Assume I have two files, script.ps1 and filename.cmd, and I run .\script.ps1 from a Powershell prompt:
script.ps1
Write-Host "About to run filename.cmd"
$proc = Start-Process -FilePath filename.cmd -NoNewWindow -Wait
Write-Host "proc: [$proc]"
Write-Host "LASTEXITCODE: [$LASTEXITCODE]
filename.cmd
@echo off
ECHO File returns ErrorLevel=1
exit /b 1
Output:
About to run filename.cmd
proc: []
LASTEXITCODE: []
Both proc and LASTEXITCODE are $null. My understanding was that somehow I could access the ErrorCode?
How do I read the failed error level (in this case 1) in my Powershell script?
To synchronously execute console applications, including batch files, call them directly, do not use Start-Process - see this answer.
Therefore:
Write-Host "About to run filename.cmd"
# For security reasons, PowerShell requires that you explicitly
# signal the intent to run an executable located *in the current directory*,
# hence the need for `./` (or `.\`)
# Only direct invocation of external programs (batch files) sets
# the automatic $LASTEXITCODE variable.
./filename.cmd
Write-Host "LASTEXITCODE: [$LASTEXITCODE]
As for what you tried:
Start-Process outputs nothing by default - except if you pass the -PassThru switch, in which case a System.Diagnostics.Process instance representing the newly started process is returned.
Assuming you've also specified -Wait, as in your case, you can then access the returned object's .ExitCode property to determine the exit code immediately afterwards.
Note that automatic variable $LASTEXITCODE is only set after direct invocation of external programs, as shown above.
Therefore, if you were to use Start-Process - which is not necessary in this case, as explained above - you'd have to use the following:
Write-Host "About to run filename.cmd"
$proc = Start-Process -PassThru -FilePath filename.cmd -NoNewWindow -Wait
Write-Host "proc: [$proc]"
Write-Host "exit coe: [$($proc.ExitCode)]