Linux-AWK/C2/Variables-and-Operators-in-awk/English-timed - Revision history

Sandhya.np14 at 15:20, 16 July 2019

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Sandhya.np14 at 09:26, 16 July 2019

2019-07-16T09:26:44Z

Sandhya.np14 at 11:43, 15 July 2019

2019-07-15T11:43:16Z

Sandhya.np14 at 11:42, 15 July 2019

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Sandhya.np14 at 15:09, 9 July 2019

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Sandhya.np14 at 12:01, 9 July 2019

2019-07-09T12:01:22Z

PoojaMoolya: Created page with " {| border=1 | '''Time''' | '''Narration''' |- | 00:01 | Hello and welcome to this spoken tutorial on variables and operators in '''awk comm..."

2018-12-14T06:07:02Z

Created page with " {| border=1 | <center>'''Time'''</center> | <center>'''Narration'''</center> |- | 00:01 | Hello and welcome to this spoken tutorial on variables and operators in '''awk comm..."

New page

{| border=1
| <center>'''Time'''</center>
| <center>'''Narration'''</center>

|-
| 00:01
| Hello and welcome to this spoken tutorial on variables and operators in '''awk command'''.

|-
| 00:07
| In this tutorial we will learn about- '''User defined variables '''

|-
| 00:12
| '''Operators '''

'''BEGIN and END statements'''

|-
| 00:17
| We will do this through some examples.

|-
| 00:20
| To record this tutorial, I am using '''Ubuntu Linux 16.04'''

|-
|00:26
| To practice this tutorial, you should have gone through the earlier '''Linux''' tutorials on this website.

|-
|00:33
| You should be familiar with '''basic operators''' used in general programming languages like '''C''' or '''C++'''.

|-
| 00:41
| If not, then please go through the corresponding tutorials on our website.

|-
| 00:47
| '''awk''' combines the power of a filter and a programming language.

|-
| 00:52
| So, it supports '''variables, constants, operators, '''etc.

|-
|00:58
| Let’s see what a '''variable '''in '''awk '''is.

|-
| 01:02
| A '''variable '''is an identifier that references a value.

|-
| 01:07
| '''Awk '''supports both '''user-defined variables '''and '''built-in variables'''.

|-
| 01:12
| We will learn about '''user-defined variables '''in this tutorial.

|-
| 01:17
| For '''user-defined variables''', '''variable '''declaration is not required.

|-
| 01:22
| '''Variables '''do not have to be initialized explicitly.

|-
| 01:26
| '''Awk '''automatically initializes them to zero or '''null string'''.

|-
| 01:32
| A '''variable '''must begin with a letter and continue with letters, digits and underscores.

'''Variables '''are case-sensitive.

|-
| 01:43
| So, '''Salary '''with capital “S” and '''salary '''with small “s” are two different '''variables'''.

|-
| 01:50
| Let us look at some examples now.

|-
| 01:53
| Open the '''terminal '''by pressing '''CTRL + ALT and T '''keys.

|-
| 01:58
| On the '''terminal''', type- '''awk space '''opening single quote opening curly brace small '''x '''equal to '''1 '''semicolon''' '''capital '''X '''equal to''' '''within double quotes '''capital A '''semicolon''' small a equal to '''within double quotes '''awk '''semicolon''' small b equal to '''within double quotes '''tutorial.'''

Press '''Enter.'''

|-
| 02:25
| '''type print x''' Press '''Enter'''

|-
| 02:29
| '''print capital X '''Press '''Enter'''

|-
| 02:34
| '''print a '''Press '''Enter'''

|-
| 02:37
| '''print b '''Press '''Enter'''

|-
| 02:40
| '''print a space b '''Press '''Enter'''

|-
| 02:44
| '''print small x space b '''Press '''Enter'''

|-
| 02:49
| '''print small x plus capital X '''closing curly brace closing single quote''' and press Enter '''

|-
| 02:57
| Since we have not given a filename, '''awk '''would need some input from '''standard input'''.

|-
| 03:03
| And hence, we can type any letter, say '''a '''and then press '''Enter.'''

|-
| 03:10
| This example shows a couple of things.

'''Variables''' can be initialized with a number.

|-
| 03:18
| It can also be initialized with value as a single character or a '''string.'''

|-
| 03:23
| If the value is a character or a string, variable is initialized with value within '''double quotes'''.

|-
| 03:31
| We can see the values of the '''variables'''.

|-
| 03:35
| Observe that small '''x''' and capital '''X''' are treated as different '''variables'''.

|-
| 03:41
| This proves that '''variables '''are '''case sensitive.'''

|-
| 03:45
| Also, it shows how two '''strings''' can be '''concatenated'''.

|-
| 03:50
| Here '''variables''' small '''a''' and small '''b''' are '''concatenated'''.

|-
| 03:55
| So, '''string concatenation operator''' is simply a '''space'''.

|-
| 04:00
| Similarly, when we '''concatenate''' small '''x,''' which is a number and '''string b''', '''x''' is auto-converted into '''string'''.

And the '''concatenated''' output becomes '''1tutorial. '''

|-
| 04:13
| Why does the auto-conversion to '''string '''happen?

|-
| 04:16
| That's because '''awk '''finds a '''string concatenation operator space '''here between '''x''' and '''b'''.

|-
| 04:25
| Now, look at the output of small '''x plus '''capital '''X'''.

Here, we have the '''arithmetic operator plus. '''

|-
| 04:33
| So, '''X''' is auto-converted to numeric zero.

And the addition output becomes numeric '''1'''.

|-
| 04:42
| Until now, we have seen a couple of '''operators'''.

Let’s look at what other '''operators''' we can use.

|-
| 04:49
| A variety of '''operators''' can be used in '''expressions'''.

|-
| 04:53
| Please pause the video here and take a look at all the '''operators''' mentioned here.

|-
| 04:58
| I assume you are familiar with these basic '''operators'''.

|-
| 05:02
| If not, then kindly visit our website for tutorials on '''operators''' in '''C and C++''' series.

|-
| 05:09
| I am not going to discuss the working of all these '''operators '''in detail.

|-
| 05:14
| Only exception is the '''string matching operator, '''which may be new to you.

Let us understand this with an example.

|-
| 05:23
| A file named '''awkdemo.txt '''has been provided in the '''Code files '''link.

Please download it on your computer.

|-
| 05:31
| Switch to the '''terminal'''

Let us end the previous process by pressing '''Ctrl''' and '''D''' keys.

|-
| 05:38
| Let me clear the '''terminal'''.

|-
| 05:41
| Now go to the folder in which you saved the '''awkdemo.txt''' file using the '''cd''' command.

|-
| 05:48
| Let us have a look at this file now.

|-
| 05:52
| Let's say we want to find the students who have passed but have marks less than 80.

|-
| 05:58
| In this case, we need to compare two different fields.

|-
| 06:02
| For such situations, we can use '''awk's relational operators.'''

|-
| 06:07
| These '''operators''' can compare both '''strings''' and '''numbers'''.

|-
| 06:12
| So, on the '''terminal''' type

'''''awk space hyphen capital F within double quotes vertical bar space Within single quotes dollar 5 equal to equal to within double quotes Pass space ampersand ampersand space dollar 4 less than 80 space within curly braces print space plus plus x coma dollar 2 coma dollar 4 coma dollar 5 space awkdemo.txt and press Enter.'''''

|-
| 06:54
| This command shows a number of things.

One, we compare a '''string '''with the fifth field.

|-
| 07:01
| Second, we only compare the fourth field with a number.

|-
| 07:06
| Third, we see that we can join two or more comparisons using '''ampersand operator.'''

|-
| 07:13
| Instead of specific numbers or '''strings''', we can also compare '''regular expressions.'''

|-
| 07:19
| As we have seen in the slide, we have the '''tilde '''and the '''exclamation tilde '''operators for this purpose.

|-
| 07:27
| Now suppose, we want to find computer science students who have passed.

|-
| 07:32
| Since computers can have both a small and capital '''C''', we would use a '''regular expression.'''

|-
| 07:40
| We would type

'''''awk space hyphen capital F within double quotes pipe symbol space within single quote dollar 5 equal to equal to within double quotes Pass ampersand ampersand space dollar 3 tilde slash within square brackets small c capital C computers slash space within curly braces print space plus plus small x comma dollar 2 comma dollar 3 coma dollar 5 space awkdemo.txt and press Enter.'''''

|-
| 08:24
| If we want to negate the comparison, we can do so using the '''exclamation tilde operator'''.

|-
| 08:30
| Say now we want a list of all non-computer students who have passed.

|-
| 08:35
| Use the up arrow to get the previous command.

|-
| 08:39
| Next to '''dollar 3''' add '''exclamation symbol''' and press '''Enter.'''

|-
| 08:47
| Next, let's count the number of blank lines in the same file.

|-
| 08:52
| Open the file and check how many blank lines are there are.

So, it has 3 blank lines.

|-
| 09:00
| Now to count the number of empty lines using '''awk''', type

'''''awk space within single quote within front slash caret symbol dollar space within curly braces x equal to x plus 1 semicolon space print x space awkdemo.txt'' '''

Press '''Enter'''.

|-
| 09:26
| We got 3 as our final answer.

|-
| 09:30
| The caret sign signifies start of a line while dollar signifies the end of a line.

|-
| 09:37
| Hence an empty line would be matched by the '''regular expression caret-dollar.'''

|-
| 09:43
| Note, we have not initialized the value of '''x'''.

'''Awk '''has initialized '''x '''to the initial value zero.

|-
| 09:51
| This command gives us the running count of blank lines.

This is because every time a blank line is found, '''x '''would be incremented and then printed.

|-
| 10:02
| In our last command, we have seen running count of blank lines.

But say we only want to print the total number of blank lines.

|-
| 10:12
| Then we need to print '''x '''only once, after the entire file has been traversed.

|-
| 10:19
| We may also want to give a heading saying what the output means.

|-
| 10:25
| For such requirements '''awk '''provides the '''BEGIN '''and the '''END '''sections.

|-
| 10:30
| The '''BEGIN '''section contains procedures for pre-processing.

|-
| 10:34
| This section is executed before the '''main input loop '''is executed.

|-
| 10:40
| The '''END '''section can contain procedures for post-processing.

|-
| 10:45
| This section is executed after the main input loop has terminated.

The '''BEGIN '''and '''END '''procedures are optional.

|-
| 10:55
| Let's learn how to do this.

In the terminal type

'''''awk space opening single quote BEGIN incaps within curly brace print space within double quotes The number of empty lines in awkdemo are ''''' press''' Enter.'''

|-
| 11:14
| '''''within front slash caret symbol dollar symbol space within curly braces x equal to x plus 1 '''''

press '''Enter.'''

|-
| 11:26
| '''''end space within curly braces print space x close single quote space awkdemo.txt and press Enter.'''''

|-
| 11:39
| See, we did not get the desired output!

We should get the output as 3, because we have 3 blank lines in the file.

|-
| 11:48
| What do you think happened?

Actually, we should have written '''end '''as upper case '''END.'''

|-
| 11:54
| So, let us modify the command.

|-
| 11:57
| Press the up arrow key to get the previous executed command on the '''terminal'''.

|-
| 12:03
| Now modify lower case '''end '''to upper case '''END. '''

And press''' Enter.'''

|-
| 12:11
| Now the total number of empty lines is displayed in the output.

|-
| 12:16
| Next, let's find the average salary of all the students that we found in the '''awkdemo.txt '''file.

|-
| 12:24
| To get that, type the command as shown in the '''terminal'''

And press '''Enter'''.

And we get the desired output.

|-
| 12:35
| This brings us to the end of this tutorial. Let us summarize.

|-
| 12:40
| In this tutorial we learnt about

'''User defined variables '''in '''awk'''

|-
| 12:45
| '''Operators '''

'''BEGIN and END statements'''

|-
| 12:49
| As an assignment print every line where the value of the last field is more than 5000

And the student belongs to '''Electrical department'''.

|-
| 13:00
| Print the average marks of all the students with the heading “'''Average marks'''” in the output.

|-
| 13:07
| The video at the following link summarises the Spoken Tutorial project.

Please download and watch it.

|-
| 13:14
| The '''Spoken Tutorial Project''' team conducts workshops using spoken tutorials

and gives certificates on passing online test.

|-
| 13:23
| For more details, please write to us.

|-
| 13:27
| Do you have questions in THIS Spoken Tutorial?

Please visit this site.

|-
| 13:32
| Choose the minute and second where you have the question.

Explain your question briefly.

Someone from our team will answer them.

|-
| 13:42
| The Spoken Tutorial forum is for specific questions on this tutorial.

|-
| 13:47
| Please do not post unrelated and general questions on them.

|-
| 13:51
| This will help reduce the clutter.

With less clutter, we can use these discussion as instructional material.

|-
| 13:59
| Spoken Tutorial Project is funded by NMEICT, MHRD, Government of India.

More information on this mission is available at this link.

|-
|14:10
| The script has been contributed by Antara and this is Praveen from IIT Bombay signing off.

Thank you for joining.

|}

@@ Line 17: / Line 17: @@
 |  '''Operators, '''
-'''BEGIN and END statements.'''
+'''BEGIN''' and '''END''' statements.
 |-

@@ Line 101: / Line 101: @@
 |-
 | 02:25
-| Type '''print x''', press '''Enter'''.
+| Type: '''print x''', press '''Enter'''.
 |-

@@ Line 334: / Line 334: @@
 |-
 | 08:52
-| Open the file and check how many blank lines are there are.
+| Open the file and check how many blank lines are there.
 So, it has 3 blank lines.

@@ Line 460: / Line 460: @@
 |-
 | 12:24
-| To get that, type the command as shown in the '''terminal'''
+| To get that, type the command as shown in the '''terminal''' and press '''Enter'''.
-And press '''Enter'''.
+And, we get the desired output.
-−
-And we get the desired output.
 |-

@@ Line 6: / Line 6: @@
 |-
 | 00:01
-| Hello and welcome to this spoken tutorial on variables and operators in '''awk command'''.
+| Hello and welcome to this '''spoken tutorial''' on '''Variables and operators in awk command'''.
 |-
 | 00:07
-| In this tutorial we will learn about- '''User defined variables '''
+| In this tutorial, we will learn about-
 |-
 | 00:12
-|  '''Operators '''
+|  '''Operators, '''
-'''BEGIN and END statements'''
+'''BEGIN and END statements.'''
 |-
@@ Line 28: / Line 29: @@
 |-
 |00:26
-| To practice this tutorial, you should have gone through the earlier '''Linux''' tutorials on this website.
+| To practice this tutorial, you should have gone through the earlier '''Linux''' tutorials on this '''website'''.
 |-
@@ Line 40: / Line 41: @@
 |-
 | 00:47
-| '''awk''' combines the power of a filter and a programming language.
+| '''awk''' combines the power of a '''filter''' and a programming language.
 |-
 | 00:52
-| So, it supports '''variables, constants, operators, '''etc.
+| So, it supports '''variables, constants, operators '''etc.
 |-
@@ Line 52: / Line 53: @@
 |-
 | 01:02
-| A '''variable '''is an identifier that references a value.
+| A '''variable '''is an '''identifier''' that references a value.
 |-
@@ Line 64: / Line 65: @@
 |-
 | 01:17
-| For '''user-defined variables''', '''variable '''declaration is not required.
+| For '''user-defined variables''', '''variable declaration''' is not required.
 |-
@@ Line 78: / Line 79: @@
 | A '''variable '''must begin with a letter and continue with letters, digits and underscores.
-'''Variables '''are case-sensitive.
+'''Variables '''are '''case-sensitive'''.
 |-
@@ Line 90: / Line 91: @@
 |-
 | 01:53
-| Open the '''terminal '''by pressing '''CTRL + ALT and T '''keys.
+| Open the '''terminal '''by pressing '''CTRL + ALT''' and '''T''' keys.
 |-
@@ Line 100: / Line 101: @@
 |-
 | 02:25
-| '''type print x''' Press '''Enter'''
+| Type '''print x''', press '''Enter'''.
 |-
 | 02:29
-| '''print capital X '''Press '''Enter'''
+| '''print capital X, '''press '''Enter'''.
 |-
 | 02:34
-| '''print a '''Press '''Enter'''
+| '''print a, '''press '''Enter'''.
 |-
 | 02:37
-| '''print b '''Press '''Enter'''
+| '''print b, '''press '''Enter'''.
 |-
 | 02:40
-| '''print a space b '''Press '''Enter'''
+| '''print a space b, '''press '''Enter'''.
 |-
 | 02:44
-| '''print small x space b '''Press '''Enter'''
+| '''print small x space b, '''press '''Enter'''.
 |-
 | 02:49
-| '''print small x plus capital X '''closing curly brace closing single quote''' and press Enter '''
+| '''print small x plus capital X '''closing curly brace closing single quote and press '''Enter'''.
 |-
@@ Line 146: / Line 147: @@
 |-
 | 03:23
-| If the value is a character or a string, variable is initialized with value within '''double quotes'''.
+| If the value is a character or a string, variable is initialized with value within double quotes.
 |-
@@ Line 162: / Line 163: @@
 |-
 | 03:45
-| Also, it shows how two '''strings''' can be '''concatenated'''.
+| Also, it shows how two '''strings''' can be concatenated.
 |-
 | 03:50
-| Here '''variables''' small '''a''' and small '''b''' are '''concatenated'''.
+| Here '''variables''' small '''a''' and small '''b''' are concatenated.
 |-