ForEach

ForEach-Object:

• Collecting values from a member(property or method) by -MemberName
• Value transformation by -Process
• Mimicking a function that accepts pipeline input by -Begin, -Process, -End and -RemainingScripts
• Parallel Jobs

Intrinsic ForEach has some overlap with ForEach-Object, it's not recommended but worth noting.

• Type conversion
• Collecting values from a member
• Replace a property by new value

TIP

Use foreach or % alias for ForEach-Object.

Collecting Values

• What differs ForEach-Object from Select-Object -ExpandProperty is -MemberName can accept a method name as well.

NOTE

See: help % -Parameter MemberName

# -MemberName is positional
gci | foreach -MemberName Name
# equivalent to 
gci | select -ExpandProperty Name

Evaluating from a method member is available, you can even pass parameters by -ArgumentList.

(1..3 | % GetType | select -first 1) -is [System.Type] # True

'1,2,3' | foreach -MemberName Split -ArgumentList ','
# or this, ',' is passed as ValueFromRemainingArguments for -ArgumentList
'1,2,3' | foreach Split ','

Value Transformation

The way -Process behaves is collecting implicitly returned values as an array. Every implicitly returned value will be collected as a item.

NOTE

See: help % -Parameter MemberName

# -Process is positional at 0
gci | foreach -Process { $_.Exists, $false } # True, False, True, False...

If you do want a $null return, use Out-Null to swallow the value.

# doesn't make much sense though
$null -eq (gci | foreach { $_.Name | Out-Null }) # True

Intrinsic ForEach

Type Conversion

One of overloads of ForEach takes a System.Type, and trying to cast all of them to the type.

(65..90).ForEach([char]) # A-Z

Collecting Values

('1,2,3').ForEach('Split', ',') # ArgumentList allowed
(gci -file).ForEach('Length')

Override Property Value

(gci -file).ForEach('CreationTime', (Get-Date))