command substitution

We all know that many unix shells have it and the format for powershell is $ (command ). But I can’t find it documented anywhere. In the first edition of the book powershell TFM, it is mentioned, but the later edition lacks it. is it still around? I tried mkdir $ (1+3) and received error

mkdir : A positional parameter cannot be found that accepts argument ‘4’.
At line:1 char:1

  • mkdir $ (1+3)
  •   + CategoryInfo          : InvalidArgument: (:) [mkdir], ParameterBindingException
      + FullyQualifiedErrorId : PositionalParameterNotFound,mkdir

what gives?


Is called a subexpression, and it’s valid inside double quotes. Notice there is no space between the dollar sign and the parentheses. You used a space; that passed $ as the first argument, and 4 (the result of the expression 1+3) as a second parameter. The command didn’t know what to do with the second parameter.

If your goal was to create a directory named 4, you don’t need to use a subexpression.

mkdir (1+3)

Would have worked. Parenthetical expressions are always evaluated first, and the result passed to whatever parameter.

thanks a lot. BTW. what happened to the PowerShell TFM book, the publisher announced new editions, but there are nowhere to be found. what gives?

You’d have to ask them. I’m not involved with the book any longer.