> For the complete documentation index, see [llms.txt](https://devops-3.gitbook.io/devops/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://devops-3.gitbook.io/devops/docs/module-3-bash-scripting/decision-making.md).

# Decision Making

A Shell script is a plain text file. This file contains different commands for step-by-step execution. 

These commands can be written directly into the command line but from a re-usability perceptive it is useful to store all of the inter-related commands for a specific task in a single file.

Two types of decision-making statements are used within shell scripting. They are –

* If-else statement
* case-sac statement

### If-else

If else statement is a conditional statement. It can be used to execute two different codes based on whether the given condition is satisfied or not.

There are a couple of varieties present within the if-else statement.

* if-fi 
* if-else-fi 
* if-elif-else-fi 
* nested if-else

#### if-fi

<pre class="language-bash"><code class="lang-bash">if  [[ some_test ]] 

then 	
<strong>	commands
</strong>fi
</code></pre>

Example:

```bash
#!/bin/bash 

# Bash if statement example 

read -p "What is your name? " name 

if [[ -z ${name} ]] 

then 
echo "Please enter your name!" 

fi 
```

#### if-else-fi

```bash
if  [ expression ] 

then 	
	Commands
else
	Commands
fi
```

Example:

```bash
#!/bin/bash 

# Bash if statement example 

read -p "What is your name? " name 

if [[ -z ${name} ]] 

then 

echo "Please enter your name!" 
else 
echo "Hi there ${name}" 

fi
```

#### if-elif-else

```bash
if  [ expression ] 

then 
	Commands
elif [ expression ] 

	commands
else
	Commands
fi

```

Example:

```bash
#!/bin/bash 

read -p "Enter a number: " num 

if [[ $num -gt 0 ]] ; then 

echo "The number is positive" 

elif [[ $num -lt 0 ]] ; then 

echo "The number is negative" 

else 
echo "The number is 0" 

fi
```

### Switch-case

you can use a case statement to simplify complex conditionals when there are multiple different choices.&#x20;

So rather than using a few if, and if-else statements, you could use a single case statement.

```bash
case $some_variable in 

pattern_1) 

commands 

;; 

pattern_2| pattern_3) 

commands 

;; 

*) 

default commands 

;; 
esac

```

Example

```bash
#!/bin/bash 

read -p "Enter the name of your car brand: " car 

case $car in 
Tesla) 
echo -n "${car}'s car factory is in the USA." 
;; 
BMW | Mercedes | Audi | Porsche) 
echo -n "${car}'s car factory is in Germany." 
;; 
Toyota | Mazda | Mitsubishi | Subaru) 
echo -n "${car}'s car factory is in Japan." 
;; 
*) 
echo -n "${car} is an unknown car brand" 
;; 

esac 

```