Is it possible to pipe conditionally in Powershell, i.e. execute an element of a pipeline only if a condition is met?

You can test for both conditions in your filter allowing the object down the pipeline if either one is true. If your "condition" is on the left side of the -or operator, make it result to $true if you don't want your filter condition tested.

To use your example:

| where {$_.psiscontainer}

becomes:

| where {$files -or $_.psiscontainer}

and

| where {$_.isinherited -eq 'False'}

becomes

| where {$inherited -or $_.isinherited -eq 'False'}

To generalise:

<statement> | <filter1> | <filter2> if <condition> | <filter3> | <filter4> | <filter5>

becomes:

<statement> | <filter1> | <-not condition -or filter2> | <filter3> | <filter4> | <filter5>

I think the other answer to this question misunderstands what is being asked.

The solution lies in the following:

... | %{if($_ -match "Something"){DoSomethingWith $_ }else{$_}} | ...

What this will do, is pass all elements through to the next filter, EXCEPT those that match "Something", in which case it does different logic. The logic can be changed to make it pass an altered version of the pipeline element instead of a function.

Sorry, I didn't mean to abandon this question. The answers that were posted weren't what I was driving at, but I figured out a way to do it shortly after posting, and didn't come back to the site for a long time. Since a solution hasn't been posted, here's what I came up with. It's not quite what I had in mind when I asked the question and it isn't too pretty, but apparently it's the only way to do it:

<statement> | <filter1> | foreach {if (<condition>) {$_ | <filter2>} else {$_} | <filter3> | <filter4> | <filter5>

So, in the example, the line

|where {$_.psiscontainer} `

would be changed to

|foreach {if (-not $files) {$_ | where {$_.psiscontainer}} else {$_}} `

and

|where {$_.isinherited -eq 'False'} `

would be changed to

|foreach {if (-not $inherited) {$_ | where {$_.isinherited -eq 'False'}} else {$_}} `

(Yes, normally I'd write that as |foreach {if ($files) {$_} else {$_ | where {$_.psiscontainer}}}, and |foreach {if ($inherited) {$_} else {$_ | where {$_.isinherited -eq 'False'}}} but I did it this way for clarity.)

I was hoping there might be something more elegant, that would evaluate a condition in front of the filter once to determine whether to execute or skip a stage of the pipeline. Something like this:

<statement> | <filter1> | if (<condition>) {<filter2>} | <filter3>

(a special case of if, not the usual meaning; a different keyword could be used), or maybe

<statement> | <filter1> | (<condition>) ? <filter2> | <filter3>

$_ would be invalid in the condition, unless it's defined outside the current pipeline, for example if the pipeline is contained within a switch statement, $_ in the <condition> would refer the switch statement's $_.

I think I'll make a feature suggestion to Microsoft. This would not only make the code more elegant, it would be more efficient as well, because if it's a built-in feature, <condition> could be evaluated once for the entire pipeline, rather then testing the same independent condition in each iteration.