Powershell script: Can't read return value of executed program

Question

I am using PowerShell to run a script that executes wget to fetch a web page (a simple database import script) and analyzes its output (Error message or "OK").

I am using code from the answer to this previous question of mine.

$a = c:\path_to_wget\wget.exe --quiet -O - "http://www.example.com/import_db"
$rc = $a.CompareTo("OK")
exit $rc

When the result of the wget operation is a 404 - and wget probably returns an errorlevel 1 or 127 - I get the following error message from PowerShell:

You cannot call a method on a null-valued expression.

this obviously refers to my calling the CompareTo() function.

However, wget gets executed and outputs something.

I am suspecting that wget outputs to the error console in this case, and this does not get caught by my $a operation.

How can I redirect the error output so that it gets caught by my script?

Boy, I'm sure going to be question king in the PowerShell tag this month! :)

Short question aside: If you're using PowerShell anyway, why even bother with wget? $wc = New-Object Net.WebClient; $rc = ($wc.DownloadString("http://www.example.com/import_db")).CompareTo("OK") — Joey
– Joey, Commented Jan 11, 2010 at 19:37
I looked into the WebClient documentation on the hint you gave me in my last question, and shied away from the complexity, hoping for a kind soul who would give me an example to start with. Thanks a lot, this I can work with! :) — Pekka
– Pekka, Commented Jan 11, 2010 at 19:50

Amirshk · Accepted Answer · 2010-01-11 19:03:29Z

4

To start with

# This will hold the last executed EXE return code
$LastExitCode
# For console apps, where 0 is true, else is false, this will hold either True or False
$?

As for reading the STDERR, i guess the quickest way will be to run the script with stream redirection

$a = c:\path_to_wget\wget.exe --quiet -O - "http://www.example.com/import_db" 2>&1

answered Jan 11, 2010 at 19:03

Amirshk

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2 Comments

Pekka Over a year ago

If 2>&1 works in this context, I think I'm all right already. Thanks very much!

Keith Hill Over a year ago

I would avoid using $? with console apps. I've seen too many that don't honor the convention of 0 == success. Check out the CheckLastExitCode function in this post (I use it in a lot build scripts): keithhill.spaces.live.com/Blog/…

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