For Each

How to do something to every item in a collection of things. This is where the automation really kicks in.

Basic Usage

$trees = @(
	@{name="Alder";family="Betulaceae"},
	@{name="Birch";family="Betulaceae"},
	@{name="Beech";family="Fagaceae"},
	@{name="Walnut";family="Juglandaceae"},
	@{name="Ash";family="Oleaceae"} 
)

foreach ($tree in $trees) {
	$tree.name + " is in the " + $tree.family + " family."
}

Structure of foreach

The foreach function is great for looping through items, it follows this beautifully illustrated structure:

So in the above example: First Loop: $item is $something[0], do something with value x, if [0] looks new to you refer to Indexing Second Loop: $item is $something[1], do something with value y. Third Loop: $item is $something[2], do something with value z. …

This is great in scripts and can be used for almost anything, sometimes you might want to end the loop early:

Continue, Break

For Each has a couple key words that it can use to dictate whether it can keep looping or stop early.

continue means go to the next loop please, for example:

foreach ($num in 1,2,3,4,5) {  
  if ($num -eq 2) { continue }
  $num  
 }

This skips the number 2, because we told it to continue (to the next loop) before it could get to the $num call that would display the number.

break means cut the loops off completely, if a foreach runs into a break word is will not run any further loops at all.

foreach ($num in 1,2,3,4,5,6,7) {
	if ($num -eq 5) { break }
	$num
}

Again, the loop did not display 5 as an output because the break clause was reached before the $num call to print the number.

ForEach-Object

Foreach works great for writing scripts, its great strength is readability as you can set the iterator to a sensible name like $item or $tree. However, we often just want to use foreach on the fly, sometimes even on the same line.

For this purpose we use ForEach-Object which is used in the pipeline (below we use shorthand ForEach):

get-service -DisplayName *update* | ForEach-Object {'Service "{0}" is {1}' -f $_.DisplayName, $_.Status}

In one line, we can perform an action for each object generated from the left side of the |. The only thing that differs, is having to use the $_ variable.

The Pipeline Variable _

The shorthand for the shorthand

Even further than the above, we can completely avoid using the foreach keyword and replace it with %.

Here’s the same command as above but with the shortest foreach declaration:

get-service -DisplayName *update* | % {'Service "{0}" is {1}' -f $_.DisplayName, $_.Status}

The foreach method

A similar approach to the .where() method mentioned in Where there is a .foreach() method following the same structure.

(Get-Service r*).foreach({'{0}--{1}' -f $_.name, $_.status})

This is still very useful, but can reduce readability when writing very long lines of code. The | pipeline is one of the core functions of PowerShell and has more troubleshooting resources online, which is why it is often preferred.