Difference between revisions of "Linux-AWK/C2/Built-in-Functions-in-awk/English"

• Arithmetic functions
• String functions
• Input/Output functions and
• Time-stamp functions

We will do this through some examples.

• Ubuntu Linux 16.04 operating system and
• gedit text editor 3.20.1

You can use any text editor of your choice.

You should have some knowledge of any programming language like C or C++.

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

Please download and extract them.

First we will learn about the arithmetic functions.

• sqrt(x) function returns positive square root of a number x
• int(x) truncates x to an integer value
• exp(x) gives the exponential of x

• log(x) returns natural logarithm value of x
• sin(x) and cos(x) gives sine(x) and cosine(x) respectively
• Please note that argument x should be mentioned in radians.

Let’s look at an example to understand these functions.

in Gedit

The same is available in the Code Files link.

int ()

log ()

Let us execute the file in the terminal.

awk -f arithmetic_function.awk

And press Enter to see the output.

Couple of things are clear from this output.

Highlight Square root of negative

Highlight int for positive & negative

Highlight exp of positive

Highlight exp of negative

Highlight log of positive

Highlight log of negative

Highlight sine & cosine

It returns nan or not a number if the number is negative.

int() gives the truncated integer of any positive or negative number.

exp() gives exponential of a number.

If the number is very large, the function will return inf.

Natural logarithm of positive number is given by log() function.

If the number if negative, the function returns nan.

Sine and cosine functions return corresponding values.

You can verify the value using your calculator.

• rand() returns any random number between 0 and 1.
• But never returns 0 or 1.

• Generated numbers will be random within one awk execution.
• But predictable across different executions of the awk program.

• srand(x) is used to provide seed value x for random function.
• In absence of x, date and time of day is used as the seed value.

Let us understand these with an example.

Highlight rand()*50

Highlight for (i=1;i<=5;i++)

Then the generated number will be multiplied by 50 and get printed.

So, this code will generate 5 random numbers within 50.

Let me clear the terminal.

awk -f random.awk

awk space hyphen f space random dot awk and press Enter.

Press the Up arrow key to get the previously executed command and press Enter.

Which means, awk is generating the same set of random numbers for every execution of the script.

Then how can we get a new set of random numbers in every execution?

Switch to the code once again.

srand() and [enter]

Press Crtl and S keys to the save the file.

So, we can generate a new set of random numbers using srand function, when it’s used without an argument.

length function gives the length of a particular string s

index function determines the position of string s2 within the larger string s1.

For example, index within parentheses within double quotes linux comma within double quotes n, returns 3.

Let us see an example.

Due to typing error, the roll numbers may have wrong number of digits.

We can easily detect these using awk commands.

Let me clear the terminal.

awk -F"|" 'length($1)!=4 {print}' awkdemo.txt

Highlight 'length($1)!=4 {print}'

[Enter]

Here we are checking the length of the 1st field is equal to 4 or not.

If not, then that particular record will get printed.

Press Enter.

It has three digits, whereas all others have four digits.

Let me explain the parameters.

• Here s is the string
• a denotes the position in s from which the extraction would start
• b denotes the number of characters that would be extracted.

Let us see one example.

Say we want to find the list of students, who are staying in Hostel A.

To get that, let’s switch to the terminal.

awk -F"|" 'substr($1,1,1)=="A" {print $1,$2}' awkdemo.txt

As we know $1 represents the first field, that is roll number in our case.

Press Enter to see the output.

So, I am not explaining the details here.

Please refer to the earlier awk tutorials if you have any doubt.

• system() function - helps us to run any unix command within awk.

awk 'BEGIN{system("date")}'

[Enter]

And press Enter.

awk 'BEGIN{system("date")}'

We have kept only the BEGIN section of the awk command.

In that case, we would need to execute system commands from awk command.

• systime()
• strftime()
• etc.

Browse through the Internet to know about these functions.

Let us summarize.

In this tutorial we learnt about different types of built-in functions like

• Arithmetic functions
• String functions
• Input/Output functions
• Time stamps functions

Write an awk program to print the last field of every record

• where name of the student has small u as the third letter
• using the awkdemo.txt file.

About Spoken Tutorial project

Please download and watch it.

Spoken Tutorial workshops

And gives certificates on passing online tests.

For more details, please write to us.

Forum for specific questions:

More information on this mission is available at

this link.

And this is Praveen from IIT Bombay signing off.

Thank you for joining