A loop statement allows us to execute a statement or group of statements multiple times and following is the general form of a loop statement in most of the programming languages

PowerShell loops, at their most basic, simply repeat the same set of commands a set number of times. Ideal for performing consistent actions for a set period of time or a certain number of records, loops can simplify your scripts in a big way. PowerShell in particular features a number of cmdlets -- notably those that begin with the verb Get -- which return objects containing large numbers of similar data.

There are several types of loops available in PowerShell, and in many cases more than one loop technique can be used effectively. At times determining the most efficient loop type is required, either from a performance or code readability perspective.

While

The while statement runs a statement list zero or more times based on the results of a conditional test.

$i = 0
while($i -lt 3)
{
    Write-Output $i
    $i++
}

Do While

The do while statement runs a statement list one or more times based on the affirmative results of a conditional test.

$i = 0
do
{
    Write-Output $i
    $i++
}while($i -lt 3)

Do Until

The do until statement runs a statement list one or more times based on the negative results of a conditional test.

$i = 0
do
{
    Write-Output $i
    $i++
}until($i -ge 3)

For

The for statement runs a statement list zero or more times based on an initial setting, a conditional test, and a repeated statement, most often used with numeric counters

for($i = 0; $i -lt 3; $i++)
{
    Write-Output $i
}

For loops are often nested to repeat actions, such as for rows and columns. For example:

for($i = 0; $i -lt 3; $i++)
{
    $line = ''
    for($j = 0; $j -lt 3; $j++)
    {
        $line += $i.ToString() + $j.ToString() + '  '
    }
    Write-Output $line
}

ForEach

The foreach statement runs a statement list once for each item in a collection.

$processes = Get-Process
foreach($process in $processes)
{
    if($process.PM / 1024 / 1024 -gt 100)
    {
        Write-Output ('Process ' + $process.Name + ' is using more than 100 MB RAM.')
    }
}

Continue

The continue statement immediately returns script flow to the top of the innermost While, Do, For, or ForEach loop

$processes = Get-Process
foreach($process in $processes)
{
    if($process.PM / 1024 / 1024 -le 100)
    {
        continue
    }
    Write-Output ('Process ' + $process.Name + ' is using more than 100 MB RAM.')
}

Break

The break statement causes Windows PowerShell to immediately exit the innermost While, Do, For, or ForEach loop or Switch code block

$processes = Get-Process
foreach($process in $processes)
{
    if($process.PM / 1024 / 1024 -gt 100)
    {
        Write-Output ('Process ' + $process.Name + ' is using more than 100 MB RAM.')
        break
    }
}

Exit

Exit causes Windows PowerShell to exit a script or a Windows PowerShell instance.

if()
{
    Exit 
}

Foreach-Object

The ForEach-Object cmdlet runs a command list once for each item in a collection. While the ForEach-Object cmdlet is often more convenient, the foreach statement and a coded loop usually offers better performance

Get-Process | ForEach-Object { if($_.PM / 1024 / 1024 -gt 100) {'Process ' + $_.Name + ' is using more than 100 MB RAM.'} }

Start-Sleep

The Start-Sleep cmdlet allows you to pause Windows PowerShell activity for a specified period of time. It is particularly useful with long-running scripts or infinite loops.

while($true)
{
    if((Get-Date -Format 'hh:mm') -eq '00:00')
    {
        'It''s midnight.  You should go to sleep.'
    }
    Start-Sleep -Seconds 60
}

Get-Counter

The Get-Counter cmdlet gets performance counter data from local and remote computers.

Get-Counter