Handling errors and exceptions in PowerShell

PowerShell has two kinds of errors: terminating (throw) and non-terminating (cmdlet reports an error but continues). If you want to make sure your PowerShell scripts continue running even if there are errors, use the try/catch block. This way, you control what happens when terminating errors occur.

Here's an example of the basic pattern:

try {
    # force non-terminating errors to behave like exceptions
    $content = Get-Content "C:\does-not-exist.txt" -ErrorAction Stop
    "Length: $($content.Length)"
}
catch [System.IO.IOException] {
    Write-Warning "IO error: $($_.Exception.Message)"
}
catch {
    Write-Error "Unexpected: $($_.Exception.Message)"
}
finally {
    # the "finally" block lways runs
    "Done."
}

In essence, PowerShell exception handling is very much like the one in C#. This is no coincidence, as PowerShell is based on .NET.

Here's a quick list of useful switches and variables:

-ErrorAction Stop          # make cmdlets throw on error
-ErrorVariable err         # capture errors into $err
$ErrorActionPreference     # global default for the error action (for example, "Stop")
$?                         # success of last command (True/False)
$LASTEXITCODE              # native process exit code (a number, zero often means success)
throw "message"            # generate your own terminating error

The try/catch block is a good choice for most scripts. Keep your try blocks small, catch specific exception types when you can, and log enough detail to fix the issue when it occurs.