How to output something in PowerShell

Question

I am running a PowerShell script from within a batch file. The script fetches a web page and checks whether the page's content is the string "OK".

The PowerShell script returns an error level to the batch script.

The batch script is executed by ScriptFTP, an FTP automation program. If an error occurs, I can have ScriptFTP send the full console output to the administrator via E-Mail.

In the PowerShell script, I would like to output the return value from the web site if it is not "OK", so the error message gets included in the console output, and thus in the status mail.

I am new to PowerShell and not sure which output function to use for this. I can see three:

• Write-Host
• Write-Output
• Write-Error

What would be the right thing to use to write to the Windows equivalent of stdout?

Answer 1

Simply outputting something is PowerShell is a thing of beauty - and one its greatest strengths. For example, the common Hello, World! application is reduced to a single line:

"Hello, World!"

It creates a string object, assigns the aforementioned value, and being the last item on the command pipeline it calls the .toString() method and outputs the result to STDOUT (by default). A thing of beauty.

The other Write-* commands are specific to outputting the text to their associated streams, and have their place as such.

Answer 2

I think in this case you will need Write-Output.

If you have a script like

Write-Output "test1";
Write-Host "test2";
"test3";

then, if you call the script with redirected output, something like yourscript.ps1 > out.txt, you will get test2 on the screen test1\ntest3\n in the "out.txt".

Note that "test3" and the Write-Output line will always append a new line to your text and there is no way in PowerShell to stop this (that is, echo -n is impossible in PowerShell with the native commands). If you want (the somewhat basic and easy in Bash) functionality of echo -n then see samthebest's answer.

If a batch file runs a PowerShell command, it will most likely capture the Write-Output command. I have had "long discussions" with system administrators about what should be written to the console and what should not. We have now agreed that the only information if the script executed successfully or died has to be Write-Host'ed, and everything that is the script's author might need to know about the execution (what items were updated, what fields were set, et cetera) goes to Write-Output. This way, when you submit a script to the system administrator, he can easily runthescript.ps1 >someredirectedoutput.txt and see on the screen, if everything is OK. Then send the "someredirectedoutput.txt" back to the developers.

Answer 3

I think the following is a good exhibit of Echo vs. Write-Host. Notice how test() actually returns an array of ints, not a single int as one could easily be led to believe.

function test {
    Write-Host 123
    echo 456 # AKA 'Write-Output'
    return 789
}

$x = test

Write-Host "x of type '$($x.GetType().name)' = $x"

Write-Host "`$x[0] = $($x[0])"
Write-Host "`$x[1] = $($x[1])"

Terminal output of the above:

123
x of type 'Object[]' = 456 789
$x[0] = 456
$x[1] = 789

Answer 4

You can use any of these in your scenario since they write to the default streams (output and error). If you were piping output to another commandlet you would want to use Write-Output, which will eventually terminate in Write-Host.

This article describes the different output options: PowerShell O is for Output

Answer 5

What would be the right thing to use to write to the Windows equivalent of stdout?

In effect, but very unfortunately, both Windows PowerShell and PowerShell Core as of v7.0, send all of their 6(!) output streams to stdout when called from the outside, via PowerShell's CLI.

• See this GitHub issue for a discussion of this problematic behavior, which likely won't get fixed, so as to preserve backward compatibility.

• In practice, this means that whatever PowerShell stream you send output to will be seen as stdout output by an external caller:

  • E.g., if you run the following from cmd.exe, you'll see no output, because the stdout redirection to NUL applies equally to all PowerShell streams:

    • C:\>powershell -noprofile -command "Write-Error error!" >NUL

  • However - curiously - if you redirect stderr, PowerShell does send its error stream to stderr, so that with 2> you can capture the error-stream output selectively; the following outputs just 'hi' - the success-stream output - while capturing the error-stream output in file err.txt:

    • C:\>powershell -noprofile -command "'hi'; Write-Error error!" 2>err.txt

The desirable behavior is:

• Send PowerShell's success output stream (number 1) to stdout.

• Send output from all other streams to stderr, which is the only option, given that between processes only 2 output streams exist - stdout (standard output) for data, and stderr (standard error) for error messages and all other types of messages - such as status information - that aren't data.

• It's advisable to make this distinction in your code, even though it currently isn't being respected.

---

Inside PowerShell:

• Write-Host is for display output, and bypasses the success output stream - as such, its output can neither be (directly) captured in a variable nor suppressed nor redirected.

  • Its original intent was simply to create user feedback and create simple, console-based user interfaces (colored output).

  • Due to the prior inability to be captured or redirected, PowerShell version 5 made Write-Host write to the newly introduced information stream (number 6), so since then it is possible to capture and redirect Write-Host output.

• Write-Error is meant for writing non-terminating errors to the error stream (number 2); conceptually, the error stream is the equivalent of stderr.

• Write-Output writes to the success [output] stream (number 1), which is conceptually equivalent to stdout; it is the stream to write data (results) to.

  • However, explicit use of Write-Output is rarely needed due to PowerShell's implicit output feature:
    • Output from any command or expression that isn't explicitly captured, suppressed or redirected is automatically sent to the success stream; e.g., Write-Output "Honey, I'm $HOME" and "Honey, I'm $HOME" are equivalent, with the latter not only being more concise, but also faster.
    • See this answer for more information.

Answer 6

Write-Host "Found file - " + $File.FullName -ForegroundColor Magenta

Magenta can be one of the "System.ConsoleColor" enumerator values - Black, DarkBlue, DarkGreen, DarkCyan, DarkRed, DarkMagenta, DarkYellow, Gray, DarkGray, Blue, Green, Cyan, Red, Magenta, Yellow, White.

The + $File.FullName is optional, and shows how to put a variable into the string.

Answer 7

You simply cannot get PowerShell to ommit those pesky newlines. There is no script or cmdlet that does this.

Of course Write-Host is absolute nonsense because you can't redirect/pipe from it! You simply have to write your own:

using System;

namespace WriteToStdout
{
    class Program
    {
        static void Main(string[] args)
        {
            if (args != null)
            {
                Console.Write(string.Join(" ", args));
            }
        }
    }
}

E.g.

PS C:\> writetostdout finally I can write to stdout like echo -n
finally I can write to stdout like echo -nPS C:\>