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powershellcmdline-breaks

Avoid Line break at end of cmd output?

when I use this command pwsh -c echo hello in cmd I get the following output:

C:\>pwsh -c echo hello
hello

C:\>

I do not get that line break at the end when I run it on powershell:

PS C:\> pwsh -c echo hello
hello
PS C:\>

So I think the problem is in cmd. I know this is not such a problem and have an easy fix but I have some programs uses cmd to access powershell and removing that line break is not that fun. So is there any fix to prevent cmd to add that line ?

Solution

  • Mofi has provided the crucial pointers in comments:

    • When executing a command interactively, cmd.exe unconditionally appends a a newline (line break) to the command's output, presumably for readability and perhaps also to ensure that the next prompt always starts on a new line.

      • This applies irrespective of what that command is. In other words: It doesn't matter that your command happens to be a PowerShell command.

    • However, that trailing newline does not become part of the command's output, therefore programmatic processing of a command's output is not affected, such as when you redirect > to a file or process the output lines one by one with for /f.

      • In other words: for programmatic processing you need not remove the trailing newline, because it isn't part of the actual command output.

      • Conversely, if you really need to in effect suppress the trailing newline for display, you'll have to modify the command's output - if that is even an option - so that the output itself doesn't end in a newline, as shown in this SuperUser answer for cmd.exe's own echo command; for PowerShell, you could do pwsh -c Write-Host -NoNewLine hello.

    Edge case:

    When capturing output from a batch file that is running without @echo off (or with echo on) - in which case the trailing newlines do become part of the output - you can filter out empty lines by piping to findstr /r /v /c:"^$" (as also shown in the linked answer); e.g.

    foo.cmd | findstr /r /v /c:"^$"

    However, note that all empty lines are filtered out this way - potentially including actual empty lines in the output from commands executed by the batch file.

    If preventing that is required, a more sophisticated approach is required, which, however (a) relies on the standard prompt string (e.g., C:\>) being used and (b) can still yield false positives:

    foo.cmd | powershell -nop -c "@($Input) -join \"`n\" -replace '\n(?=[a-z]:\\.*?>)'"

    Finally note that if you execute the above commands without capturing or redirecting their output, their overall output in the cmd.exe console will again have a trailing newline.