What is the difference between echo and Write-Host in PowerShell?

Question

I'm confused about the difference between echo and Write-Host in PowerShell. I have two files, POC.ps1 & validatePath.ps1. These files are on my local machine, and I'm running them on a remote machine using Invoke-Command. I am using PowerShell v3.0.

To execute both of these scripts I use the command:

.\POC.ps1 -filename C:\Users  -user Blaine 

Here are the two files:

POC.ps1:

param($filename, $user)  echo $filename echo "This" echo $user  $responseObject = Invoke-Command testcomputer -FilePath .\validatePath.ps1  -ArgumentList($filename, $user) -AsJob  while($responseObject.State -ne "Completed") {  }  $result = Receive-Job -Id $responseObject.Id -Keep echo $result 

Here is where things get weird...

validatePath.ps1:

Param([string] $filename,       [string] $user)  function ValidatePath( $filename, $user, $fileType = "container" ) {     Write-Host "This is the file name: $filename"     Write-Host "This is user: $user"  <--- Notice I'm using Write-Host here     $fileExist = $null     if( -not (test-path $filename -PathType $fileType) )     {         throw "$user, the path $filename does not exist!"      }     else     {          Write-Host "This is the second part"          echo $filename found!     }     Write-Host "This is the third part"     return $fileExist }   try {      ValidatePath($filename, $user) } catch {     $e = $_.Exception     echo $e } 

When I run the above script, this is the output:

C:\Users This Blaine This is the file name: C:\Users Blaine This is user:  <--- Notice where this line is? This is the second part This is the third part C:\Users Blaine found! 

But if I change the validatePath.ps1 to this:

Param([string] $filename,       [string] $user)  function ValidatePath( $filename, $user, $fileType = "container" ) {     Write-Host "This is the file name: $filename"     echo "This is user: $user" <---notice I'm using Echo here     $fileExist = $null     if( -not (test-path $filename -PathType $fileType) )     {         throw "$user, the path $filename does not exist!"      }     else     {          Write-Host "This is the second part"          echo $filename found!     }      Write-Host "This is the third part"     return $fileExist }   try {      ValidatePath($filename, $user) } catch {     $e = $_.Exception     echo $e } 

This is the output:

C:\Users This Blaine This is the file name: C:\Users Blaine This is the second part This is the third part This is user: <---- Notice where this line is now? C:\Users Blaine found! 

You will notice that the line "This is the user:" is in different spots. Why is this? Why does echo work differently than Write-Host?

UPDATE:

What is even more strange is that if I rerun the script twice like this:

POC.ps1:

param($filename, $user)  echo $filename echo "This" echo $user  $responseObject = Invoke-Command CAPTESTPK01 -FilePath .\validatePath.ps1  -ArgumentList $filename, $user -AsJob  while($responseObject.State -ne "Completed") {  }  $result = Receive-Job -Id $responseObject.Id -Keep echo $result   $filename = "C:\saddfasdfj"  #Here I run the command again, using a different file name $responseObject = Invoke-Command CAPTESTPK01 -FilePath .\validatePath.ps1  -ArgumentList $filename, $user -AsJob  while($responseObject.State -ne "Completed") {    if($responseObject.State -eq "Failed")    {         echo "Failed"         $result = Receive-Job -Id $responseObject.Id -Keep         echo $result         break    } }  $result = Receive-Job -Id $responseObject.Id -Keep echo $resul 

It gives me this output when using echo in validatePath.ps1:

C:\Users This Blaine This is the file name: C:\Users This is the second part This is the third part This is user: Blaine <---- This line is here C:\Users found! This is the file name: C:\saddfasdfj This is user: Blaine <---- But now it's here, where it should be? Wth? Blaine, the path C:\saddfasdfj does not exist! 

Answer 1

echo is an alias for Write-Output, which writes to the Success output stream. This allows output to be processed through pipelines or redirected into files. Write-Host writes directly to the console, so the output can't be redirected/processed any further.

Answer 2

echo is an alias for Write-Output. Where Write-Host directly writes to the 'screen', Write-Output writes to the pipeline. If the pipeline is not feed into some other command it ends on the 'screen' in the end as well. The difference you see is Write-Host getting written to the screen directly where Write-Output first goes through the pipeline and ends up on the screen after Write-Host.

Using Write-Output allows you to pipe/redirect the output to a file or to another command, where Write-Host does not. They should be used depending on what you want.

See here for more.