PowerShell Loop Hands-On

Arrays and loops are often used including when working with PowerShell scripts.

In the following example, 4 array values are created, these are called again by means of the ID.

An array is created with the following command:

PS C:\>
$array = "sandwich", "salad","beer","espresso")
Write Host $array[0,1,2,3]

Output values with For-Loop Array:

The length of the array, or the number of stored values, is read out with $array.length. The variable ($i) serves as a counter to count when to exit the loop. A start value is assigned to the counter ($i=0).The start value should increase by 1 each time the loop passes ($i++) until the final value is reached. The final value is the length of the array ($array.length). When checking the final value, there is a condition: as long as $i is less than the number of values ($i -lt $array.length).

For loop

for ($i=0; $i -lt $array.length; $i++)
  Write Host $array[$i] 
}

The For loop: for ($i=0; $i -lt $array.length; $i++)
Start value $i=0: The variable $i starts with a value of 0
is $i smaller (-lt) $i -lt $array.length condition: the For loop is executed as long as this condition is met: as long as the variable $i is less than $array.length, so as long as $i is less than 4. The action at the loop pass: $i++ means to increase the value of the variable $i by 1, with each pass of the loop $i increases by 1: 0 .. 1 .. 2 .. 3 …

while loop

$i=0
while ($i -lt $array.length)
  Write Host $array[$i] 
  $i++
}

Example with starting value $i defined before the loop ($i=0)
while ($i -lt $array.length)
Within while is the condition for the loop pass, which loop wid does not leave as long as it is fulfilled:
$i -lt $array.length … as long as $i is smaller $array.length
The variable $i is incremented by 1 within the loop: $i++

Endless Loop

while can be used for an infinite loop as follows: with break, the infinite loop can be exited again. The following example goes through the loop until break is executed, this happens when $i is no longer less than 10:

$i=0
while ($true)
  $i++
  write-host $i
  if ($i -ge 10)
}

do loop

$i=0
doo
  Write Host $array[$i] 
  $i++
while ($i -lt $array.length)

Foreach

foreach ($i in $array)
  Write Host $i 
}

foreach ($i in $array) call all values of the array ($array). The variable $i contains the currently read value for each pass.

Operator Variations:

-gt greater than
-igt greater than, case-insensitive
-cgt greater than, case-sensitive
-ge greater than or equal
-ige greater than or equal, case-insensitive
-cge greater than or equal, case-sensitive
-lt less than
-ilt less than, case-insensitive
-clt less than, case-sensitive
-le less than or equal
-ile less than or equal, case-insensitive
-cle less than or equal, case-sensitive

Tutorial