in powershell how do I grab command output while piping a variable into the command?

Question

Is there a powershell cmdlet which redirects console output into a variable (NOT a file)?

I need to pass the content of a variable into a binary's command line, and collect the binary's console response in another variable, but can't figure out how.

For example, Perforce's p4.exe returns an OK status with a text error message when this fails

$MyP4Client | p4 client -i

To abort on error I need to put a try/catch round that, then collect and check the console output from p4. When there's no input redirection involved, I can do this to get p4's console output into a variable:

Try {
    $P4response = & 'p4' sync -f //depot/myfiles/...   2>&1
}
Catch {
    ExitWithCode 1 # abort
}
if( $P4response -match "blah" ) {
    # act on p4 response text

but I'm failing dismally at finding a way to both feed the $MyP4Client variable into the p4 binary then grab the output from p4. Among many other attempts, none of these get p4's output into $P4response :

$P4response = $p4ClientSpec | & 'p4' client -i 
$P4response = ( $p4ClientSpec | p4 client -i )
$P4response = { $p4ClientSpec | & 'p4' client -i }
$p4ClientSpec | & 'p4' "client -i" | $P4response

The last gets a parser error ($P4response is an expression). It's pretty obvious I'm missing something! What's going to work, please? Thanks

Duncan · Accepted Answer · 2014-03-19 10:48:52Z

2

Your question implies you are trying to catch output to stderr as well as stdout. This should work:

$P4response = ( $p4ClientSpec | p4 client -i  2>&1 )

You will get both the stdout and stderr from the console app in the variable, but you can separate them again quite easily:

$output = $P4Response | Where-Object { $_.GetType() -ne [System.Management.Automation.ErrorRecord] }
$errors = $P4Response | Where-Object { $_.GetType() -eq [System.Management.Automation.ErrorRecord] }

and then you just check for non-empty $errors.

answered Mar 19, 2014 at 10:48

Duncan

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1 Comment

Alan Over a year ago

Many thanks Duncan - that's the answer! It gets exactly what I was groping for. Your help is much appreciated.

vonPryz · Accepted Answer · 2014-03-19 06:35:04Z

0

Try Tee-Object cmdlet. It saves command output in a file or variable and also sends it down the pipeline. Docs at Technet.

answered Mar 19, 2014 at 6:35

vonPryz

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mjolinor · Accepted Answer · 2014-03-19 11:13:50Z

0

If the executable is actually writing the error to stderr, it seems like you'd have picked it up by now with what you've already tried. If it's just writing a message directly to the console then your only option may be to use Start-Transcript to capture the console output to a file, and the parse the file contents looking for that message.

answered Mar 19, 2014 at 11:13

mjolinor

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