Difference between revisions of "BASH/C2/Arithmetic-Comparison/English"

• -eq
• -ne
• -lt
• -le
• -gt
• -ge commands

We will do this with the help of some examples.

GNU BASH version 4.2.24

Please note, GNU bash version 4 or above is recommended to practice this tutorial.

example1.sh

I have named my file as example1.sh

Open a file in any editor of your choice and type the code as shown.

You must be familiar how to do so, by now.

#!/bin/bash

This is the shebang line.

read -p "Enter filename: " y

read command reads one line of data from the standard input.

x=`cat $y | wc -w`

Backtick has a very special meaning. Everything you type between backticks is evaluated.

cat command will display the content of the file.

wc will print newline, word, and byte counts for each file.

-w will print the word count.

What will happen is -

• First the cat command will read the file. This is the input file.
• Which it then piped or sent to the wc command.
• So, this statement counts the words in a given file.
• The output is stored in variable x.

if [ $x -eq 0 ]; then

echo "$y has zero words"

fi

-eq command checks whether word count is equal to 0.

If the condition is true, we will print a message “File has zero words”.

fi is the end of first if condition.

if [ $x -ne 0 ]; then

echo "$y has $x words"

fi

Here, -ne command checks whether word count is not equal to 0.

If the condition is true, we will print a message “File has $x words”.

$x will give the word count.

This is the end of 2nd if loop.

Now, let us execute our program.

Type:

chmod +x example1.sh

Type:

./example1.sh

First we will make our file executeable.

For this type:

chmod +x example1.sh

Then type:

./example1.sh

touch list.txt

Type: touch list.txt

Type:

echo “How are you” > (greater than sign) list.txt

chmod +x example1.sh

./example1.sh

Type:

list.txt

Type:

chmod +x example1.sh

./example1.sh

Enter filename is displayed.

Type:

list.txt

The Output

list.txt has 3 words

• greater or less than 1.
• Between 1 and 100
• Or above 100

#!/bin/bash

read -p "Enter the filename: " y

wc -c`

if [ $x -lt 1 ] ;

then

echo "No characters present in $y"

fi

If the condition is true, then we print “No characters present in file”.

fi ends the first if statement.

if [ $x -gt 1 ] ;

then

echo "$y has more than one character"

First the -gt command checks whether word count is greater than 1.

If yes, then this echo statement will get executed.

if [ $x -ge 1 ] && [ $x -le 100 ]; then

echo "Number of characters ranges between 1 and 100"

fi

Here in this if statement -

• -ge command checks whether word count is greater than or equal to 1 and
• -le command checks whether word count is less than or equal to 100.

If both the conditions are satisfied, then it prints:

Number of characters ranges between 1 and 100.

Please not that both conditions should be true to satisfy the entire if condition.

This is because we have included && in between both conditions.

fi is the end of this if statement.

if [ $x -gt 100 ] ;

then

echo "Number of characters is above 100"

fi

-gt command checks whether word count is greater than 100.

If the condition is stasified, we print Number of characters is above 100.

fi is the end of this if statement.

Type

chmod +x example2.sh

Type:

./example2.sh

Come back to the terminal.

Type:

chmod +x example2.sh

Type:

./example2.sh

list.txt

We will type list.txt

Number of characters ranges between 1 and 100

will be printed on the terminal.

Then observe which if statements get executed.

Come back to our slides.

Let us summarize.

Summary

In this tutorial we learnt,

-lt

-gt

-le

-ge

-eq

Assignment

Hint: -ne

http://spoken-tutorial.org /What\_is\_a\_Spoken\_Tutorial

About the Spoken Tutorial Project

It summarises the Spoken Tutorial project

If you do not have good bandwidth, you can download and watch it

Spoken Tutorial Workshops

Conducts workshops using spoken tutorials

Gives certificates to those who pass an online test

For more details, please write to

contact@spoken-tutorial.org

Acknowledgement

It is supported by the National Mission on Education through ICT, MHRD, Government of India

More information on this Mission is available at: http://spoken-tutorial.org\NMEICT-Intro

This is Ashwini Patil from IIT Bombay signing off.

Thank you for joining.