What s the difference between Write-Host Write-Output or console WriteLine

Question

There are a number of different ways to output messages  What is the effective difference between outputting something via Write-Host  Write-Output  or  console   WriteLine    I also notice that if I use   write-host  count      count   The   gets included in the output  Why s that  Shouldn t the expression be evaluated to produce a single concatenated string before it gets written out

User · Answer

Apart from what Andy mentioned  there is another difference which could be important - write-host directly writes to the host and return nothing  meaning that you can t redirect the output  e g   to a file   ---- script a ps1 ---- write-host  hello    Now run in PowerShell   PS gt    a ps1  gt  someFile txt hello PS gt  type someFile txt PS gt    As seen  you can t redirect them into a file  This maybe surprising for someone who are not careful    But if switched to use write-output instead  you ll get redirection working as expected

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Here s another way to accomplish the equivalent of Write-Output   Just put your string in quotes    count  count    You can make sure this works the same as Write-Output by running this experiment    blah blah   gt  out txt  Write-Output  blah blah   gt  out txt  Write-Host  blah blah   gt  out txt   The first two will output  blah blah  to out txt  but the third one won t    help Write-Output  gives a hint of this behavior      This cmdlet is typically used in scripts to display strings and other   objects on the console  However  because the default behavior is to   display the objects at the end of a pipeline  it is generally not   necessary to use the cmdlet    In this case  the string itself  count  count  is the object at the end of a pipeline  and is displayed

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Regarding  Console   WriteLine   - you should use it if you are going to use pipelines in CMD  not in powershell   Say you want your ps1 to stream a lot of data to stdout  and some other utility to consume transform it  If you use Write-Host in the script it will be much slower

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From my testing Write-Output and  Console   WriteLine   perform much better than Write-Host   Depending on how much text you need to write out this may be important   Below if the result of 5 tests each for Write-Host  Write-Output and  Console   WriteLine     In my limited experience  I ve found when working with any sort of real world data I need to abandon the cmdlets and go straight for the lower level commands to get any decent performance out of my scripts   measure-command   count   0  while   count -lt 1000    Write-Host  hello    count       1312ms 1651ms 1909ms 1685ms 1788ms   measure-command    count   0  while   count -lt 1000    Write-Output  hello    count       97ms 105ms 94ms 105ms 98ms   measure-command    count   0  while   count -lt 1000     console   WriteLine  hello     count       158ms 105ms 124ms 99ms 95ms

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For usages of Write-Host  PSScriptAnalyzer produces the following diagnostic      Avoid using Write-Host because it might not work in all hosts  does not work when there is no host  and  prior to PS 5 0  cannot be suppressed  captured  or redirected  Instead  use Write-Output  Write-Verbose  or Write-Information    See the documentation behind that rule for more information  Excerpts for posterity      The use of Write-Host is greatly discouraged unless in the use of commands with the Show verb  The Show verb explicitly means  show on the screen  with no other possibilities        Commands with the Show verb do not have this check applied    Jeffrey Snover has a blog post Write-Host Considered Harmful in which he claims Write-Host is almost always the wrong thing to do because it interferes with automation and provides more explanation behind the diagnostic  however the above is a good summary

User · Answer

Write-Output should be used when you want to send data on in the pipe line  but not necessarily want to display it on screen  The pipeline will eventually write it to out-default if nothing else uses it first   Write-Host should be used when you want to do the opposite     console   WriteLine is essentially what Write-Host is doing behind the scenes   Run this demonstration code and examine the result    function Test-Output       Write-Output  Hello World     function Test-Output2       Write-Host  Hello World  -foreground Green    function Receive-Output       process   Write-Host    -foreground Yellow       Output piped to another function  not displayed in first  Test-Output   Receive-Output   Output not piped to 2nd function  only displayed in first  Test-Output2   Receive-Output    Pipeline sends to Out-Default at the end  Test-Output    You ll need to enclose the concatenation operation in parentheses  so that PowerShell processes the concatenation before tokenizing the parameter list for Write-Host  or use string interpolation  write-host   count      count    or write-host  count  count    BTW - Watch this video of Jeffrey Snover explaining how the pipeline works  Back when I started learning PowerShell I found this to be the most useful explanation of how the pipeline works

[powershell] What's the difference between "Write-Host", "Write-Output", or "[console]::WriteLine"?

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