Splatting your way to reduced duplicated code

Posted on September 23, 2014  •  2 minutes  • 315 words

Splatting is a great way of making cmdlet calls with a lot of parameters more legible. You create a hashtable of of the parameter names and their values, which you can format nicely, and pass the hashtable to the cmdlet.

A good example of this in action from the TechNet magazine is turning:

{% highlight powershell %}Get-WmiObject -computername SERVER-R2 -class Win32_LogicalDisk -filter “DriveType=3” -credential “Administrator”{% endhighlight %}

into:

$parms = @{'class'='Win32_BIOS';
           'computername'='SERVER-R2';
           'filter'='drivetype=3';
           'credential'='Administrator'
}

Get-WmiObject @parms

Readability isn’t the only reason to splat your parameters. It can also help you reduce mostly duplicated cmdlets calls. In an advanced function I wrote to wrap around the Send-MailMessage , you could specify TO, From, CC, SmtpServer, Subject and Body though parameters. To, From, SmtpServer and Subject all have default values, but Body and CC did not.

In order to not get errors trying to pass null variables Send-MailMessage, you could use a complex series of if statements:

if ($Body -ne $null -and $Body -ne '')
{
    if ($CC -ne $null -and $CC -ne '')
    {
        Send-MailMessage -SmtpServer $SmtpServer -From $From -To $To -CC $CC -Body $Body -Subject $Subject
    }
    else
    {
        Send-MailMessage -SmtpServer $SmtpServer -From $From -To $To -Body $Body -Subject $Subject
    }
}
else
{
    if ($CC -ne $null -and $CC -ne '')
    {
        Send-MailMessage -SmtpServer $SmtpServer -From $From -To $To -CC $CC -Subject $Subject
    }
    else
    {
        Send-MailMessage -SmtpServer $SmtpServer -From $From -To $To -Subject $Subject
    }
}

Four different possible Send-MailMessage calls with largely the same parameters for each. Not very efficient, or readable. Imagine if another parameter or two without default values were added. Splatting, and the ability to add Key=Value pairs to hastables makes this situation a lot more manageable.

$splat = @{'SmtpServer'=$SmtpServer;
           'From'=$From;
           'To'=$To;
           'Subject'=$Subject;
}

if ($Body -ne $null -and $Body -ne '')
{
    $splat.Add('Body',$Body)
}

if ($CC -ne $null -and $CC -ne '')
{
    $splat.Add('CC',$CC)
}

Send-MailMessage @splat