Automatic-variables

Automatic variables as parameters or local variables

See

help about_Automatic_Variables

Automatic variables are maintained by the core and normally should not be used as parameters or local variables. This is easy to forget, especially with some simple variable names.

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$Args and $Input as parameters

$Args

Contains an array of the undeclared parameters and/or parameter values that are passed to a function, script, or script block.

Test-1.Args.ps1 shows that $Args can be used as a parameter but it does not work as one may expect.

$Input

Contains an enumerator that enumerates all input that is passed to a function.

Test-2.Input.ps1 shows that $Input can be used as a parameter but it does not work as one may expect.

• Stack Overflow Args/params not being populated
• Stack Overflow Function parameter always empty why?
• Stack Overflow Why Pester does not mock a cmdlet with two parameters?

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$$ and $^ as local variables

$$

Contains the last token in the last line received by the session.

$^

Contains the first token in the last line received by the session.

It is unlikely that $^ is used accidentally. But $$ is the easiest to type variable, so it may be tempting to use it. In many cases these variables may be used without problems but there are cases with issues.

Test-3.Dollar.ps1 and Test-4.Caret.ps1 show a case when $$ and $^ do not work as normal variables in PowerShell v3+.

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$This as a local variable

$This

In a script block that defines a script property or script method, the $This variable refers to the object that is being extended.

Test-5.This.ps1 shows an exotic case that may cause a crash or a strange error PowerShell v3. In PowerShell v2 it works with expected errors. See testing commands in the comments.

• Microsoft Connect 1423742