Invoke-Expression iex

Output

PS> $uf1 = '%Y%m%dT%H%M%S'
PS> $tsc = {Get-Date -uFormat "$uf1"}
PS> $tsq = 'Get-Date -uFormat "$uf1"'
PS>
PS> Get-Variable ts?

Name                           Value
----                           -----
tsc                            Get-Date -uFormat "$uf1"
tsq                            Get-Date -uFormat "$uf1"


PS> & $tsc
20170707T015431
PS> & $tsq
& : The term 'Get-Date -uFormat "$uf1"' is not recognized as the name of a cmdlet, function, script file, or operable program. Check the spelling of the name, or if a path was included, verify that the path is correct and try again.
At line:1 char:3
+ & $tsq
+   ~~~~
    + CategoryInfo          : ObjectNotFound: (Get-Date -uFormat "$uf1":String) [], CommandNotFoundException
    + FullyQualifiedErrorId : CommandNotFoundException

PS>
PS> Invoke-Expression $tsc
Invoke-Expression : Cannot evaluate parameter 'Command' because its argument is specified as a script block and there is no input. A script block cannot be evaluated without input.
At line:1 char:19
+ Invoke-Expression $tsc
+                   ~~~~
    + CategoryInfo          : MetadataError: (:) [Invoke-Expression], ParameterBindingException
    + FullyQualifiedErrorId : ScriptBlockArgumentNoInput,Microsoft.PowerShell.Commands.InvokeExpressionCommand

PS> Invoke-Expression $tsq
20170707T015636
PS>

考察

Quotes 括りの文字列の場合は、コマンドとして認識しないが、braces{} Script Block　であれば、コマンドを認識している。

reference

about_Comparison_Operators