While Loops
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In this lecture, I am going to discuss While Loops.
Now, what I am going to do first is open PowerShell ISE as an Administrator.
Let's discuss what a While Loop is. A loop that will repeat a set of commands indefinitely until a condition is met.
It is somewhat similar to the For Loops except for the fact that a For Loop is just counting from 0 to 5, or 0 to 10, or whatever the number may be, and only repeat the set of instructions until a count is done.
A While Loop will run these instructions indefinitely until a condition is met.
If we were to write a For Loop you might remember we write it like this:
for ($i = 0; $i -lt 5; $i++) {
$i
}
If we execute this we get 0 through 4
And, if we want to repeat this in a While Loop we will type:
$i = 0
while ($i -lt 5) {
$I
$I++
}
If we execute this code we get the same result
You might be wondering, why would we ever use a While Loop if we can use a For Loop? Well, if you are going to be counting from 0 to 5 you want to use a For Loop but if you have other dependencies or other conditions there may be cases where you want to use a While Loop.
For example, let’s make a While Loop:
while ((Read-Host “Type ‘xyz’ to stop the loop”) -ne “xyz”) {
echo “You did not type ‘xyz’ so I am going to continue the loop”
}
So if we execute this script it will continue to run indefinitely until I enter “xyz”
Now, there’s also another way you accomplish the same goal and we can do this with a variable. Instead of using Read-Host in the While Loop, we can store that Read-host in a variable and then check that variable against the While Loop.
So let’s type the following using a variable.
while ($userInput -ne “xyz”) {
$userInput = Read-Host “Please type ‘xyz’ to stop the loop”
}
If you execute the code you will see it finishes and is because $userInput is cached. Type the following to confirm:
To clear this issue we need to add to the code the following:
while ($userInput -ne “xyz”) {
$userInput = Read-Host “Please type ‘xyz’ to stop the loop”
}
$userInput = $null
Run it once and you will see it exits one time but it assigns at the end the $null value. Let’s execute it again to enter the loop.
Once running you can enter anything and the loop will continue running indefinitely until I type “xyz” to exit.
Now, let’s create another While Loop and we will base it on the previous While Loop.
while ($userInput -ne “quit”) {
# Gather user input
$userInput = Read-Host “Say ‘yes’ if you like scripting (enter ‘quit’ to stop the loop)”
# Evaluate the user input
If ($userInput -eq “yes”) { echo “I also love scripting! That’s cool” }
}
$userInput = $null
Now, if we execute this script I can type “yes’ and it will continue to execute. If I type “quit” it exits the loop.
And we can build out the script and type more like:
while ($userInput -ne “quit”) {
# Gather user input
$userInput = Read-Host “Say ‘yes’ if you like scripting (enter ‘quit’ to stop the loop)”
# Evaluate the user input
If ($userInput -eq “yes”) { echo “I also love scripting! That’s cool” }
elseif ($userInput -eq “no”) { echo “I really hate scripting too”}
}
$userInput = $null
I can type “yes”, “no”, a blank space to test, and “quit” to exit the script.
So, that’s a good example of how you can use While Loops and why they are different from For Loops.
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