Capturing standard out and error with Start-Process

Question

Is there a bug in PowerShell s Start-Process command when accessing the StandardError and StandardOutput properties   If I run the following I get no output    process   Start-Process -FilePath ping -ArgumentList localhost -NoNewWindow -PassThru -Wait  process StandardOutput  process StandardError   But if I redirect the output to a file I get the expected result    process   Start-Process -FilePath ping -ArgumentList localhost -NoNewWindow -PassThru -Wait -RedirectStandardOutput stdout txt -RedirectStandardError stderr txt

User · Answer

I also had this issue and ended up using Andy's code to create a function to clean things up when multiple commands need to be run.

It'll return stderr, stdout, and exit codes as objects. One thing to note: the function won't accept .\ in the path; full paths must be used.

Function Execute-Command ($commandTitle, $commandPath, $commandArguments)
{
    $pinfo = New-Object System.Diagnostics.ProcessStartInfo
    $pinfo.FileName = $commandPath
    $pinfo.RedirectStandardError = $true
    $pinfo.RedirectStandardOutput = $true
    $pinfo.UseShellExecute = $false
    $pinfo.Arguments = $commandArguments
    $p = New-Object System.Diagnostics.Process
    $p.StartInfo = $pinfo
    $p.Start() | Out-Null
    $p.WaitForExit()
    [pscustomobject]@{
        commandTitle = $commandTitle
        stdout = $p.StandardOutput.ReadToEnd()
        stderr = $p.StandardError.ReadToEnd()
        ExitCode = $p.ExitCode
    }
}

Here's how to use it:

$DisableACMonitorTimeOut = Execute-Command -commandTitle "Disable Monitor Timeout" -commandPath "C:\Windows\System32\powercfg.exe" -commandArguments " -x monitor-timeout-ac 0"

User · Answer

That s how Start-Process was designed for some reason  Here s a way to get it without sending to file    pinfo   New-Object System Diagnostics ProcessStartInfo  pinfo FileName    ping exe   pinfo RedirectStandardError    true  pinfo RedirectStandardOutput    true  pinfo UseShellExecute    false  pinfo Arguments    localhost   p   New-Object System Diagnostics Process  p StartInfo    pinfo  p Start     Out-Null  p WaitForExit    stdout    p StandardOutput ReadToEnd    stderr    p StandardError ReadToEnd   Write-Host  stdout   stdout  Write-Host  stderr   stderr  Write-Host  exit code       p ExitCode

User · Answer

IMPORTANT   We have been using the function as provided above by LPG   However  this contains a bug you might encounter when you start a process that generates a lot of output  Due to this you might end up with a deadlock when using this function  Instead use the adapted version below   Function Execute-Command   commandTitle   commandPath   commandArguments      Try        pinfo   New-Object System Diagnostics ProcessStartInfo      pinfo FileName    commandPath      pinfo RedirectStandardError    true      pinfo RedirectStandardOutput    true      pinfo UseShellExecute    false      pinfo Arguments    commandArguments      p   New-Object System Diagnostics Process      p StartInfo    pinfo      p Start     Out-Null      pscustomobject            commandTitle    commandTitle         stdout    p StandardOutput ReadToEnd           stderr    p StandardError ReadToEnd           ExitCode    p ExitCode            p WaitForExit         Catch        exit         Further information on this issue can be found at MSDN      A deadlock condition can result if the parent process calls p WaitForExit before p StandardError ReadToEnd and the child process writes enough text to fill the redirected stream  The parent process would wait indefinitely for the child process to exit  The child process would wait indefinitely for the parent to read from the full StandardError stream

User · Answer

To get both stdout and stderr  I use  Function GetProgramOutput  string  exe   string  arguments         process   New-Object -TypeName System Diagnostics Process      process StartInfo FileName    exe      process StartInfo Arguments    arguments       process StartInfo UseShellExecute    false      process StartInfo RedirectStandardOutput    true      process StartInfo RedirectStandardError    true      process Start         output    process StandardOutput ReadToEnd           err    process StandardError ReadToEnd         process WaitForExit         output      err     exe    quot cmd quot   arguments     c echo hello 1 gt  amp 2     this writes  hello  to stderr   runResult    GetProgramOutput  exe  arguments   stdout    runResult -2   stderr    runResult -1    System Console   WriteLine  quot Standard out   quot     stdout   System Console   WriteLine  quot Standard error   quot     stderr

User · Answer

Here is my version of function that is returning standard System Diagnostics Process with 3 new properties  Function Execute-Command   commandTitle   commandPath   commandArguments        Try            pinfo   New-Object System Diagnostics ProcessStartInfo          pinfo FileName    commandPath          pinfo RedirectStandardError    true          pinfo RedirectStandardOutput    true          pinfo UseShellExecute    false          pinfo WindowStyle    Hidden           pinfo CreateNoWindow    True          pinfo Arguments    commandArguments          p   New-Object System Diagnostics Process          p StartInfo    pinfo          p Start     Out-Null          stdout    p StandardOutput ReadToEnd            stderr    p StandardError ReadToEnd            p WaitForExit            p   Add-Member  commandTitle   commandTitle          p   Add-Member  stdout   stdout          p   Add-Member  stderr   stderr           Catch              p

User · Answer

In the code given in the question  I think that reading the ExitCode property of the initiation variable should work    process   Start-Process -FilePath ping -ArgumentList localhost -NoNewWindow -PassThru -Wait  process ExitCode   Note that  as in your example  you need to add the -PassThru and -Wait parameters  this caught me out for a while

User · Answer

I really had troubles with those examples from Andy Arismendi and from LPG  You should always use    stdout    p StandardOutput ReadToEnd     before calling   p WaitForExit     A full example is    pinfo   New-Object System Diagnostics ProcessStartInfo  pinfo FileName    ping exe   pinfo RedirectStandardError    true  pinfo RedirectStandardOutput    true  pinfo UseShellExecute    false  pinfo Arguments    localhost   p   New-Object System Diagnostics Process  p StartInfo    pinfo  p Start     Out-Null  stdout    p StandardOutput ReadToEnd    stderr    p StandardError ReadToEnd    p WaitForExit   Write-Host  stdout   stdout  Write-Host  stderr   stderr  Write-Host  exit code       p ExitCode

User · Answer

Here s a kludgy way to get the output from another powershell process   start-process -wait -nonewwindow powershell  ps   Export-Clixml out xml   import-clixml out xml

[powershell] Capturing standard out and error with Start-Process

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