operator
00:53	to compare two equal strings.
00:56	2) Second: != (not equal to) operator.
00:59	to compare two not equal strings.
01:03	Let us look at an example.
01:06	I have a simple program here that checks the user ID.
01:11	Open a file in your editor and save it as strcompare dot sh.
01:19	Now type the code as shown here, in your strcompare dot sh file.
01:26	Let me explain the code.
01:28	This is shebang line.
01:31	whoami command gives the username of the current user.
01:36	The if statement checks the output of the variable whoami against the string “root”.
01:44	We have used not-equal to operator here to compare the strings.
01:50	If the current user is not the root user, then it will echo this statement -
01:57	“You have no permission to run 'strcompare dot sh' as non-root user.”
02:05	Here $0 (dollar zero) is the zeroth argument which is a 'file-name' itself.
02:13	If the user is the root user, it will echo - “Welcome root!”.
02:18	Then we have the exit statement for the program.
02:23	And here with fi we end the if statement.
02:28	Let us switch back to our slides to know more about the exit statement.
02:34	Every program returns an exit status.
02:38	A successful command returns a 0 (zero).
02:42	An erroneous command returns a non-zero value.
02:47	It can be interpreted as an error code.
02:51	We can customize return value of the exit statement .
02:56	Now, let's execute the program.
02:58	Open the terminal by pressing Ctrl+Alt and T keys simultaneously on your keyboard.
03:08	First, let's check the current user of the system.
03:12	Type whoami.
03:15	Press Enter.
03:17	This will output the name of the current user.
03:21	Now let's make our script executable.
03:25	Type: chmod +x strcompare dot sh
03:32	Type: dot slash strcompare dot sh
03:37	The output is displayed as:
03:39	You have no permission to run dot slash strcompare dot sh as non-root user.
03:47	Now let's execute the same program as root user.
03:52	Type: sudo dot slash strcompare dot sh
03:58	It will prompt for an password.
04:01	Give your password here.
04:04	The output is displayed as: Welcome root!.
04:08	Now, let's learn about the file attributes comparison.
04:13	I already have a working example of the code.
04:17	In this program, we will check whether a given file exists or not.
04:23	file1 is the variable in which we save the path of the file.
04:29	-(hyphen) f command checks whether the file exists or not.
04:33	And whether it is a normal file.
04:37	If the condition is True, it will echo "File exists and is a normal file" .
04:44	Else, it will echo "File does not exist" .
04:48	Switch back to the terminal. Let us execute our file.
04:53	Type: chmod plus x fileattrib dot sh
05:00	Type: dot slash fileattrib dot sh
05:05	The output is displayed as:
05:07	File exists and is a normal file.
05:11	Now we will check whether the file is empty or not.
05:16	Before executing our program, I will create an empty file named as empty dot sh.
05:24	Type: gedit empty dot sh ampersand sign.
05:31	Click on Save, close the file.
05:35	Let us replace - (hyphen) f attrib with - (hyphen) s attribute.
05:41	Replace the filename here as well.
05:45	Type empty dot sh .
05:47	Now, replace the first echo statement with:
05:51	“File exists and is not empty”.
05:54	And the second echo statement with:
05:57	“File is empty”.
05:59	Click on Save.
06:01	Come back to the terminal.
06:03	Let me clear the prompt.
06:06	Let's execute.
06:08	Type: dot slash fileattrib dot sh press Enter.
06:13	The output is File is empty.
06:17	Now, let us see another file attribute which will check the write permission of any file.
06:24	Come back to our program.
06:26	Let us replace the - (hyphen) s attribute with - (hyphen) w.
06:32	Now replace the first echo statement with:
06:36	“User has write permission to this file”.
06:40	And the second echo statement with:
06:43	“User doesn't have write permission to this file”.
06:47	Click on Save.
06:49	I will use a different file for this example.
06:53	I will select a file which is not a readable file or which does not have write permission.
07:01	Let me change the file path to
07:04	“slash etc slash mysql slash debian dot cnf”
07:10	Click on Save.
07:12	Let us execute our program.
07:15	Press the up-arrow key. Press Enter.
07:19	We see that the output is displayed as:
07:21	User doesn't have write permission to this file.
07:26	Now, let us see another example based on file attributes.
07:31	In this example, we will check whether file1 is newer than file2.
07:38	Let us see the program.
07:40	Note that our file-name is fileattrib2 dot sh
07:46	Let's go through the code.
07:48	Here we have two variables file1 and file2.
07:53	The two files have already been created and are empty.
07:58	Here we check whether file1 is newer than file2.
08:04	If the condition is True, we print file1 is newer than file2.
08:09	Else, file2 is newer than file1.
08:14	This is another if statement.
08:16	Here we check whether file1 is older than file2.
08:21	If the condition is True, we print file1 is older than file2.
08:27	Else, we print file2 is older than file1.
08:32	Come back to our terminal.
08:35	First, we will edit empty1 dot sh file.
08:39	I will just add an echo statement in it.
08:42	Type: echo within double quotes Hiii after the double quotes greater than sign empty one dot sh. Press Enter.
08:53	Now, let us make our script executable.
08:57	Type: chmod plus x fileattrib2 dot sh
09:03	Now type dot slash fileattrib2 dot sh
09:09	We see the output as:
09:11	file1 is newer than file2
09:15	file2 is older than file1
09:19	Now let's edit empty2 dot sh file.
09:23	Here also I will add an echo statement.
09:27	Type: echo within double quotes How are you after the quotes (greater than sign) >empty2 dot sh.
09:38	Let me clear the prompt.
09:41	Now let us execute our script again.
09:45	Press the up-arrow key.
09:47	Go to dot slash fileattrib2 dot sh Press Enter.
09:53	Now the output is displayed as:
09:55	file2 is newer than file1
09:59	And file1 is older than file2.
10:03	This brings us to the end of this tutorial.
10:06	Let us summarize.
10:08	In this tutorial, we learnt:
10:11	* String comparison
10:12	* file attributes
10:14	* ==(equal to equal to)
10:16	* != (not equal to)
10:17	* -f (hyphen f)
10:18	* -s(hyphen s)
10:19	* -w(hyphen w)
10:21	* -nt(hyphen nt)and
10:22	* -ot (hyphen ot) attributes.
10:25	As an assignment-
10:26	explore some more attributes.
10:29	Ex: -r -xand -o
10:33	Watch the video available at the link shown below.
10:36	It summarizes the Spoken Tutorial project.
10:40	If you do not have good bandwidth, you can download and watch it.
10:45	The Spoken Tutorial Project team:
10:47	Conducts workshops using spoken tutorials.
10:51	Gives certificates to those who pass an online test.
10:55	For more details, please write to contact@spoken-tutorial.org
11:02	Spoken Tutorial project is a part of the Talk to a Teacher project.
11:06	It is supported by the National Mission on Education through ICT, MHRD, Government of India.
11:14	More information on this mission is available at the link shown below .
11:19	The script has been contributed by Fossee and spoken-tutorial team.
11:25	This is Ashwini Patil from IIT Bombay, signing off.
11:29	Thank You for joining.

Contributors and Content Editors

PoojaMoolya, Pratik kamble, Ranjana, Sandhya.np14