Loops

Loops enable programs to execute the same set of statements multiple times until a stop condition is met. There are five types of loops in PowerShell:

• for
• while
• do..while
• do..until
• foreach

for Loop

The for loop executes the enclosed code until the given condition is met. It has three parts:

• The initialization of a counter variable
• The stop condition
• The increment/decrement of the counter variable

for ($i = 1; $i -le 5; $i++) {
  $square = $i * $i
  Write-Host "The square of" $i "is" $square
}

The above for loop prints squares of numbers up to 5.

foreach Loop

The foreach loop is specifically for iterating over items in an array.

$array = 51,12,31,4,15
foreach ($element in $array) {
  if ($element % 2 -eq 0) {
    Write-Host $element "is" Even
  } else {
    Write-Host $element "is" Odd
  }
}

The example above code is equivalent to using the foreach method of arrays:

$array.foreach({
  if ($PSItem % 2 -eq 0) {
    Write-Host $PSItem "is" Even
  } else {
    Write-Host $PSItem "is" Odd
  }
})

Note: $PSItem can be replaced with its shorthand alias $_.

while Loop

The while loop executes statements repeatedly as long as the condition is True. The following example counts by 3 until $count reaches 15.

$count = 0
while($count -lt 15) {
  $count += 3
  Write-Host The count is $count
}

do..while Loop

The do..while loop is a slight variation of the while loop in which statements are executed once before the condition is checked.

$answer = 4
do {
  $input = Read-Host "Guess my number"
} while ($input -ne $answer)
Write-Host "Correct!"

do..until Loop

The do..until loop is the same as the do..while loop except that the loop exits when the condition is True.

$answer = 4
do {
  $input = Read-Host "Guess my number"
} until ($input -eq $answer)
Write-Host "Correct!"

break and continue Statements

break and continue are special statements for exiting loops early and skipping iterations, respectively.

for ($i = 0; $i -lt 5; $i++) {
  if ($i -eq 2) {
    break
  }
  Write-Host $i
}

The above example prints 0 and 1 since the loop exits when $i becomes 2. If continue is used instead of break, like in the example below, the iteration when $i is 2 is skipped and it prints 0, 1, 3, 4.

for ($i = 0; $i -lt 5; $i++) {
  if ($i -eq 2) {
    continue
  }
  Write-Host $i
}