Checking for bound parameters

I recently read an email where someone was asking how they could check in their function if a value had been provided to one of the parameters.  Consider for example,

The usual way I’ve seen people deal this problem is by providing a default value which gets assigned to $x in the case that a value wasn’t provided by the caller and then checking for that value. 

That works in the majority of cases, but let’s say that you wanted to differentiate between a default $null value and $null being passed by the caller.  What would you do?

If you’re on v2, a simple solution is to look at $PSBoundParameters.  It’s a hashtable containing the parameters that were bound and what values were bound to them.  Try this:

PS >foo 1

Key                                                                       Value

—                                                                       —–

x                                                                             1

PS >foo 1 ‘foo’

Key                                                                       Value

—                                                                       —–

x                                                                             1

y                                                                           foo

With $PSBoundParameters containing all the bound parameters, to check if a parameter was given a value, it’s a simple matter of checking if $PSBoundParameters contains a key for it.

– Marcel Ortiz Soto [MSFT]