Question

Here is the command I have been using to back up one of my MySQL databases:

mysqldump.exe --user=myuser --password=mypassword --databases --opt MyDatabase > "C:\MyDatabase.sql"

I’d like to use this command in a PowerShell script. However, if an error occurs, I don’t want it to be outputted to the console. Instead, I would like it captured in a variable. I’ve been trying various methods of doing this, but all have failed. Any assistance would be appreciated. Thanks!

Answer 1

Firstly, beware > if your database dump does not need to be in Unicode, but rather ASCII. You would instead use | out-file $filepath -enc ascii to make sure it writes in ASCII encoding. (My databases are in latin1. If I use Powershell’s > the dump file is twice as large as when dumped using > from normal console.)

That said, I got it to dump to a file in ASCII format and put the errors in a variable in this way (forcing an error by trying to dump a nonexistent database, but mysqldump outputs a number of initializing lines of the dump before it throws the error):

$err = (mysqldump -uroot -p --databases nonexistent | out-file C:\backup.sql -enc ascii) 2>&1

This wraps the execution so that stdout is piped to out-file, but after that wrapping, stderr is redirected to stdout so that it can be assigned to variable $err.

$err is 1 ErrorRecord or more. A single error has a TargetObject property containing the original stderr output. Here’s a demo of printing every error string to the console:

if ($err -is [system.array]) {
    $err | % { write-host $_.TargetObject }
} else {
    write-host $err.TargetObject
}

Alternately, you can ensure that $err is an array by slightly modifying the original dump statement by wrapping it an @() (good idea, Mike):

$err = @((mysqldump -uroot -p --databases nonexistent | out-file C:\backup.sql -enc ascii) 2>&1)