What does "- <" mean when you run powershell?

Question

The recommended way to run scripts is

powershell.exe -NonInteractive -Command " & some.ps1 "

However for example TeamCity PowerShell runner uses:

powershell.exe -NonInteractive -Command - < some.ps1

I do not have an idea what "- <" means and cannot find any information on subject. Any help?

Answer 1

Because powershell.exe is being invoked through the Windows shell, it is the same as if you were on a normal command prompt (cmd.exe). In that situation < pipes a file to the standard input (stdin) of the previous command. The help for powershell.exe states that if the value of -Command is simply -, the command text is read from standard input.

Here's a more self-documenting demonstration of < in cmd.exe:

processSomeFile.exe outputFileName.ext < intputFile.ext

Answer 2

1. If the value of Command is "-", the command text is read from standard input.

2. < is just the stdout -> stdin redirection operator