Does it loop? ForEach experiences with an empty variable

Does an empty variable loop in PowerShell? My first instinct was: no. But the correct answer is: it depends.

Uninitialized variable with foreach

$noValue -eq $null  # True – an unregistered variable is $null

foreach ($oneValue in $noValue) {
    'Do not run.'
}
# Result: does NOT enter the loop

Uninitialized variable with ForEach-Object

$noValue | ForEach-Object { 'Runs' }
# Result: DOES execute the loop body – surprising!

Empty array with foreach

$noArray = @()
foreach ($oneValue in $noArray) {
    'Do not run.'
}
# Result: does NOT enter the loop

Empty array with ForEach-Object

$noArray | ForEach-Object { 'Runs' }
# Result: does NOT execute the loop body

Summary

Input	foreach	ForEach-Object
$null	❌ skips	✅ runs once
@()	❌ skips	❌ skips

To avoid surprises, initialise your variables at the start of your script.

Why does this happen?

Bruce Payette (PowerShell co-creator) explained it:

The foreach statement and ForEach-Object had identical, consistent behaviour in version 1 but users complained about the foreach statement iterating over null. As a result, we changed the behaviour in v2 (or v3 – I can’t remember which) adding a deliberate inconsistency.