Expand line without Invoke-Expression

Question

Provide the following code:

# Script Start
$WelcomeMessage = "Hello $UserName, today is $($Date.DayOfWeek)"

..
..
# 100 lines of other functions and what not...
..

function Greet-User
{
    $Username = Get-UserNameFromSomewhereFancy
    $Date = Get-DateFromSomewhereFancy

    $WelcomeMessage
}

This is a very simple example, but what he is trying to show is a script where there is $WelcomeMessageone that the person running the script can install at the top of the script and controls how / what the message is displayed.

First of all: why do something like this? Well, if you pass your script to several people, they may want different messages. Maybe they do not like $($Date.DayOfWeek)and want to get the full date. They may not want to show username, whatever.

-, script? . 1000 script, , , script, , . .., , .

, . Greet-User (, / - ...) Greet-User Hello , today is.

, , script, $UserName $Date.

Invoke-Expression . - . :.

$WelcomeMessage = 'Hello $env:USERNAME'
Invoke-Expression $WelcomeMessage

- , , :

$WelcomeMessage = 'Hello $env:USERNAME'
$InvokeExpression = "`"$WelcomeMessage`""

...

, . - , - ...

$WelcomeMessage 'Hello $([void] (Remove-Item C:\Windows -Force -Recurse))'

(, , , )

, script, , script, , , - script, , - - , .

... Invoke-Expression, , :)

Answer 1

, :

$WelcomeMessage = 'Hello {0}, today is {1}'

# 100 lines of other functions and what not...

function Greet-User
{
    $Username = Get-UserNameFromSomewhereFancy
    $Date = Get-DateFromSomewhereFancy

    $WelcomeMessage -f $Username, $Date
}

Answer 2

/ , $ExecutionContext.InvokeCommand.ExpandString() .

:

PS C:\> $s = '$env:COMPUTERNAME'
PS C:\> $s
$env:COMPUTERNAME
PS C:\> $ExecutionContext.InvokeCommand.ExpandString($s)
FOO

:

$WelcomeMessage = 'Hello $UserName, today is $($Date.DayOfWeek)'

...
...
...

function Greet-User {
  $Username = Get-UserNameFromSomewhereFancy
  $Date = Get-DateFromSomewhereFancy

  $ExecutionContext.InvokeCommand.ExpandString($WelcomeMessage)
}

Answer 3

-; , , , , .

$WelcomeMessage = {param($UserName,$Date);"Hello $UserName, today is $($Date.DayOfWeek) $([void](remove-item c:\test\test.txt))"}

#...
# 100 lines of other functions and what not...
#...

"testfile" >> c:\test\test.txt #ensure we have a test file to be deleted

function Get-UserNameFromSomewhereFancy(){return "myUsername";}
function Get-DateFromSomewhereFancy(){return (get-date);}

function Greet-User
{
    $Username = Get-UserNameFromSomewhereFancy
    $Date = Get-DateFromSomewhereFancy

    $WelcomeMessage.invoke($username,$date)
}

cls
Greet-User

, ; (, .DayOfWeek)

$WelcomeMessage = 'Hello $Username, today is $($Date.DayOfWeek) $([void](remove-item c:\test\test.txt))'
#...
# 100 lines of other functions and what not...
#...

"testfile" >> c:\test\test.txt #ensure we have a test file to be deleted

function Get-UserNameFromSomewhereFancy(){return "myUsername";}
function Get-DateFromSomewhereFancy(){return (get-date);}
function Resolve-WelcomeMessage(){
    write-output {param($UserName,$Date);"$WelcomeMessage";}
}
function Greet-User
{
    $Username = Get-UserNameFromSomewhereFancy
    $Date = Get-DateFromSomewhereFancy
    $temp = $WelcomeMessage 
    get-variable | ?{@('$','?','^') -notcontains $_.Name} | sort name -Descending | %{
        $temp  = $temp -replace ("\`${0}" -f $_.name),$_.value
    }
    $temp 
}

cls
Greet-User

To avoid code injection, used -whatif; this will only help where the code you entered supports whatif functionality, but hopefully better than nothing ...

Also, the code now does not require declaration of parameters; but just accepts those variables that are available at runtime.

$WelcomeMessage = {"Hello $Username, today is $($Date.DayOfWeek) $([void](remove-item c:\test\test.txt))"}

#...
# 100 lines of other functions and what not...
#...

function Get-UserNameFromSomewhereFancy(){return "myUsername";}
function Get-DateFromSomewhereFancy(){return (get-date);}
function Resolve-WelcomeMessage(){
    write-output {param($UserName,$Date);"$WelcomeMessage";}
}

"testfile" >> c:\test\test.txt #ensure we have a test file to be deleted

function Greet-User {
    [cmdletbinding(SupportsShouldProcess=$True)]
    param()
    begin {$original = $WhatIfPreference; $WhatIfPreference = $true;}
    process {
        $Username = Get-UserNameFromSomewhereFancy
        $Date = Get-DateFromSomewhereFancy
        & $WelcomeMessage 
    }
    end {$WhatIfPreference = $original;}
}

cls
Greet-User