Nancyvarkey at 04:23, 22 November 2017

2017-11-22T04:23:35Z

Pravin1389: Created page with "'''Title of script''': Variables and Operators in Awk '''Author: '''Antara Roy Choudhury '''Keywords: '''Linux, awk commands, Variables in awk, operators in awk, String Conc..."

2017-11-13T10:38:37Z

Created page with "'''Title of script''': Variables and Operators in Awk '''Author: '''Antara Roy Choudhury '''Keywords: '''Linux, awk commands, Variables in awk, operators in awk, String Conc..."

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'''Title of script''': Variables and Operators in Awk

'''Author: '''Antara Roy Choudhury

'''Keywords: '''Linux, awk commands, Variables in awk, operators in awk, String Concatenation in awk, Regular expressions in awk, BEGIN and END statement in awk, Spoken Tutorial, Video Tutorial.

{| style="border-spacing:0;"
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| <center>'''Visual Cue'''</center>
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| <center>'''Narration'''</center>

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Slide 1: Introduction
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Hello and welcome to this spoken tutorial on variables and operators in awk command.

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Slide 2: Learning Objectives
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| In this tutorial we will learn about-

* '''User defined variables '''
* '''Operators '''
* '''BEGIN and END statements'''

We will do this through some examples.

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Slide 3: System requirement
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| To record this tutorial, I am using '''Ubuntu Linux 16.04'''

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Slide 4: Prerequisite
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| To practice this tutorial, you should have gone through the earlier '''Linux''' tutorials on this website.

You should be familiar with '''basic operators''' used in general programming languages like '''C''' or '''C++'''.

If not, then please go through the corresponding tutorials on our website.

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Slide 5: awk
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| '''awk''' combines the power of a filter and a programming language.

So, it supports '''variables, constants, operators, '''etc.

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Slide 6: Variable
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Let’s see what a '''variable '''in '''awk '''is.

A '''variable '''is an identifier that references a value.

'''Awk '''supports both '''user-defined variables '''and '''built-in variables'''.

We will learn about '''user-defined variables '''in this tutorial.

For '''user-defined variables''', '''variable '''declaration is not required.

'''Variables '''do not have to be initialized explicitly.

'''Awk '''automatically initializes them to zero or '''null string'''.

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Slide 7: Variable

| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| A '''variable '''must begin with a letter and continue with letters, digits and underscores.

'''Variable '''are case-sensitive.

So, '''Salary '''with capital “S” and '''salary '''with small “s” are two different '''variables'''.

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"|
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Let us look at some examples now.

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Open the '''terminal''' by pressing '''CTRL + ALT''' and '''T''' keys
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Open the '''terminal '''by pressing '''CTRL + ALT and T '''keys.

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Type

awk '{x=1;X="A";a="awk";b="tutorial"''<nowiki>[enter]</nowiki>''

print x ''<nowiki>[enter]</nowiki>''

print X ''<nowiki>[enter]</nowiki>''

print a ''<nowiki>[enter]</nowiki>''

print b ''<nowiki>[enter]</nowiki>''

print a b

print x b

print x+X}' ''<nowiki>[enter]</nowiki>''

| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| 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.'''

'''type print x''' Press '''Enter'''

'''print capital X '''Press '''Enter'''

'''print a '''Press '''Enter'''

'''print b '''Press '''Enter'''

'''print a space b '''Press '''Enter'''

'''print x space b '''Press '''Enter'''

'''print small x plus capital X '''closing curly brace closing single quote''' and press Enter '''

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| a ''<nowiki>[enter]</nowiki>''
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Since we have not given a filename, '''awk '''would need some input from '''stdin'''.

And hence, we can type any letter.

say '''a '''and then press '''Enter.'''

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Hover your mouse over x=1; X="A" and a="awk"
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| This example shows a couple of things.

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

It can also be initialized with value as a single character or a '''string.'''

If the value is a character or a string, variable is initialized with value within '''double quotes'''.

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Hover your mouse over the values of small x and capital X
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| We can see the values of the '''variables'''.

Observe that small '''x''' and capital '''X''' are treated as different '''variables'''.

This proves that '''variables '''are '''case sensitive.'''

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Hover your mouse over the output of “print a b”
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Also, it shows how two '''strings''' can be '''concatenated'''.

Here '''variables''' small '''a''' and small '''b''' are '''concatenated'''.

So, '''string concatenation operator''' is simply a '''space'''.

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Hover your mouse over the output of “print x b”

| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| 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. '''

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Continue to hover your mouse over the output of “print x b”
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Why does the auto-conversion to '''string '''happen?

That's because '''awk '''finds a '''string concatenation operator space '''here between '''x''' and '''b'''.

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Hover your mouse over the output of print x+X
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Now, look at the output of small '''x plus '''capital '''X'''.

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

So, '''X''' is auto-converted to numeric zero.

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

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"|
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Until now, we have seen a couple of '''operators'''.

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

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Slide 8: Operators
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| A variety of '''operators''' can be used in '''expressions'''.

Please pause the video here and take a look at all the '''operators''' mentioned here.

I assume you are familiar with these basic '''operators'''.

If not, then kindly visit our website for tutorials on '''operators''' in '''C and C++''' series.

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Same slide but highlight the relevant line item
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| I am not going to discuss the working of all these '''operators '''in detail.

Only exception is the '''string matching operator, '''which may be new to you.

Let understand this with an example.

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"|
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| A file named '''awkdemo.txt '''has been provided in the '''Code files '''link.

Pls download it on your computer.

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Switch to '''terminal'''

| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Switch to the '''terminal'''

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

Let me clear the '''terminal'''.

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| <nowiki>cd /<saved folder></nowiki>
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Now go to the folder in which you saved the '''awkdemo.txt''' file using the '''cd''' command.

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"|
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Let us have a look at this file now.

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Show the file opened
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Let's say we want to find the students who have passed but have marks less than 80.

In this case, we need to compare two different fields.

For such situations, we can use '''awk's relational operators.'''

These '''operators''' can compare both '''strings''' and '''numbers'''.

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| awk -F "|" <nowiki>'$5=="Pass" && $4<80 {print ++x,$2,$4,$5}' </nowiki>awkdemo.txt

<nowiki>[enter]</nowiki>
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| 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.'''''

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Show the output of the previous command

| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| This command shows a number of things.

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

Second, we only compare the fourth field with a number.

Third, we see that we can join two or more comparisons using '''ampersand operator.'''

Instead of specific numbers or '''strings''', we can also compare '''regular expressions.'''

As we have seen in the slide, we have the '''tilde '''and the '''exclamation tilde '''operators for this purpose.

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Show the awkdemo.txt file and highlight Computers with different case.
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Now suppose, we want to find computer science students who have passed.

Since computers can have both a small and capital '''C''', we would use a '''regular expression.'''

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Type:

awk -F "|" '$5=="Pass" && <nowiki>$3~/[cC]omputers/ {print ++x,$2,$3,$5}' awkdemo.txt</nowiki>
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| 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 ++x coma dollar 2 coma dollar 3 coma dollar 5 space awkdemo.txt and press Enter.'''''

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"|
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| If we want to negate the comparison, we can do so using the '''exclamation tilde operator'''.

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Type:

awk -F "|" '$5=="Pass" && <nowiki>$3!~/[cC]omputers/ {print ++x,$2,$3,$5}' awkdemo.txt</nowiki>
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Say now we want a list of all non-computer students who passed.

Use the up arrow to get the previous command.

Next to '''dollar 3''' add '''exclamation symbol''' and press '''Enter.'''

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"|
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Next, let's count the number of blank lines in the same file.

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Show the awkdemo.txt file and highlight blank lines
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Open the file and check how many blank lines are there are.

So, it has 3 blank lines.

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Type

<nowiki>awk '/^$/ {x=x+1; print x}' awkdemo.txt [enter] </nowiki>

| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| 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'''.

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Highlight the output
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| We get 3 as our final answer.

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Highlight the caret sign (^) >> then the dollar($) sign
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| The caret sign signifies start of a line while dollar signifies the end of a line.

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Highlight '''caret-dollar (^$)'''.
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Hence an empty line would be matched by the '''regular expression caret-dollar.'''

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Highlight '''x'''
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Note, we have not initialized the value of '''x'''.

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

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Highlight the output of the command executed
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| 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.

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Slide 9: BEGIN and END sections
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| 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.

Then we need to print '''x '''only once, after the entire file has been traversed.

We may also want to give a heading saying what the output means.

For such requirements '''awk '''provides the '''BEGIN '''and the '''END '''sections.

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Slide 10: BEGIN and END sections
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| The '''BEGIN '''section contains procedures for pre-processing.

This section is executed before the '''main input loop '''is executed.

The '''END '''section can contain procedures for

post-processing.

This section is executed after the main input loop has terminated.

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

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Type

<nowiki>awk 'BEGIN{print "The number of empty lines in awkdemo are"} [press enter]</nowiki>

<nowiki>/^$/ {x=x+1} [press enter]</nowiki>

<nowiki>end {print x}' awkdemo.txt[press enter]</nowiki>

| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| 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.'''

'''''within front slash caret symbol dollar symbol space within curly brace x equal to x plus 1 '''''

press '''Enter.'''

'''''end space within curly braces print space x close single quote space awkdemo.txt and press Enter.'''''

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Highlight the output
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| See, we did not get the desired output!

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

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Point to '''end '''in lowercase

| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| What do you think happened?

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

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"|
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| So, let us modify the command.

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| <nowiki>awk 'BEGIN{print "The number of empty lines in awkdemo are"} [press enter]</nowiki>

<nowiki>/^$/ {x=x+1} [press enter]</nowiki>

<nowiki>END {print x}' awkdemo.txt [press enter]</nowiki>
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Press up arrow key to get the previous executed command on the '''terminal'''.

Now modify lower case '''end '''to upper case '''END. '''

And press''' Enter.'''

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Highlight the output
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Now the total number of empty lines is displayed in the output.

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"|
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Next, let's find the average salary of all the students that we found in the '''awkdemo.txt '''file.

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Type

<nowiki>awk -F"|" 'BEGIN {printf "%-3s %-25s %10s\n", "Sl","Student","Stipend"} [enter] {x=x+1; total = total+$6; printf"%-3d %-25s %-10d\n",x,$2,$6} [enter]</nowiki>

<nowiki>END{avg=total/x; print "The average stipend is" avg}' awkdemo.txt [Enter]</nowiki>
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| To get that, type the command as shown in the '''terminal'''

And press '''Enter'''.

And we get the desired output.

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Slide 11: Summary
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| This brings us to the end of this tutorial. Let us summarize.

In this tutorial we learnt about

* '''User defined variables '''in '''awk'''
* '''Operators '''
* '''BEGIN and END statements'''

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Slide 12: Assignment

| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| As an assignment print every line where the value of the last field is more than 5000

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

Print the average marks of all the students with the heading “'''Average marks'''” in the output.

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Slide 13: About Spoken Tutorial project
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| The video at the following link summarises the Spoken Tutorial project.

Please download and watch it.

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Slide 14: Spoken Tutorial workshops
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| The '''Spoken Tutorial Project''' team conducts workshops using spoken tutorials

and gives certificates on passing online test.

For more details, please write to us.

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Slide 15: Forum for specific questions:
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Do you have questions in THIS Spoken Tutorial?

Please visit this site.

Choose the minute and second where you have the question.

Explain your question briefly.

Someone from our team will answer them.

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Slide 16: Forum for specific questions:
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| The Spoken Tutorial forum is for specific questions on this tutorial.

*

Please do not post unrelated and general questions on them.

This will help reduce the clutter.

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

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Slide 17: Acknowledgement
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Spoken Tutorial Project is funded by NMEICT, MHRD, Government of India.

More information on this mission is available at

this link.

|-
| style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Slide 18: Thank You
| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| The script has been contributed by Antara and this is Praveen from IIT Bombay signing off.

Thank you for joining.

|}

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

Nancyvarkey: Nancyvarkey moved page Linux/C3/Variables-and-Operators-in-awk/English to Linux-AWK/C2/Variables-and-Operators-in-awk/English without leaving a redirect: New series

Nancyvarkey at 04:23, 22 November 2017

Pravin1389: Created page with "'''Title of script''': Variables and Operators in Awk '''Author: '''Antara Roy Choudhury '''Keywords: '''Linux, awk commands, Variables in awk, operators in awk, String Conc..."

← Older revision	Revision as of 11:04, 22 March 2018
(No difference)

@@ Line 13: / Line 13: @@
 |-
 | style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Slide 1: Introduction
-| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Hello and welcome to this spoken tutorial on variables and operators in awk command.
+| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Hello and welcome to this spoken tutorial on variables and operators in '''awk command'''.
 |-
 | style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Slide 2: Learning Objectives
 | style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| In this tutorial we will learn about-
 * '''User defined variables '''
 * '''Operators '''
@@ Line 77: / Line 75: @@
-'''Variable '''are case-sensitive.
+'''Variables '''are case-sensitive.
@@ Line 136: / Line 134: @@
 |-
 | style="border-top:1pt solid #000001;border-bottom:1pt solid #000001;border-left:1pt solid #000001;border-right:none;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| a ''<nowiki>[enter]</nowiki>''
-| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Since we have not given a filename, '''awk '''would need some input from '''stdin'''.
+| style="border:1pt solid #000001;padding-top:0in;padding-bottom:0in;padding-left:0.0313in;padding-right:0.075in;"| Since we have not given a filename, '''awk '''would need some input from '''standard input'''.
-−
-−
-And hence, we can type any letter.
-say '''a '''and then press '''Enter.'''
+And hence, we can type any letter, say '''a '''and then press '''Enter.'''
 |-