12

is there an easy way in powershell to output a string to variable and console at the same time?

i want to capture the output of my script to a variable so i can analyze it in the end of the script, save it to a log file and also email to an operator.

my intent is to have a variable $output and add any output strings to it and also output to console immediately something like

$output="Process started"

$output=+"Doing step 1"
"Doing step 1"

$output=+"Doing step 2"
"Doing step 2"

so in the end I can save $output to a log file, email it and parse it.

I played with tee-object that might work for that purpose but unfortunately it would rewrite my $output variable instead of appending a string to it.

UPDATE This is the final solution I decided to go with - thanks to manojlds!

$script:output = ""

filter mylog {
    $script:output+= $_+"`n"
    return $_
}


"doing step {0}" -f 1 | mylog
"doing step {0}" -f 2 | mylog
"doing step {0}" -f 3 | mylog

#in the end of the script
$script:output
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7 Answers 7

Reset to default
6

There are so many ways to get your end goal:

In your script just have something like this:

"Process started"
<step1>
"Doing step 1"
<step2>
"Doing step 2"
...

Then run the script as 

.\test.ps1 | Tee-Object -file log.txt

Note that the output is available to Tee-Object and hence the console as and when it occurs. You don't get the output only after the entire script runs. This is how pipeline works in Powershell. Objects are passed along downstream as and when they occur. Insert a sleep 10 in between as steps and see that the output comes as soon as it is available.

Also, you don't necessarily have to have another script ( the launcher.ps1 ) you are talking about. You can use functions, scriptblock etc. within your script.

Some other ways:

function test {

"Process started"
sleep 5
"Doing step 1"
sleep 5
"Doing step 2"

}

test | %{$output+=$_;$_}
#use output
write-host -fore blue $output

You can create a filter:

$script:output = ""

filter appendOutput {

    $script:output+= $_
    return $_
}

"Process started" | appendOutput
sleep 5
"Doing step 1" | appendOutput
sleep 5
"Doing step 2" | appendOutput
#use output
write-host -fore blue $script:output

There are probably many more ways of doing this.

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7 Comments

this is how I implemented this first but ended up with two scripts. I have more complex script now and need to do some analysis in the calling script which makes my calling script complex. I just found this post get-powershell.com/post/2008/06/26/… and I am thinking now if I can do something like that overriding out-default
sorry just to make myself clear...I have my main script (let's say main.ps) and launcher.ps (something like your .\test.ps1 | Tee-Object -file log.txt) so launcher will capture the output of the main script. While it works i have two issues with such approach - i do not see anything in console until my main script is finished and i cannot do any analysis/parsing in my main script
@mishking - .\test.ps1 | Tee-Object -file log.txt - if you are doing that, you will see the output in the console as and when it happens. Add a sleep 10 in between the strings in the above script and see. Also see my updated answer
thank you for you help! the log file is optional in my script that's why I thought i would collect the output first in a variable and when in the end of the script, based on parameters passed to the script it can be saved to a log file and/or emailed. I was not using dot sourcing in my launcher script just captured the output of the main script in $output variable - I guess that's why I did not see console output in the realtime
the way you are suggesting will work great if i always need to output the log file, but what if this is an optional thing like in my case? I would also like to have one script instead of two and variable in the end of it which i can parse for some keywords and having console output in the realtime. Is it possible to have all of that?
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6

Here's a nice trick, enclose your variable assignment in parenthesis. You can find more on this in the PowerShell language specification (section 7.1.1 Grouping parentheses) available to download here or view it online here:

PS > ($var=1)
1
PS >
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1 Comment

awesome! it is a really cool trick and thanks for that spec - tons of good info in there. This trick won't help in my case too much though because if I need to accumulate output in a single var something like: $output="" ($output+="doing step {0}" -f 1) ($output+="doing step {0}" -f 2) and I will get: doing step 1 doing step 1doing step 2 I would stick with a filter for now like manojlds suggested above.
1

I haven't messed with powershell enough to give a concrete answer, but if I were to do this in C I would exploit side effects.

//Psuedo-C
string con (oldString, newString) {
  print(newString);
  return oldString + newString;
}

Use function like so:

myString = con(myString, "Process started");

It would have the desired effect. (leaving aside correct C syntax and pedantry such as dealing with newlines) I don't know how to translate this to powershell.

What you want to do may be considered messy however. It might be clearer if you just explicitly output and log output and log one after the other in your code. Side effects inevitably come back to bite you. Keep things modular.

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Comments

1

I was looking at something similar to this, with the exception I did not need to analyze it afterwards, just collect the output.

Something someone else might look at since it seems you have your answer is using PowerShell transcripts (Start-Transcript and Stop-Transcript).I found from this site that it does have some issues when you hit a server error, but he shows how he handled it.

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1 Comment

thanks! it might work for some people and I looked into that as well but it has limitations like the one described here blogs.msdn.com/b/powershell/archive/2010/01/04/…
0

To expand a bit on @manojlds answer, you can simply use the Tee-Object cmdlet, but rather than specifying a file for it to write to, you can tell it to write directly to a variable, like so:

.\test.ps1 | Tee-Object -Variable output

All of the output from the script/cmdlet/function/etc will be written to the console screen in real-time, as well as stored in the $output variable when the script finishes running. So you could then analyze it or write it to a file using that variable. This avoids you having to read the file contents into a variable after the operation completed.

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Comments

0

Script will write data on output screen as well as store the same data in variable

get-process | Tee-Object -Variable test

$test can use further
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Comments

-1 
("Process started" | out-host) | Set-Variable x ; $x
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2 Comments

thanks but it does not work - $x will be reset every time while i need it to accumulate all the script output
-1 . This doesn't even work! $x would be empty, because out-host has already got the string, you will get output of that to set-variable, which is nothing ( writing to host doesn't mean it is available down the pipeline).

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