How does pipeline affect Select-Object? - powershell

Question

I'm trying to make a table in PowerShell with custom headers, I am able to do this with
"var" | Select #{n="First";e={"1"}}, #{n="Second";e={"2"}},#{n="Third";e={"3"}}
First Second Third
----- ------ -----
1 2 3
However, without the initial object, there is no output
Select #{n="First";e={"1"}}, #{n="Second";e={"2"}},#{n="Third";e={"3"}}
I can't tell the difference between these other than one is after a pipeline while the other isn't. Why won't this work?
Why doesn't this work?

Answer 1

The cmdlet Select-Object (alias Select) has one required parameter which is -inputObject Which also happens to be the object that gets passed through the pipeline.
Select-Object -InputObject "Example" -Property #{n="First";e={"1"}}, #{n="Second";e={"2"}},#{n="Third";e={"3"}}
Will have the output
First Second Third
----- ------ -----
1 2 3
While without -InputObject, it will not have an output because there is no input (Thanks #mklement0).
Select-Object "Example" -Property #{n="First";e={"1"}}, #{n="Second";e={"2"}},#{n="Third";e={"3"}}
# No Output
and with the pipeline, it will
"Example" | Select-Object "Example" -Property #{n="First";e={"1"}}, #{n="Second";e={"2"}},#{n="Third";e={"3"}}
First Second Third
----- ------ -----
1 2 3
The -inputObject Parameter will usually contain the table you would like to select columns from or other things (if you are not using expressions).

Answer 2

Although the answer from #Neko answers the exact question, I think it is important to mention that the Select-Object cmdlet is not mentioned to construct new custom objects:
Quote from the Get-Help Select-Object -Online:
The Select-Object cmdlet selects specified properties of an object
or set of objects.
In other words; the object needs to exist in order to select its properties.
For what you are doing with
"var" | Select #{n="First";e={"1"}}, #{n="Second";e={"2"}},#{n="Third";e={"3"}}`
you're creating a new pscustomobject by removing all the default properties from the "Var" (string) object and adding new properties with a hard-coded (static) expression which is a long-winded syntax and quiet expensive for building a new object.
To construct a new pscustomobject ("table"), you can simply use the constructor syntax:
[pscustomobject]#{First = '1'; Second = '2'; Third = '3'}
For legacy (prior PSv3) POwerShell versions:
New-Object PSObject -Property #{First = '1'; Second = '2'; Third = '3'}