Why does a continue in this ForEach-Object loop cause Powershell to error

Question

When piping the output of a command to a ForEach-Object loop in PowerShell, using a continue statement causes it to error out.

Works as expected:

ipconfig | ForEach-Object {
  $_
}

Errors:

ipconfig | ForEach-Object {
  $_
  continue
}

The error is

Program 'ipconfig.exe' failed to run: System error.At C:\Users\test\ps.ps1:1 char:1
+ nslookup google.com | ForEach-Object {
+ ~~~~~~~~~~~~~~~~~~~.
At C:\Users\test\ps.ps1:1 char:1
+ nslookup google.com | ForEach-Object {
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : ResourceUnavailable: (:) [], ApplicationFailedException
    + FullyQualifiedErrorId : NativeCommandFailed

This seems to happen with any external command, such as nslookup and net

I thought maybe this had to do with some type conversion, but the object inside the loop is always a string. Saving the command output to a variable, and then doing a $var | ForEach-Object works.

What's the point of using continue as the very last statement in the block? — Mathias R. Jessen
– Mathias R. Jessen, Commented Mar 20, 2024 at 16:23
There is no point, but it's to keep the minimal reproducible example short and easy — DeadChex
– DeadChex, Commented Mar 20, 2024 at 17:17

DeadChex · Accepted Answer · 2024-03-20 16:18:47Z

3

continue statements in PowerShell can only be used within loop constructs. While ForEach-Object seems like a loop, it's not.

In PowerShell, you can technically use continue outside of a loop, but it causes PowerShell to not find a loop, and just terminate the current runspace.¹

This means PowerShell can actually terminate the caller¹, and looking at the callstack, that caller is the "parent" line and so it is terminated.

Callstack right before the continue executes:

ScriptLineNumber : 4
Position         : continue
FunctionName     : <ScriptBlock>


ScriptLineNumber : 1
Position         : net help | ForEach-Object {
                       $_.GetType()
                       continue
                   }
FunctionName     : <ScriptBlock>

Instead, use a return statement.

Reference

1 - https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.core/about/about_continue?view=powershell-5.1

answered Mar 20, 2024 at 16:18

DeadChex

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2 Comments

mklement0 Over a year ago

Nice; worth nothing that the same applies analogously to break

mklement0 Over a year ago

More specifically: When break or continue are used in a statement that isn't loop-like (doesn't itself support these keywords), PowerShell walks up the call stack to find a loop, and breaks out of / continues the first one found (which may be unrelated to what you're trying to do). Only if no loop is found anywhere on the call stack is the runspace quietly exited. E.g., do { 1..10 | ForEach-Object { if ($_ -gt 5) { break }; $_ } } while ($false) causes the break to exit the enclosing do loop, a technique that can be leveraged to exit a pipeline prematurely.

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