CODEWITHSUNDEEP
bashpowershellscriptingparameter-passing
Michael
Michael

Reputation: 672

Building and executing Command-String in Powershell

Good day!

I stumbled across a small "problem" the other day...

I have learned scripting through the linux-shell. There, one can construct commands through strings and exceute them as is.

For Example:

#!bin/bash
LS_ARGS='-lad'  
LS_CMD='ls'

CMD="$LS_CMD $LS_ARGS /home"    
$CMD

But now I had to switch to windows powershell:

If ( $BackgroundColor ) {
    Write-Host -BackgroundColor $BackgroundColor
}
If ( $ForegroundColor ) {
    Write-Host -ForegroundColor $ForegroundColor
}
If ( $ForegroundColor -AND $BackgroundColor ) {
    Write-Host -ForegroundColor $ForegroundColor
               -BackgroundColor $BackgroundColor
}

If ( $NoNewline ) {
    If ( $BackgroundColor ) { ... }
    ElseIf ( $ForegroundColor ) { ... }
    ElseIf ( $ForegroundColor -AND $BackgroundColor ) { ... }
    Else { ... }
}

I think you know what I mean ;) Does anyone know a way of cutting this down like:

[string] $LS_CMD  = 'Write-Host'
[string] $LS_ARGS = '-BackgroundColor Green -NoNewLine'
[string] $CMD     = "$LS_CMD C:\temp $LS_ARGS"

Maybe I am trying to change something that should not be changed due to these stupid comparisons with other languages. The main reason I want to do this is because I am trying to reduce all the unnecessary conditions and passages from my scripts. Trying to make them more legible... Would be nice if someone could help me out here.

Michael

Upvotes: 5

Views: 7478

Answers (3)

Emperor XLII
Emperor XLII

Reputation: 13452

The simplest way to build up a set of arguments for a cmdlet is to use a hashtable and splatting:

$arguments = @{}
if( $BackgroundColor ) { $arguments.BackgroundColor = $BackgroundColor }
if( $ForegroundColor ) { $arguments.ForegroundColor = $ForegroundColor }
if( $NoNewline ) { $arguments.NoNewline = $NoNewline }
...

Write-Host text @arguments

The @ in Write-Host text @arguments causes the values in $arguments to be applied to the parameters of the Write-Host cmdlet.

Upvotes: 2

Michael
Michael

Reputation: 672

As I skimmed through the current powershell questions here I stumbled over:
How to dynamically create an array and use it in Powershell

One can use the "Invoke-Expression" Cmdlet:
The Invoke-Expression cmdlet evaluates or runs a specified string as a command and returns the results of the expression or command. Without Invoke-Expression, a string submitted at the command line would be returned (echoed) unchanged.

[string] $Cmd = ""
if ( $BackgroundColor ) {
   $Cmd += ' -BackgroundColor Green'
}
if ( $ForegroundColor ) {
   $Cmd += ' -ForegroundColor Black'
}
if ( $NoNewLine ) {
   $Cmd += '-NoNewLine'
}

Invoke-Expression $Cmd

Is there anything wrong with that solution?
It looks pretty to me ;)

Sorry.. Now I look like I did no research and googling :/ Just stumbled over the answer by accident. Thanks Andi Arismendi

Upvotes: 2

Andy Arismendi
Andy Arismendi

Reputation: 52689

You can build a string and execute using Invoke-Expression:

Invoke-Expression "$cmd $cmd_args"

Upvotes: 7

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