What s the better cleaner way to ignore output in PowerShell

Question

Let s say you have a method or a cmdlet that returns something  but you don t want to use it and you don t want to output it  I found these two ways   Add-Item  gt   null   void Add-Item  Add-Item   Out-Null   What do you use  Which is the better cleaner approach  Why

User · Accepted Answer

I just did some tests of the four options that I know about.

Measure-Command {$(1..1000) | Out-Null}

TotalMilliseconds : 76.211

Measure-Command {[Void]$(1..1000)}

TotalMilliseconds : 0.217

Measure-Command {$(1..1000) > $null}

TotalMilliseconds : 0.2478

Measure-Command {$null = $(1..1000)}

TotalMilliseconds : 0.2122

## Control, times vary from 0.21 to 0.24
Measure-Command {$(1..1000)}

TotalMilliseconds : 0.2141

So I would suggest that you use anything but Out-Null due to overhead. The next important thing, to me, would be readability. I kind of like redirecting to $null and setting equal to $null myself. I use to prefer casting to [Void], but that may not be as understandable when glancing at code or for new users.

I guess I slightly prefer redirecting output to $null.

Do-Something > $null

Edit

After stej's comment again, I decided to do some more tests with pipelines to better isolate the overhead of trashing the output.

Here are some tests with a simple 1000 object pipeline.

## Control Pipeline
Measure-Command {$(1..1000) | ?{$_ -is [int]}}

TotalMilliseconds : 119.3823

## Out-Null
Measure-Command {$(1..1000) | ?{$_ -is [int]} | Out-Null}

TotalMilliseconds : 190.2193

## Redirect to $null
Measure-Command {$(1..1000) | ?{$_ -is [int]} > $null}

TotalMilliseconds : 119.7923

In this case, Out-Null has about a 60% overhead and > $null has about a 0.3% overhead.

Addendum 2017-10-16: I originally overlooked another option with Out-Null, the use of the -inputObject parameter. Using this the overhead seems to disappear, however the syntax is different:

Out-Null -inputObject ($(1..1000) | ?{$_ -is [int]})

And now for some tests with a simple 100 object pipeline.

## Control Pipeline
Measure-Command {$(1..100) | ?{$_ -is [int]}}

TotalMilliseconds : 12.3566

## Out-Null
Measure-Command {$(1..100) | ?{$_ -is [int]} | Out-Null}

TotalMilliseconds : 19.7357

## Redirect to $null
Measure-Command {$(1..1000) | ?{$_ -is [int]} > $null}

TotalMilliseconds : 12.8527

Here again Out-Null has about a 60% overhead. While > $null has an overhead of about 4%. The numbers here varied a bit from test to test (I ran each about 5 times and picked the middle ground). But I think it shows a clear reason to not use Out-Null.

User · Answer

There is also the Out-Null cmdlet  which you can use in a pipeline  for example  Add-Item   Out-Null  Manual page for Out-Null NAME     Out-Null  SYNOPSIS     Deletes output instead of sending it to the console    SYNTAX     Out-Null  -inputObject  lt psobject gt     lt CommonParameters gt     DETAILED DESCRIPTION     The Out-Null cmdlet sends output to NULL  in effect  deleting it    RELATED LINKS     Out-Printer     Out-Host     Out-File     Out-String     Out-Default  REMARKS      For more information  type   quot get-help Out-Null -detailed quot        For technical information  type   quot get-help Out-Null -full quot

User · Answer

Personally  I use       Out-Null because  as others have commented  that looks like the more  PowerShellish  approach compared to      gt   null and  void         null       is exploiting a specific automatic variable and can be easy to overlook  whereas the other methods make it obvious with additional syntax that you intend to discard the output of an expression   Because       Out-Null and      gt   null come at the end of the expression I think they effectively communicate  take everything we ve done up to this point and throw it away   plus you can comment them out easier for debugging purposes  e g          Out-Null   compared to putting  null   or  void  before the expression to determine what happens after executing it   Let s look at a different benchmark  though  not the amount of time it takes to execute each option  but the amount of time it takes to figure out what each option does   Having worked in environments with colleagues who were not experienced with PowerShell or even scripting at all  I tend to try to write my scripts in a way that someone coming along years later that might not even understand the language they re looking at can have a fighting chance at figuring out what it s doing since they might be in a position of having to support or replace it   This has never occurred to me as a reason to use one method over the others until now  but imagine you re in that position and you use the help command or your favorite search engine to try to find out what Out-Null does   You get a useful result immediately  right   Now try to do the same with  void  and  null     Not so easy  is it   Granted  suppressing the output of a value is a pretty minor detail compared to understanding the overall logic of a script  and you can only try to  dumb down  your code so much before you re trading your ability to write good code for a novice s ability to read   not-so-good code   My point is  it s possible that some who are fluent in PowerShell aren t even familiar with  void    null    etc   and just because those may execute faster or take less keystrokes to type  doesn t mean they re the best way to do what you re trying to do  and just because a language gives you quirky syntax doesn t mean you should use it instead of something clearer and better-known      I am presuming that Out-Null is clear and well-known  which I don t know to be  true   Whichever option you feel is clearest and most accessible to future readers and editors of your code  yourself included   regardless of time-to-type or time-to-execute  that s the option I m recommending you use

User · Answer

I would consider using something like   function GetList               a   new-object Collections ArrayList       a Add 5        a Add  next 5         Out-Null    a    x   GetList   Output from  a Add is not returned -- that holds for all  a Add method calls  Otherwise you would need to prepend  void  before each the call   In simple cases I would go with  void  a Add because it is quite clear that output will not be used and is discarded

User · Answer

I realize this is an old thread  but for those taking  JasonMArcher s accepted answer above as fact  I m surprised it has not been corrected many of us have known for years it is actually the PIPELINE adding the delay and NOTHING to do with whether it is Out-Null or not   In fact  if you run the tests below you will quickly see that the same  faster  casting to  void  and  void  that for years we all used thinking it was faster  are actually JUST AS SLOW and in fact VERY SLOW when you add ANY pipelining whatsoever   In other words  as soon as you pipe to anything  the whole rule of not using out-null goes into the trash   Proof  the last 3 tests in the list below   The horrible Out-null was 32339 3792 milliseconds  but wait - how much faster was casting to  void   34121 9251 ms     WTF   These are REAL  s on my system  casting to VOID was actually SLOWER   How about   null   34217 685ms     still friggin SLOWER   So  as the last three simple tests show  the Out-Null is actually FASTER in many cases when the pipeline is already in use   So  why is this   Simple   It is and always was 100  a hallucination that piping to Out-Null was slower   It is however that PIPING TO ANYTHING is slower  and didn t we kind of already know that through basic logic   We just may not have know HOW MUCH slower  but these tests sure tell a story about the cost of using the pipeline if you can avoid it   And  we were not really 100  wrong because there is a very SMALL number of true scenarios where out-null is evil   When   When adding Out-Null is adding the ONLY pipeline activity   In other words    the reason a simple command like   1  1000    Out-Null as shown above showed true   If you simply add an additional pipe to Out-String to every test above  the  s change radically  or just paste the ones below  and as you can see for yourself  the Out-Null actually becomes FASTER in many cases    GetProcess   Get-Process    Batch 1 - Test 1   Measure-Command    for   i   1   i -lt 99   i         GetProcess   Out-Null        TotalMilliseconds    Batch 1 - Test 2   Measure-Command    for   i   1   i -lt 99   i         void   GetProcess         TotalMilliseconds    Batch 1 - Test 3   Measure-Command    for   i   1   i -lt 99   i         null    GetProcess        TotalMilliseconds    Batch 2 - Test 1   Measure-Command    for   i   1   i -lt 99   i         GetProcess   Select-Object -Property ProcessName   Out-Null        TotalMilliseconds    Batch 2 - Test 2   Measure-Command    for   i   1   i -lt 99   i         void   GetProcess   Select-Object -Property ProcessName          TotalMilliseconds    Batch 2 - Test 3   Measure-Command    for   i   1   i -lt 99   i         null    GetProcess   Select-Object -Property ProcessName        TotalMilliseconds    Batch 3 - Test 1   Measure-Command    for   i   1   i -lt 99   i         GetProcess   Select-Object -Property Handles  NPM  PM  WS  VM  CPU  Id  SI  Name   Out-Null        TotalMilliseconds    Batch 3 - Test 2   Measure-Command    for   i   1   i -lt 99   i         void   GetProcess   Select-Object -Property Handles  NPM  PM  WS  VM  CPU  Id  SI  Name          TotalMilliseconds    Batch 3 - Test 3   Measure-Command    for   i   1   i -lt 99   i         null    GetProcess   Select-Object -Property Handles  NPM  PM  WS  VM  CPU  Id  SI  Name        TotalMilliseconds    Batch 4 - Test 1   Measure-Command    for   i   1   i -lt 99   i         GetProcess   Out-String   Out-Null        TotalMilliseconds    Batch 4 - Test 2   Measure-Command    for   i   1   i -lt 99   i         void   GetProcess   Out-String          TotalMilliseconds    Batch 4 - Test 3   Measure-Command    for   i   1   i -lt 99   i         null    GetProcess   Out-String        TotalMilliseconds

[powershell] What's the better (cleaner) way to ignore output in PowerShell?

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