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

• equal to
• not equal to
• less than
• less than equal to
• greater than
• greater than equal to commands

We will do this with the help of some examples.

• Ubuntu Linux 12.04 Operating System and
• GNU BASH version 4.1.10

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

example1.sh

I have named my file example1.sh

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.

- (hyphen) w will print the word count.

What will happen is -

• First the cat command will read the file. This is the input file.
• Which is 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

- (hyphen) eq command checks whether word count is equal to zero.

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, - (hyphen) ne command checks whether word count is not equal to zero.

If the condition is true, we will print “File has so-and-so words”.

$ (dollar) x will give the word count.

This is the end of 2nd if condition.

Now, let us execute our program.

touch list.txt

Type: touch list.txt

Type:

echo double quotes How are you after the double quotes greater than sign list.txt

chmod +x example1.sh

./example1.sh

Type:

list.txt

Type:

chmod plus x example1 dot sh

Now type dot slash example1.sh

Enter filename is displayed.

Type:

list.txt

The Output

list.txt has 3 words

• greater or less than one
• Between one and hundred
• Or above hundred

#!/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 if statement.

if [ $x -gt 1 ] ;

then

echo "$y has more than one character"

First the - (hyphen) gt command checks whether word count is greater than one.

If yes, then this echo statement will be executed.

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

echo "Number of characters ranges between 1 and 100"

fi

Here, in this if

• - (hyphen) ge command checks whether word count is greater than or equal to one and
• - (hyphen) le command checks whether word count is less than or equal to hundred.

If both the conditions are satisfied, then it prints:

Number of characters ranges between 1 and 100.

Please note that both conditions should be true to satisfy the entire if condition.

This is because we have included ampersand in-between both the conditions.

fi is the end of this if statement.

if [ $x -gt 100 ] ;

then

echo "Number of characters is above 100"

fi

- (hyphen) gt command checks whether word count is greater than hundred.

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

fi is the end of if statement.

Type

chmod +x example2.sh

Type:

./example2.sh

Type: chmod plus x example2 dot sh

Type: dot slash example2 dot sh

Number of characters ranges between one and hundred

Then observe which if statement gets executed.

Let us summarize.

Summary

In this tutorial we learnt,

• equal to
• not equal to
• less than
• less than equal to
• greater than
• greater than equal to commands

Assignment

Hint: - (hyphen) ne

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Thank you for joining.